import SwiftUI

struct PRDetailView: View {
    @StateObject private var vm: PRDetailViewModel
    @Environment(\.dismiss) private var dismiss
    @State private var selectedTab: DetailTab? = .overview
    @State private var showCommentSheet = false
    @State private var showMergeSheet = false
    @State private var showCloseConfirm = false
    @State private var showRerunConfirm: ActionRun?
    @State private var requestChangesMode = false
    @State private var showMergeSuccess = false

    enum DetailTab: String, CaseIterable, Identifiable, Hashable {
        case overview = "Overview"
        case conversation = "Conversation"
        case files = "Files"
        case checks = "Checks"

        var id: String { rawValue }

        var icon: String {
            switch self {
            case .overview: return "doc.text"
            case .conversation: return "bubble.left.and.bubble.right"
            case .files: return "doc.plaintext"
            case .checks: return "checkmark.circle"
            }
        }
    }

    init(repo: Repository, prNumber: Int) {
        _vm = StateObject(wrappedValue: PRDetailViewModel(repo: repo,
                                                          prNumber: prNumber))
    }

    var body: some View {
        Group {
            if let pr = vm.pr {
                content(pr)
            } else if vm.isLoading {
                ProgressView("Loading…")
            } else if let err = vm.errorMessage {
                ContentUnavailableView("Couldn't load PR",
                                       systemImage: "exclamationmark.triangle",
                                       description: Text(err))
                    .toolbar { ToolbarItem(placement: .primaryAction) { reloadButton } }
            } else {
                ProgressView("Loading…")
            }
        }
        .navigationTitle("#\(vm.prNumber)")
        .navigationBarTitleDisplayMode(.inline)
        .task { await vm.load() }
        .alert("Error", isPresented: .init(
            get: { vm.errorMessage != nil },
            set: { if !$0 { vm.errorMessage = nil } })) {
            Button("OK", role: .cancel) {}
        } message: { Text(vm.errorMessage ?? "") }
        .overlay { if vm.busyMessage != nil { busyOverlay } }
        .overlay { if showMergeSuccess { mergeSuccessOverlay } }
        .confirmationDialog("Close this PR?", isPresented: $showCloseConfirm, titleVisibility: .visible) {
            Button("Close", role: .destructive) { Task { await vm.setState("closed") } }
            Button("Cancel", role: .cancel) {}
        } message: { Text("This will close the pull request.") }
        .sheet(isPresented: $showCommentSheet) {
            CommentSheet(vm: vm,
                         mode: requestChangesMode ? .requestChanges : .comment)
                .onDisappear { requestChangesMode = false }
        }
        .sheet(isPresented: $showMergeSheet) {
            MergeSheet(vm: vm) {
                // Merge succeeded: show the success animation, then pop back
                // to the landing page.
                withAnimation(.spring(response: 0.4, dampingFraction: 0.6)) {
                    showMergeSuccess = true
                }
                Task {
                    try? await Task.sleep(nanoseconds: 1_200_000_000)
                    dismiss()
                }
            }
        }
        .confirmationDialog("Re-run workflow?",
                            isPresented: .init(
                                get: { showRerunConfirm != nil },
                                set: { if !$0 { showRerunConfirm = nil } }),
                            titleVisibility: .visible) {
            Button("Re-run") {
                if let run = showRerunConfirm {
                    Task { await vm.rerun(runID: run.id) }
                }
                showRerunConfirm = nil
            }
            Button("Cancel", role: .cancel) {}
        } message: {
            Text("Re-run \"\(showRerunConfirm?.name ?? "workflow")\"?")
        }
    }

    @ViewBuilder
    private func content(_ pr: PullRequest) -> some View {
        VStack(spacing: 0) {
            header(pr)

            // Vertical scroll — has always rendered correctly (a horizontal
            // ScrollView/TabView broke NavigationLink and mangled markdown).
            ScrollView {
                switch selectedTab {
                case .overview: OverviewTab(pr: pr)
                case .conversation: ConversationTab(vm: vm)
                case .files: FilesTab(vm: vm)
                case .checks: ChecksTab(vm: vm, onRerun: { showRerunConfirm = $0 })
                case .none: OverviewTab(pr: pr)
                }
            }

            bottomTabBar
        }
        .toolbar {
            if prIsOpen {
                ToolbarItem(placement: .primaryAction) { mergeButton }
                ToolbarItem(placement: .primaryAction) {
                    // Disable while a review submission is in flight so rapid
                    // taps can't stack duplicate reviews.
                    reviewMenu.disabled(vm.busyMessage != nil)
                }
            }
        }
    }

