//! The **Spec** artifact: spec-driven development made auditable.
//!
//! The field converged on spec-driven development — the spec, not the code, is
//! the canonical artifact, and agents derive plans and implementations from
//! it. What no methodology layer provides is *proof of traceability*: nothing
//! binds the code that shipped to the spec that was approved, so "we followed
//! the spec" is testimony, not evidence.
//!
//! This crate closes that gap with three artifacts in the family's house
//! style (canonical det-CBOR, BLAKE3 content addresses, Ed25519 over
//! `id ‖ context` preimages):
//!
//! - a [`Spec`]: an intent plus ordered, individually addressable **clauses**
//!   (requirements, constraints, and — first-class — non-goals), signed by its
//!   author and content-addressed, with revisions chained by `parent` so spec
//!   evolution is itself tamper-evident history;
//! - a [`Citation`]: a signed binding from one coding operation
//!   (`joule-code-cargo::CodingOp`, by `op_id`) to the clauses it claims to
//!   implement — the op cites the spec the way a receipt cites the op;
//! - a [`Coverage`] report: the deterministic audit over a spec and a set of
//!   citations — which clauses are implemented, which are still open, which
//!   ops claim no clause at all, and which citations name clauses the spec
//!   does not contain (a *mis-citation* is never silently dropped).
//!
//! Together with the existing chain (op → receipt → attested build), this
//! completes: **spec → clause → op → receipt** — every joule and every edit
//! traceable to an approved, signed requirement, and every requirement
//! checkable for whether anything implements it.
//!
//! Nothing here invokes a model. Brainstorming produces the spec text
//! upstream however the deployment likes; this crate is the part an auditor
//! can hold.

use ed25519_dalek::{Signature, Signer, SigningKey, Verifier, VerifyingKey};
use joule_code_cargo::SignedOp;
use joule_code_schema::ContentId;
use serde::{Deserialize, Serialize};

/// Signature algorithm id for Ed25519 (matches `joule-code-schema`).
pub const ALG_ED25519: u8 = 0x01;

/// Errors from spec construction, signing, or verification.
#[derive(Debug, thiserror::Error)]
pub enum SpecError {
    #[error("spec must contain at least one clause")]
    Empty,
    #[error("clause ids must be unique: duplicate {0:?}")]
    DuplicateClause(String),
    #[error("clause id must be non-empty and contain no whitespace: {0:?}")]
    BadClauseId(String),
    #[error("clause text must be non-empty: {0:?}")]
    EmptyClause(String),
    #[error("intent must be non-empty")]
    EmptyIntent,
    #[error("unsupported algorithm id {0:#04x}")]
    BadAlg(u8),
    #[error("signature verification failed")]
    BadSignature,
    #[error("citation must name at least one clause")]
    EmptyCitation,
    #[error("schema: {0}")]
    Schema(#[from] joule_code_schema::SchemaError),
    #[error("cargo: {0}")]
    Cargo(#[from] joule_code_cargo::CargoError),
}

/// What kind of statement a clause is. Non-goals are first-class: writing
/// down what the system must *not* do is half the value of a brainstorm, and
/// an auditor checks them the same way.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub enum ClauseKind {
    /// Behavior the implementation must exhibit.
    Requirement,
    /// A bound the implementation must stay inside (style, dependency,
    /// energy, interface).
    Constraint,
    /// Behavior deliberately out of scope. An op citing a non-goal is a
    /// design conversation, not an implementation.
    NonGoal,
}

/// One individually addressable statement of the spec.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Clause {
    /// Stable id within the spec (`"C1"`, `"auth-2"`, …). Unique, no
    /// whitespace — it appears verbatim in citations and audit output.
    pub id: String,
    /// The testable statement.
    pub text: String,
    /// Requirement, constraint, or non-goal.
    pub kind: ClauseKind,
}

/// The canonical spec artifact (unsigned form).
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Spec {
    /// Signature algorithm id (`0x01` = Ed25519).
    pub alg: u8,
    /// The distilled intent — *why* this exists, in the author's words.
    pub intent: String,
    /// Ordered, non-empty clauses with unique ids.
    pub clauses: Vec<Clause>,
    /// The spec this one revises, if any — revisions chain by content
    /// address, so the history of what was approved is tamper-evident.
    pub parent: Option<ContentId>,
    /// The author's Ed25519 verifying key.
    pub author: [u8; 32],
}

impl Spec {
    /// Structural validation: non-empty intent, at least one clause, unique
    /// well-formed clause ids, known algorithm.
    pub fn validate(&self) -> Result<(), SpecError> {
        if self.alg != ALG_ED25519 {
            return Err(SpecError::BadAlg(self.alg));
        }
        if self.intent.trim().is_empty() {
            return Err(SpecError::EmptyIntent);
        }
        if self.clauses.is_empty() {
            return Err(SpecError::Empty);
        }
        let mut seen = std::collections::BTreeSet::new();
        for clause in &self.clauses {
            if clause.id.is_empty() || clause.id.chars().any(char::is_whitespace) {
                return Err(SpecError::BadClauseId(clause.id.clone()));
            }
            if clause.text.trim().is_empty() {
                return Err(SpecError::EmptyClause(clause.id.clone()));
            }
            if !seen.insert(clause.id.as_str()) {
                return Err(SpecError::DuplicateClause(clause.id.clone()));
            }
        }
        Ok(())
    }

