use anyhow::{Context as _, Result};
use const_format::{concatcp, formatcp};
use fs::Fs;
use futures::StreamExt;
use gpui::{Global, SharedString};
use serde::{Deserialize, Serialize};
use std::path::{Path, PathBuf};
use std::sync::Arc;
use url::Url;
use util::paths::component_matches_ignore_ascii_case;

/// First segment of the skills directory path: `.agents`.
pub const AGENTS_DIR_NAME: &str = ".agents";

/// Second segment of the skills directory path: `skills`.
pub const SKILLS_DIR_NAME: &str = "skills";

/// User-facing display form of the global skills directory path — i.e.
/// what a human should see in messages and prompts, with the platform's
/// native path separator and home-directory shorthand.
///
/// Windows doesn't recognize `~` as the home directory, so the env-var
/// form is used there instead.
#[cfg(target_os = "windows")]
pub const GLOBAL_SKILLS_DIR_DISPLAY: &str =
    concatcp!("%USERPROFILE%\\", AGENTS_DIR_NAME, "\\", SKILLS_DIR_NAME);
#[cfg(not(target_os = "windows"))]
pub const GLOBAL_SKILLS_DIR_DISPLAY: &str = concatcp!("~/", AGENTS_DIR_NAME, "/", SKILLS_DIR_NAME);

/// Opaque identifier for the project scope a skill was loaded from.
///
/// `agent_skills` is a leaf crate and intentionally does not depend on
/// `worktree`. Callers (e.g. the `agent` crate) construct these from
/// `worktree::WorktreeId::to_usize()` and recover the original ID via
/// `worktree::WorktreeId::from_usize()` when needed.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct SkillScopeId(pub usize);

/// Cap on concurrent filesystem operations during skill discovery and loading.
/// Without this bound, a `.agents/skills` directory containing thousands of
/// entries would fan out an equally large number of concurrent OS-level I/O
/// operations, potentially exhausting file descriptors or stalling the app.
const SKILL_IO_CONCURRENCY: usize = 16;

/// Maximum size for a single SKILL.md file (100KB)
pub const MAX_SKILL_FILE_SIZE: usize = 100 * 1024;

/// Maximum total size for skill descriptions in system prompt (50KB)
pub const MAX_SKILL_DESCRIPTIONS_SIZE: usize = 50 * 1024;

/// The name of the skill definition file
pub const SKILL_FILE_NAME: &str = "SKILL.md";

/// Represents a loaded skill with all its metadata and content.
#[derive(Debug, Clone)]
pub struct Skill {
    pub name: String,
    pub description: String,
    pub source: SkillSource,
    /// Absolute path to the skill directory
    pub directory_path: PathBuf,
    /// Absolute path to the SKILL.md file
    pub skill_file_path: PathBuf,
    /// When `true`, this skill is hidden from the model's catalog and the
    /// `skill` tool refuses to load it. The user can still invoke it as a
    /// slash command.
    pub disable_model_invocation: bool,
    /// For built-in skills whose content is compiled into the binary,
    /// this holds the full SKILL.md body so the skill tool can serve it
    /// without a filesystem read.
    pub embedded_body: Option<&'static str>,
}

/// Indicates where a skill was loaded from.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum SkillSource {
    /// Compiled into the Zed binary. These are always available and have
    /// the lowest override priority (global and project-local skills can
    /// shadow them).
    BuiltIn,
    /// From ~/.agents/skills/
    Global,
    /// From {project}/.agents/skills/
    ProjectLocal {
        worktree_id: SkillScopeId,
        worktree_root_name: Arc<str>,
    },
}

impl SkillSource {
    /// Precedence for resolving same-named skills. Higher values shadow
    /// lower ones: `ProjectLocal` > `Global` > `BuiltIn`. Two sources
    /// returning equal precedence (e.g. two project-local skills from
    /// different worktrees) leave the winner up to the caller, which by
    /// convention keeps the first one in iteration order.
    ///
    /// Adding a new `SkillSource` variant should be a one-line change
    /// here — every consumer routes through this method so the hierarchy
    /// stays in sync.
    pub fn precedence(&self) -> u8 {
        match self {
            Self::BuiltIn => 0,
            Self::Global => 1,
            Self::ProjectLocal { .. } => 2,
        }
    }

    /// Scope prefix used in the `/<prefix>:<name>` slash-command
    /// syntax that the autocomplete popup inserts. Global skills use
    /// an empty prefix (so the inserted text is `/:<name>`), and
    /// project-local skills use their worktree root name (so the
    /// inserted text is `/<worktree>:<name>`).
    ///
    /// Using an empty prefix for globals rather than a literal
    /// `global` means a worktree literally named `global` is no
    /// longer ambiguous with the global source: the global skill is
    /// invoked as `/:<name>`, and the worktree's skill is invoked as
    /// `/global:<name>`. The two grammars never collide on the
    /// inserted text.
    /// Human-readable label for this source, used in the UI to
    /// distinguish skills from different origins.
    pub fn display_label(&self) -> &str {
        match self {
            Self::BuiltIn => "built-in",
            Self::Global => "global",
            Self::ProjectLocal {
                worktree_root_name, ..
            } => worktree_root_name.as_ref(),
        }
    }

    pub fn scope_prefix(&self) -> &str {
        match self {
            Self::BuiltIn | Self::Global => "",
            Self::ProjectLocal {
                worktree_root_name, ..
            } => worktree_root_name.as_ref(),
        }
    }

    /// Whether this source matches the given scope qualifier from a
    /// `/<scope>:<name>` slash command. The empty scope is reserved
    /// for global skills; non-empty scopes match a project-local
    /// skill whose worktree root name equals the scope.
    ///
    /// Hand-typed `/global:<name>` is NOT treated as an alias for
    /// `/:<name>`. It looks for a project-local skill from a worktree
    /// named `global` and fails if none exists. The popup always
    /// inserts the unambiguous form (`/:<name>` for globals), so this
    /// strictness only affects users typing by memory.
    pub fn matches_scope(&self, scope: &str) -> bool {
        match self {
            Self::BuiltIn | Self::Global => scope.is_empty(),
            Self::ProjectLocal {
                worktree_root_name, ..
            } => !scope.is_empty() && worktree_root_name.as_ref() == scope,
        }
    }
}

/// App-wide index of loaded skills, published by NativeAgent and read
/// by any UI that needs to display the skill list (e.g. Settings UI).
#[derive(Default)]
pub struct SkillIndex {
    pub global_skills: Vec<Skill>,
    pub project_skills: Vec<ProjectSkillGroup>,
}

#[derive(Clone)]
pub struct ProjectSkillGroup {
    pub worktree_id: SkillScopeId,
    pub worktree_root_name: SharedString,
    pub skills: Vec<Skill>,
}

impl Global for SkillIndex {}

/// Just the frontmatter, used for parsing
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SkillMetadata {
    pub name: String,
    pub description: String,
    #[serde(default, rename = "disable-model-invocation")]
    pub disable_model_invocation: bool,
}

/// Minimal skill info for system prompt (not full content).
///
/// `Serialize` is required for handlebars rendering of the system prompt
/// template (see `ProjectContext` in `prompt_store`). `PartialEq, Eq` lets
/// the agent compare freshly-built `ProjectContext`s and skip pushing an
/// unchanged value through the project_context entity (which would
/// otherwise look like a system-prompt change to the model and invalidate
/// the API's prompt cache).
#[derive(Debug, Clone, Eq, PartialEq, Serialize)]
pub struct SkillSummary {
    pub name: String,
    pub description: String,
    /// Absolute path to the SKILL.md file, so the model can resolve
    /// references relative to the skill's directory when reading bundled
    /// resources.
    pub location: String,
}

impl From<&Skill> for SkillSummary {
    fn from(skill: &Skill) -> Self {
        Self {
            name: skill.name.clone(),
            description: skill.description.clone(),
            location: skill.skill_file_path.to_string_lossy().into_owned(),
        }
    }
}

