import Foundation
import os

// MARK: - Comment

/// One comment: a UUID-named folder under a card's `comments/`, holding `index.md` and optionally
/// `attachments/` — "a card's anatomy one level down" (01-storage-format.md § Enhanced schema,
/// storage specified 2026-07-29).
///
/// The field table is the common schema minus two and plus one: **no `title`, no `order`**, and
/// `author` — self-reported *content* that survives every app write, unlike `modified-by`.
///
/// `Card`'s shape deliberately, one level down: identity, the lenient fields as `FieldValue`s, the
/// attachment listing, and the whole parsed document so unknown and reserved keys ride along
/// uninterpreted.
public struct Comment: Identifiable, Sendable, Equatable {
    public let id: ItemID

    /// The schema number as read. Lenient here, unlike every other level: a comment defect never
    /// refuses anything (§ Enhanced schema), so a missing or unreadable `schema` costs the thread a
    /// rendered comment, never a load.
    public let schema: FieldValue<Int>

    /// Who says they wrote it — the app writes the macOS account's full name, agents write their
    /// own, tracker sync writes the remote author verbatim. **Missing renders unattributed**; there
    /// is no identity system behind it and none is implied.
    public let author: FieldValue<String>

    /// Load-bearing, unlike anywhere else in the schema: the thread's order *is* `created`
    /// ascending (§ Enhanced schema — "Ordering is chronology, not ranks").
    public let created: FieldValue<Date>
    public let modified: FieldValue<Date>
    public let modifiedBy: FieldValue<String>

    /// The comment's attachment file names — flat, top-level regular files, Finder order, through
    /// the same enumeration a card's listing uses (`BoardLoader.attachmentNames`), so a chip row and
    /// a card's sidebar can never disagree about what a folder holds.
    public let attachments: [String]

    /// The full parsed `index.md`; unknown and reserved keys ride along uninterpreted.
    public let document: FrontmatterDocument

    /// The comment's Markdown — the card-body subset. Equivalent to `document.body`.
    public var body: String { document.body }

    /// **The edited indicator is `modified` differing from `created`, and no extra field**
    /// (§ Enhanced schema). A post writes both from one `Date`, so a comment that has never been
    /// edited reads `false` by construction; one of the pair missing is not evidence of an edit.
    public var isEdited: Bool {
        guard let created = created.value, let modified = modified.value else { return false }
        return modified != created
    }
}

// MARK: - CommentDraft

/// The card's single draft, as the composer needs it: the text to restore, and the chips to draw.
///
/// **Two fields and no identity**, which is the difference between a draft and a comment stated as a
/// type: `comments/.draft/` is a claimed name the composer edits in place, and it becomes a `Comment`
/// only at the post, where the rename mints the id (`BoardWriter.postComment`).
public struct CommentDraft: Sendable, Equatable {

    /// `index.md`'s body — what the composer shows when the window opens.
    public let body: String

    /// The draft's `attachments/`, through the same enumeration a comment's listing uses, so the
    /// composer's chips and a posted comment's chips can never disagree about what a folder holds.
    public let attachments: [String]

    public init(body: String, attachments: [String]) {
        self.body = body
        self.attachments = attachments
    }

    /// Whether a save of `body` would delete the folder — **the emptied-draft rule, asked before the
    /// write** (01-storage-format.md § Enhanced schema; `BoardWriter.saveCommentDraft`'s own gate).
    ///
    /// It is the composer's Post validation read backwards: there is nothing to post exactly when
    /// there would be nothing to keep.
    public var isEmpty: Bool {
        body.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty && attachments.isEmpty
    }
}

// MARK: - CommentThread

/// A card's comment thread, read from disk — **window-scoped, outside the board snapshot**
/// (01-storage-format.md § Enhanced schema: "the walk stays O(cards): the card window reads its own
/// thread … and the board snapshot never loads comment content").
///
/// ### It never refuses
///
/// There is no `throws` anywhere in this type, and that is the ruling rather than convenience:
/// "**Comment defects never refuse the board** — worst case is the stray posture (tolerated, logged,
/// unrendered): a broken leaf annotation must not brick a load; deliberate, proportionate divergence
/// from card fail-fast". A folder that is not identity-shaped, one with no `index.md`, one whose
/// frontmatter does not parse, one that is not UTF-8 — each is skipped with a log line, preserved
/// verbatim on disk, and the rest of the thread renders.
///
/// ### The two dot-named folders are not comments
///
/// `comments/.draft/` and `comments/.trash/` are excluded from the listing (§ Enhanced schema), and
/// they are excluded *for free*: both are dot-prefixed, and `BoardLoader.directoryCandidates` skips
/// hidden entries. The exclusion is stated in the enumeration's own rule rather than re-implemented
/// here, exactly as `.trash/` is at board level.
public struct CommentThread: Sendable, Equatable {