    /// The spec id: content address of the canonical form. Validates first —
    /// a non-canonical spec has no id.
    pub fn spec_id(&self) -> Result<ContentId, SpecError> {
        self.validate()?;
        Ok(ContentId::of_canonical(self)?)
    }

    /// The signature preimage: `spec_id ‖ parent` (the empty string when this
    /// is a root spec) — signing binds the revision to its lineage, the same
    /// shape as the op's `op_id ‖ prior`.
    fn preimage(&self) -> Result<Vec<u8>, SpecError> {
        let spec_id = self.spec_id()?;
        let mut pre = spec_id.as_str().as_bytes().to_vec();
        if let Some(parent) = &self.parent {
            pre.extend_from_slice(parent.as_str().as_bytes());
        }
        Ok(pre)
    }

    /// Sign with the author's key, producing a [`SignedSpec`].
    pub fn sign(self, key: &SigningKey) -> Result<SignedSpec, SpecError> {
        let sig = key.sign(&self.preimage()?);
        Ok(SignedSpec { spec: self, sig: sig.to_bytes().to_vec() })
    }

    /// Begin a revision of this spec: same intent and clauses (edit them
    /// before signing), `parent` set to this spec's id, author replaced by
    /// the reviser.
    pub fn revise(&self, author: [u8; 32]) -> Result<Spec, SpecError> {
        Ok(Spec {
            alg: self.alg,
            intent: self.intent.clone(),
            clauses: self.clauses.clone(),
            parent: Some(self.spec_id()?),
            author,
        })
    }
}

/// A spec plus its author's signature.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SignedSpec {
    pub spec: Spec,
    /// Ed25519 signature (64 bytes) over `spec_id ‖ parent`.
    pub sig: Vec<u8>,
}

impl SignedSpec {
    /// Verify structure, content address, and signature.
    pub fn verify(&self) -> Result<ContentId, SpecError> {
        let pre = self.spec.preimage()?;
        let key =
            VerifyingKey::from_bytes(&self.spec.author).map_err(|_| SpecError::BadSignature)?;
        let sig_bytes: [u8; 64] =
            self.sig.as_slice().try_into().map_err(|_| SpecError::BadSignature)?;
        key.verify(&pre, &Signature::from_bytes(&sig_bytes))
            .map_err(|_| SpecError::BadSignature)?;
        self.spec.spec_id()
    }
}

/// A signed binding from one coding operation to the spec clauses it claims
/// to implement. The op stays wire-identical (`joule-code-cargo` is
/// untouched); traceability is an additive artifact, the way the receipt is.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Citation {
    /// Signature algorithm id (`0x01` = Ed25519).
    pub alg: u8,
    /// The op making the claim.
    pub op_id: ContentId,
    /// The spec being cited.
    pub spec_id: ContentId,
    /// The clause ids the op claims to implement. Non-empty.
    pub clauses: Vec<String>,
    /// The citing author's Ed25519 verifying key (normally the op's author).
    pub author: [u8; 32],
}

impl Citation {
    /// Structural validation.
    pub fn validate(&self) -> Result<(), SpecError> {
        if self.alg != ALG_ED25519 {
            return Err(SpecError::BadAlg(self.alg));
        }
        if self.clauses.is_empty() {
            return Err(SpecError::EmptyCitation);
        }
        Ok(())
    }

    /// The citation id: content address of the canonical form.
    pub fn citation_id(&self) -> Result<ContentId, SpecError> {
        self.validate()?;
        Ok(ContentId::of_canonical(self)?)
    }

    /// Preimage: `citation_id ‖ op_id ‖ spec_id`.
    fn preimage(&self) -> Result<Vec<u8>, SpecError> {
        let id = self.citation_id()?;
        let mut pre = id.as_str().as_bytes().to_vec();
        pre.extend_from_slice(self.op_id.as_str().as_bytes());
        pre.extend_from_slice(self.spec_id.as_str().as_bytes());
        Ok(pre)
    }

    /// Sign, producing a [`SignedCitation`].
    pub fn sign(self, key: &SigningKey) -> Result<SignedCitation, SpecError> {
        let sig = key.sign(&self.preimage()?);
        Ok(SignedCitation { citation: self, sig: sig.to_bytes().to_vec() })
    }
}