/// Error that occurred while loading a skill
#[derive(Debug, Clone)]
pub struct SkillLoadError {
    pub path: PathBuf,
    pub message: String,
}

impl std::fmt::Display for SkillLoadError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}: {}", self.path.display(), self.message)
    }
}

impl std::error::Error for SkillLoadError {}

/// Parse the frontmatter of a SKILL.md file into a `Skill` struct.
///
/// The file must have YAML frontmatter between `---` delimiters containing
/// `name` and `description` fields. The body (everything after the closing
/// `---`) is intentionally NOT returned — it's read on demand via
/// `read_skill_body` when the skill is actually being materialized for the
/// model, so we don't pay N × body-size in memory for N skills.
///
/// `content` only needs to contain bytes up through the closing `---`; any
/// trailing body bytes are ignored.
pub fn parse_skill_frontmatter(
    skill_file_path: &Path,
    content: &str,
    source: SkillSource,
) -> Result<Skill> {
    let (metadata, _body) = parse_skill_file_content(content)?;

    let directory_path = skill_file_path
        .parent()
        .context("SKILL.md file has no parent directory")?
        .to_path_buf();

    Ok(Skill {
        name: metadata.name,
        description: metadata.description,
        source,
        directory_path,
        skill_file_path: skill_file_path.to_path_buf(),
        disable_model_invocation: metadata.disable_model_invocation,
        embedded_body: None,
    })
}

/// Extract the YAML frontmatter and body from a SKILL.md file without
/// validating the metadata fields.
pub fn extract_skill_frontmatter(content: &str) -> Result<(SkillMetadata, &str)> {
    if content.len() > MAX_SKILL_FILE_SIZE {
        anyhow::bail!(
            "SKILL.md file exceeds maximum size of {}KB",
            MAX_SKILL_FILE_SIZE / 1024
        );
    }

    extract_frontmatter(content)
}

/// Parse and validate the YAML frontmatter and body from a SKILL.md file.
pub fn parse_skill_file_content(content: &str) -> Result<(SkillMetadata, &str)> {
    let (metadata, body) = extract_skill_frontmatter(content)?;

    validate_name(&metadata.name).map_err(anyhow::Error::msg)?;
    validate_description(&metadata.description).map_err(anyhow::Error::msg)?;

    Ok((metadata, body))
}

fn extract_frontmatter(content: &str) -> Result<(SkillMetadata, &str)> {
    let content = content.trim_start();

    if !content.starts_with("---") {
        anyhow::bail!("SKILL.md must start with YAML frontmatter (---)");
    }

    // Find every candidate closing `---` line: a line consisting EXACTLY of
    // `---` (followed by `\n`, `\r\n`, or EOF) at column 0, excluding the
    // opening line itself. The opener occupies bytes 0..(first line ending),
    // and our scan starts after each `\n`, so the opener is naturally skipped.
    //
    // For each candidate we record the byte position right after its line
    // ending; that's both where the YAML stream slice ends and where the body
    // begins.
    let bytes = content.as_bytes();
    let mut candidates: Vec<usize> = Vec::new();
    for (i, &b) in bytes.iter().enumerate() {
        if b != b'\n' {
            continue;
        }
        let line_start = i + 1;
        if line_start + 3 > bytes.len() {
            continue;
        }
        if &bytes[line_start..line_start + 3] != b"---" {
            continue;
        }
        let after_dashes = line_start + 3;
        let end = if after_dashes == bytes.len() {
            after_dashes
        } else if bytes[after_dashes] == b'\n' {
            after_dashes + 1
        } else if after_dashes + 1 < bytes.len()
            && bytes[after_dashes] == b'\r'
            && bytes[after_dashes + 1] == b'\n'
        {
            after_dashes + 2
        } else {
            // Line is something like `---trailing` or `----`; not a candidate.
            continue;
        };
        candidates.push(end);
    }

    if candidates.is_empty() {
        anyhow::bail!("SKILL.md missing closing frontmatter delimiter (---)");
    }

    // Try each candidate in order: slice content up through the candidate's
    // terminator and ask `serde_yaml_ng` to parse it as a YAML stream. If the
    // first document deserializes into `SkillMetadata`, that candidate is the
    // real closer. Otherwise an earlier candidate may have cut the YAML in the
    // middle of a scalar / quoted string; try the next one.
    let mut last_error: Option<anyhow::Error> = None;
    for end in candidates {
        let prefix = &content[..end];
        let mut docs = serde_yaml_ng::Deserializer::from_str(prefix);
        let Some(first_doc) = docs.next() else {
            continue;
        };
        match SkillMetadata::deserialize(first_doc) {
            Ok(metadata) => return Ok((metadata, &content[end..])),
            Err(e) => last_error = Some(anyhow::Error::new(e)),
        }
    }

    Err(last_error
        .unwrap_or_else(|| anyhow::anyhow!("could not parse YAML frontmatter"))
        .context("Invalid YAML frontmatter"))
}

/// Maximum length for a valid skill name. Mirrors the upper bound enforced
/// by [`validate_name`].
pub const MAX_SKILL_NAME_LEN: usize = 64;

/// Maximum length (in bytes) for a valid skill description. Mirrors the
/// upper bound enforced by [`validate_description`].
///
/// Byte-based rather than char-based because that's what `.len()` returns
/// and what every caller currently measures; the UI also surfaces this
/// limit as a byte count so the editor's counter matches the validator.
pub const MAX_SKILL_DESCRIPTION_LEN: usize = 1024;

/// Convert an arbitrary human-readable string into a valid skill name, or
/// return `None` if no valid name can be produced (e.g. the input contains
/// no ASCII alphanumeric characters at all).
///
/// The transformation:
///
/// 1. Replaces each `&` with the word `and` (with separators on either
///    side), so titles like "rock & roll" or "AT&T" round-trip something
///    meaningful (`rock-and-roll`, `at-and-t`) rather than dropping the
///    `&` and silently mashing the neighbours together.
/// 2. ASCII-lowercases every ASCII letter.
/// 3. Replaces each space with `-`. Existing `-` characters are kept.
/// 4. **Drops** every other non-alphanumeric character entirely (NOT
///    replaced with a dash). So `foo!bar` slugifies to `foobar`, not
///    `foo-bar` — only word boundaries the user actually wrote (spaces)
///    become dashes.
/// 5. Collapses runs of `-` into a single `-`.
/// 6. Trims leading and trailing `-`.
/// 7. Truncates to [`MAX_SKILL_NAME_LEN`] bytes (then re-trims trailing `-`
///    in case the truncation landed on one).
///
/// The result, if `Some`, always satisfies [`validate_name`].
pub fn slugify_skill_name(input: &str) -> Option<String> {
    // Substitute `&` with `-and-` BEFORE the per-character pass; the
    // existing dash-collapsing and edge-trimming logic then handles the
    // boundary cases (`foo & bar`, `&foo`, `foo&`, `&&`, etc.) for free.
    let input = input.replace('&', "-and-");
    let mut slug = String::with_capacity(input.len());
    let mut last_was_dash = true; // suppress a leading `-`
    for ch in input.chars() {
        let mapped = if ch.is_ascii_alphanumeric() {
            Some(ch.to_ascii_lowercase())
        } else if ch == ' ' || ch == '-' {
            Some('-')
        } else {
            // Drop the character entirely — and importantly, do NOT touch
            // `last_was_dash`. That way `foo!bar` stays one run of
            // alphanumerics (`foobar`) rather than getting a fake
            // separator inserted (`foo-bar`).
            None
        };
        let Some(c) = mapped else { continue };
        if c == '-' {
            if last_was_dash {
                continue;
            }
            last_was_dash = true;
        } else {
            last_was_dash = false;
        }
        slug.push(c);
    }
    if slug.ends_with('-') {
        slug.pop();
    }
    if slug.len() > MAX_SKILL_NAME_LEN {
        slug.truncate(MAX_SKILL_NAME_LEN);
        while slug.ends_with('-') {
            slug.pop();
        }
    }
    if slug.is_empty() { None } else { Some(slug) }
}

/// Validate a skill name against the rules enforced by both the loader
/// and the create-skill UI.
///
/// Rules:
/// * non-empty
/// * at most [`MAX_SKILL_NAME_LEN`] bytes
/// * ASCII lowercase letters, digits, and hyphens only
/// * must not start or end with a hyphen — [`slugify_skill_name`]
///   already guarantees this for its output, so requiring it in the
///   validator keeps hand-written `SKILL.md` files consistent with
///   slugifier output
///
/// Error messages are returned as `&'static str` (interpolated at
/// compile time via `formatcp!`) so that UI surfaces can store them in
/// `Option<&'static str>` fields without allocating, and loader callers
/// can convert them to `anyhow::Error` via `anyhow::Error::msg`.
pub fn validate_name(name: &str) -> Result<(), &'static str> {
    if name.is_empty() {
        return Err("Skill name cannot be empty");
    }
    if name.len() > MAX_SKILL_NAME_LEN {
        return Err(formatcp!(
            "Skill name must be at most {MAX_SKILL_NAME_LEN} characters"
        ));
    }
    if name.starts_with('-') || name.ends_with('-') {
        return Err("Skill name must not start or end with a hyphen");
    }
    if !name
        .chars()
        .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-')
    {
        return Err("Skill name must contain only lowercase letters, numbers, and hyphens");
    }
    Ok(())
}

