import ByreAPI
import SwiftUI

typealias TaskChanges = Components.Schemas.TaskChanges
typealias FileChange = Components.Schemas.FileChange

private let statusLetter: [FileChange.StatusPayload: String] = [
    .added: "A",
    .modified: "M",
    .deleted: "D",
    .renamed: "R",
    .typeChanged: "T",
]

enum ChangeMode {
    case main, turn, step
}

private let emptyText: [ChangeMode: String] = [
    .main: "No changes from the default branch.",
    .turn: "No changes this turn.",
    .step: "This step changed nothing.",
]

struct ChangesMemory {
    var open: Set<String> = []
    var range = ChangeMode.main
    var pinRange = ChangeMode.step
}

func untilCancelled() async {
    while !Task.isCancelled {
        try? await Task.sleep(for: .seconds(3600))
    }
}

@MainActor
@Observable
final class ChangesModel {
    let store: Store
    let compact: Bool
    private(set) var changes: TaskChanges?
    private(set) var error = ""
    private(set) var diffs: [String: Result<String, ApiError>] = [:]
    private(set) var open: Set<String>
    private(set) var range: ChangeMode
    private(set) var pinRange: ChangeMode
    @ObservationIgnored private var loading = false
    @ObservationIgnored private var again = false
    @ObservationIgnored private var timer: Task<Void, Never>?
    @ObservationIgnored private var loadedSince: String?
    @ObservationIgnored private var target = 0
    @ObservationIgnored private var fetching: Set<String> = []

    init(_ store: Store, compact: Bool) {
        self.store = store
        self.compact = compact
        open = store.changesMemory.open
        range = store.changesMemory.range
        pinRange = store.changesMemory.pinRange
    }

    var pinned: Int? {
        compact ? nil : store.pinned
    }

    var mode: ChangeMode {
        compact ? .main : pinned != nil ? pinRange : range
    }

    var empty: String {
        emptyText[mode]!
    }

    private func turnStart() -> String? {
        store.transcript.last { $0.kind == "user.message" && $0.payload.value["head"] is String }?.payload.value["head"] as? String
    }

    func load() async {
        guard let taskId = store.selectedTaskId else {
            changes = nil
            return
        }
        let snapshot = pinned
        let since = snapshot == nil && mode == .turn ? turnStart() : nil
        if snapshot == nil && mode == .turn && since == nil {
            changes = nil
            error = "No turn has started in this task yet."
            return
        }
        if loading {
            again = true
            return
        }
        loading = true
        let started = target
        do {
            let query: Operations.GetTaskChanges.Input.Query = snapshot == nil ? .init(since: since) : .init(snapshot: snapshot, step: pinRange == .step)
            let fresh = try await store.api.client.getTaskChanges(path: .init(taskId: taskId), query: query).ok.body.json
            if started == target {
                loadedSince = since
                if fresh.tree != changes?.tree || fresh.base != changes?.base {
                    diffs = [:]
                }
                changes = fresh
                error = ""
            }
        } catch {
            if started == target {
                self.error = errorText(error)
            }
        }
        loading = false
        if again {
            again = false
            await load()
        }
    }

    func retarget() {
        target += 1
        timer?.cancel()
        changes = nil
        diffs = [:]
        error = ""
        Task {
            await load()
        }
    }

    private func soon() {
        timer?.cancel()
        timer = Task {
            try? await Task.sleep(for: .milliseconds(1500))
            if !Task.isCancelled {
                await load()
            }
        }
    }

    func stop() {
        target += 1
        timer?.cancel()
    }

    func transcript(_ fresh: [ByreEvent]) {
        if pinned != nil {
            return
        }
        if mode == .turn && turnStart() != loadedSince {
            Task {
                await load()
            }
            return
        }
        if fresh.contains(where: { $0.kind == "agent.tool_result" || $0.kind == "turn.ended" }) {
            soon()
        }
    }

    func setRange(_ r: ChangeMode) {
        if range == r {
            return
        }
        range = r
        store.changesMemory.range = r
        retarget()
    }

    func setPinRange(_ r: ChangeMode) {
        if pinRange == r {
            return
        }
        pinRange = r
        store.changesMemory.pinRange = r
        retarget()
    }

    func setOpen(_ path: String, _ on: Bool) {
        if on {
            open.insert(path)
        } else {
            open.remove(path)
        }
        store.changesMemory.open = open
    }

