import SwiftUI

struct MRView: View {

    @State private var model: MRDetailViewModel
    @State private var commentText = ""
    @State private var commentFormat = "md"
    @State private var confirmingMerge = false
    @State private var confirmingClose = false
    @State private var editing = false
    @State private var draftTitle = ""
    @State private var draftBody = ""
    @State private var draftFormat = "md"
    @State private var editingReviewer = ""
    @State private var retargeting = false
    @State private var pendingRetarget: String?

    init(client: GitbayClient, repo: String, number: Int64) {
        _model = State(initialValue: MRDetailViewModel(
            client: client, repoPath: repo, number: number
        ))
    }

    var body: some View {
        List {
            if let mr = model.state.value {
                header(mr)

                if let error = model.actionError {
                    Section {
                        GBNotice(error, .gbWarn)
                    }
                }

                if let body = mr.body, !body.isEmpty {
                    Section {
                        FormattedBodyView(text: body, format: mr.bodyFormat)
                            .padding(.vertical, 4)
                    }
                }

                milestoneSection(mr)
                stackSection(mr)
                reviewersSection(mr)
                diffSection
                if !model.revisions.isEmpty {
                    revisionsSection
                }

                if let commits = mr.commits, !commits.isEmpty {
                    commitsSection(commits)
                }
                if let checks = mr.checks, !checks.isEmpty {
                    checksSection(checks, combined: mr.checksCombined)
                }
                if let reviews = mr.reviews, !reviews.isEmpty {
                    reviewsSection(reviews)
                }
                if !model.threads.isEmpty {
                    threadsSection
                }
                commentsSection(mr.comments ?? [])
            }
        }
        .overlay { LoadStateOverlay(state: model.state) }
        .navigationTitle("!\(model.number)")
        .navigationBarTitleDisplayMode(.inline)
        .toolbar { toolbar }
        .task { await model.load() }
        .refreshable { await model.load() }
        .confirmationDialog("Merge !\(model.number)?", isPresented: $confirmingMerge) {
            if let mr = model.state.value, !mr.stacked.isEmpty {
                Button("Merge") { Task { await model.merge() } }
                Button("Fast-forward") { Task { await model.merge(strategy: "ff") } }
            } else {
                Button("Merge") { Task { await model.merge() } }
                Button("Squash") { Task { await model.merge(strategy: "squash") } }
                Button("Fast-forward") { Task { await model.merge(strategy: "ff") } }
                Button("Rebase") { Task { await model.merge(strategy: "rebase") } }
            }
            Button("Cancel", role: .cancel) {}
        } message: {
            if let mr = model.state.value, !mr.stacked.isEmpty {
                Text("Merge requests are stacked on this one. Squash and rebase are unavailable — they would rewrite the commits the stack builds on.")
            } else {
                Text("The server enforces approvals, threads and checks — a refusal will say why.")
            }
        }
        .confirmationDialog("Close !\(model.number) without merging?", isPresented: $confirmingClose) {
            Button("Close", role: .destructive) { Task { await model.close() } }
            Button("Cancel", role: .cancel) {}
        }
        .confirmationDialog(
            "Retarget to \(pendingRetarget ?? "")?",
            isPresented: .init(
                get: { pendingRetarget != nil },
                set: { if !$0 { pendingRetarget = nil } }
            ),
            titleVisibility: .visible
        ) {
            Button("Retarget") {
                guard let branch = pendingRetarget else { return }
                pendingRetarget = nil
                Task { await model.retarget(to: branch) }
            }
            Button("Cancel", role: .cancel) { pendingRetarget = nil }
        } message: {
            Text("Existing approvals were of the diff against the old target and will no longer apply.")
        }
        .sheet(isPresented: $retargeting) {
            RetargetSheet(model: model) { branch in
                retargeting = false
                pendingRetarget = branch
            }
        }
        .sheet(isPresented: $editing) {
            ComposeSheet(
                heading: "Edit !\(model.number)",
                submitLabel: "Save",
                working: model.working,
                errorMessage: model.actionError,
                title: $draftTitle,
                bodyText: $draftBody,
                format: $draftFormat
            ) {
                Task {
                    await model.edit(title: draftTitle, body: draftBody, format: draftFormat)
                    if model.actionError == nil { editing = false }
                }
            }
        }
    }

