import SwiftUI

// MARK: - The git-mode section's state

/// **What the popover's git section shows on a git-mode board** — a pure function of four facts, so
/// the surface 06-history-undo.md describes is assertable without a popover on screen.
///
/// It exists for the same reason `BoardGitSection.resolve` does one level up: the *posture* is the
/// part worth pinning, and the SwiftUI that renders it is not. Three rules live here —
///
/// - **A paused repository names its state and disables the controls** (06 ▸ Rules ▸ Abnormal repo
///   states: "Undo/Redo and the branch controls disable … the popover's git section names the state
///   plainly … and says resolving it belongs to the tool that created it").
/// - **A read-only board disables them too** (02-architecture.md ▸ The lock's scope, which names "the
///   popover's git controls" outright).
/// - **A switch in flight disables them**, so a second click cannot start a second checkout.
struct BoardGitBranchSurface: Equatable {

    /// What the branch line reads — the branch name, the short hash on a detached HEAD
    /// (`GitRepository.branchName` decides which), or the placeholder while the first read is in
    /// flight.
    let branchLabel: String

    /// Whether that label is the placeholder rather than an answer.
    let isReadingBranch: Bool

    /// The pause's own sentence (`GitRepositoryPause.explanation`), or `nil` when the surface is live.
    let pauseExplanation: String?

    /// Whether the branch picker and the create action accept a click.
    let controlsEnabled: Bool

    /// The line the branch display is read as by VoiceOver.
    var accessibilityLabel: String {
        isReadingBranch ? "Reading branch" : "Branch \(branchLabel)"
    }

    static let placeholder = "…"

    /// The second half of the paused sentence — 06's "says resolving it belongs to the tool that
    /// created it", said in the app's own voice and paired with the promise that makes it safe to
    /// wait: the app is not going to touch the repository behind the user's back.
    static let pauseCaption =
        "Finishing it belongs to the tool that started it; Lanework leaves the repository untouched."

    static func resolve(
        branch: String?,
        pause: GitRepositoryPause?,
        isSwitching: Bool,
        isWritable: Bool
    ) -> BoardGitBranchSurface {
        BoardGitBranchSurface(
            branchLabel: branch ?? placeholder,
            isReadingBranch: branch == nil,
            pauseExplanation: pause?.explanation,
            controlsEnabled: pause == nil && isWritable && !isSwitching
        )
    }
}

// MARK: - The git-mode section

/// **The popover's git section on a board that has a repository** (03-board-ui.md ▸ Board popover;
/// 06-history-undo.md ▸ Branch switching, ▸ Interaction with external writers).
///
/// Three surfaces, in the order the design lists them: the branch display with switching and
/// creation, the pause explanation when there is one, and the commit-identity fields.
///
/// **Shaped for the half that is not here yet.** Remote tracking, Pull/Push, push-on-commit and the
/// authentication surface are 07-sync-collab.md's own cards, and this section is arranged so they
/// join as one more block between the branch controls and the identity fields — nothing here is
/// nested inside anything they would have to be pulled out of, and nothing about the branch controls
/// assumes there is no upstream to show beside them.
struct BoardGitControls: View {

    let git: HistoryStore

    /// The read-only lock's reach (02-architecture.md ▸ The lock's scope): a board that refuses writes
    /// refuses a checkout most of all — it rewrites the tree the lock exists to stop describing.
    let isEnabled: Bool

    @State private var isNaming = false
    @State private var draftBranch = ""

    private var surface: BoardGitBranchSurface {
        BoardGitBranchSurface.resolve(
            branch: git.branch,
            pause: git.committer?.pause,
            isSwitching: git.switcher?.isSwitching ?? false,
            isWritable: isEnabled
        )
    }

    var body: some View {
        VStack(alignment: .leading, spacing: 8) {
            branchRow

            if isNaming {
                newBranchField
            }

            if let explanation = surface.pauseExplanation {
                pauseNote(explanation)
            }

            if let failure = git.switcher?.lastFailure {
                caption(failure.message, tone: .red)
            }

            BoardGitIdentityFields(git: git, isEnabled: isEnabled)
        }
        // Every read the section needs, taken when it appears rather than held live: the popover is
        // built fresh on each open (`BoardInfoWidget`), and none of these is a fact the board's
        // watcher could deliver — `.git` is filtered out of the watch by design.
        .task {
            await git.refreshBranch()
            await git.committer?.refreshPause()
            await git.switcher?.refreshBranches()
        }
    }