    func shows(_ a: LineAnchor) -> Bool {
        guard open.contains(a.path), case .success(let patch)? = diffs[a.path] else {
            return false
        }
        let lines = patch.components(separatedBy: "\n")
        guard let start = lines.firstIndex(where: { $0.hasPrefix("@@") }) else {
            return false
        }
        return patchRows(lines[start...], a.path).contains { $0.anchor == a }
    }

    func ensureDiff(_ c: TaskChanges, _ f: FileChange) async {
        guard let taskId = store.selectedTaskId, diffs[f.path] == nil, !fetching.contains(f.path) else {
            return
        }
        fetching.insert(f.path)
        defer {
            fetching.remove(f.path)
        }
        let result: Result<String, ApiError>
        do {
            result = .success(try await store.api.client.getTaskDiff(path: .init(taskId: taskId), query: .init(base: c.base, tree: c.tree, path: f.path, oldPath: f.oldPath)).ok.body.json.patch)
        } catch {
            result = .failure(ApiError(status: 0, message: errorText(error)))
        }
        if changes?.base == c.base && changes?.tree == c.tree {
            diffs[f.path] = result
        }
    }
}

struct ChangesView: View {
    var compact = false
    @Environment(Store.self) private var store
    @ViewState private var model: ChangesModel?

    var body: some View {
        VStack(spacing: 0) {
            if let model {
                ChangesHead(model: model)
                if !compact {
                    ChangesList(model: model)
                }
            }
        }
        .frame(maxHeight: compact ? nil : .infinity, alignment: .top)
        .task(id: store.selectedTaskId) {
            let m = model ?? ChangesModel(store, compact: compact)
            model = m
            m.retarget()
            let off = store.selectedFeed?.appended.add { [weak m] events in
                m?.transcript(events)
            }
            await untilCancelled()
            off?()
            m.stop()
        }
        .onChange(of: store.pinned) {
            if !compact {
                model?.retarget()
            }
        }
    }
}

private struct ChangesHead: View {
    let model: ChangesModel
    @Environment(Store.self) private var store
    @Environment(Overlays.self) private var overlays

    var body: some View {
        HStack(alignment: .center, spacing: 12) {
            VStack(alignment: .leading, spacing: 4) {
                if let n = model.pinned {
                    SnapWhere(n: n)
                }
                summary
                    .font(Fonts.font(11))
                    .foregroundStyle(Palette.muted)
                    .textSelection(.enabled)
            }
            Spacer(minLength: 0)
            if !model.compact, let taskId = store.selectedTaskId, let drafts = store.drafts {
                let n = drafts.lineComments(taskId).filter { !trimmed($0.text).isEmpty }.count
                if n > 0 {
                    Button("Send \(n) \(n == 1 ? "comment" : "comments")") {
                        sendComments(taskId, drafts)
                    }
                    .buttonStyle(WebButtonStyle(primary: true))
                    .fixedSize()
                    .help("Send the line comments to the task's agent as one message")
                }
            }
            toggle
        }
        .modifier(HeaderBar())
    }

    private func sendComments(_ taskId: String, _ drafts: Drafts) {
        let sent = drafts.takeLineComments(taskId)
        Task {
            do {
                try await store.messageTask(taskId, commentsMessage(sent))
            } catch {
                drafts.restoreLineComments(taskId, sent)
                overlays.showAlert(errorText(error))
            }
        }
    }

    @ViewBuilder
    private var summary: some View {
        if let c = model.changes {
            let adds = c.files.reduce(0) { $0 + $1.additions }
            let dels = c.files.reduce(0) { $0 + $1.deletions }
            HStack(spacing: 0) {
                Text("\(c.files.count) \(c.files.count == 1 ? "file" : "files") ")
                Text("+\(adds)").foregroundStyle(Palette.ok)
                Text(" ")
                Text("−\(dels)").foregroundStyle(Palette.danger)
                Text(" vs \(String(c.base.prefix(8)))").help(c.base)
                if !model.error.isEmpty {
                    Text(" \(model.error)").foregroundStyle(Palette.danger)
                }
            }
        } else {
            Text(!model.error.isEmpty ? model.error : store.selectedTaskId != nil ? "Loading changes…" : "No task selected.")
        }
    }

