import AppKit
import Observation
import SwiftUI
import os

// MARK: - The focused card window's printable card

/// **What a card window offers File ▸ Print…**: the card as the last snapshot found it, the lane it is in,
/// the board it belongs to, its folder, and the thread it is showing.
///
/// A handle of its own rather than a reuse of `cardComments` or `cardAttachments`, because neither carries
/// the card: the comments pane knows a title and a folder (it announces about them), the attachments
/// section knows a folder, and printing needs the whole `Card` — its `icon`, its reserved `labels`, its
/// body. `CardAttachments`' shape and for its reasons: one per window, `@State` in the host, published
/// through the focus system so a **menu row** reaches the frontmost card window without anyone keeping a
/// which-window-is-key register (`FocusedBoardStoreKey`).
///
/// **Re-derived from every snapshot**, like the window's title and subtitle: a card renamed, restyled or
/// moved between lanes mid-session prints as it is now, not as it was when the window opened.
@MainActor
@Observable
final class CardPrintSubject {

    /// `nil` until the window has joined its board — which is also exactly when there is nothing to print.
    var card: Card?

    /// The lane the card is in, for the print's context line. `nil` renders as the same "Untitled"
    /// placeholder a lane header shows (`PrintDocumentBuilder.untitled`).
    var laneTitle: String?

    /// The board's display name (`AppModel.displayName(of:)`), for the running head.
    var boardTitle = ""

    /// The card's folder — the anchor a relative image in its body resolves against (`BodyTarget.resolve`).
    var cardFolder: URL?

    /// The thread as the pane last read it, read again at print time.
    ///
    /// A closure rather than a stored value for `CardComments.readThread`'s reason: comments are
    /// window-scoped and outside the snapshot, so there is nothing to republish from — the pane re-reads
    /// from disk, and a print asks the same question at the moment it is asked to print.
    @ObservationIgnored
    var readThread: (() -> CommentThread)?

    init() {}
}

struct FocusedCardPrintKey: FocusedValueKey {
    typealias Value = CardPrintSubject
}

extension FocusedValues {
    var cardPrint: CardPrintSubject? {
        get { self[FocusedCardPrintKey.self] }
        set { self[FocusedCardPrintKey.self] = newValue }
    }
}

// MARK: - File ▸ Print…

/// **File ▸ Print… (⌘P)** — 11-command-nexus.md's Print row, and the retirement of that document's "No
/// Print story in v1 (⌘P unused)" line.
///
/// ### Two scopes, one row
///
/// The board window prints **the board**: its lanes left to right, each lane's cards top to bottom, as a
/// linear document rather than a picture of the strip (`PrintSource.board`). The card window prints **that
/// card**. One menu row for both, which is what the platform means by Print — the frontmost window's
/// document — and which is why the row reaches its subject through the focus system rather than through the
/// app model.
///
/// The two are told apart by which focused value is present, and cannot both be: a card window publishes no
/// `boardStore` (`CardWindowHost`), so the board branch is scopeless there. The order below therefore
/// decides nothing, and it follows `RevealInFinderCommand`'s — the board in front wins, the card-window
/// branch stands when a card window is.
///
/// ### Validation is scope and nothing else
///
/// Neither the read-only lock nor the focused-editor rule closes it, unlike every mutating row in
/// `BoardCommands.swift`: a print is a **read**, and a locked board is exactly the board someone wants a
/// paper copy of (`RevealInFinderCommand`'s posture, and `BoardInfoCommand`'s). An inline title editor is no
/// obstacle either — the print takes the snapshot as it stands, which is what is on screen.
///
/// A board with **nothing to print** — no lanes, or every card empty of every included component — still
/// enables the row, deliberately: the honest place to discover that is the panel's own preview, and a ⌘P
/// that greys out on a board the user is looking at reads as a broken app rather than as an empty document.
/// The refusal, when it happens, is `PrintCoordinator`'s and it says so.
struct PrintCommand: View {

    let appModel: AppModel

    @FocusedValue(\.boardStore) private var store
    @FocusedValue(\.cardPrint) private var cardPrint

    var body: some View {
        Button("Print…") {
            print()
        }
        .keyboardShortcut("p", modifiers: .command)
        .disabled(!isEnabled)
    }

