import AppKit
import SwiftUI

/// **The board popover** — "the one board-level surface" (03-board-ui.md § Board popover), and the
/// widget in the window's titlebar that opens it.
///
/// Three sections, in the design's own order: the board rename, the embedded style editor aimed at
/// the board, and the git slot. The first two are this milestone's; the third is a *reserved place*
/// — see `BoardGitSlot` for what m7 grows there and why an honest placeholder beats an absent
/// section.
///
/// ### One home, deliberately
///
/// The popover has **no toolbar item** (§ Toolbar: "the window-title widget is its committed home
/// … and a second entry would muddy it"). It has exactly two ways in: the widget, and File ▸ Board
/// Info ⌘I, which is the same widget's popover reached from the keyboard (11-command-nexus.md's
/// class **C** — "the keyboard path is reachability … not bindings").

// MARK: - Presentation state

/// Whether **this window's** board popover is open.
///
/// Per window rather than per board or per app, and that is the point: ⌘I has to mean "the board in
/// front", so the flag travels with the window through the focus system (`FocusedValues.boardInfo`)
/// exactly as the store does. Two board windows each hold their own and can never toggle each
/// other's — which a flag on the store could not promise the day a board is allowed two windows.
///
/// It is also why this is not in `TransientBoardState`: everything there is *board*-scoped and
/// shared with the board's card windows, and a popover living in one window's titlebar is not that.
@MainActor
@Observable
final class BoardInfoPresentation {

    var isPresented = false

    /// ⌘I's whole behaviour and the widget's alike. **Toggling, not opening**: a shortcut aimed at a
    /// disclosure that could only ever open would leave the popover with no keyboard way out.
    func toggle() {
        isPresented.toggle()
    }
}

/// The focused board window's popover, beside `FocusedValues.boardStore` — see that key for why
/// board-window menu items reach their window this way rather than through the app model.
struct FocusedBoardInfoKey: FocusedValueKey {
    typealias Value = BoardInfoPresentation
}

extension FocusedValues {
    var boardInfo: BoardInfoPresentation? {
        get { self[FocusedBoardInfoKey.self] }
        set { self[FocusedBoardInfoKey.self] = newValue }
    }
}

// MARK: - The window-title widget

/// The titlebar widget: a quiet disclosure chevron whose one job is this popover.
///
/// **The popover is anchored to the widget itself** — it hangs from the chevron rather than from
/// the window or the board — which is what makes the affordance and the surface read as one thing.
/// A `.popover` rather than a hand-driven `NSPopover` because SwiftUI's is already transient (a
/// click outside dismisses it), and because the content is SwiftUI either way; the AppKit half of
/// this is only the *placement* (`boardInfoTitlebarAccessory`).
struct BoardInfoWidget: View {

    let store: BoardStore
    let recents: StyleRecents

    @Bindable var presentation: BoardInfoPresentation

    var body: some View {
        Button {
            presentation.toggle()
        } label: {
            Image(systemName: "chevron.down")
                .imageScale(.small)
                .fontWeight(.semibold)
                .foregroundStyle(.secondary)
                // Sized like a titlebar control rather than by its glyph: the hit target has to be
                // clickable at titlebar scale, where the chevron alone is a few points across.
                .frame(width: 20, height: 18)
                .contentShape(Rectangle())
        }
        .buttonStyle(.plain)
        .help("Board Info")
        .accessibilityLabel("Board Info")
        .popover(isPresented: $presentation.isPresented, arrowEdge: .bottom) {
            BoardInfoView(store: store, recents: recents)
        }
    }
}

/// The widget wearing AppKit's clothes, because SwiftUI has no way to put a view in the titlebar:
/// an `NSTitlebarAccessoryViewController` hosting the button, laid out `.leading` so it sits in the
/// title bar beside the window title rather than in the window's content.
///
/// `HostedWindowController.installTitlebarAccessory` owns the rest of the lifecycle — one per
/// window, removed on detach — for the same reason it owns the delegate proxying: the window is
/// SwiftUI's, and anything hung on it has to be taken back off.
@MainActor
func boardInfoTitlebarAccessory(
    store: BoardStore,
    recents: StyleRecents,
    presentation: BoardInfoPresentation
) -> NSTitlebarAccessoryViewController {
    let hosting = NSHostingView(
        rootView: BoardInfoWidget(store: store, recents: recents, presentation: presentation)
    )
    // The titlebar lays its accessories out by fitting size, and a hosting view that measured itself
    // as zero would be an invisible, unclickable widget.
    hosting.sizingOptions = [.intrinsicContentSize]
    hosting.frame = NSRect(x: 0, y: 0, width: 20, height: 18)

    let controller = NSTitlebarAccessoryViewController()
    controller.view = hosting
    controller.layoutAttribute = .leading
    return controller
}

// MARK: - The popover's content

/// The three sections, one view (03-board-ui.md § Board popover).
///
/// Width is the style editor's — 268 points, the number that keeps the Style… popover narrow enough
/// to sit beside a card — so the embedded editor lays out here exactly as it does at its other two
/// anchors rather than being stretched by a container with its own opinion.
struct BoardInfoView: View {

    let store: BoardStore
    let recents: StyleRecents

    /// The style editor brings its own padding, so the sections around it carry the same number by
    /// hand instead of an outer padding that would double up on it.
    private let inset: CGFloat = 14

    var body: some View {
        VStack(alignment: .leading, spacing: 0) {
            VStack(alignment: .leading, spacing: 6) {
                sectionHeader("Title")
                BoardRenameField(store: store)
            }
            .padding(inset)

            Divider()