/// Validate a skill description against the rules enforced by both the
/// loader and the create-skill UI.
pub fn validate_description(description: &str) -> Result<(), &'static str> {
    if description.trim().is_empty() {
        return Err("Skill description cannot be empty");
    }
    if description.len() > MAX_SKILL_DESCRIPTION_LEN {
        return Err(formatcp!(
            "Skill description must be at most {MAX_SKILL_DESCRIPTION_LEN} bytes"
        ));
    }
    Ok(())
}

pub async fn load_skills_from_directory(
    fs: &Arc<dyn Fs>,
    directory: &Path,
    source: SkillSource,
) -> Vec<Result<Skill, SkillLoadError>> {
    if !fs.is_dir(directory).await {
        return Vec::new();
    }

    let skill_files = find_skill_files(fs, directory).await;

    let mut results: Vec<Result<Skill, SkillLoadError>> = futures::stream::iter(skill_files)
        .map(|path| {
            let fs = fs.clone();
            let source = source.clone();
            async move { load_skill_frontmatter(fs, path, source).await }
        })
        .buffer_unordered(SKILL_IO_CONCURRENCY)
        .collect()
        .await;

    // Sort by path so name-conflict resolution in `apply_skill_overrides`
    // is deterministic — `fs.read_dir` order is filesystem-dependent.
    results.sort_by(|a, b| {
        let path_a: &Path = match a {
            Ok(skill) => &skill.skill_file_path,
            Err(error) => &error.path,
        };
        let path_b: &Path = match b {
            Ok(skill) => &skill.skill_file_path,
            Err(error) => &error.path,
        };
        path_a.cmp(path_b)
    });

    results
}

/// Find every `<skills_root>/<name>/SKILL.md` directly under `directory`.
///
/// Discovery is intentionally one level deep: a skill is the immediate
/// child directory of the skills root, and `SKILL.md` is the file that
/// names it. See `crates/agent_skills/README.md` for why we don't recurse.
async fn find_skill_files(fs: &Arc<dyn Fs>, directory: &Path) -> Vec<PathBuf> {
    let Ok(mut entries) = fs.read_dir(directory).await else {
        return Vec::new();
    };

    let mut entry_paths = Vec::new();
    while let Some(entry) = entries.next().await {
        if let Ok(entry_path) = entry {
            entry_paths.push(entry_path);
        }
    }

    futures::stream::iter(entry_paths)
        .map(|entry_path| {
            let fs = fs.clone();
            async move {
                let Ok(Some(metadata)) = fs.metadata(&entry_path).await else {
                    return None;
                };
                if !metadata.is_dir {
                    return None;
                }
                let skill_file = entry_path.join(SKILL_FILE_NAME);
                fs.is_file(&skill_file).await.then_some(skill_file)
            }
        })
        .buffer_unordered(SKILL_IO_CONCURRENCY)
        .filter_map(|x| async move { x })
        .collect()
        .await
}

/// Read `skill_file_path` from disk and parse its frontmatter. The
/// SKILL.md body is parsed away by `parse_skill_frontmatter` and not
/// surfaced here; it's re-read on demand via `read_skill_body` when a
/// skill is actually being loaded for the model.
///
/// We load the whole file in one go rather than streaming up to the
/// closing `---`. `MAX_SKILL_FILE_SIZE` is 100KB and the metadata check
/// below caps the worst case at that, so the peak transient cost is
/// trivially small (≤ `MAX_SKILL_FILE_SIZE` × `SKILL_IO_CONCURRENCY`).
pub async fn load_skill_frontmatter(
    fs: Arc<dyn Fs>,
    skill_file_path: PathBuf,
    source: SkillSource,
) -> Result<Skill, SkillLoadError> {
    // Short-circuit on oversized files before reading any of their
    // contents, so a stray multi-GB file named `SKILL.md` can't OOM the
    // app. If metadata is unavailable, refuse to read.
    let metadata = fs
        .metadata(&skill_file_path)
        .await
        .map_err(|e| SkillLoadError {
            path: skill_file_path.clone(),
            message: format!("Failed to read SKILL.md metadata: {}", e),
        })?;
    if let Some(metadata) = metadata
        && metadata.len > MAX_SKILL_FILE_SIZE as u64
    {
        return Err(SkillLoadError {
            path: skill_file_path.clone(),
            message: format!(
                "SKILL.md file exceeds maximum size of {}KB",
                MAX_SKILL_FILE_SIZE / 1024
            ),
        });
    }

    let content = fs
        .load(&skill_file_path)
        .await
        .map_err(|e| SkillLoadError {
            path: skill_file_path.clone(),
            message: format!("Failed to read file: {}", e),
        })?;

    parse_skill_frontmatter(&skill_file_path, &content, source).map_err(|e| SkillLoadError {
        path: skill_file_path.clone(),
        message: e.to_string(),
    })
}

/// Read the body of a SKILL.md from disk — everything after the closing
/// `---`. Called only when a skill is being materialized for the model
/// (via `SkillTool` or a slash invocation). The body is intentionally
/// NOT kept in memory between materializations.
pub async fn read_skill_body(
    fs: &dyn Fs,
    skill_file_path: &Path,
) -> Result<String, SkillLoadError> {
    let content = fs.load(skill_file_path).await.map_err(|e| SkillLoadError {
        path: skill_file_path.to_path_buf(),
        message: format!("Failed to read file: {}", e),
    })?;

    let (_metadata, body) = extract_frontmatter(&content).map_err(|e| SkillLoadError {
        path: skill_file_path.to_path_buf(),
        message: e.to_string(),
    })?;

    Ok(body.trim().to_string())
}

/// Content of the built-in `create-skill` SKILL.md, embedded at compile time.
const CREATE_SKILL_CONTENT: &str = include_str!("builtin/create-skill/SKILL.md");

/// Returns the set of skills that are compiled into the Zed binary.
pub fn builtin_skills() -> Vec<Skill> {
    let mut skills = Vec::new();
    if let Ok(skill) = parse_builtin_skill("create-skill", CREATE_SKILL_CONTENT) {
        skills.push(skill);
    }
    skills
}

/// Parse a built-in skill from its embedded SKILL.md content. The skill
/// gets a synthetic `<built-in>` path since it doesn't live on disk.
fn parse_builtin_skill(name: &str, content: &'static str) -> Result<Skill> {
    let (metadata, body) = extract_frontmatter(content)?;
    validate_name(&metadata.name).map_err(anyhow::Error::msg)?;
    validate_description(&metadata.description).map_err(anyhow::Error::msg)?;

    let synthetic_dir = PathBuf::from(format!("<built-in>/{}", name));
    let synthetic_path = synthetic_dir.join(SKILL_FILE_NAME);

    Ok(Skill {
        name: metadata.name,
        description: metadata.description,
        source: SkillSource::BuiltIn,
        directory_path: synthetic_dir,
        skill_file_path: synthetic_path,
        disable_model_invocation: metadata.disable_model_invocation,
        embedded_body: Some(body.trim()),
    })
}

/// All built-in skills as `(name, raw_content)` pairs. Used by
/// `builtin_skill_content` to serve the full SKILL.md without disk I/O.
const BUILTIN_SKILL_ENTRIES: &[(&str, &str)] = &[("create-skill", CREATE_SKILL_CONTENT)];

/// Look up the full embedded content of a built-in skill by its
/// synthetic file path. Returns `None` if the path doesn't match any
/// built-in skill.
pub fn builtin_skill_content(skill_file_path: &Path) -> Option<&'static str> {
    BUILTIN_SKILL_ENTRIES.iter().find_map(|(name, content)| {
        let expected = PathBuf::from(format!("<built-in>/{}", name)).join(SKILL_FILE_NAME);
        (expected == skill_file_path).then_some(*content)
    })
}