    @ViewBuilder
    private var toggle: some View {
        if !model.compact {
            HStack(spacing: 4) {
                if model.pinned != nil {
                    RangeTabButton(label: "Since main", active: model.pinRange == .main) {
                        model.setPinRange(.main)
                    }
                    RangeTabButton(label: "This step", active: model.pinRange == .step) {
                        model.setPinRange(.step)
                    }
                    RangeTabButton(label: "Live", active: false, help: "Back to the live worktree") {
                        store.pinSnapshot(nil)
                    }
                } else {
                    RangeTabButton(label: "Since main", active: model.range == .main) {
                        model.setRange(.main)
                    }
                    RangeTabButton(label: "This turn", active: model.range == .turn) {
                        model.setRange(.turn)
                    }
                }
            }
            .fixedSize()
        }
    }
}

private struct SnapWhere: View {
    let n: Int
    @Environment(Store.self) private var store

    var body: some View {
        let snaps = store.snapshots()
        let snap = snaps.first { $0.n == n }
        HStack(spacing: 0) {
            Text("snapshot \(n)")
            if let snap {
                Text(" · \(snap.trigger.rawValue) · \(clockText(snap.createdAt))")
            }
            Text(" · ")
            step(n - 1, "← #\(n - 1)", snaps)
            Text(" ")
            step(n + 1, "#\(n + 1) →", snaps)
        }
        .font(Fonts.font(12))
    }

    private func step(_ to: Int, _ label: String, _ snaps: [Snapshot]) -> some View {
        Button(label) {
            store.pinSnapshot(to)
        }
        .buttonStyle(SmallLinkButtonStyle(color: Palette.text))
        .disabled(!snaps.contains { $0.n == to })
    }
}

private struct ChangesList: View {
    let model: ChangesModel
    @Environment(Store.self) private var store

    var body: some View {
        if let taskId = store.selectedTaskId, let drafts = store.drafts {
            let hidden = drafts.lineComments(taskId).filter { !model.shows($0.anchor) }
            let files = model.changes?.files ?? []
            if files.isEmpty && hidden.isEmpty {
                EmptyText(text: model.changes != nil ? model.empty : model.error.isEmpty ? "Loading…" : "")
            } else {
                ScrollView {
                    LazyVStack(alignment: .leading, spacing: 6) {
                        if !hidden.isEmpty {
                            HiddenComments(drafts: drafts, taskId: taskId, comments: hidden)
                        }
                        if let c = model.changes {
                            ForEach(c.files.sorted { $0.path.localizedCompare($1.path) == .orderedAscending }, id: \.path) { f in
                                FileRow(model: model, changes: c, file: f)
                            }
                        }
                    }
                    .padding(.horizontal, 16)
                    .padding(.top, 8)
                    .padding(.bottom, 16)
                }
            }
        } else {
            EmptyText(text: "No task selected.")
        }
    }
}

private struct HiddenComments: View {
    let drafts: Drafts
    let taskId: String
    let comments: [LineComment]

    var body: some View {
        VStack(alignment: .leading, spacing: 8) {
            Text("Comments on lines not in the diff shown")
                .font(Fonts.font(11))
                .foregroundStyle(Palette.muted)
            ForEach(comments, id: \.anchor) { c in
                VStack(alignment: .leading, spacing: 2) {
                    Text("\(c.anchor.path):\(c.anchor.line)\(c.anchor.old ? " (removed line)" : "")")
                        .font(Fonts.font(11))
                        .foregroundStyle(Palette.muted)
                    Text(verbatim: c.anchor.quote)
                        .font(Fonts.font(11))
                        .lineLimit(1)
                        .truncationMode(.tail)
                    LineCommentBox(drafts: drafts, taskId: taskId, anchor: c.anchor)
                }
            }
        }
        .padding(.bottom, 6)
    }
}

private struct FileRow: View {
    let model: ChangesModel
    let changes: TaskChanges
    let file: FileChange