/// A citation plus its signature.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SignedCitation {
    pub citation: Citation,
    /// Ed25519 signature (64 bytes) over `citation_id ‖ op_id ‖ spec_id`.
    pub sig: Vec<u8>,
}

impl SignedCitation {
    /// Verify structure and signature.
    pub fn verify(&self) -> Result<ContentId, SpecError> {
        let pre = self.citation.preimage()?;
        let key = VerifyingKey::from_bytes(&self.citation.author)
            .map_err(|_| SpecError::BadSignature)?;
        let sig_bytes: [u8; 64] =
            self.sig.as_slice().try_into().map_err(|_| SpecError::BadSignature)?;
        key.verify(&pre, &Signature::from_bytes(&sig_bytes))
            .map_err(|_| SpecError::BadSignature)?;
        self.citation.citation_id()
    }
}

/// Cite a signed op against a signed spec: verifies both artifacts, checks
/// every named clause exists in the spec, and returns the signed citation.
/// This is the convenience path; the artifacts compose manually too.
pub fn cite(
    op: &SignedOp,
    spec: &SignedSpec,
    clauses: &[&str],
    key: &SigningKey,
) -> Result<SignedCitation, SpecError> {
    let spec_id = spec.verify()?;
    let op_id = op.op.op_id()?;
    let known: std::collections::BTreeSet<&str> =
        spec.spec.clauses.iter().map(|c| c.id.as_str()).collect();
    for clause in clauses {
        if !known.contains(clause) {
            return Err(SpecError::BadClauseId((*clause).to_string()));
        }
    }
    Citation {
        alg: ALG_ED25519,
        op_id,
        spec_id,
        clauses: clauses.iter().map(|c| (*c).to_string()).collect(),
        author: key.verifying_key().to_bytes(),
    }
    .sign(key)
}

/// The deterministic spec-coverage audit.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Coverage {
    /// Clause ids with at least one valid citation, with the citing op ids.
    pub covered: Vec<(String, Vec<ContentId>)>,
    /// Requirement/constraint clause ids no op cites — open obligations.
    pub uncovered: Vec<String>,
    /// Non-goal clause ids that ARE cited — each one a flag, not a pass:
    /// an op claims to implement something the spec says not to build.
    pub non_goals_cited: Vec<String>,
    /// Ops in the citation set whose citations failed verification or named
    /// unknown clauses — never silently dropped.
    pub invalid: Vec<ContentId>,
}

impl Coverage {
    /// A spec is satisfied when every requirement and constraint is covered,
    /// no non-goal is cited, and no citation is invalid.
    pub fn is_complete(&self) -> bool {
        self.uncovered.is_empty() && self.non_goals_cited.is_empty() && self.invalid.is_empty()
    }
}

/// Audit a spec against a set of citations. Citations for other specs are
/// counted invalid (they cannot witness this spec); so are citations that
/// fail signature verification or name clauses the spec lacks.
pub fn coverage(spec: &SignedSpec, citations: &[SignedCitation]) -> Result<Coverage, SpecError> {
    let spec_id = spec.verify()?;
    let mut by_clause: std::collections::BTreeMap<&str, Vec<ContentId>> =
        spec.spec.clauses.iter().map(|c| (c.id.as_str(), Vec::new())).collect();
    let mut invalid = Vec::new();

    for signed in citations {
        let ok = signed.verify().is_ok()
            && signed.citation.spec_id == spec_id
            && signed
                .citation
                .clauses
                .iter()
                .all(|c| by_clause.contains_key(c.as_str()));
        if !ok {
            invalid.push(signed.citation.op_id.clone());
            continue;
        }
        for clause in &signed.citation.clauses {
            by_clause
                .get_mut(clause.as_str())
                .expect("validated above")
                .push(signed.citation.op_id.clone());
        }
    }

    let mut covered = Vec::new();
    let mut uncovered = Vec::new();
    let mut non_goals_cited = Vec::new();
    for clause in &spec.spec.clauses {
        let ops = &by_clause[clause.id.as_str()];
        match clause.kind {
            ClauseKind::NonGoal => {
                if !ops.is_empty() {
                    non_goals_cited.push(clause.id.clone());
                }
            }
            ClauseKind::Requirement | ClauseKind::Constraint => {
                if ops.is_empty() {
                    uncovered.push(clause.id.clone());
                } else {
                    covered.push((clause.id.clone(), ops.clone()));
                }
            }
        }
    }
    Ok(Coverage { covered, uncovered, non_goals_cited, invalid })
}