    /// The thread in display order — `created` ascending (see `sorted(_:)` for the fallback).
    public let comments: [Comment]

    /// Folders under `comments/` that are not comments — reported for the log's sake and rendered by
    /// nothing. The tolerate tier, one level down.
    public let strays: [Stray]

    /// Pending work and coerce-tier observations this read found — claimed names squatted inside
    /// `comments/` or inside one comment, and every lenient field that had no sensible reading. The
    /// same typed stream the board walk fills (`IntegrityRules.Defect`), so the heal engine needs no
    /// second vocabulary for a thread.
    public let defects: [IntegrityRules.Defect]

    /// Whether the card has a draft on disk. The composer reads its bytes itself; what a *thread*
    /// needs to know is only that one exists, which is the answer restore-on-reopen turns on.
    public let hasDraft: Bool

    /// One folder under `comments/` the thread would not render, and why — never an error, always a
    /// log line.
    public struct Stray: Sendable, Equatable {
        public enum Reason: Sendable, Equatable {
            /// Not identity-shaped: a hand-made folder, a nested clone. The shape-only identity
            /// predicate one level down.
            case notIdentityShaped
            /// Identity-shaped with no `index.md` — two-step-create tolerance, verbatim from the
            /// card rule (01-storage-format.md § Fractal layout ▸ Rules).
            case missingIndex
            /// The bytes are there and could not be read as a comment: not UTF-8, frontmatter that
            /// does not parse. The one reason a *card* would have failed the whole load.
            case unreadable(message: String)
        }

        public let name: String
        public let reason: Reason
    }

    public static let empty = CommentThread(comments: [], strays: [], defects: [], hasDraft: false)

    // MARK: - Where a thread lives

    /// `<card>/comments/` — named but never created here. One place, so the loader's read and every
    /// write in `CommentWriter.swift` can never disagree about where a thread is
    /// (`BoardWriter.trashFolder(inBoard:)`'s precedent).
    public static func folder(inCard cardFolder: URL) -> URL {
        cardFolder.appendingPathComponent(IntegrityRules.commentsFolderName, isDirectory: true)
    }

    /// `<card>/comments/.draft/` — the card's single draft.
    public static func draftFolder(inCard cardFolder: URL) -> URL {
        folder(inCard: cardFolder)
            .appendingPathComponent(IntegrityRules.commentDraftFolderName, isDirectory: true)
    }

    /// `<card>/comments/.trash/` — undo's backing store, purged at window close.
    public static func trashFolder(inCard cardFolder: URL) -> URL {
        folder(inCard: cardFolder)
            .appendingPathComponent(IntegrityRules.commentTrashFolderName, isDirectory: true)
    }

    /// `<card>/comments/<id>/` — one posted comment.
    public static func commentFolder(_ id: ItemID, inCard cardFolder: URL) -> URL {
        folder(inCard: cardFolder).appendingPathComponent(id.rawValue, isDirectory: true)
    }

    /// `<card>/comments/.trash/<id>/` — one deleted comment, waiting for the close purge or a ⌘Z.
    public static func trashedCommentFolder(_ id: ItemID, inCard cardFolder: URL) -> URL {
        trashFolder(inCard: cardFolder).appendingPathComponent(id.rawValue, isDirectory: true)
    }

    /// The identities currently sitting in `comments/.trash/` — what a close purge would remove, and
    /// what the crash-residue sweep signs its memo with.
    ///
    /// The listing rule is the thread's own (`directoryCandidates` narrowed by the identity
    /// predicate), so a stray a hand-editor put in there is neither counted nor purged — the same
    /// honesty `emptyTrash` keeps at board level.
    public static func trashedCommentIDs(inCard cardFolder: URL) -> [ItemID] {
        ((try? BoardLoader.directoryCandidates(in: trashFolder(inCard: cardFolder))) ?? [])
            .filter { IntegrityRules.isIdentityShaped($0.lastPathComponent) }
            .map { ItemID(rawValue: $0.lastPathComponent) }
    }

