lanework/Kanban/Git/GitAutoCommitter.swift

import Foundation
import os

// MARK: - GitAutoCommitter

/// **Every settled change becomes a commit** (06-history-undo.md ▸ Rules ▸ Auto-commit), debounced
/// past drag and typing churn, on git-mode boards and nowhere else.
///
/// ### Structurally unreachable off Pro
///
/// One of these exists per `HistoryStore` in mode `git`, and a `HistoryStore` exists only under Pro
/// (`HistoryStore.compose` is the tier gate). The free tier therefore has no committer to disable,
/// no debounce to cancel and no `.git` to touch — 12-editions.md's inert posture as a shape rather
/// than as a flag, which `InertGitTests` pins against real bytes.
///
/// ### What arms it
///
/// Two signals, both from `BoardStore` through `HistoryCommitSeam`, and both meaning "the tree may
/// have moved":
///
/// - **A write bracket closed.** The app just wrote. This is also where receipts are *harvested* —
///   see `HarvestedReceipt` for why the committer cannot simply read the ledger two seconds later.
/// - **A reload landed.** Which covers foreign changes on the same debounce as app-mediated ones:
///   "Agent and hand edits arrive through the watcher like any change and get auto-committed on the
///   same debounce" (06 ▸ Interaction with external writers). It covers strays too — the reload
///   lands whether or not the snapshot changed, and "its commit condition is the *tree*, not the
///   snapshot diff, so a stray-only window commits".
///
/// The committer's own commits do not re-arm it: `FolderWatcher` filters `.git`'s internals, so
/// writing an index, an object and a ref produces no event at all. The pathfinder relied on the
/// clean-tree no-op to break that echo; here there is no echo to break.
///
/// ### Isolation
///
/// `@MainActor` for the state — the debounce task, the harvest, the session registry — and every
/// piece of libgit2 work runs in a `Task.detached` over `Sendable` values (`FlushInput`), which is
/// `GitRepository`'s rule restated: the main actor never blocks on libgit2, and libgit2 never sees
/// two threads on one handle. The **one** deliberate exception is `noteWillWrite()`; see its note.
@MainActor
@Observable
public final class GitAutoCommitter {

    // MARK: - Identity

    /// The board this commits, which in git mode is also the repository's working-tree root.
    public let boardRoot: URL

    /// **This board's write-provenance ledger** (`BoardStore.echoes`), read — never written — at the
    /// close of every write bracket.
    @ObservationIgnored
    private let ledger: EchoLedger

    // MARK: - Seams

    /// **The debounce** — how long the tree must be quiet before a commit.
    ///
    /// Two seconds is the pathfinder's interval, kept because the cadence constraint (06 ▸ Rules)
    /// asks the same thing of it as the pathfinder did: long enough that a drag, a multi-select
    /// delete and a burst of typing each land as one commit, short enough that a board's history is
    /// never far behind its files. Settable for `CardBodyEditSession.debounceInterval`'s reason
    /// exactly — a test must not have to spend it.
    @ObservationIgnored
    public var debounceInterval: Duration = .seconds(2)

    /// How long to wait between attempts when `index.lock` is held, and how many times.
    ///
    /// "If the auto-committer finds the index locked (an agent's commit in flight), it backs off
    /// briefly and retries; if the lock persists, it simply re-debounces" (06 ▸ Interaction with
    /// external writers). *Briefly* is the operative word: a held lock is another writer doing its
    /// job, and the pending changes lose nothing by waiting for the next quiet moment.
    @ObservationIgnored
    public var lockRetryDelay: Duration = .milliseconds(120)

    @ObservationIgnored
    public var lockRetryAttempts = 3

    /// How long a held repository waits before re-checking its own state.
    ///
    /// **Not a retry** — nothing is attempted — but the pause has to end somehow: "edits keep landing
    /// on disk and commit as one settled batch when the state clears", and a rebase finished in a
    /// terminal that moves only refs produces no watcher event at all (`.git` is filtered), so
    /// nothing else would ever nudge this board again. A `git_repository_state` read is a handful of
    /// `stat`s; at this cadence, only while a pause stands, it is the cheapest thing that keeps the
    /// promise. 07's "never hammer" is about not retrying the *operation*, which this never does.
    @ObservationIgnored
    public var holdRecheckInterval: Duration = .seconds(15)

    /// **What a commit says** — the seam the semantic composer plugs into (next card).
    @ObservationIgnored
    public var composer: any CommitMessageComposing = InterimCommitMessage()

    /// The board as the app last read it, for the composer's "current" half. `nil` where no store is
    /// attached, which is every storeless test.
    @ObservationIgnored
    public var currentSnapshot: (@MainActor () -> BoardModel?)?