            VStack(alignment: .leading, spacing: 0) {
                sectionHeader("Styling")
                    .padding(.horizontal, inset)
                    .padding(.top, inset)
                // Always the board, whatever is selected. The ⌥⌘S anchor is the selection-aware one
                // ("nothing selected = the board"); this embed is the surface that exists *because*
                // the board is a style target, so it can have no other target (§ Styling ▸
                // Controls: "the board popover's target is the board itself").
                StyleEditorView(store: store, recents: recents, target: .board)
            }

            Divider()

            VStack(alignment: .leading, spacing: 8) {
                sectionHeader("Git")
                BoardGitSlot()
            }
            .padding(inset)
        }
        .frame(width: 268)
    }

    /// The section titles, matching the style editor's own headers so the popover reads as one
    /// surface rather than three borrowed ones.
    private func sectionHeader(_ title: String) -> some View {
        Text(title)
            .font(.subheadline.weight(.semibold))
    }
}

// MARK: - Rename

/// The board rename field (03-board-ui.md § Board popover; 01-storage-format.md § Board naming).
///
/// The exits are the inline editors' — Return and focus loss commit, Escape abandons — but the
/// **placeholder is the whole of the board-naming rule made visible**: an empty field shows the
/// folder name, because that is what the window title will say, and committing empty is how a user
/// asks for exactly that. "Untitled" appears nowhere; boards do not have it.
///
/// **It is not born focused**, unlike the three inline editors. Those are each opened by a gesture
/// that means "edit this now"; this one is one control among several on a configuration surface,
/// where the keyboard path is Tab-reachability rather than a caret waiting in the first field
/// (11-command-nexus.md's class **C**).
///
/// Every handler is idempotent, for `InlineTitleField`'s reason: the exits overlap by construction —
/// Return commits and then something takes focus, which fires the focus-loss commit an instant
/// later — and `BoardStore.renameBoard` skips an unchanged title, so the second call writes nothing.
private struct BoardRenameField: View {

    let store: BoardStore

    @State private var draft = ""
    @FocusState private var isFocused: Bool

    var body: some View {
        TextField(fallbackName, text: $draft)
            .textFieldStyle(.roundedBorder)
            .lineLimit(1)
            .focused($isFocused)
            .onSubmit { store.renameBoard(draft) }
            // **Escape steps outward one layer per press** (04-interactions.md ▸ Grammar): a dirty
            // field abandons its edit and keeps the popover open, and an unedited one lets the press
            // through to the popover's own dismissal. Reverting first is also what makes a dismissal
            // safe on the paths where the press never reaches here — the focus-loss commit that
            // follows sees a draft equal to what is on disk and writes nothing.
            .onKeyPress(.escape) {
                guard draft != committed else { return .ignored }
                draft = committed
                return .handled
            }
            .onChange(of: isFocused) { _, focused in
                guard !focused else { return }
                store.renameBoard(draft)
            }
            .onAppear { draft = committed }
            // A foreign rename — an agent, a hand edit, a sync — landing behind an open popover
            // updates the field, but never under the user's fingers: a draft being typed is the
            // user's, and the reload is not an edit to it (02-architecture.md § Live-reload
            // resilience, the same courtesy the inline editors get by tracking their UUID).
            .onChange(of: committed) { _, title in
                guard !isFocused else { return }
                draft = title
            }
            // The popover can be dismissed without the field ever reporting focus loss, and a
            // dismissal is a commit like any other click-away. Idempotent with the handler above.
            .onDisappear { store.renameBoard(draft) }
            // The read-only lock disables every mutating surface (02-architecture.md § The lock's
            // scope) — and the popover *stays open* under it, which is the style popover's settled
            // precedent: the lock is a condition the banner is already explaining, not a reason to
            // yank a surface away. `acceptsBoardMutations` rather than `isReadOnly` alone so this
            // field and the editor below it disable as one surface rather than in halves.
            .disabled(!store.acceptsBoardMutations)
    }

    /// The `title` on disk, as the last reload read it — "" for a board that has none.
    private var committed: String { store.snapshot.title.value ?? "" }

    /// The folder name, sans extension: what the window title shows when `title` is absent
    /// (01-storage-format.md § Board naming), and therefore the honest thing for an empty field to
    /// promise. Read off `rootURL` rather than `snapshot.rootURL` so a Finder rename absorbed
    /// mid-session shows here immediately.
    private var fallbackName: String {
        store.rootURL.deletingPathExtension().lastPathComponent
    }
}

// MARK: - Git

/// The git section — **a reserved slot, not a feature** (03-board-ui.md § Board popover).
///
/// Every board is mode-none today, because the app has no git at all yet: there is no detection, no
/// repository, and nothing to init. So this renders the one honest thing a mode-none board can say
/// and offers its action disabled, rather than hiding the section — an absent section would teach
/// that the board popover has two parts, and the design says it has three.
///
/// m7-git: this slot grows the whole inventory in 11-command-nexus.md § Configuration controls ▸
/// Board popover — add-git on mode none, the this-board-lives-inside-a-repository explanation on
/// repo-nested boards (06-history-undo.md), branch display/switch/create, the commit-identity
/// name/email fields, add/change remote, the credential and SSH-key surfaces (machine key with Copy
/// and Verify, key import, the per-host picker, confirm-gated regeneration), the
/// Authentication-needed badge, and ahead/behind with Pull/Push and push-on-commit
/// (07-sync-collab.md). The mode-aware branching starts here, where this placeholder is.
private struct BoardGitSlot: View {

    var body: some View {
        VStack(alignment: .leading, spacing: 8) {
            Text("This board has no repository. Version history, undo, and sync arrive with Lanework's git integration.")
                .font(.caption)
                .foregroundStyle(.secondary)
                .fixedSize(horizontal: false, vertical: true)

            Button("Add Git…") {}
                .disabled(true)
        }
    }
}