    // MARK: - Sections

    @ViewBuilder
    private func header(_ mr: MRDetail) -> some View {
        Section {
            VStack(alignment: .leading, spacing: 6) {
                Text(mr.title)
                    .font(.gbSans(.headline))
                HStack(spacing: 6) {
                    MRStateBadge(state: mr.state)
                    if mr.draft {
                        GBChip("draft", .secondary)
                    }
                    Text(mr.source.isEmpty ? "(source gone)" : mr.source)
                        .lineLimit(1)
                    Image(systemName: "arrow.right")
                        .font(.gbSans(.caption2))
                    Text(mr.targetRef)
                }
                .font(.gbSans(.caption))
                .foregroundStyle(.secondary)
                HStack(spacing: 6) {
                    Text("by \(mr.author)")
                    Text(mr.createdAt, format: .relative(presentation: .named))
                        .foregroundStyle(.tertiary)
                }
                .font(.gbSans(.caption))
                .foregroundStyle(.secondary)
                resolution(mr)
            }
            .padding(.vertical, 2)
        }
    }

    /// What became of the merge request, once it is no longer open. The
    /// actor is absent for imported rows, which carry only a time.
    @ViewBuilder
    private func resolution(_ mr: MRDetail) -> some View {
        if let at = mr.mergedAt {
            stampLine("merged", by: mr.mergedBy, at: at)
        } else if let at = mr.closedAt {
            stampLine("closed without merging", by: mr.closedBy, at: at)
        }
    }

    private func stampLine(_ verb: String, by actor: String?, at: Date) -> some View {
        HStack(spacing: 6) {
            Text(actor.map { "\(verb) by \($0)" } ?? verb)
            Text(at, format: Self.stamp)
                .foregroundStyle(.tertiary)
        }
        .font(.gbSans(.caption))
        .foregroundStyle(.secondary)
    }

    /// Reviews and checks are read for when they happened, so they carry
    /// the date rather than "3 days ago".
    private static let stamp = Date.FormatStyle.dateTime
        .year().month(.abbreviated).day().hour().minute()

    private func milestoneSection(_ mr: MRDetail) -> some View {
        Section("Milestone") {
            Menu {
                Button("None") { Task { await model.setMilestone(nil) } }
                ForEach(model.availableMilestones ?? []) { milestone in
                    Button("\(milestone.title) (\(milestone.closed)/\(milestone.open + milestone.closed))") {
                        Task { await model.setMilestone(milestone.title) }
                    }
                }
            } label: {
                HStack {
                    Label(mr.milestone ?? "None", systemImage: "flag")
                        .font(.gbSans(.subheadline))
                    Spacer()
                    Image(systemName: "chevron.up.chevron.down")
                        .font(.gbSans(.caption2))
                        .foregroundStyle(.secondary)
                }
            }
            .disabled(model.working)
            .task { await model.loadMilestones() }
            .accessibilityIdentifier("mr-milestone-menu")
        }
    }

    /// Shown only when this merge request is part of a stack. Each row
    /// spells out its own direction — "stacked on" vs. "is stacked on
    /// this" mean opposite things and look alike if abbreviated.
    @ViewBuilder
    private func stackSection(_ mr: MRDetail) -> some View {
        if mr.stackedOn != nil || !mr.stacked.isEmpty {
            Section("Stack") {
                if let base = mr.stackedOn {
                    NavigationLink(value: MRRoute.mr(repo: model.repoPath, number: base.number)) {
                        Label("stacked on !\(base.number) — \(base.title)", systemImage: "arrow.up.to.line")
                            .font(.gbSans(.subheadline))
                            .lineLimit(1)
                    }
                }
                ForEach(mr.stacked) { ref in
                    NavigationLink(value: MRRoute.mr(repo: model.repoPath, number: ref.number)) {
                        Label("!\(ref.number) is stacked on this — \(ref.title)", systemImage: "arrow.down.to.line")
                            .font(.gbSans(.subheadline))
                            .lineLimit(1)
                    }
                }
            }
        }
    }