/// Returns the global skills directory: `~/.agents/skills`.
///
/// Other agents (e.g. Claude Code) already write skill files into this
/// location, so a Zed installation may have skills here even before the
/// rest of Zed's skills support ships.
///
/// In test builds, `paths::home_dir()` is hardcoded to a fixed path
/// (e.g. `/Users/zed`), so all tests using this function operate on the
/// same simulated home directory. Each test should use its own `FakeFs`
/// instance to keep skill setups from leaking across tests.
pub fn global_skills_dir() -> PathBuf {
    paths::home_dir()
        .join(AGENTS_DIR_NAME)
        .join(SKILLS_DIR_NAME)
}

/// Project-local skills live at this path relative to a worktree root,
/// e.g. `<worktree>/.agents/skills/<skill>/SKILL.md`.
pub fn project_skills_relative_path() -> &'static str {
    ".agents/skills"
}

/// Returns `true` if `path` looks like it points into an agent skills
/// directory — i.e. it contains `AGENTS_DIR_NAME` immediately followed by
/// `SKILLS_DIR_NAME` as two consecutive path components, anywhere in the
/// path. Comparison is case-insensitive so it agrees with classifiers
/// that canonicalize against `~/.agents/skills` on case-insensitive
/// filesystems (macOS/Windows by default).
///
/// The path arriving here can be any of:
///
///   1. Bare relative-to-worktree-root: `.agents/skills/...`
///   2. Worktree-name prefixed:         `<worktree>/.agents/skills/...`
///   3. Absolute:                       `/path/to/worktree/.agents/skills/...`
///
/// Any-depth matching has a known cost: a `.agents/skills` directory
/// nested inside vendored sources (e.g. `vendor/x/.agents/skills/...`)
/// would also be flagged. We accept that as the safer-failing direction —
/// an extra confirmation prompt for a vendored file is annoying, while
/// silently letting the agent overwrite a `.agents/skills` tree the user
/// didn't expect to be touched is unsafe.
pub fn is_agents_skills_path(path: &Path) -> bool {
    let mut components = path.components().map(|c| c.as_os_str());
    let Some(mut prev) = components.next() else {
        return false;
    };
    for curr in components {
        if component_matches_ignore_ascii_case(prev, AGENTS_DIR_NAME)
            && component_matches_ignore_ascii_case(curr, SKILLS_DIR_NAME)
        {
            return true;
        }
        prev = curr;
    }
    false
}

/// The `joule://` scheme used by share links.
const SKILL_SHARE_LINK_SCHEME: &str = "zed";
/// The host (the part after `joule://`) that identifies a skill share link.
const SKILL_SHARE_LINK_HOST: &str = "skill";
/// The query parameter that carries the embedded `SKILL.md` payload.
const SKILL_SHARE_LINK_DATA_PARAM: &str = "data";

/// The `joule://` deep-link prefix for a shared skill. Opening a link with this
/// prefix prompts the recipient to review and install the embedded skill.
pub const SKILL_SHARE_LINK_PREFIX: &str =
    concatcp!(SKILL_SHARE_LINK_SCHEME, "://", SKILL_SHARE_LINK_HOST);

/// Build a shareable `joule://skill?data=…` link that fully embeds the given
/// `SKILL.md` file contents.
///
/// The contents are base64url-encoded (no padding) so the link is
/// self-contained and URL-safe: the recipient doesn't need the skill to be
/// hosted anywhere. Recover the contents with [`decode_skill_share_link`].
pub fn encode_skill_share_link(skill_file_content: &str) -> String {
    use base64::Engine as _;
    let data =
        base64::engine::general_purpose::URL_SAFE_NO_PAD.encode(skill_file_content.as_bytes());
    let mut url = Url::parse(SKILL_SHARE_LINK_PREFIX).expect("skill share link prefix is valid");
    url.query_pairs_mut()
        .append_pair(SKILL_SHARE_LINK_DATA_PARAM, &data);
    url.into()
}

/// Recover the `SKILL.md` contents embedded in a `joule://skill?data=…` link
/// produced by [`encode_skill_share_link`].
pub fn decode_skill_share_link(link: &str) -> Result<String> {
    use base64::Engine as _;
    let url = Url::parse(link).context("skill share link is not a valid URL")?;
    anyhow::ensure!(
        url.scheme() == SKILL_SHARE_LINK_SCHEME && url.host_str() == Some(SKILL_SHARE_LINK_HOST),
        "not a skill share link"
    );
    let data = url
        .query_pairs()
        .find_map(|(key, value)| (key == SKILL_SHARE_LINK_DATA_PARAM).then_some(value))
        .context("skill share link is missing the `data` parameter")?;
    let bytes = base64::engine::general_purpose::URL_SAFE_NO_PAD
        .decode(data.as_bytes())
        .context("skill share link `data` is not valid base64")?;
    anyhow::ensure!(
        bytes.len() <= MAX_SKILL_FILE_SIZE,
        "shared skill exceeds the maximum size of {MAX_SKILL_FILE_SIZE} bytes"
    );
    let content = String::from_utf8(bytes).context("skill share link `data` is not valid UTF-8")?;
    Ok(content)
}

#[cfg(test)]
mod tests {
    use super::*;
    use fs::FakeFs;
    use gpui::TestAppContext;

    #[test]
    fn test_skill_source_precedence_is_total_and_ordered() {
        // Pin the hierarchy: project-local > global > built-in. Every
        // override and conflict-resolution site routes through this,
        // so the rest of the codebase relies on it being correct.
        let built_in = SkillSource::BuiltIn.precedence();
        let global = SkillSource::Global.precedence();
        let project = SkillSource::ProjectLocal {
            worktree_id: SkillScopeId(1),
            worktree_root_name: "my-project".into(),
        }
        .precedence();

        assert!(built_in < global, "global must shadow built-in");
        assert!(global < project, "project-local must shadow global");

        // Two project-local skills from different worktrees tie. The
        // "first wins" convention is enforced by the callers, but the
        // precedence itself must be equal so neither silently shadows
        // the other.
        let other_project = SkillSource::ProjectLocal {
            worktree_id: SkillScopeId(2),
            worktree_root_name: "other-project".into(),
        }
        .precedence();
        assert_eq!(project, other_project);
    }

    #[test]
    fn test_parse_valid_skill() {
        let content = r#"---
name: my-skill
description: A test skill for testing purposes
---

# My Skill

## Instructions
Do the thing.
"#;

        let result = parse_skill_frontmatter(
            Path::new("/skills/my-skill/SKILL.md"),
            content,
            SkillSource::Global,
        );
        let skill = result.expect("Should parse successfully");

        assert_eq!(skill.name, "my-skill");
        assert_eq!(skill.description, "A test skill for testing purposes");
        assert_eq!(skill.directory_path, Path::new("/skills/my-skill"));
        // Default: skill is invocable by both model and user.
        assert!(!skill.disable_model_invocation);
    }

    #[test]
    fn test_parse_skill_file_content_returns_body() {
        let content = r#"---
name: my-skill
description: A test skill for testing purposes
---

# My Skill

Do the thing.
"#;

        let (metadata, body) = parse_skill_file_content(content)
            .expect("valid skill content should parse successfully");

        assert_eq!(metadata.name, "my-skill");
        assert_eq!(metadata.description, "A test skill for testing purposes");
        assert_eq!(body.trim(), "# My Skill\n\nDo the thing.");
    }

    #[test]
    fn test_parse_disable_model_invocation_true() {
        let content = r#"---
name: deploy
description: Deploy the application to production.
disable-model-invocation: true
---

Steps to deploy.
"#;

        let skill = parse_skill_frontmatter(
            Path::new("/skills/deploy/SKILL.md"),
            content,
            SkillSource::Global,
        )
        .expect("should parse");
        assert!(skill.disable_model_invocation);
    }

    #[test]
    fn test_parse_disable_model_invocation_explicit_false() {
        let content = r#"---
name: helper
description: A helper skill.
disable-model-invocation: false
---

Help.
"#;

        let skill = parse_skill_frontmatter(
            Path::new("/skills/helper/SKILL.md"),
            content,
            SkillSource::Global,
        )
        .expect("should parse");
        assert!(!skill.disable_model_invocation);
    }

    #[test]
    fn test_parse_missing_frontmatter() {
        let content = "# My Skill\n\nNo frontmatter here.";