    /// One answer for both the `disabled` state and the action — the codebase's usual shape, for its usual
    /// reason: two derivations of a rule are two chances to disagree.
    private var isEnabled: Bool {
        Self.isEnabled(hasBoard: store != nil, hasPrintableCard: cardPrint?.card != nil)
    }

    /// The row's validation as a pure function of the two facts it turns on, extracted from `isEnabled` for
    /// `SaveAsTemplateCommand.allowsSave`'s reason: a rule that can only be exercised through a menu is a
    /// rule nobody tests.
    ///
    /// **Two disjuncts and nothing else.** No lock, no focused-editor rule, no is-there-anything-to-print —
    /// see the type's doc comment for why each of those is deliberately absent. A card window whose board
    /// has not loaded yet publishes a subject with no card, which is the second disjunct's whole point:
    /// scope alone would enable the row over a window with nothing behind it.
    static func isEnabled(hasBoard: Bool, hasPrintableCard: Bool) -> Bool {
        hasBoard || hasPrintableCard
    }

    private func print() {
        if let store {
            PrintCoordinator.printBoard(store: store, profiles: appModel.printProfiles)
            return
        }
        if let cardPrint {
            PrintCoordinator.printCard(cardPrint, profiles: appModel.printProfiles)
        }
    }
}

// MARK: - PrintCoordinator

/// **The AppKit half of ⌘P**: build the session, hand the panel our accessory, run the operation.
///
/// ### Why the operation is sheeted on the window rather than run modally
///
/// `runModal()` would block the main thread inside a nested run loop for as long as the panel is up, which
/// is the shape `NSSavePanel`'s uses in `DuplicateBoardCommand` — and is right there, because that panel
/// answers a question the copy is *waiting* on. A print is not: the board keeps reloading, the watcher keeps
/// running, an agent may be writing. So this uses the sheeted form, whose completion is where the Last Used
/// capture lands.
///
/// ### The one refusal
///
/// A document with no pages is refused with an alert instead of printed. It is reachable two ways — a board
/// with no cards, and every component toggled off — and both deserve a sentence rather than a sheet of
/// running heads over blank paper. The alert is the whole response: nothing failed, so this is not
/// 02-architecture.md's write-failure banner surface, which is about writes.
@MainActor
enum PrintCoordinator {

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

    // MARK: Entry points

    /// **The board**, as of this moment (`PrintSource`'s frozen-snapshot note).
    static func printBoard(store: BoardStore, profiles: PrintProfileStore) {
        let snapshot = store.snapshot
        let title = AppModel.displayName(of: store)

        let session = PrintSession(
            provider: PrintSourceProvider(
                withoutComments: PrintSource.board(snapshot, titled: title),
                // Deferred, and read at most once — the comments toggle decides whether a board print pays
                // a thread read per card (`PrintSourceProvider`).
                withComments: {
                    PrintSource.board(snapshot, titled: title) { card in
                        PrintComment.list(of: store.commentThread(inCard: card.id))
                    }
                }
            ),
            profiles: profiles,
            // No single folder is right for every card's relative images, so a board print resolves none
            // (`PrintDocumentRenderer.appendBody`).
            cardFolder: nil,
            jobTitle: title,
            boardTitle: title
        )
        run(session)
    }

    /// **One card**, with the thread read now.
    static func printCard(_ subject: CardPrintSubject, profiles: PrintProfileStore) {
        guard let card = subject.card else { return }
        let comments = subject.readThread.map { PrintComment.list(of: $0()) } ?? []
        let source = PrintSource.card(
            card,
            laneTitle: subject.laneTitle,
            boardTitle: subject.boardTitle,
            comments: comments
        )
        let session = PrintSession(
            provider: PrintSourceProvider(complete: source),
            profiles: profiles,
            cardFolder: subject.cardFolder,
            jobTitle: card.title.value ?? PrintDocumentBuilder.untitled,
            boardTitle: subject.boardTitle
        )
        run(session)
    }

    // MARK: The operation

    private static func run(_ session: PrintSession) {
        guard !session.blocks().isEmpty else {
            refuse(session)
            return
        }