    /// Every head the merge request has had. A revision after the first
    /// links to the range-diff from the one before it.
    private var revisionsSection: some View {
        Section("Revisions") {
            ForEach(Array(model.revisions.enumerated()), id: \.element.id) { index, revision in
                let row = HStack {
                    Text("v\(revision.n)")
                        .font(.gbSans(.subheadline).weight(.medium))
                    Text(String(revision.sha.prefix(10)))
                        .font(.gbMono(.caption))
                        .foregroundStyle(.secondary)
                    Spacer()
                    if revision.isCurrent {
                        GBChip("current", .secondary)
                    }
                    Text(revision.createdAt.prefix(10))
                        .font(.gbSans(.caption))
                        .foregroundStyle(.tertiary)
                }
                if index > 0 {
                    NavigationLink(value: MRRoute.rangeDiff(
                        repo: model.repoPath, number: model.number,
                        from: model.revisions[index - 1].sha, to: revision.sha)
                    ) {
                        row
                    }
                } else {
                    row
                }
            }
        }
    }

    private func reviewersSection(_ mr: MRDetail) -> some View {
        Section("Reviewers") {
            reviewerFlow(mr.reviewRequests)
            HStack {
                TextField("Request review", text: $editingReviewer)
                    .autocorrectionDisabled()
                    .textInputAutocapitalization(.never)
                Button {
                    let user = editingReviewer.trimmingCharacters(in: .whitespaces)
                    editingReviewer = ""
                    Task { await model.requestReview(from: user) }
                } label: {
                    Image(systemName: "plus.circle.fill")
                }
                .disabled(editingReviewer.trimmingCharacters(in: .whitespaces).isEmpty || model.working)
            }
        }
    }

    /// The same add/remove chip shape `IssueView` uses for labels and
    /// assignees.
    @ViewBuilder
    private func reviewerFlow(_ items: [String]) -> some View {
        if !items.isEmpty {
            ScrollView(.horizontal, showsIndicators: false) {
                HStack(spacing: 6) {
                    ForEach(items, id: \.self) { item in
                        HStack(spacing: 3) {
                            Text(item)
                            Button {
                                Task { await model.removeReviewRequest(item) }
                            } label: {
                                Image(systemName: "xmark.circle.fill")
                                    .foregroundStyle(.tertiary)
                            }
                            .disabled(model.working)
                        }
                        .font(.gbSans(.caption))
                        .padding(.horizontal, 8)
                        .padding(.vertical, 3)
                        .background(Color.secondary.opacity(0.07), in: gbChipShape)
                        .overlay(gbChipShape.stroke(Color.secondary.opacity(0.35), lineWidth: 1))
                    }
                }
            }
        }
    }

    private var diffSection: some View {
        Section {
            NavigationLink(value: MRRoute.diff(repo: model.repoPath, number: model.number)) {
                HStack {
                    Label("Diff", systemImage: "plus.forwardslash.minus")
                    Spacer()
                    if let diff = model.diff {
                        Text("+\(diff.additions)")
                            .foregroundStyle(Color.gbOK)
                        Text("−\(diff.deletions)")
                            .foregroundStyle(Color.gbBad)
                    }
                }
                .font(.gbSans(.subheadline))
            }
        }
    }

    private func commitsSection(_ commits: [MRDetail.MRCommit]) -> some View {
        Section("Commits") {
            ForEach(commits) { commit in
                HStack(spacing: 8) {
                    Text(commit.shortSHA)
                        .font(.gbMono(.caption))
                        .foregroundStyle(.secondary)
                    Text(commit.subject)
                        .font(.gbSans(.subheadline))
                        .lineLimit(1)
                }
            }
        }
    }

    private func checksSection(_ checks: [MRDetail.Check], combined: String?) -> some View {
        Section("Checks" + (combined.map { " — \($0)" } ?? "")) {
            ForEach(checks, id: \.context) { check in
                VStack(alignment: .leading, spacing: 2) {
                    HStack {
                        Image(systemName: checkIcon(check.state))
                            .foregroundStyle(checkColor(check.state))
                        Text(check.context)
                            .font(.gbSans(.subheadline))
                        Spacer()
                        Text(check.state)
                            .font(.gbSans(.caption))
                            .foregroundStyle(.secondary)
                    }
                    timing(check.updatedAt, duration: check.duration)
                }
            }
        }
    }