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        assert!(
            result
                .unwrap_err()
                .to_string()
                .contains("must start with YAML frontmatter")
        );
    }

    #[test]
    fn test_parse_missing_closing_delimiter() {
        let content = r#"---
name: test
description: Test
# No closing delimiter
"#;

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        assert!(
            result
                .unwrap_err()
                .to_string()
                .contains("missing closing frontmatter delimiter")
        );
    }

    #[test]
    fn test_parse_empty_frontmatter_closing_on_next_line() {
        // An empty frontmatter (closer immediately after the opener) is a real
        // authoring case. Parsing should ultimately fail because the empty YAML
        // doc lacks `name` and `description`, but the error must be the proper
        // YAML/missing-field error rather than "missing closing frontmatter
        // delimiter" — the closer is right there.
        let content = "---\n---\nbody\n";

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        let err = result.unwrap_err();
        let err_chain = format!("{:?}", err);
        assert!(
            !err_chain.contains("missing closing frontmatter delimiter"),
            "Error should NOT be the missing-closer error since the closer is present: {}",
            err_chain
        );
        assert!(
            err_chain.contains("missing field")
                || err_chain.contains("name")
                || err_chain.contains("description")
                || err_chain.contains("Invalid YAML"),
            "Error should mention missing name/description field or invalid YAML: {}",
            err_chain
        );
    }

    #[test]
    fn test_parse_missing_name() {
        let content = r#"---
description: A test skill
---

Content here.
"#;

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        let err = result.unwrap_err();
        let err_chain = format!("{:?}", err);
        assert!(
            err_chain.contains("missing field")
                || err_chain.contains("name")
                || err_chain.contains("Invalid YAML"),
            "Error should mention missing name field or invalid YAML: {}",
            err_chain
        );
    }

    #[test]
    fn test_parse_missing_description() {
        let content = r#"---
name: test-skill
---

Content here.
"#;

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        let err = result.unwrap_err();
        let err_chain = format!("{:?}", err);
        assert!(
            err_chain.contains("missing field")
                || err_chain.contains("description")
                || err_chain.contains("Invalid YAML"),
            "Error should mention missing description field or invalid YAML: {}",
            err_chain
        );
    }

    #[test]
    fn test_parse_name_too_long() {
        let long_name = "a".repeat(65);
        let content = format!(
            r#"---
name: {long_name}
description: Test
---

Content.
"#
        );

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            &content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        let expected = format!("at most {MAX_SKILL_NAME_LEN} characters");
        assert!(result.unwrap_err().to_string().contains(&expected));
    }

    #[test]
    fn test_parse_name_invalid_chars() {
        let content = r#"---
name: My_Skill
description: Test
---

Content.
"#;

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        assert!(
            result
                .unwrap_err()
                .to_string()
                .contains("lowercase letters, numbers, and hyphens")
        );
    }

    #[test]
    fn test_slugify_basic() {
        assert_eq!(
            slugify_skill_name("My Cool Skill").as_deref(),
            Some("my-cool-skill")
        );
    }

    #[test]
    fn test_slugify_strips_invalid_chars() {
        // Punctuation is dropped; spaces between words still produce dashes.
        // `Hello,` → `hello`, then `␣` → `-`, then `World!` → `world`, etc.
        assert_eq!(
            slugify_skill_name("Hello, World! (v2)").as_deref(),
            Some("hello-world-v2")
        );
    }

    #[test]
    fn test_slugify_drops_punctuation_in_middle_no_spaces() {
        // Punctuation between alphanumerics is dropped entirely — it does
        // NOT become a dash. Only user-written spaces become dashes.
        assert_eq!(slugify_skill_name("foo!bar").as_deref(), Some("foobar"));
        assert_eq!(slugify_skill_name("foo?bar").as_deref(), Some("foobar"));
        assert_eq!(slugify_skill_name("foo%bar").as_deref(), Some("foobar"));
        assert_eq!(slugify_skill_name("100%sure").as_deref(), Some("100sure"));
        assert_eq!(
            slugify_skill_name("what's that").as_deref(),
            Some("whats-that")
        );
        // `&` is special-cased to become `and` — see
        // `test_slugify_ampersand_becomes_and` for the full coverage.
        assert_eq!(
            slugify_skill_name("don't&won't").as_deref(),
            Some("dont-and-wont")
        );
    }

    #[test]
    fn test_slugify_ampersand_becomes_and() {
        // No spaces around `&`.
        assert_eq!(
            slugify_skill_name("foo&bar").as_deref(),
            Some("foo-and-bar")
        );
        assert_eq!(
            slugify_skill_name("rock&roll").as_deref(),
            Some("rock-and-roll")
        );
        // Spaces around `&`: collapses to a single dash on each side.
        assert_eq!(
            slugify_skill_name("foo & bar").as_deref(),
            Some("foo-and-bar")
        );
        // Asymmetric spacing.
        assert_eq!(
            slugify_skill_name("foo& bar").as_deref(),
            Some("foo-and-bar")
        );
        assert_eq!(
            slugify_skill_name("foo &bar").as_deref(),
            Some("foo-and-bar")
        );
        // Leading/trailing `&`: the substituted spaces become leading/
        // trailing dashes which then get trimmed.
        assert_eq!(slugify_skill_name("&foo").as_deref(), Some("and-foo"));
        assert_eq!(slugify_skill_name("foo&").as_deref(), Some("foo-and"));
        // `&` alone slugifies to the word `and`, not to `None`.
        assert_eq!(slugify_skill_name("&").as_deref(), Some("and"));
        assert_eq!(slugify_skill_name(" & ").as_deref(), Some("and"));
        // Multiple `&`s with various spacing all collapse properly.
        assert_eq!(slugify_skill_name("&&").as_deref(), Some("and-and"));
        assert_eq!(
            slugify_skill_name("foo & & bar").as_deref(),
            Some("foo-and-and-bar")
        );
        // Mixed with other punctuation (other punctuation is still dropped).
        assert_eq!(slugify_skill_name("AT&T").as_deref(), Some("at-and-t"));
        assert_eq!(slugify_skill_name("Q&A!").as_deref(), Some("q-and-a"));
    }

    #[test]
    fn test_slugify_punctuation_surrounded_by_spaces() {
        // `foo ! bar` → `foo-bar`: the two spaces would each produce a
        // dash, but consecutive dashes are collapsed.
        assert_eq!(slugify_skill_name("foo ! bar").as_deref(), Some("foo-bar"));
        assert_eq!(slugify_skill_name("foo ? bar").as_deref(), Some("foo-bar"));
        assert_eq!(
            slugify_skill_name("100 % sure").as_deref(),
            Some("100-sure")
        );
        assert_eq!(
            slugify_skill_name("foo @ bar @ baz").as_deref(),
            Some("foo-bar-baz")
        );
    }

    #[test]
    fn test_slugify_punctuation_adjacent_to_space() {
        // `foo! bar` and `foo !bar` both produce `foo-bar` — the
        // punctuation contributes nothing, the single space contributes
        // the dash.
        assert_eq!(slugify_skill_name("foo! bar").as_deref(), Some("foo-bar"));
        assert_eq!(slugify_skill_name("foo !bar").as_deref(), Some("foo-bar"));
        assert_eq!(slugify_skill_name("foo? bar").as_deref(), Some("foo-bar"));
    }

    #[test]
    fn test_slugify_leading_and_trailing_punctuation() {
        // Punctuation at the edges is dropped; there's no leading/trailing
        // dash to trim because the punctuation never became a dash in the
        // first place.
        assert_eq!(slugify_skill_name("!foo").as_deref(), Some("foo"));
        assert_eq!(slugify_skill_name("foo!").as_deref(), Some("foo"));
        assert_eq!(slugify_skill_name("!!!foo!!!").as_deref(), Some("foo"));
        assert_eq!(slugify_skill_name("?foo?").as_deref(), Some("foo"));
        assert_eq!(slugify_skill_name("...foo...").as_deref(), Some("foo"));
    }

    #[test]
    fn test_slugify_only_punctuation_returns_none() {
        assert_eq!(slugify_skill_name("!!!"), None);
        assert_eq!(slugify_skill_name("?@$"), None);
        assert_eq!(slugify_skill_name("()[]{}"), None);
        assert_eq!(slugify_skill_name(".,;:"), None);
    }