#[cfg(test)]
mod tests {
    use super::*;
    use joule_code_cargo::{Anchor, CodingOp, Edit};
    use joule_code_schema::Tier;

    fn sk(s: u8) -> SigningKey {
        SigningKey::from_bytes(&[s; 32])
    }

    fn spec_fixture(author: &SigningKey) -> SignedSpec {
        Spec {
            alg: ALG_ED25519,
            intent: "a minesweeper with persistent state".into(),
            clauses: vec![
                Clause {
                    id: "C1".into(),
                    text: "board state survives a page reload".into(),
                    kind: ClauseKind::Requirement,
                },
                Clause {
                    id: "C2".into(),
                    text: "no network calls".into(),
                    kind: ClauseKind::Constraint,
                },
                Clause {
                    id: "NG1".into(),
                    text: "no multiplayer".into(),
                    kind: ClauseKind::NonGoal,
                },
            ],
            parent: None,
            author: author.verifying_key().to_bytes(),
        }
        .sign(author)
        .expect("valid spec signs")
    }

    fn op_fixture(author: &SigningKey, marker: u8) -> SignedOp {
        CodingOp {
            alg: 0x01,
            prior: ContentId::of_bytes(&[marker]),
            edits: vec![Edit {
                path: "src/store.rs".into(),
                anchor: Anchor::ByteRange { start: 0, end: 0 },
                replacement: vec![marker],
            }],
            author: author.verifying_key().to_bytes(),
            intent: "persist board state".into(),
            tier: Tier::L3,
        }
        .sign(author)
        .expect("valid op signs")
    }

    #[test]
    fn a_spec_signs_verifies_and_is_tamper_evident() {
        let author = sk(1);
        let signed = spec_fixture(&author);
        let id = signed.verify().expect("verifies");
        // flip one clause character → different artifact, dead signature
        let mut tampered = signed.clone();
        tampered.spec.clauses[0].text = "board state survives a page reload!".into();
        assert!(tampered.verify().is_err());
        assert_ne!(tampered.spec.spec_id().unwrap(), id);
    }

    #[test]
    fn revisions_chain_by_content_address() {
        let author = sk(1);
        let v1 = spec_fixture(&author);
        let v1_id = v1.verify().unwrap();
        let reviser = sk(2);
        let mut v2 = v1.spec.revise(reviser.verifying_key().to_bytes()).unwrap();
        v2.clauses.push(Clause {
            id: "C3".into(),
            text: "dark mode".into(),
            kind: ClauseKind::Requirement,
        });
        let v2 = v2.sign(&reviser).unwrap();
        assert_eq!(v2.spec.parent.as_ref(), Some(&v1_id));
        v2.verify().expect("revision verifies");
    }

    #[test]
    fn citing_an_unknown_clause_is_refused() {
        let author = sk(1);
        let spec = spec_fixture(&author);
        let op = op_fixture(&author, 7);
        let err = cite(&op, &spec, &["C99"], &author).unwrap_err();
        assert!(matches!(err, SpecError::BadClauseId(_)));
    }

    #[test]
    fn coverage_finds_open_obligations_and_flags_non_goals() {
        let author = sk(1);
        let spec = spec_fixture(&author);
        let op1 = op_fixture(&author, 1);
        let c1 = cite(&op1, &spec, &["C1"], &author).unwrap();
        let report = coverage(&spec, std::slice::from_ref(&c1)).unwrap();
        assert_eq!(report.covered.len(), 1); // C1 witnessed by op1
        assert_eq!(report.uncovered, vec!["C2".to_string()]); // C2 still open
        assert!(!report.is_complete());

        // an op citing the non-goal is flagged, not passed
        let op2 = op_fixture(&author, 2);
        let ng = cite(&op2, &spec, &["NG1"], &author).unwrap();
        let report = coverage(&spec, &[c1.clone(), ng]).unwrap();
        assert_eq!(report.non_goals_cited, vec!["NG1".to_string()]);
        assert!(!report.is_complete());

        // covering C2 (and dropping the non-goal op) completes the spec
        let op3 = op_fixture(&author, 3);
        let c2 = cite(&op3, &spec, &["C2"], &author).unwrap();
        let report = coverage(&spec, &[c1, c2]).unwrap();
        assert!(report.is_complete());
    }

    #[test]
    fn a_citation_against_a_different_spec_is_invalid_not_dropped() {
        let author = sk(1);
        let spec_a = spec_fixture(&author);
        let mut other = spec_a.spec.clone();
        other.intent = "a different product".into();
        let spec_b = other.sign(&author).unwrap();
        let op = op_fixture(&author, 9);
        let citation_b = cite(&op, &spec_b, &["C1"], &author).unwrap();
        let report = coverage(&spec_a, &[citation_b]).unwrap();
        assert_eq!(report.invalid.len(), 1); // recorded, never silently dropped
        assert!(!report.is_complete());
    }
}