    private func reviewsSection(_ reviews: [MRDetail.Review]) -> some View {
        Section("Reviews") {
            ForEach(reviews) { review in
                VStack(alignment: .leading, spacing: 2) {
                    HStack {
                        Image(systemName: review.verdict == "approve"
                            ? "checkmark.circle.fill" : "exclamationmark.circle.fill")
                            .foregroundStyle(review.verdict == "approve" ? Color.gbOK : Color.gbWarn)
                        Text(review.reviewer)
                            .font(.gbSans(.subheadline))
                        Spacer()
                        if review.stale {
                            GBChip("stale", .gbWarn)
                        }
                    }
                    timing(review.createdAt)
                }
            }
        }
    }

    /// When a review or check last said something, and for a CI check how
    /// long its build ran. Nothing renders against a server that does not
    /// report the time.
    @ViewBuilder
    private func timing(_ at: Date?, duration: String? = nil) -> some View {
        if let at {
            HStack(spacing: 6) {
                Text(at, format: Self.stamp)
                if let duration {
                    Text("·")
                    Text(duration)
                }
            }
            .font(.gbSans(.caption))
            .foregroundStyle(.tertiary)
        }
    }

    private var threadsSection: some View {
        Section("Threads — \(model.unresolvedCount) unresolved") {
            ForEach(model.threads) { thread in
                ReviewThreadView(thread: thread, model: model)
            }
        }
    }

    private func commentsSection(_ comments: [MRDetail.MRComment]) -> some View {
        Section("Comments") {
            ForEach(comments) { comment in
                VStack(alignment: .leading, spacing: 4) {
                    HStack {
                        Text(comment.author)
                            .font(.gbSans(.caption).weight(.semibold))
                        Text(comment.createdAt, format: .relative(presentation: .named))
                            .font(.gbSans(.caption))
                            .foregroundStyle(.tertiary)
                    }
                    FormattedBodyView(text: comment.body, format: comment.bodyFormat)
                        .font(.gbSans(.subheadline))
                }
                .padding(.vertical, 2)
            }

            HStack {
                TextField("Comment", text: $commentText, axis: .vertical)
                    .lineLimit(1...5)
                Picker("Format", selection: $commentFormat) {
                    Text("Markdown").tag("md")
                    Text("Org").tag("org")
                }
                .pickerStyle(.segmented)
                .labelsHidden()
                .fixedSize()
                .accessibilityIdentifier("mr-comment-format")
                Button {
                    let text = commentText
                    commentText = ""
                    Task { await model.comment(text, format: commentFormat) }
                } label: {
                    Image(systemName: "arrow.up.circle.fill")
                }
                .disabled(commentText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
                    || model.working)
            }
        }
    }

    @ToolbarContentBuilder
    private var toolbar: some ToolbarContent {
        ToolbarItem(placement: .topBarTrailing) {
            if let mr = model.state.value, mr.isOpen {
                Menu {
                    Button {
                        draftTitle = mr.title
                        draftBody = mr.body ?? ""
                        draftFormat = mr.bodyFormat ?? "md"
                        editing = true
                    } label: {
                        Label("Edit", systemImage: "pencil")
                    }
                    Divider()
                    Button {
                        Task { await model.review(.approve) }
                    } label: {
                        Label("Approve", systemImage: "checkmark.circle")
                    }
                    Button {
                        Task { await model.review(.requestChanges) }
                    } label: {
                        Label("Request Changes", systemImage: "exclamationmark.circle")
                    }
                    Divider()
                    Button {
                        Task { await model.setDraft(!mr.draft) }
                    } label: {
                        Label(mr.draft ? "Mark as ready" : "Mark as draft",
                              systemImage: mr.draft ? "checkmark.circle" : "pencil.circle")
                    }
                    Button {
                        retargeting = true
                    } label: {
                        Label("Retarget", systemImage: "arrow.triangle.branch")
                    }
                    Divider()
                    Button {
                        confirmingMerge = true
                    } label: {
                        Label(mr.draft ? "Merge (mark as ready first)" : "Merge",
                              systemImage: "arrow.triangle.merge")
                    }
                    .disabled(mr.draft)
                    Button(role: .destructive) {
                        confirmingClose = true
                    } label: {
                        Label("Close", systemImage: "xmark.circle")
                    }
                } label: {
                    if model.working {
                        ProgressView()
                    } else {
                        Image(systemName: "ellipsis.circle")
                    }
                }
                .disabled(model.working)
                .accessibilityIdentifier("mr-actions-menu")
            }
        }
    }