    #[test]
    fn test_slugify_mixed_punctuation_spaces_and_dashes() {
        // A messy realistic input: combination of punctuation, spaces,
        // existing dashes, and casing.
        assert_eq!(
            slugify_skill_name("  -- Hello, World!! -- ").as_deref(),
            Some("hello-world")
        );
        assert_eq!(
            slugify_skill_name("C++ vs. Rust?").as_deref(),
            Some("c-vs-rust")
        );
        assert_eq!(
            slugify_skill_name("v1.2.3-beta").as_deref(),
            Some("v123-beta")
        );
    }

    #[test]
    fn test_slugify_underscores_are_dropped() {
        // Underscores aren't a valid skill-name character and aren't
        // separators — only spaces become dashes — so underscores get
        // dropped entirely.
        assert_eq!(slugify_skill_name("foo_bar").as_deref(), Some("foobar"));
        assert_eq!(slugify_skill_name("FOO_BAR").as_deref(), Some("foobar"));
        assert_eq!(
            slugify_skill_name("snake_case style").as_deref(),
            Some("snakecase-style")
        );
    }

    #[test]
    fn test_slugify_collapses_consecutive_dashes() {
        assert_eq!(
            slugify_skill_name("foo   ---  bar").as_deref(),
            Some("foo-bar")
        );
    }

    #[test]
    fn test_slugify_trims_leading_and_trailing_dashes() {
        assert_eq!(slugify_skill_name("---foo---").as_deref(), Some("foo"));
        assert_eq!(slugify_skill_name("  foo  ").as_deref(), Some("foo"));
    }

    #[test]
    fn test_slugify_lowercases() {
        assert_eq!(slugify_skill_name("FOO BAR").as_deref(), Some("foo-bar"));
        assert_eq!(
            slugify_skill_name("MyCoolSkill").as_deref(),
            Some("mycoolskill")
        );
    }

    #[test]
    fn test_slugify_strips_non_ascii_letters() {
        // Non-ASCII chars are replaced with `-`, then collapsed.
        assert_eq!(slugify_skill_name("abc\u{00e9}").as_deref(), Some("abc"));
        assert_eq!(slugify_skill_name("\u{4e2d}\u{6587}"), None);
    }

    #[test]
    fn test_slugify_returns_none_for_empty_or_unmappable() {
        assert_eq!(slugify_skill_name(""), None);
        assert_eq!(slugify_skill_name("   "), None);
        assert_eq!(slugify_skill_name("!!!"), None);
        assert_eq!(slugify_skill_name("---"), None);
    }

    #[test]
    fn test_slugify_truncates_long_inputs() {
        let input = "a".repeat(200);
        let slug = slugify_skill_name(&input).expect("should slugify");
        assert_eq!(slug.len(), MAX_SKILL_NAME_LEN);
        assert!(slug.chars().all(|c| c == 'a'));
    }

    #[test]
    fn test_slugify_truncation_does_not_leave_trailing_dash() {
        // The 64th byte lands on a `-`, which we must strip post-truncation.
        let mut input = "a".repeat(63);
        input.push_str(" extra");
        let slug = slugify_skill_name(&input).expect("should slugify");
        assert!(!slug.ends_with('-'));
        assert!(slug.len() <= MAX_SKILL_NAME_LEN);
    }

    #[test]
    fn test_slugify_output_passes_validate_name() {
        for input in [
            "My Cool Skill",
            "Hello, World!",
            "---foo---",
            "123 abc",
            "a".repeat(200).as_str(),
        ] {
            let slug = slugify_skill_name(input).expect("should slugify");
            validate_name(&slug).unwrap_or_else(|err| {
                panic!("slug {slug:?} from {input:?} failed validation: {err}")
            });
        }
    }

    #[test]
    fn test_parse_description_too_long() {
        let long_desc = "a".repeat(1025);
        let content = format!(
            r#"---
name: test
description: {long_desc}
---

Content.
"#
        );

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            &content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        let expected = format!("at most {MAX_SKILL_DESCRIPTION_LEN} bytes");
        assert!(result.unwrap_err().to_string().contains(&expected));
    }

    #[test]
    fn test_parse_empty_description() {
        let content = r#"---
name: test
description: ""
---

Content.
"#;

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        assert!(result.unwrap_err().to_string().contains("cannot be empty"));
    }

    #[test]
    fn test_parse_file_too_large() {
        let large_content = format!(
            r#"---
name: test
description: Test skill
---

{}"#,
            "x".repeat(MAX_SKILL_FILE_SIZE + 1)
        );

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            &large_content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        assert!(result.unwrap_err().to_string().contains("exceeds maximum"));
    }

    #[test]
    fn test_parse_empty_body_after_frontmatter() {
        let content = r#"---
name: minimal-skill
description: A skill with no body content
---
"#;

        let result = parse_skill_frontmatter(
            Path::new("/skills/minimal/SKILL.md"),
            content,
            SkillSource::Global,
        );

        let skill = result.expect("Empty body should be allowed");
        assert_eq!(skill.name, "minimal-skill");
        assert_eq!(skill.description, "A skill with no body content");
    }

    #[test]
    fn test_parse_whitespace_only_body() {
        let content = "---\nname: whitespace-skill\ndescription: Test\n---\n\n   \n\n   \n";

        let result = parse_skill_frontmatter(
            Path::new("/skills/ws/SKILL.md"),
            content,
            SkillSource::Global,
        );

        let skill = result.expect("Whitespace-only body should be allowed");
        assert_eq!(skill.name, "whitespace-skill");
    }

    #[test]
    fn test_parse_skill_with_crlf_line_endings() {
        let content = "---\r\nname: crlf-skill\r\ndescription: A skill with CRLF line endings\r\n---\r\n\r\n# CRLF Skill\r\n\r\nDo the thing.\r\n";

        let result = parse_skill_frontmatter(
            Path::new("/skills/crlf-skill/SKILL.md"),
            content,
            SkillSource::Global,
        );
        let skill = result.expect("CRLF document should parse successfully");

        assert_eq!(skill.name, "crlf-skill");
        assert_eq!(skill.description, "A skill with CRLF line endings");
    }

    #[test]
    fn test_parse_skill_with_mixed_line_endings() {
        let content = "---\r\nname: mixed-skill\r\ndescription: Frontmatter uses CRLF, body uses LF\r\n---\r\n\n# Mixed Skill\n\nBody uses LF only.\n";

        let result = parse_skill_frontmatter(
            Path::new("/skills/mixed-skill/SKILL.md"),
            content,
            SkillSource::Global,
        );
        let skill = result.expect("Mixed line endings should parse successfully");

        assert_eq!(skill.name, "mixed-skill");
        assert_eq!(skill.description, "Frontmatter uses CRLF, body uses LF");
    }

    #[test]
    fn test_parse_rejects_closing_delimiter_with_trailing_chars() {
        // The only `---` after the opener has trailing junk on the same line,
        // so it isn't a valid closing delimiter and parsing must error.
        let content = "---\nname: foo\ndescription: bar\n---trailing-junk\nbody content\n";

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        assert!(
            result
                .unwrap_err()
                .to_string()
                .contains("missing closing frontmatter delimiter")
        );
    }

    #[test]
    fn test_parse_accepts_only_truly_terminated_closing_delimiter() {
        // The first `---trailing` appears inside a quoted YAML string and is
        // NOT alone on its line, so it must not be treated as the closer.
        // The real closer comes later as `\n---\n`.
        let content = "---\nname: skill-name\ndescription: A real description\nsummary: \"---trailing\"\n---\nbody content\n";

        let skill = parse_skill_frontmatter(
            Path::new("/skills/skill-name/SKILL.md"),
            content,
            SkillSource::Global,
        )
        .expect("Should pick the truly-terminated closing delimiter");

        assert_eq!(skill.name, "skill-name");
        assert_eq!(skill.description, "A real description");
    }

    #[test]
    fn test_parse_accepts_four_dashes_as_invalid_closer() {
        // A line of four dashes is NOT a valid closing delimiter; with no
        // valid closer following, parsing must error.
        let content = "---\nname: foo\ndescription: bar\n----\nbody content\n";

        let result = parse_skill_frontmatter(
            Path::new("/skills/test/SKILL.md"),
            content,
            SkillSource::Global,
        );
        assert!(result.is_err());
        assert!(
            result
                .unwrap_err()
                .to_string()
                .contains("missing closing frontmatter delimiter")
        );
    }