    /// **A genuine commit failure** — disk full, repo corruption (06: "files stay safe on disk but
    /// history stops advancing; surfaced per 02-architecture.md ▸ Write-failure surfacing, retried
    /// on the next debounce"). Wired to `BannerCenter.suspendHistory(reason:)`.
    ///
    /// Deliberately **not** called for lock contention, which "is never an error", nor for a held
    /// repository, whose surface is the popover's badge (the branch-switching card's).
    @ObservationIgnored
    public var reportFailure: (@MainActor (GitOperationFailure) -> Void)?

    /// History is advancing again — the standing suspension's clearing rule
    /// (`BannerCenter.clearHistorySuspension`), which is "the ordinary shape of commit succeeded".
    @ObservationIgnored
    public var reportRecovery: (@MainActor () -> Void)?

    // MARK: - Observable state

    /// **The repository state the engine is holding for**, or `nil` when it is free to commit
    /// (06 ▸ Rules ▸ Abnormal repo states).
    ///
    /// Queryable rather than merely internal because the *UI* surface of the pause — the popover's
    /// badge and its plain-language explanation, and disabling Undo/Redo, the branch controls, Pull
    /// and Push with it — is the branch-switching card's, and it needs exactly this fact. What this
    /// card owns is the hold itself.
    public private(set) var pause: GitRepositoryPause?

    /// The last genuine failure, or `nil` if history is advancing. Beside `pause` for the popover's
    /// sake, and because `HistoryStore.lastFailure` is add-git's, not this.
    public private(set) var lastFailure: GitOperationFailure?

    /// Commits this committer has landed, and the newest OID — the debounce's own testimony, which a
    /// test would otherwise have to infer from a commit walk.
    public private(set) var commitCount = 0
    public private(set) var lastCommitOIDs: [String] = []

    // MARK: - Private state

    /// Receipts copied out of the ledger at bracket close, keyed by absolute path. Cleared when a
    /// flush commits them — the window is over, and a stale receipt would vouch for the next window's
    /// changes.
    @ObservationIgnored
    private var harvested: [String: HarvestedReceipt] = [:]

    /// **Whether this window holds a change nobody vouched for** — the flush-before-overwrite gate.
    @ObservationIgnored
    private var holdsForeignChanges = false

    /// Open Edit sessions, each answering with the folder to stage around *right now*.
    ///
    /// A closure per session rather than a stored URL, because a card can move lane, or into the
    /// trash, in the middle of a session — its folder is a fact about the current snapshot, not
    /// about when Edit was entered.
    @ObservationIgnored
    private var editSessions: [UUID: @MainActor () -> URL?] = [:]

    @ObservationIgnored
    private var pending: Task<Void, Never>?

    @ObservationIgnored
    private var isFlushing = false

    private static let logger = Logger(subsystem: "dev.rzen.indie.Kanban", category: "git")

    init(boardRoot: URL, ledger: EchoLedger) {
        self.boardRoot = boardRoot
        self.ledger = ledger
    }

    // MARK: - Lifecycle

    /// **Launch catch-up** (06 ▸ Commit messages: "changes found pending at board open … through the
    /// same composer, instead of committing blind").
    ///
    /// One armed debounce and nothing else: a board that opens clean spends one `git status` and
    /// commits nothing, and a board that opens dirty commits through the ordinary engine — same
    /// split, same authorship, same message seam. Everything found pending classifies **foreign**,
    /// which is not a shortcut but the doctrine: the ledger is empty because the app was not running,
    /// and "the app never vouches for changes it didn't witness".
    public func start() {
        arm()
    }

    /// Stops the engine and forgets the window. Called at teardown so a closed board's debounce
    /// cannot fire against a store that has gone.
    public func stop() {
        pending?.cancel()
        pending = nil
    }

    // MARK: - Inbound signals

    /// **A write bracket closed** — harvest, then arm.
    ///
    /// The harvest is the whole reason this signal exists separately from the reload: receipts
    /// describe a completed write and are consumed by the landing reload that classifies them, so
    /// this is the only moment at which the committer can still see them (`HarvestedReceipt`).
    public func noteWriteBracketClosed() {
        harvest()
        arm()
    }