    // MARK: - Reading

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

    /// Reads one card's thread. Total: a card with no `comments/`, an unreadable one, or one held by
    /// a file answers `.empty`, which is what "no comments yet" looks like and is not a defect this
    /// read has any business inventing — the squatted-name case *is* reported, as work.
    ///
    /// - Parameter path: the card folder's path relative to the board root (`<lane>/<card>`, or
    ///   `.trash/<card>` for a trashed one — "a trashed card carries its `comments/`"). Carried into
    ///   every defect so the heal lands wherever the board lives at write time, and into the log
    ///   lines so a stray names something a human can find.
    public static func load(inCard cardFolder: URL, path: String) -> CommentThread {
        let threadFolder = folder(inCard: cardFolder)
        var defects: [IntegrityRules.Defect] = []

        switch IntegrityRules.node(at: threadFolder) {
        case nil:
            return .empty
        case .directory:
            break
        case .file, .symlink:
            // The claimed name held by the wrong kind of node. Detection only, like every other
            // defect in this app — the displacement is the store's, through the Writer. Nothing else
            // about the thread can be read while a file wears the name, so the listing is empty and
            // the work is the whole answer.
            return CommentThread(
                comments: [],
                strays: [],
                defects: IntegrityRules.squattedClaimedNames(inCardAt: cardFolder, path: path)
                    .map(IntegrityRules.Defect.claimedNameSquatted),
                hasDraft: false
            )
        }

        for squatter in IntegrityRules.squattedClaimedNames(inCommentThreadAt: threadFolder, cardPath: path) {
            defects.append(.claimedNameSquatted(squatter))
            logger.warning(
                "\(path, privacy: .public)/comments/\(squatter.name, privacy: .public): claimed name held by \(squatter.found.description, privacy: .public) — to be displaced"
            )
        }

        var comments: [Comment] = []
        var strays: [Stray] = []
        // Hidden entries and symlinks are already out, which is exactly how `.draft` and `.trash` are
        // excluded from the thread — see the type's own note.
        for commentURL in (try? BoardLoader.directoryCandidates(in: threadFolder)) ?? [] {
            let name = commentURL.lastPathComponent
            let commentPath = path + "/" + IntegrityRules.commentsFolderName + "/" + name

            guard IntegrityRules.isIdentityShaped(name) else {
                strays.append(Stray(name: name, reason: .notIdentityShaped))
                logger.warning("\(commentPath, privacy: .public): not a comment identity — ignored")
                continue
            }
            let indexURL = commentURL.appendingPathComponent(IntegrityRules.indexFileName)
            guard let data = try? Data(contentsOf: indexURL) else {
                strays.append(Stray(name: name, reason: .missingIndex))
                logger.warning("\(commentPath, privacy: .public): no index.md — ignored")
                continue
            }
            let document: FrontmatterDocument
            do {
                document = try BoardLoader.parseDocument(data, path: commentPath)
            } catch {
                strays.append(Stray(name: name, reason: .unreadable(message: error.reason.description)))
                logger.warning(
                    "\(commentPath, privacy: .public): \(error.reason.description, privacy: .public) — ignored"
                )
                continue
            }

            let fields = document.coercedFields
            if !fields.isEmpty {
                let indexPath = commentPath + "/" + IntegrityRules.indexFileName
                defects.append(.coercedFrontmatter(CoercedFrontmatter(path: indexPath, fields: fields)))
                for field in fields {
                    logger.info(
                        "\(indexPath, privacy: .public): '\(field.key, privacy: .public)' has no sensible reading — \(field.raw, privacy: .public) — rendering the field's default"
                    )
                }
            }
            for squatter in IntegrityRules.squattedClaimedNames(inCommentAt: commentURL, path: commentPath) {
                defects.append(.claimedNameSquatted(squatter))
                logger.warning(
                    "\(commentPath, privacy: .public)/\(squatter.name, privacy: .public): claimed name held by \(squatter.found.description, privacy: .public) — to be displaced"
                )
            }

            comments.append(Comment(
                id: ItemID(rawValue: name),
                schema: document.schema,
                author: document.author,
                created: document.created,
                modified: document.modified,
                modifiedBy: document.modifiedBy,
                attachments: BoardLoader.attachmentNames(in: commentURL),
                document: document
            ))
        }

        return CommentThread(
            comments: sorted(comments),
            strays: strays,
            defects: defects,
            hasDraft: IntegrityRules.node(at: draftFolder(inCard: cardFolder)) == .directory
        )
    }

    /// **The composer's own file, read** — `comments/.draft/`, which the thread listing deliberately
    /// excludes (see the type's note) and which the composer therefore has to ask for by name.
    ///
    /// It answers a pair rather than a `Comment` because a draft has **no identity**: it is a claimed
    /// *name*, not a UUID (`CommentPath.Kind.draft` — "the one member of the thread that is a name
    /// rather than an id"), and minting an `ItemID` for it here would put a lie in the one type whose
    /// whole job is that a comment's folder name *is* its id.
    ///
    /// Total, like `load(inCard:path:)`: a card with no draft, an unreadable one, or a `.draft` held
    /// by a file answers `nil` — which is what "nothing to restore" looks like and is not a defect
    /// this read invents (the squatted-name case is reported by the thread read beside it).
    ///
    /// **This is the whole of restore-on-reopen**: the composer's backing file is the draft, so
    /// reading it at open is all the mechanism there is (05-card-window.md ▸ The comments column).
    public static func loadDraft(inCard cardFolder: URL) -> CommentDraft? {
        let folder = draftFolder(inCard: cardFolder)
        guard IntegrityRules.node(at: folder) == .directory else { return nil }
        let indexURL = folder.appendingPathComponent(IntegrityRules.indexFileName)
        let attachments = BoardLoader.attachmentNames(in: folder)