    // MARK: The branch line

    /// The branch display and the switch, as one control: the line *is* the picker, which is what
    /// makes "branch/source display, branch switching and creation" one affordance rather than a label
    /// with a button beside it.
    private var branchRow: some View {
        HStack(spacing: 6) {
            Image(systemName: "arrow.triangle.branch")
                .imageScale(.small)
                .foregroundStyle(.secondary)

            Menu {
                ForEach(otherBranches, id: \.self) { name in
                    Button(name) {
                        Task { await git.switcher?.switchTo(name) }
                    }
                }
                if !otherBranches.isEmpty {
                    Divider()
                }
                Button("New Branch…") {
                    draftBranch = ""
                    isNaming = true
                }
            } label: {
                Text(surface.branchLabel)
                    .font(.callout)
                    .foregroundStyle(surface.isReadingBranch ? .secondary : .primary)
            }
            .menuStyle(.borderlessButton)
            .fixedSize()
            .disabled(!surface.controlsEnabled)
            .accessibilityLabel(surface.accessibilityLabel)
            .accessibilityHint("Switch branches or create a branch")

            if git.switcher?.isSwitching == true {
                ProgressView()
                    .controlSize(.small)
                    .accessibilityLabel("Switching branches")
            }
        }
    }

    /// Every local branch except the one already checked out — a picker offering the current branch
    /// would be offering a no-op, and the switch refuses one anyway.
    private var otherBranches: [String] {
        (git.switcher?.branches ?? []).filter { $0 != git.branch }
    }

    // MARK: Create and switch

    /// Named inline rather than in a sheet: the popover is where the operation was asked for, and a
    /// sheet over a transient popover would dismiss the surface it came from.
    private var newBranchField: some View {
        HStack(spacing: 6) {
            TextField("New branch name", text: $draftBranch)
                .textFieldStyle(.roundedBorder)
                .lineLimit(1)
                .onSubmit { create() }
                // Escape steps outward one layer (04-interactions.md ▸ Grammar): it abandons the
                // naming rather than dismissing the popover under it.
                .onKeyPress(.escape) {
                    isNaming = false
                    draftBranch = ""
                    return .handled
                }
            Button("Create", action: create)
                .disabled(trimmedDraft.isEmpty)
        }
        .disabled(!surface.controlsEnabled)
    }

    private var trimmedDraft: String {
        draftBranch.trimmingCharacters(in: .whitespacesAndNewlines)
    }

    private func create() {
        let name = trimmedDraft
        guard !name.isEmpty else { return }
        isNaming = false
        draftBranch = ""
        Task { await git.switcher?.createAndSwitch(to: name) }
    }

    // MARK: The pause

    /// **The abnormal-state surface** (06 ▸ Rules ▸ Abnormal repo states) — deferred here from the
    /// auto-commit card, which built the hold this explains.
    ///
    /// Two sentences, both of them the design's: what the repository is doing, and whose job it is to
    /// finish. Never a Repair button — "the app never mutates repo state it didn't create".
    private func pauseNote(_ explanation: String) -> some View {
        VStack(alignment: .leading, spacing: 2) {
            Text(explanation)
                .font(.caption)
                .foregroundStyle(.primary)
                .fixedSize(horizontal: false, vertical: true)
            Text(BoardGitBranchSurface.pauseCaption)
                .font(.caption)
                .foregroundStyle(.secondary)
                .fixedSize(horizontal: false, vertical: true)
        }
        .accessibilityElement(children: .combine)
    }

    private func caption(_ text: String, tone: Color) -> some View {
        Text(text)
            .font(.caption)
            .foregroundStyle(tone)
            .fixedSize(horizontal: false, vertical: true)
    }
}