    /// **A reload landed** — the tree settled, and here is whether any of it was somebody else's.
    ///
    /// - Parameter sawForeignChange: what the landing reload's own `EchoLedger.verdicts` concluded.
    ///   It arms flush-before-overwrite and nothing else; the commit split re-derives provenance per
    ///   *file* at flush time, because this is one bit about a whole reload.
    public func noteReloadLanded(sawForeignChange: Bool) {
        if sawForeignChange { holdsForeignChanges = true }
        arm()
    }

    /// **Flush-before-overwrite** (06 ▸ Rules): "before an app write overwrites on-disk state that
    /// differs from the last-loaded snapshot … the pending auto-commit is flushed so the external
    /// version enters history first. *Both versions exist as commits* is thereby a guarantee, not a
    /// likelihood."
    ///
    /// ### The gate
    ///
    /// It fires **only when the window holds a change the app does not vouch for**. That is exactly
    /// the condition under which overwriting can bury someone else's uncommitted version; a window
    /// of nothing but the app's own writes has nothing to protect, and flushing there would commit
    /// once per gesture and make the cadence constraint's "unbearable shared log" come true.
    ///
    /// ### The two costs, recorded
    ///
    /// **It runs on the main actor, synchronously.** `performWrite` is synchronous — it is a
    /// gesture's write path — so an ordering guarantee *before* it can only be kept by a synchronous
    /// commit. 02's hang-avoidance doctrine and 06's ordering guarantee genuinely conflict here, and
    /// the guarantee wins for an operation that is rare (foreign change pending), bounded (one
    /// stage-and-commit over a board-sized tree), and load-bearing (the alternative is losing a
    /// version of somebody's file with no commit to recover it from).
    ///
    /// **A foreign write the watcher has not delivered yet is invisible to it.** The gate learns
    /// about foreign changes from landed reloads, so a write that lands inside the watcher's own
    /// debounce is not yet known to be pending. Bounded by that debounce, and the same window
    /// 05-card-window.md's dirty-buffer rule already calls last-writer-wins — but it is a real gap in
    /// "guarantee", and it is recorded here rather than discovered later.
    public func noteWillWrite() {
        guard holdsForeignChanges, !isFlushing, let input = makeInput() else { return }
        isFlushing = true
        defer { isFlushing = false }
        pending?.cancel()
        pending = nil
        // One attempt, no lock backoff: this path cannot suspend, and a held lock here simply means
        // the foreign version commits on the next quiet debounce instead — which is the same
        // "re-debounce" answer contention gets everywhere else.
        apply(Self.execute(input))
    }

    // MARK: - Edit sessions

    /// **Registers an open Edit session's card folder** (06 ▸ Rules ▸ Auto-commit: "The committer
    /// stages around open Edit sessions: a board change committing mid-session excludes the session
    /// card's folder from staging, so a lane move never sweeps half-typed body text into its
    /// commit").
    ///
    /// The exclusion is absolute where it applies: "whole-root staging widening *what* commits, never
    /// overriding the exclusion" (06 ▸ Commit messages ▸ Non-snapshot files commit too). A stray
    /// dropped inside the session card's folder therefore waits for the session to end, along with
    /// the body.
    ///
    /// - Parameters:
    ///   - token: the window's identity, so ending twice is idempotent.
    ///   - cardFolder: asked at every flush rather than stored, so a card moved mid-session is staged
    ///     around at wherever it now is.
    public func beginEditSession(_ token: UUID, cardFolder: @escaping @MainActor () -> URL?) {
        editSessions[token] = cardFolder
    }

    /// Ends one, and **nudges** — which is what makes "exactly one body commit per session" true:
    /// the session's debounced saves committed nothing while it was open, and this is the moment its
    /// whole diff becomes committable (06 ▸ Rules ▸ Auto-commit: the Edit→Preview flip is "the
    /// effective Save button"; raw-source entry and window close end the session too).
    public func endEditSession(_ token: UUID) {
        guard editSessions.removeValue(forKey: token) != nil else { return }
        arm()
    }

    /// Whether a card window's folder is currently staged around — the stage-around rule, made
    /// assertable without reaching into private state.
    public var stagedAroundFolders: [URL] {
        editSessions.values.compactMap { $0() }
    }