    #[gpui::test]
    async fn test_load_skills_from_empty_directory(cx: &mut TestAppContext) {
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree("/skills", serde_json::json!({})).await;

        let results = load_skills_from_directory(
            &(fs as Arc<dyn Fs>),
            Path::new("/skills"),
            SkillSource::Global,
        )
        .await;
        assert!(results.is_empty());
    }

    #[gpui::test]
    async fn test_load_single_skill(cx: &mut TestAppContext) {
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "my-skill": {
                    "SKILL.md": "---\nname: my-skill\ndescription: Test skill\n---\n\n# Instructions\nDo stuff."
                }
            }),
        )
        .await;

        let results = load_skills_from_directory(
            &(fs as Arc<dyn Fs>),
            Path::new("/skills"),
            SkillSource::Global,
        )
        .await;

        assert_eq!(results.len(), 1);
        let skill = results[0].as_ref().expect("Should load successfully");
        assert_eq!(skill.name, "my-skill");
        assert_eq!(skill.description, "Test skill");
    }

    #[gpui::test]
    async fn test_load_nested_skills(cx: &mut TestAppContext) {
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "skill-one": {
                    "SKILL.md": "---\nname: skill-one\ndescription: First skill\n---\n\nContent one"
                },
                "skill-two": {
                    "SKILL.md": "---\nname: skill-two\ndescription: Second skill\n---\n\nContent two"
                }
            }),
        )
        .await;

        let results = load_skills_from_directory(
            &(fs as Arc<dyn Fs>),
            Path::new("/skills"),
            SkillSource::Global,
        )
        .await;

        assert_eq!(results.len(), 2);
        let names: Vec<&str> = results
            .iter()
            .filter_map(|r| r.as_ref().ok())
            .map(|s| s.name.as_str())
            .collect();
        assert!(names.contains(&"skill-one"));
        assert!(names.contains(&"skill-two"));
    }

    #[gpui::test]
    async fn test_load_skills_returns_results_sorted_by_path(cx: &mut TestAppContext) {
        // `apply_skill_overrides` resolves same-source name collisions
        // by keeping the first entry in iteration order. Without a
        // stable sort here, the result depends on `fs.read_dir`, which
        // is OS/filesystem-dependent. Assert the contract: results
        // come back sorted by skill file path regardless of insertion
        // order.
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "charlie": {
                    "SKILL.md": "---\nname: charlie\ndescription: C\n---\n\nC"
                },
                "alpha": {
                    "SKILL.md": "---\nname: alpha\ndescription: A\n---\n\nA"
                },
                "bravo": {
                    "SKILL.md": "---\nname: bravo\ndescription: B\n---\n\nB"
                },
                "delta": {
                    "SKILL.md": "No frontmatter, will fail"
                },
            }),
        )
        .await;

        let results = load_skills_from_directory(
            &(fs as Arc<dyn Fs>),
            Path::new("/skills"),
            SkillSource::Global,
        )
        .await;

        assert_eq!(results.len(), 4);

        let paths: Vec<PathBuf> = results
            .iter()
            .map(|r| match r {
                Ok(skill) => skill.skill_file_path.clone(),
                Err(error) => error.path.clone(),
            })
            .collect();

        let mut expected = paths.clone();
        expected.sort();
        assert_eq!(paths, expected);
    }

    #[gpui::test]
    async fn test_load_ignores_non_skill_files(cx: &mut TestAppContext) {
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "my-skill": {
                    "SKILL.md": "---\nname: my-skill\ndescription: Test\n---\n\nContent"
                },
                "not-a-skill.txt": "This is not a skill",
                "some-dir": {
                    "other-file.md": "Not a SKILL.md"
                }
            }),
        )
        .await;

        let results = load_skills_from_directory(
            &(fs as Arc<dyn Fs>),
            Path::new("/skills"),
            SkillSource::Global,
        )
        .await;

        assert_eq!(results.len(), 1);
        let skill = results[0].as_ref().expect("Should load successfully");
        assert_eq!(skill.name, "my-skill");
    }

    #[gpui::test]
    async fn test_load_returns_errors_for_invalid_skills(cx: &mut TestAppContext) {
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "valid-skill": {
                    "SKILL.md": "---\nname: valid-skill\ndescription: Valid\n---\n\nContent"
                },
                "invalid-skill": {
                    "SKILL.md": "No frontmatter here"
                }
            }),
        )
        .await;

        let results = load_skills_from_directory(
            &(fs as Arc<dyn Fs>),
            Path::new("/skills"),
            SkillSource::Global,
        )
        .await;

        assert_eq!(results.len(), 2);

        let (successes, errors): (Vec<_>, Vec<_>) = results.iter().partition(|r| r.is_ok());

        assert_eq!(successes.len(), 1);
        assert_eq!(errors.len(), 1);

        let error = errors[0].as_ref().unwrap_err();
        assert!(error.path.to_string_lossy().contains("invalid-skill"));
    }

    #[gpui::test]
    async fn test_load_from_nonexistent_directory(cx: &mut TestAppContext) {
        let fs = FakeFs::new(cx.executor());

        let results = load_skills_from_directory(
            &(fs as Arc<dyn Fs>),
            Path::new("/nonexistent"),
            SkillSource::Global,
        )
        .await;

        assert!(results.is_empty());
    }

    #[test]
    fn test_skill_summary_from_skill() {
        let skill = Skill {
            name: "test-skill".to_string(),
            description: "A test description".to_string(),
            source: SkillSource::Global,
            directory_path: PathBuf::from("/skills/test-skill"),
            skill_file_path: PathBuf::from("/skills/test-skill/SKILL.md"),
            disable_model_invocation: false,
            embedded_body: None,
        };

        let summary = SkillSummary::from(&skill);
        assert_eq!(summary.name, "test-skill");
        assert_eq!(summary.description, "A test description");
        assert_eq!(summary.location, "/skills/test-skill/SKILL.md");
    }

    #[gpui::test]
    async fn test_nested_skill_md_inside_skill_resources_is_not_loaded(cx: &mut TestAppContext) {
        // We only look at immediate children of the skills root, so a
        // `SKILL.md` nested inside a skill's resources directory cannot
        // accidentally be picked up as a separate skill.
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "outer": {
                    "SKILL.md": "---\nname: outer\ndescription: Outer skill\n---\n\nBody",
                    "references": {
                        "SKILL.md": "---\nname: bogus-inner\ndescription: Should not load\n---\n\nBody"
                    },
                },
            }),
        )
        .await;

        let results = load_skills_from_directory(
            &(fs as Arc<dyn Fs>),
            Path::new("/skills"),
            SkillSource::Global,
        )
        .await;

        let names: Vec<&str> = results
            .iter()
            .filter_map(|r| r.as_ref().ok())
            .map(|s| s.name.as_str())
            .collect();
        assert_eq!(names, vec!["outer"]);
    }

    #[gpui::test]
    async fn test_load_oversized_skill_file_short_circuits(cx: &mut TestAppContext) {
        // A `SKILL.md` whose size exceeds `MAX_SKILL_FILE_SIZE` must be
        // rejected via metadata before we read its contents into memory.
        // Otherwise a stray multi-GB file dropped into a skill directory
        // would OOM the application before `parse_skill`'s size check fires.
        let fs = FakeFs::new(cx.executor());
        let oversized_body = "x".repeat(MAX_SKILL_FILE_SIZE + 1);
        let oversized_content = format!(
            "---\nname: huge\ndescription: Too big\n---\n\n{}",
            oversized_body
        );
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "huge": {
                    "SKILL.md": oversized_content,
                }
            }),
        )
        .await;

        let results = load_skills_from_directory(
            &(fs as Arc<dyn Fs>),
            Path::new("/skills"),
            SkillSource::Global,
        )
        .await;

        assert_eq!(results.len(), 1);
        let err = results[0].as_ref().expect_err("Oversized file must error");
        assert!(
            err.message.contains("exceeds maximum size"),
            "unexpected error message: {}",
            err.message
        );
    }