    private func checkIcon(_ state: String) -> String {
        switch state {
        case "success": "checkmark.circle.fill"
        case "failure", "error": "xmark.circle.fill"
        case "pending", "running": "circle.dotted"
        default: "questionmark.circle"
        }
    }

    private func checkColor(_ state: String) -> Color {
        switch state {
        case "success": .gbOK
        case "failure", "error": .gbBad
        case "pending", "running": .gbWarn
        default: .secondary
        }
    }
}

/// One review thread: anchor, comments, reply, resolve.
struct ReviewThreadView: View {

    let thread: ReviewThread
    let model: MRDetailViewModel
    @State private var replyText = ""

    var body: some View {
        VStack(alignment: .leading, spacing: 6) {
            HStack(spacing: 6) {
                Image(systemName: thread.isResolved
                    ? "checkmark.bubble" : "bubble.left.and.exclamationmark.bubble.right")
                    .font(.gbSans(.caption))
                    .foregroundStyle(thread.isResolved ? Color.gbOK : Color.gbWarn)
                Text("\(thread.path):\(thread.line)")
                    .font(.gbMono(.caption))
                    .lineLimit(1)
                if thread.stale {
                    GBChip("stale", .gbWarn)
                }
                Spacer()
                Button(thread.isResolved ? "Reopen" : "Resolve") {
                    Task { await model.setResolved(thread, !thread.isResolved) }
                }
                .font(.gbSans(.caption))
                .buttonStyle(.bordered)
                .disabled(model.working)
            }
            ForEach(thread.comments) { comment in
                VStack(alignment: .leading, spacing: 2) {
                    HStack {
                        Text(comment.author)
                            .font(.gbSans(.caption).weight(.semibold))
                        Text(comment.createdAt, format: .relative(presentation: .named))
                            .font(.gbSans(.caption2))
                            .foregroundStyle(.tertiary)
                    }
                    Text(comment.body)
                        .font(.gbSans(.subheadline))
                }
            }
            if !thread.isResolved {
                HStack {
                    TextField("Reply", text: $replyText, axis: .vertical)
                        .font(.gbSans(.subheadline))
                        .lineLimit(1...4)
                    Button {
                        let text = replyText
                        replyText = ""
                        Task { await model.reply(to: thread, text) }
                    } label: {
                        Image(systemName: "arrow.up.circle.fill")
                    }
                    .disabled(replyText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
                        || model.working)
                }
            }
        }
        .padding(.vertical, 4)
    }
}

/// A single-purpose branch picker for retarget. `model.branches` is
/// `nil` while loading and `model.branchesError` distinguishes a failed
/// `repo refs` fetch from a repository that genuinely has no other
/// branches — an empty list must not read as a failed load.
private struct RetargetSheet: View {

    let model: MRDetailViewModel
    let onPick: (String) -> Void

    @Environment(\.dismiss) private var dismiss

    var body: some View {
        NavigationStack {
            Group {
                if let error = model.branchesError {
                    ContentUnavailableView {
                        Label("Could not load branches", systemImage: "wifi.exclamationmark")
                    } description: {
                        Text(error)
                    }
                } else if let branches = model.branches {
                    if branches.isEmpty {
                        ContentUnavailableView {
                            Label("No other branches", systemImage: "arrow.triangle.branch")
                        } description: {
                            Text("This repository has no other branches to retarget to.")
                        }
                    } else {
                        List(branches, id: \.self) { branch in
                            Button(branch) { onPick(branch) }
                        }
                    }
                } else {
                    ProgressView()
                }
            }
            .navigationTitle("Retarget !\(model.number)")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .cancellationAction) {
                    Button("Cancel") { dismiss() }
                }
            }
            .task { await model.loadBranches() }
        }
    }
}