    // MARK: - Flushing

    /// **Commits now**, cancelling the debounce — the close/quit path, and File ▸ Duplicate's
    /// pending-work step.
    ///
    /// 02-architecture.md § Windows fixes where it sits: "closing a board window (and app quit) first
    /// closes the board's card windows — each open Edit session ends with its normal session commit —
    /// then flushes pending debounced work, editor saves before the pending auto-commit, before the
    /// store tears down". `CloseFlushCoordinator.committerFlush` is this, and by the time it runs the
    /// sessions have ended, so nothing is staged around any more.
    public func flushNow() async {
        await flush()
    }

    /// Arms (or re-arms) the debounce. Every signal funnels through here, so "debounced past drag and
    /// typing churn" is one timer rather than a rule each call site remembers.
    private func arm(after interval: Duration? = nil) {
        pending?.cancel()
        let delay = interval ?? debounceInterval
        pending = Task { [weak self] in
            try? await Task.sleep(for: delay)
            guard !Task.isCancelled, let self else { return }
            self.pending = nil
            await self.flush()
        }
    }

    private func flush() async {
        guard !isFlushing else { return }
        isFlushing = true
        defer { isFlushing = false }
        pending?.cancel()
        pending = nil

        guard let input = makeInput() else { return }

        // The brief backoff. Off the main actor for the git work, on it for the sleep, so a held
        // lock costs a couple of suspended turns rather than a blocked UI.
        for attempt in 0...max(0, lockRetryAttempts) {
            let outcome = await Task.detached(priority: .utility) { Self.execute(input) }.value
            if case .locked = outcome, attempt < max(0, lockRetryAttempts) {
                try? await Task.sleep(for: lockRetryDelay)
                continue
            }
            apply(outcome)
            return
        }
    }

    // MARK: - The plan

    /// Everything one flush needs, as values — so the whole of it can cross to a detached task.
    private struct FlushInput: Sendable {
        let boardRoot: URL
        let excludedFolders: [String]
        let receipts: [String: HarvestedReceipt]
        let composer: any CommitMessageComposing
        let snapshot: BoardModel?
    }

    private func makeInput() -> FlushInput? {
        FlushInput(
            boardRoot: boardRoot,
            excludedFolders: editSessions.values.compactMap { $0() }.map(EchoLedger.key),
            receipts: harvested,
            composer: composer,
            snapshot: currentSnapshot?()
        )
    }

    /// **One whole flush**, off the main actor: read the state, list the tree's changes, stage around
    /// the open sessions, split by provenance, compose, commit.
    private nonisolated static func execute(_ input: FlushInput) -> GitCommitOutcome {
        let reading = GitCommitOperation.reading(at: input.boardRoot)
        if let pause = reading.pause { return .held(pause) }
        if reading.isIndexLocked { return .locked }

        // `nil` is "the survey could not be taken" — an unwritable object store, a corrupt index —
        // and it must not read as a clean tree: that would no-op silently and let history stop
        // advancing with nothing on the banner strip (06 ▸ Interaction with external writers, the
        // genuine-failure clause).
        guard let surveyed = GitCommitOperation.surveyChangedPaths(at: input.boardRoot) else {
            return .failed(GitOperationFailure(
                operation: "Recording this board's history",
                message: "this board's repository could not be read"
            ))
        }
        let changed = surveyed
            .filter { !isExcluded($0.path, under: input.boardRoot, by: input.excludedFolders) }
        guard !changed.isEmpty else { return .nothingToCommit }

        return GitCommitOperation.perform(
            at: input.boardRoot,
            commits: plan(changed, reading: reading, input: input)
        )
    }

    /// The three-way split turned into commits — or, on an unborn HEAD, the one commit 06 fixes.
    private nonisolated static func plan(
        _ changed: [GitChangedPath],
        reading: GitRepositoryReading,
        input: FlushInput
    ) -> [PlannedCommit] {
        let user = GitCommitOperation.userIdentity(at: input.boardRoot)