    #[gpui::test]
    async fn test_load_skill_frontmatter_parses_metadata_without_body(cx: &mut TestAppContext) {
        // `load_skill_frontmatter` should read just enough of the file to
        // parse the frontmatter and return a `Skill` with name/description/
        // disable_model_invocation populated. The body is intentionally not
        // surfaced; callers go through `read_skill_body` for that.
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "my-skill": {
                    "SKILL.md": "---\nname: my-skill\ndescription: A skill for tests\ndisable-model-invocation: true\n---\n\n# Body\n\nLots of body text here.\n"
                }
            }),
        )
        .await;

        let skill = load_skill_frontmatter(
            fs as Arc<dyn Fs>,
            PathBuf::from("/skills/my-skill/SKILL.md"),
            SkillSource::Global,
        )
        .await
        .expect("frontmatter should parse");

        assert_eq!(skill.name, "my-skill");
        assert_eq!(skill.description, "A skill for tests");
        assert!(skill.disable_model_invocation);
        assert_eq!(
            skill.skill_file_path,
            PathBuf::from("/skills/my-skill/SKILL.md")
        );
        assert_eq!(skill.directory_path, PathBuf::from("/skills/my-skill"));
    }

    #[gpui::test]
    async fn test_read_skill_body_returns_trimmed_body(cx: &mut TestAppContext) {
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "my-skill": {
                    "SKILL.md": "---\nname: my-skill\ndescription: Test skill\n---\n\n# Instructions\n\nDo the thing.\n\n"
                }
            }),
        )
        .await;

        let body = read_skill_body(fs.as_ref(), Path::new("/skills/my-skill/SKILL.md"))
            .await
            .expect("body should load");

        // Trimmed: no leading blank line after the closing `---`, and no
        // trailing whitespace.
        assert_eq!(body, "# Instructions\n\nDo the thing.");
    }

    #[gpui::test]
    async fn test_read_skill_body_for_skill_without_body(cx: &mut TestAppContext) {
        let fs = FakeFs::new(cx.executor());
        fs.insert_tree(
            "/skills",
            serde_json::json!({
                "empty": {
                    "SKILL.md": "---\nname: empty\ndescription: No body\n---\n"
                }
            }),
        )
        .await;

        let body = read_skill_body(fs.as_ref(), Path::new("/skills/empty/SKILL.md"))
            .await
            .expect("body should load");

        assert!(body.is_empty(), "expected empty body, got: {body:?}");
    }

    #[test]
    fn is_agents_skills_path_simple_positive() {
        assert!(is_agents_skills_path(Path::new(
            "foo/.agents/skills/my-skill/SKILL.md"
        )));
    }

    #[test]
    fn is_agents_skills_path_simple_negative() {
        assert!(!is_agents_skills_path(Path::new("foo/bar/baz")));
    }

    #[test]
    fn is_agents_skills_path_double_agents() {
        // `foo/.agents/.agents/skills` contains a `.agents/skills` pair at
        // depths 2-3. Any-depth matching catches it; this is intentional, so
        // a `.agents/skills` directory the user wasn't expecting to be
        // touched still prompts for confirmation.
        assert!(is_agents_skills_path(Path::new(
            "foo/.agents/.agents/skills"
        )));
    }

    #[test]
    fn is_agents_skills_path_agents_without_skills() {
        assert!(!is_agents_skills_path(Path::new("foo/.agents/other")));
    }

    #[test]
    fn is_agents_skills_path_at_start() {
        assert!(is_agents_skills_path(Path::new(".agents/skills")));
    }

    #[test]
    fn is_agents_skills_path_trailing_agents() {
        assert!(!is_agents_skills_path(Path::new("foo/.agents")));
    }

    #[test]
    fn is_agents_skills_path_deep_match() {
        // Any-depth matching: nested `.agents/skills` directories — e.g.
        // inside vendored sources — are flagged too. We prefer the extra
        // prompt over silently letting the agent edit something named
        // `.agents/skills`.
        assert!(is_agents_skills_path(Path::new("a/b/.agents/skills/x.txt")));
        assert!(is_agents_skills_path(Path::new(
            "some/random/place/.agents/skills/foo"
        )));
    }

    #[test]
    fn is_agents_skills_path_absolute() {
        // Absolute paths into a project-local `.agents/skills/` are caught
        // by the same consecutive-component match.
        assert!(is_agents_skills_path(Path::new(
            "/Users/foo/project/.agents/skills/my-skill/SKILL.md"
        )));
        assert!(!is_agents_skills_path(Path::new("/etc/hosts")));
    }

    #[test]
    fn is_agents_skills_path_case_insensitive() {
        // Filesystems on macOS/Windows are case-insensitive by default; the
        // classifier must agree.
        assert!(is_agents_skills_path(Path::new(".AGENTS/skills/foo")));
        assert!(is_agents_skills_path(Path::new(".agents/SKILLS/foo")));
        assert!(is_agents_skills_path(Path::new(
            "project/.AGENTS/SKILLS/foo"
        )));
    }

    #[test]
    fn validate_name_accepts_valid_names() {
        assert!(validate_name("draft-pr").is_ok());
        assert!(validate_name("a").is_ok());
        assert!(validate_name("skill1").is_ok());
        assert!(validate_name(&"a".repeat(MAX_SKILL_NAME_LEN)).is_ok());
    }

    #[test]
    fn validate_name_rejects_empty() {
        assert!(validate_name("").is_err());
    }

    #[test]
    fn validate_name_rejects_uppercase() {
        assert!(validate_name("Draft-PR").is_err());
    }

    #[test]
    fn validate_name_rejects_leading_and_trailing_hyphens() {
        assert!(validate_name("-draft").is_err());
        assert!(validate_name("draft-").is_err());
    }

    #[test]
    fn validate_name_rejects_invalid_chars() {
        assert!(validate_name("draft_pr").is_err());
        assert!(validate_name("draft pr").is_err());
        assert!(validate_name("draft.pr").is_err());
    }

    #[test]
    fn validate_name_rejects_too_long() {
        assert!(validate_name(&"a".repeat(MAX_SKILL_NAME_LEN + 1)).is_err());
    }

    #[test]
    fn validate_description_accepts_valid() {
        assert!(validate_description("A useful skill").is_ok());
    }

    #[test]
    fn validate_description_rejects_empty_and_whitespace_only() {
        assert!(validate_description("").is_err());
        assert!(validate_description("   ").is_err());
        assert!(validate_description("\t\n ").is_err());
    }

    #[test]
    fn validate_description_rejects_too_long() {
        assert!(validate_description(&"a".repeat(MAX_SKILL_DESCRIPTION_LEN + 1)).is_err());
    }

    #[test]
    fn validate_description_length_is_measured_in_bytes() {
        // "é" is 2 bytes in UTF-8. A string of MAX/2 + 1 "é" characters has
        // only ~MAX/2 + 1 chars but exceeds MAX bytes, so it must be
        // rejected by a byte-based validator (and accepted by a char-based
        // one). This regression-tests the byte semantics that the loader
        // and UI both rely on.
        let chars = MAX_SKILL_DESCRIPTION_LEN / 2 + 1;
        let description = "é".repeat(chars);
        assert!(description.chars().count() <= MAX_SKILL_DESCRIPTION_LEN);
        assert!(description.len() > MAX_SKILL_DESCRIPTION_LEN);
        assert!(validate_description(&description).is_err());
    }

    #[test]
    fn slugify_output_always_passes_validate_name() {
        for input in [
            "foo",
            "Foo Bar",
            "rock & roll",
            "---weird---",
            "a".repeat(200).as_str(),
        ] {
            if let Some(slug) = slugify_skill_name(input) {
                assert!(
                    validate_name(&slug).is_ok(),
                    "slug {slug:?} from {input:?} failed validate_name"
                );
            }
        }
    }

    #[test]
    fn skill_share_link_round_trips() {
        let content =
            "---\nname: my-skill\ndescription: Does a thing.\n---\n\n## Steps\n\nDo the thing.\n";
        let link = encode_skill_share_link(content);
        let data = link
            .strip_prefix("joule://skill?data=")
            .expect("link should start with the skill share prefix");
        // base64url (no-pad) output must not require percent-encoding.
        assert!(!data.contains('+') && !data.contains('/') && !data.contains('='));
        assert_eq!(decode_skill_share_link(&link).unwrap(), content);
    }

    #[test]
    fn decode_skill_share_link_rejects_non_skill_links() {
        assert!(decode_skill_share_link("joule://settings/agent.skills").is_err());
        assert!(decode_skill_share_link("joule://skill").is_err());
        assert!(decode_skill_share_link("joule://skill?other=1").is_err());
        assert!(decode_skill_share_link("joule://skill?data=!!!notbase64").is_err());
    }
}