// The native sink's C interface (wai/extensions/native-sink.md §9), wrapped for Swift: one
// `WaiSink` is one playback session. Every call passes JSON across the boundary as the
// extension's tables list it, and every answer comes back as the JSON the library wrote.
import Foundation
import WaiFFI

/// An error the library returned: its status and `wai_last_error`'s message, which starts with
/// the reason for an input that does not read (`native_input_invalid`, …).
public struct WaiSinkError: Error, CustomStringConvertible, Equatable {
    public let status: Int32
    public let message: String
    /// The reason code the message starts with.
    public var reason: String { String(message.split(separator: ":", maxSplits: 1).first ?? "") }
    public var description: String { "wai_sink status \(status): \(message)" }
}

/// One session of the native sink (native-sink §3).
public final class WaiSink: @unchecked Sendable {
    /// What a session requires of what it is given (native-sink §3.1).
    public struct Config: Equatable {
        public var channel: String
        public var owner: String
        public var presentation: String?
        public var windowUs: UInt64?
        public var adClasses: [String]
        public var contentAddressed: Bool
        public var requireSigned: Bool
        public var unseenGraceMs: UInt64?
        public var idleMs: UInt64?

        public init(channel: String, owner: String, presentation: String? = nil, windowUs: UInt64? = nil, adClasses: [String] = [],
                    contentAddressed: Bool = false, requireSigned: Bool = false, unseenGraceMs: UInt64? = nil, idleMs: UInt64? = nil) {
            self.channel = channel
            self.owner = owner
            self.presentation = presentation
            self.windowUs = windowUs
            self.adClasses = adClasses
            self.contentAddressed = contentAddressed
            self.requireSigned = requireSigned
            self.unseenGraceMs = unseenGraceMs
            self.idleMs = idleMs
        }

        /// The configuration JSON of §3.1.
        public var json: [String: Any] {
            var o: [String: Any] = ["channel": channel, "owner": owner, "ad_classes": adClasses, "content_addressed": contentAddressed,
                                    "require": requireSigned ? "signed" : "nothing"]
            if let p = presentation { o["presentation"] = p }
            if let w = windowUs { o["window_us"] = w }
            if let g = unseenGraceMs { o["unseen_grace_ms"] = g }
            if let i = idleMs { o["idle_ms"] = i }
            return o
        }
    }

    /// How a session ends (stream-audit §8.2).
    public enum Ended: String, Sendable {
        case ended, user, hidden, idle, error
    }

    private let handle: OpaquePointer

    /// The ABI version the linked library implements.
    public static var abiVersion: UInt32 { wai_sink_abi_version() }

    /// The host's clock, in microseconds since 1970.
    public static var nowUs: UInt64 { wai_sink_now_us() }

    /// Open a session from a configuration JSON object. `seed` is for conformance vectors and
    /// tests only: a viewer's session takes a fresh key (`seed` nil).
    public init(configJSON: [String: Any], seed: Data? = nil, startUs: UInt64 = WaiSink.nowUs) throws {
        guard WaiSink.abiVersion == UInt32(WAI_SINK_ABI_VERSION) else {
            throw WaiSinkError(status: -1, message: "native_abi_mismatch: the linked library implements ABI \(WaiSink.abiVersion)")
        }
        let cfg = try WaiSink.text(configJSON)
        var out: OpaquePointer?
        let st: Int32 = cfg.withCString { c in
            if let seed {
                return seed.withUnsafeBytes { p in wai_sink_open(c, p.bindMemory(to: UInt8.self).baseAddress, UInt(seed.count), startUs, &out) }
            }
            return wai_sink_open(c, nil, 0, startUs, &out)
        }
        guard st == 0, let h = out else { throw WaiSink.error(st) }
        handle = h
    }

    public convenience init(config: Config, seed: Data? = nil, startUs: UInt64 = WaiSink.nowUs) throws {
        try self.init(configJSON: config.json, seed: seed, startUs: startUs)
    }

    deinit { wai_sink_free(handle) }

    // MARK: calls

    /// The session's identity: `channel`, `owner`, `player`, `session`, `start_us`,
    /// `presentation`, `ended`.
    public func info() throws -> [String: Any] {
        try WaiSink.object(try call { wai_sink_info(handle, &$0) })
    }

    /// The receipt file to fetch beside a playlist, relative to it: `mr/<BLAKE3>.json`.
    public static func receiptName(_ playlist: Data) -> String {
        var out = wai_buffer_t(data: nil, len: 0, cap: 0)
        let st = playlist.withUnsafeBytes { p in wai_sink_receipt_name(p.bindMemory(to: UInt8.self).baseAddress, UInt(playlist.count), &out) }
        defer { wai_buffer_free(out) }
        guard st == 0 else { return "" }
        return String(decoding: WaiSink.bytes(out), as: UTF8.self)
    }

    /// A playlist the player fetched, with its receipt where one was served (§4.2).
    public func playlist(url: String, bytes: Data, receipt: Data?) throws -> [String: Any] {
        try WaiSink.object(try call { out in
            url.withCString { u in
                bytes.withUnsafeBytes { b in
                    let bp = b.bindMemory(to: UInt8.self).baseAddress
                    if let receipt {
                        return receipt.withUnsafeBytes { r in
                            wai_sink_playlist(handle, u, bp, UInt(bytes.count), r.bindMemory(to: UInt8.self).baseAddress ?? UnsafePointer(bitPattern: 1), UInt(receipt.count), &out)
                        }
                    }
                    return wai_sink_playlist(handle, u, bp, UInt(bytes.count), nil, 0, &out)
                }
            }
        })
    }