        // **The root commit is not split** (06 ▸ Rules ▸ Abnormal repo states): "it commits the whole
        // tree as *Initial board state*, never a folded diff-from-empty: there is no last-committed
        // snapshot to diff against". Splitting a repository's first commit three ways by the
        // provenance of files that mostly predate the app knowing about them would be a fiction; the
        // whole tree arriving at once is the event, and it is the user's own opt-in that caused it,
        // so it is authored as the user. (Recorded as a judgment call: DESIGN fixes the subject and
        // the shape, not the author.)
        guard !reading.isUnborn else {
            return [PlannedCommit(
                paths: changed.map(\.path),
                message: input.composer.message(for: CommitMessageRequest(
                    boardRoot: input.boardRoot,
                    changedPaths: changed,
                    authorship: .user,
                    isRootCommit: true,
                    snapshot: input.snapshot
                )),
                author: user,
                committer: user
            )]
        }

        let split = CommitAttribution.split(changed, under: input.boardRoot, receipts: input.receipts)
        return split.ordered.map { group in
            let authorship: CommitAuthorship
            switch group.kind {
            case .foreign:
                authorship = .foreign(
                    CommitAttribution.foreignIdentity(for: group.paths, under: input.boardRoot)
                )
            // **A heal is authored by the user**, recorded as a judgment call: DESIGN fixes that a
            // heal's paths commit *separately* and says nothing about who they are by. The healer is
            // the app acting on the user's behalf — its writes are app-mediated, receipt and all — so
            // authoring them as the user is the honest reading, and authoring them as `Lanework
            // External` would blame the outside world for the app's own repair.
            case .heal: authorship = .heal
            case .user: authorship = .user
            }
            let author: GitIdentity
            if case let .foreign(identity) = authorship { author = identity } else { author = user }
            return PlannedCommit(
                paths: group.paths.map(\.path),
                message: input.composer.message(for: CommitMessageRequest(
                    boardRoot: input.boardRoot,
                    changedPaths: group.paths,
                    authorship: authorship,
                    isRootCommit: false,
                    snapshot: input.snapshot
                )),
                author: author,
                committer: user
            )
        }
    }

    /// Whether a changed path lives inside a folder staged around.
    private nonisolated static func isExcluded(
        _ relativePath: String,
        under boardRoot: URL,
        by folders: [String]
    ) -> Bool {
        guard !folders.isEmpty else { return false }
        let absolute = EchoLedger.key(boardRoot.appendingPathComponent(relativePath))
        return folders.contains { absolute == $0 || absolute.hasPrefix($0 + "/") }
    }

    // MARK: - Outcomes

    private func apply(_ outcome: GitCommitOutcome) {
        switch outcome {
        case let .committed(oids):
            pause = nil
            lastFailure = nil
            commitCount += oids.count
            lastCommitOIDs = oids
            // The window is over: its receipts have said everything they can say, and keeping them
            // would let them vouch for the *next* window's changes to the same paths.
            harvested.removeAll()
            holdsForeignChanges = false
            reportRecovery?()
            Self.logger.debug("auto-commit landed \(oids.count, privacy: .public) commit(s)")

        case .nothingToCommit:
            // **The happy path, not a malfunction** (06): an agent committed its own work, or the
            // whole window was staged around. Silent, and the window closes either way.
            pause = nil
            lastFailure = nil
            harvested.removeAll()
            holdsForeignChanges = false
            reportRecovery?()

        case .locked:
            // "No banner, no log-worthy failure: a held lock is another writer doing its job." The
            // changes are still pending and the harvest is still held, so the next quiet moment
            // commits them with their provenance intact.
            Self.logger.debug("index.lock held — re-debouncing")
            arm()

        case let .held(reason):
            pause = reason
            Self.logger.notice("auto-commit held: \(reason.rawValue, privacy: .public)")
            arm(after: holdRecheckInterval)

        case let .failed(failure):
            pause = nil
            lastFailure = failure
            Self.logger.error("auto-commit failed: \(failure.description, privacy: .public)")
            reportFailure?(failure)
            arm()
        }
    }

    // MARK: - Harvest

    /// Copies the ledger's current receipts into this window's own record.
    ///
    /// Whole-ledger rather than bracket-scoped, deliberately: the Writer's primitives drop receipts
    /// without telling anyone which paths they were, and a diff of key sets would miss a
    /// *supersession* (the same key, newer bytes) — which is exactly the case that must not be
    /// missed, since the newest write is the one disk will be compared against. Copying is cheap:
    /// the ledger holds tens of entries, and the harvest happens once per gesture.
    private func harvest() {
        for (path, entry) in ledger.outstandingEntries() {
            harvested[path] = entry
        }
    }
}