        // `NSPrintInfo.shared`, deliberately: it is where the panel's paper, orientation and margins are
        // remembered between prints, which is exactly the continuity a user expects from a print dialog —
        // and an app with no `NSDocument` has no per-document print info for them to live in instead.
        let printInfo = NSPrintInfo.shared
        // Both modes are moot while the view answers `knowsPageRange` itself — AppKit takes the view's page
        // rects and does not subdivide them further — and they are set anyway to say what the document is:
        // one column exactly as wide as the page, which never spills sideways.
        printInfo.horizontalPagination = .clip
        printInfo.verticalPagination = .automatic

        let view = PrintDocumentView(session: session, printInfo: printInfo)
        let operation = NSPrintOperation(view: view, printInfo: printInfo)
        operation.jobTitle = session.jobTitle
        operation.showsPrintPanel = true
        operation.showsProgressPanel = true

        let panel = operation.printPanel
        // The preview is what makes the accessory worth having (`PrintOptionsAccessoryController`), and the
        // page-setup group is what lets the paper questions be answered in the same dialog rather than in a
        // second one this app does not have (there is no File ▸ Page Setup… row — 11-command-nexus.md).
        panel.options.formUnion([.showsPreview, .showsPaperSize, .showsOrientation, .showsScaling, .showsCopies, .showsPageRange])
        panel.addAccessoryController(PrintOptionsAccessoryController(session: session))

        // **The Last Used capture happens when the operation ends, and only if it ran** — see
        // `PrintCompletion`, which is also the reason the sheeted form needs a delegate at all.
        if let window = keyWindow() {
            let completion = PrintCompletion(session: session)
            operation.runModal(
                for: window,
                delegate: completion,
                didRun: #selector(PrintCompletion.printOperationDidRun(_:success:contextInfo:)),
                contextInfo: nil
            )
        } else {
            // No window to sheet on — which should not happen for a command scoped to a focused window, but
            // a print is still a legitimate thing to do and a modal run is the honest fallback. `run()` is
            // synchronous, so the capture is an ordinary line rather than a callback.
            if operation.run() {
                session.profiles.captureLastUsed(session.options)
            }
        }
    }

    /// The window the sheet hangs on: the app's key window, which for a command validated against the focus
    /// system *is* the window that published the subject. Asked of AppKit rather than threaded through the
    /// focus system because a `NSWindow` is not a value a `FocusedValue` should carry, and because
    /// `WindowAccessor`'s per-window controllers exist for window *lifecycle*, not for presenting over one.
    private static func keyWindow() -> NSWindow? {
        NSApp.keyWindow ?? NSApp.mainWindow
    }

    private static func refuse(_ session: PrintSession) {
        logger.notice("print refused: the document has no content")
        let alert = NSAlert()
        alert.messageText = "Nothing to Print"
        alert.informativeText = session.options.describesAnyContent
            ? "'\(session.jobTitle)' has no cards with any of the content you chose to include."
            : "Turn on at least one of Title, Icon & Labels, Body or Comments."
        alert.addButton(withTitle: "OK")
        alert.runModal()
    }
}

/// The sheeted operation's delegate — **and the only place the Last Used capture can honestly happen.**
///
/// `runModal(for:delegate:didRun:contextInfo:)` presents the panel as a sheet and **returns immediately**,
/// which is the whole reason this class exists: capturing on the line after that call would record the
/// options the panel *opened* with, before the user touched a control. A synchronous capture is only
/// available on the windowless `run()` fallback, which is where `PrintCoordinator` puts one.
///
/// **The gate is `success`, so a cancelled print rewrites nothing.** Cancel and a printer failure are
/// indistinguishable here — both arrive as `success == false` — and of the two possible mistakes the
/// asymmetry is clear: capturing on Cancel would overwrite the user's remembered settings with ones they
/// abandoned, while declining to capture on a jam merely leaves Last Used where it was. So the settings a
/// jammed print was configured with are not remembered; that is the cheaper loss, and the print system's
/// own queue window is where the user retries the job anyway.
///
/// **It retains itself until the callback.** `NSPrintOperation` holds its delegate weakly, and the sheeted
/// form outlives every local in the method that presented it — so the object hands its own reference back
/// only once the callback has landed.
@MainActor
private final class PrintCompletion: NSObject {

    private let session: PrintSession
    private var untilTheCallback: PrintCompletion?

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

    init(session: PrintSession) {
        self.session = session
        super.init()
        untilTheCallback = self
    }

    @objc func printOperationDidRun(_ operation: NSPrintOperation, success: Bool, contextInfo: UnsafeMutableRawPointer?) {
        Self.logger.info("print operation finished — success: \(success, privacy: .public)")
        if success {
            session.profiles.captureLastUsed(session.options)
        }
        untilTheCallback = nil
    }
}