    @ViewBuilder
    private func header(_ pr: PullRequest) -> some View {
        VStack(alignment: .leading, spacing: 8) {
            Text(pr.title)
                .font(.title3.weight(.bold))
            HStack(spacing: 6) {
                Text("\(vm.repo.fullName)#\(pr.number)")
                    .font(.caption)
                    .foregroundColor(.secondary)
                CICircle(status: vm.ciStatus)
                if vm.reviewState != .unknown {
                    ReviewBadge(state: vm.reviewState)
                }
                if pr.draft == true {
                    Text("Draft").font(.caption2).foregroundColor(.secondary)
                }
            }
        }
        .padding()
        .frame(maxWidth: .infinity, alignment: .leading)
        .background(Color(.secondarySystemBackground))
    }

    /// Bottom tab bar: a floating, frosted-glass pill inset from the screen
    /// edges (like the SideStore tab bar), with a highlighted capsule behind
    /// the active tab. Icon + text per tab.
    private var bottomTabBar: some View {
        HStack(spacing: 4) {
            ForEach(DetailTab.allCases) { tab in
                Button {
                    selectedTab = tab
                } label: {
                    VStack(spacing: 2) {
                        Image(systemName: tab.icon)
                            .font(.system(size: 20, weight: .medium))
                        Text(tab.rawValue)
                            .font(.caption2.weight(.medium))
                    }
                    .foregroundColor(selectedTab == tab ? .accentColor : .secondary)
                    .frame(maxWidth: .infinity)
                    .padding(.vertical, 6)
                    .background(
                        selectedTab == tab
                            ? AnyShapeStyle(.ultraThinMaterial)
                            : AnyShapeStyle(.clear)
                    )
                    .clipShape(Capsule())
                }
                .buttonStyle(.plain)
            }
        }
        .padding(.horizontal, 6)
        .padding(.vertical, 6)
        .background(
            Capsule()
                .fill(.regularMaterial)
                .shadow(color: .black.opacity(0.15), radius: 10, y: 4)
        )
        .padding(.horizontal, 20)
        .padding(.bottom, 8)
        // Swipe across the bar to change sections (iOS 26 feel). Taps on the
        // individual tab buttons still work — simultaneous gesture.
        .simultaneousGesture(
            DragGesture(minimumDistance: 20)
                .onEnded { value in
                    let tabs = DetailTab.allCases
                    guard let current = selectedTab ?? .overview,
                          let idx = tabs.firstIndex(of: current) else { return }
                    if value.translation.width < -40, idx < tabs.count - 1 {
                        withAnimation { selectedTab = tabs[idx + 1] }
                    } else if value.translation.width > 40, idx > 0 {
                        withAnimation { selectedTab = tabs[idx - 1] }
                    }
                }
        )
    }

    private var reviewMenu: some View {
        Menu {
            Button("Comment") { requestChangesMode = false; showCommentSheet = true }
            Button("Approve") { Task { await vm.submitReview(state: "approved", comment: nil) } }
            Button("Request changes") { requestChangesMode = true; showCommentSheet = true }
            Divider()
            if prIsOpen {
                Button("Close", role: .destructive) { showCloseConfirm = true }
            } else {
                Button("Reopen") { Task { await vm.setState("open") } }
            }
        } label: {
            Image(systemName: "checkmark.bubble")
        }
    }

    private var mergeButton: some View {
        Button {
            showMergeSheet = true
        } label: {
            Image(systemName: "arrow.triangle.merge")
        }
        .disabled(vm.ciStatus == .failure &&
                  SettingsStore.shared.mergeGateMode == .block)
    }

    private var prIsOpen: Bool {
        (vm.pr?.state.lowercased() ?? "") == "open"
    }

    private var reloadButton: some View {
        Button { Task { await vm.load() } } label: {
            Image(systemName: "arrow.clockwise")
        }
    }

    private var busyOverlay: some View {
        ZStack {
            Color.black.opacity(0.15)
            ProgressView(vm.busyMessage ?? "")
                .padding()
                .background(.regularMaterial)
                .clipShape(RoundedRectangle(cornerRadius: 12))
        }
        .ignoresSafeArea()
    }

    /// Full-screen success animation shown briefly after a merge, then the
    /// view pops back to the landing page.
    private var mergeSuccessOverlay: some View {
        ZStack {
            Color.black.opacity(0.4)
                .ignoresSafeArea()
            VStack(spacing: 12) {
                Image(systemName: "checkmark.circle.fill")
                    .font(.system(size: 72))
                    .foregroundColor(.green)
                    .scaleEffect(showMergeSuccess ? 1 : 0.3)
                    .opacity(showMergeSuccess ? 1 : 0)
                Text("Merged")
                    .font(.title2.weight(.semibold))
                    .foregroundColor(.white)
            }
        }
        .transition(.opacity)
    }
}