    /// The parent receipt a verdict named in `need_parent`, or nil when it was not served.
    public func playlistParent(url: String, name: String, bytes: Data?) throws {
        let st: Int32 = url.withCString { u in
            name.withCString { n in
                if let bytes {
                    return bytes.withUnsafeBytes { b in wai_sink_playlist_parent(handle, u, n, b.bindMemory(to: UInt8.self).baseAddress ?? UnsafePointer(bitPattern: 1), UInt(bytes.count)) }
                }
                return wai_sink_playlist_parent(handle, u, n, nil, 0)
            }
        }
        guard st == 0 else { throw WaiSink.error(st) }
    }

    /// A response body the player received, its content codings removed (§4.3).
    public func object(meta: [String: Any], bytes: Data) throws -> [String: Any] {
        let m = try WaiSink.text(meta)
        return try WaiSink.object(try call { out in
            m.withCString { c in
                bytes.withUnsafeBytes { b in wai_sink_object(handle, c, b.bindMemory(to: UInt8.self).baseAddress, UInt(bytes.count), &out) }
            }
        })
    }

    /// A log event (§5.2).
    public func event(_ name: String, atUs: UInt64) throws {
        let st = name.withCString { wai_sink_event(handle, $0, atUs) }
        guard st == 0 else { throw WaiSink.error(st) }
    }

    /// An observation (§5.1): the ending the termination rule gives, if any (§6.1).
    @discardableResult
    public func observe(_ obs: [String: Any]) throws -> Ended? {
        let o = try WaiSink.text(obs)
        let v = try WaiSink.object(try call { out in o.withCString { wai_sink_observe(handle, $0, &out) } })
        return (v["end"] as? String).flatMap(Ended.init(rawValue:))
    }

    /// A role's energy entry (§7).
    public func energy(_ entry: [String: Any]) throws {
        let e = try WaiSink.text(entry)
        let st = e.withCString { wai_sink_energy(handle, $0) }
        guard st == 0 else { throw WaiSink.error(st) }
    }

    /// Attach another signed record of the session (stream-audit §8.3).
    public func attach(name: String, bytes: Data) throws {
        let st = name.withCString { n in bytes.withUnsafeBytes { wai_sink_attach(handle, n, $0.bindMemory(to: UInt8.self).baseAddress, UInt(bytes.count)) } }
        guard st == 0 else { throw WaiSink.error(st) }
    }

    /// The Event-mode CMCD batch of the log since the last call.
    public func takeCMCD() throws -> String {
        String(decoding: try call { wai_sink_take_cmcd(handle, &$0) }, as: UTF8.self)
    }

    /// End the session: the bundle (stream-audit §9), the JSON a host posts to the collector.
    public func end(_ ended: Ended, atUs: UInt64) throws -> Data {
        try call { out in ended.rawValue.withCString { wai_sink_end(handle, $0, atUs, &out) } }
    }

    /// Verify a bundle as the owner's collector does (stream-audit §10): the outcome JSON.
    public static func verifyBundle(_ bundle: Data, owner: Data, channels: [String]) throws -> [String: Any] {
        precondition(owner.count == 32, "an owner key is 32 bytes")
        let ch = try text(channels)
        var out = wai_buffer_t(data: nil, len: 0, cap: 0)
        let st: Int32 = ch.withCString { c in
            bundle.withUnsafeBytes { b in
                owner.withUnsafeBytes { o in wai_audit_verify_bundle(b.bindMemory(to: UInt8.self).baseAddress, UInt(bundle.count), o.bindMemory(to: UInt8.self).baseAddress, c, &out) }
            }
        }
        defer { wai_buffer_free(out) }
        guard st == 0 else { throw error(st) }
        return try object(bytes(out))
    }

    // MARK: plumbing

    private func call(_ f: (inout wai_buffer_t) -> Int32) throws -> Data {
        var out = wai_buffer_t(data: nil, len: 0, cap: 0)
        let st = f(&out)
        defer { wai_buffer_free(out) }
        guard st == 0 else { throw WaiSink.error(st) }
        return WaiSink.bytes(out)
    }

    static func bytes(_ b: wai_buffer_t) -> Data {
        guard let p = b.data, b.len > 0 else { return Data() }
        return Data(bytes: p, count: Int(b.len))
    }

    static func error(_ st: Int32) -> WaiSinkError {
        WaiSinkError(status: st, message: wai_last_error().map { String(cString: $0) } ?? "")
    }

    static func text(_ v: Any) throws -> String {
        String(decoding: try JSONSerialization.data(withJSONObject: v, options: [.fragmentsAllowed]), as: UTF8.self)
    }

    static func object(_ d: Data) throws -> [String: Any] {
        guard let o = try JSONSerialization.jsonObject(with: d, options: [.fragmentsAllowed]) as? [String: Any] else {
            throw WaiSinkError(status: -1, message: "native_answer_unreadable")
        }
        return o
    }
}