// MARK: - Commit identity

/// **The name and email that repo-local `.git/config` carries** (06-history-undo.md ▸ Interaction
/// with external writers: "The board settings sheet's identity section … exposes name/email fields
/// that write that repo-local config — the setting *is* the file, portable to any git client,
/// per-board by nature").
///
/// **Its home is the sheet, and the sheet is not built yet.** The 2026-07-31 popover/sheet split moved
/// every setup-shaped control — add-git, branch creation, these fields, remote and credentials — out
/// of the popover and into a board settings sheet (03-board-ui.md ▸ Board settings sheet), leaving the
/// popover the daily face. This view is the fields, hosted where they were; the sheet's card moves
/// them, along with the visibility-scoped poll below, which 06 says "rides with the fields".
///
/// ### The placeholder is the whole of the identity rule made visible
///
/// An empty field shows the **derived default** — the macOS account's full name and
/// `shortname@hostname` — as a placeholder, never as a value. That is the difference between "this
/// repository says nothing, so the app signs commits with a sensible guess" and "this repository says
/// this", and the file is where the difference lives: 06 forbids the app writing its own derived
/// value into config, because it would then outrank the user's global `~/.gitconfig` for their own
/// terminal commits in that board. A field pre-filled with the derived value would write it on the
/// first focus loss.
///
/// ### The dirty-buffer courtesy, copied from `BoardRenameField`
///
/// A foreign config edit landing while the popover is open updates an *unfocused* field and never a
/// focused one: "a focused field keeps the user's keystrokes" (03-board-ui.md ▸ Board popover). The
/// trigger is a poll rather than a reload, and that is honest rather than lazy: `FolderWatcher`
/// filters `.git` out of the watch by design, so no board event can ever carry a config change, and
/// the alternative to a small periodic read is a field that is stale for as long as the popover
/// stays open. The poll lives and dies with this view.
private struct BoardGitIdentityFields: View {

    let git: HistoryStore
    let isEnabled: Bool

    @State private var name = ""
    @State private var email = ""
    @FocusState private var focused: Field?

    private enum Field: Hashable {
        case name
        case email
    }

    /// **The fields re-read the config at 2 s while the surface is visible** (06 ▸ Interaction with
    /// external writers, blessed 2026-07-31): "the watcher never delivers `.git`, so no board event
    /// can carry a terminal-side config edit — the unfocused-resync courtesy needs its own signal, and
    /// a visibility-scoped poll is the 15 s paused-state re-read's shape at sheet cadence (a focused
    /// field keeps its keystrokes; dismissing the sheet stops the poll)."
    private static let pollInterval: Duration = .seconds(2)

    var body: some View {
        VStack(alignment: .leading, spacing: 6) {
            Divider()

            Text("Commit Identity")
                .font(.caption.weight(.semibold))
                .foregroundStyle(.secondary)

            field("Name", text: $name, placeholder: git.derivedIdentity?.name ?? "", tag: .name)
            field("Email", text: $email, placeholder: git.derivedIdentity?.email ?? "", tag: .email)

            if let failure = git.identityFailure {
                Text(failure.message)
                    .font(.caption)
                    .foregroundStyle(.red)
                    .fixedSize(horizontal: false, vertical: true)
            }
        }
        .task {
            // The first read, then the courtesy poll. Cancellation is the view's disappearance, which
            // is the popover closing.
            while !Task.isCancelled {
                await git.refreshIdentity()
                try? await Task.sleep(for: Self.pollInterval)
            }
        }
        .onAppear {
            name = git.identityName
            email = git.identityEmail
        }
        .onChange(of: git.identityName) { _, value in
            guard focused != .name else { return }
            name = value
        }
        .onChange(of: git.identityEmail) { _, value in
            guard focused != .email else { return }
            email = value
        }
        // A dismissal is a commit like any other click-away — `BoardRenameField`'s rule, and the same
        // idempotence makes the overlap harmless.
        .onDisappear { commit() }
    }

    private func field(
        _ label: String,
        text: Binding<String>,
        placeholder: String,
        tag: Field
    ) -> some View {
        HStack(spacing: 6) {
            Text(label)
                .font(.caption)
                .foregroundStyle(.secondary)
                .frame(width: 44, alignment: .leading)
            TextField(placeholder, text: text)
                .textFieldStyle(.roundedBorder)
                .lineLimit(1)
                .focused($focused, equals: tag)
                .onSubmit { commit() }
                .disabled(!isEnabled)
                .accessibilityLabel("Commit \(label.lowercased())")
        }
        .onChange(of: focused) { previous, _ in
            // Focus leaving *this* field is this field's commit — the inline editors' exit, applied
            // to a form where Tab moves between two of them.
            guard previous == tag else { return }
            commit()
        }
    }

    /// Writes both fields, and only when one of them differs from what the file says — an unchanged
    /// value must not rewrite `.git/config` every time the popover closes.
    private func commit() {
        guard isEnabled else { return }
        guard name != git.identityName || email != git.identityEmail else { return }
        Task { await git.writeIdentity(name: name, email: email) }
    }
}