        // A folder with no readable `index.md` is a draft that exists — the two-step-create shape, and
        // the shape a drop-before-a-keystroke leaves. Its body is empty, its chips are real, and
        // reporting `nil` would hide files the user can see in Finder.
        guard let data = try? Data(contentsOf: indexURL),
              let document = try? BoardLoader.parseDocument(data, path: IntegrityRules.commentDraftFolderName)
        else {
            return CommentDraft(body: "", attachments: attachments)
        }
        return CommentDraft(body: document.body, attachments: attachments)
    }

    /// **Board search's read** — every posted comment's body under `cardFolder`, and nothing else
    /// (04-interactions.md ▸ Search: "an async sweep of `comments/*/index.md` bodies (`.draft` and
    /// `comments/.trash/` excluded)").
    ///
    /// It is a second entry point rather than `load(inCard:path:)` reused, and the difference is
    /// deliberately narrow: **it is silent and it reports nothing**. The thread read logs every stray,
    /// records every coerce-tier field and hands back the claimed-name work a heal will act on — all of
    /// which is right for a window opening a thread and wrong for a sweep that re-runs whenever a
    /// reload lands under a live query. A warning per stray per keystroke's re-sweep would be a log a
    /// human could not read, and defects surfaced from a *search* would be repaired by a gesture the
    /// user never made.
    ///
    /// `nonisolated` and total: this runs on a detached task (`CommentSearchIndex.sweep`), and a card
    /// with no `comments/`, one whose thread is held by a file, and one whose comments are all
    /// unreadable each answer `[]` — the same shrug the thread read gives, minus the paperwork.
    ///
    /// The two exclusions are the enumeration's, exactly as in `load`: `.draft` and `.trash` are
    /// dot-prefixed, and `BoardLoader.directoryCandidates` skips hidden entries.
    public static func searchableBodies(inCard cardFolder: URL) -> [String] {
        let threadFolder = folder(inCard: cardFolder)
        guard IntegrityRules.node(at: threadFolder) == .directory else { return [] }

        var bodies: [String] = []
        for commentURL in (try? BoardLoader.directoryCandidates(in: threadFolder)) ?? [] {
            guard IntegrityRules.isIdentityShaped(commentURL.lastPathComponent),
                  let data = try? Data(contentsOf: commentURL.appendingPathComponent(IntegrityRules.indexFileName)),
                  // A malformed comment is *tolerated*, which here means unsearched: a body the parser
                  // could not find is not a body a query can honestly be said to miss, and searching
                  // the raw bytes would let a query match frontmatter the thread never renders.
                  let document = try? BoardLoader.parseDocument(data, path: commentURL.lastPathComponent),
                  !document.body.isEmpty
            else {
                continue
            }
            bodies.append(document.body)
        }
        return bodies
    }

    /// **Chronology, with the undated after the dated** (01-storage-format.md § Enhanced schema,
    /// ruled 2026-07-29): "the thread sorts by `created` ascending … ties and missing/malformed
    /// `created` (coerce-tier fallback, logged) sort after dated siblings, folder-name order".
    ///
    /// The folder-name tie-break compares the **canonical lowercase spelling**, the corpus-wide rule
    /// for every folder-name tie-break (§ Ordering: "ordering follows the value-based identity model,
    /// never an uppercase folder's ASCII accident") — an agent's uppercase `uuidgen` output must not
    /// sort into a different place than the same identity spelled lowercase.
    static func sorted(_ comments: [Comment]) -> [Comment] {
        comments.sorted { lhs, rhs in
            switch (lhs.created.value, rhs.created.value) {
            case let (left?, right?):
                left == right ? isOrderedByName(lhs, rhs) : left < right
            case (.some, .none):
                true
            case (.none, .some):
                false
            case (.none, .none):
                isOrderedByName(lhs, rhs)
            }
        }
    }

    private static func isOrderedByName(_ lhs: Comment, _ rhs: Comment) -> Bool {
        IntegrityRules.canonicalIdentity(lhs.id.rawValue)
            < IntegrityRules.canonicalIdentity(rhs.id.rawValue)
    }
}