    var body: some View {
        let open = model.open.contains(file.path)
        VStack(alignment: .leading, spacing: 0) {
            Button {
                model.setOpen(file.path, !open)
            } label: {
                HStack(alignment: .firstTextBaseline, spacing: 10) {
                    Text(statusLetter[file.status]!)
                        .font(Fonts.font(13, weight: 700))
                        .foregroundStyle(statusColor)
                        .help(file.status.rawValue.replacingOccurrences(of: "_", with: " "))
                    Text(file.oldPath.map { "\($0) → \(file.path)" } ?? file.path)
                        .lineLimit(1)
                        .truncationMode(.tail)
                        .frame(maxWidth: .infinity, alignment: .leading)
                    Group {
                        if file.binary {
                            Text("binary").foregroundStyle(Palette.muted)
                        } else {
                            HStack(spacing: 0) {
                                Text("+\(file.additions)").foregroundStyle(Palette.ok)
                                Text(" ")
                                Text("−\(file.deletions)").foregroundStyle(Palette.danger)
                            }
                        }
                    }
                    .font(Fonts.font(11))
                    .fixedSize()
                }
                .padding(.horizontal, 10)
                .padding(.vertical, 4)
                .contentShape(Rectangle())
            }
            .buttonStyle(.plain)
            if open {
                Group {
                    switch model.diffs[file.path] {
                    case .none:
                        Text("loading…").foregroundStyle(Palette.muted).padding(.horizontal, 10).padding(.vertical, 6)
                    case .failure(let e):
                        Text(e.message).foregroundStyle(Palette.danger).padding(.horizontal, 10).padding(.vertical, 6)
                    case .success(let patch):
                        PatchView(patch: patch, path: file.path, taskId: model.store.selectedTaskId)
                    }
                }
                .frame(maxWidth: .infinity, alignment: .leading)
                .background(Palette.raised)
                .overlay(alignment: .top) {
                    Rectangle().fill(Palette.border).frame(height: 1)
                }
                .task(id: "\(changes.base) \(changes.tree)") {
                    await model.ensureDiff(changes, file)
                }
            }
        }
        .background(Palette.surface, in: RoundedRectangle(cornerRadius: 8))
        .clipShape(RoundedRectangle(cornerRadius: 8))
        .overlay(RoundedRectangle(cornerRadius: 8).stroke(Palette.border))
    }

    private var statusColor: Color {
        switch file.status {
        case .added: Palette.ok
        case .deleted: Palette.danger
        case .renamed, .modified: Palette.accent
        case .typeChanged: Palette.muted
        }
    }
}

private let hunkHead = Re(#"^@@ -(\d+)(?:,\d+)? \+(\d+)(?:,\d+)? @@"#)

private func patchRows(_ lines: ArraySlice<String>, _ path: String) -> [DiffRow] {
    var old = 0
    var new = 0
    return lines.map { l in
        var row = DiffRow(text: l, kind: PatchLine(l))
        switch row.kind {
        case .hunk:
            if let m = hunkHead.exec(l) {
                old = Int(m[1]!) ?? 0
                new = Int(m[2]!) ?? 0
            }
        case .add:
            row.anchor = LineAnchor(path: path, line: new, old: false, quote: l)
            new += 1
        case .del:
            row.anchor = LineAnchor(path: path, line: old, old: true, quote: l)
            old += 1
        case .ctx:
            if l.hasPrefix(" ") {
                row.anchor = LineAnchor(path: path, line: new, old: false, quote: l)
                old += 1
                new += 1
            }
        case .meta:
            break
        }
        return row
    }
}

func commentsMessage(_ comments: [LineComment]) -> String {
    comments.map { c in
        "`\(c.anchor.path):\(c.anchor.line)`\(c.anchor.old ? " (removed line)" : "")\n> \(c.anchor.quote)\n\n\(trimmed(c.text))"
    }.joined(separator: "\n\n")
}

struct PatchView: View {
    let patch: String
    let path: String
    let taskId: String?

    var body: some View {
        let lines = patch.components(separatedBy: "\n")
        if let start = lines.firstIndex(where: { $0.hasPrefix("@@") }) {
            DiffLines(rows: patchRows(lines[start...], path), taskId: taskId)
        } else {
            Text("No textual changes.")
                .foregroundStyle(Palette.muted)
                .padding(.horizontal, 10)
                .padding(.vertical, 6)
        }
    }
}

struct DiffRow {
    let text: String
    let kind: PatchLine
    var lineno: String?
    var mark = false
    var anchor: LineAnchor?
}

struct DiffLines: View {
    let rows: [DiffRow]
    var taskId: String?
    @Environment(Store.self) private var store
    @ViewState private var width: CGFloat = 0

    var body: some View {
        ScrollView(.horizontal) {
            StretchColumn(minWidth: width) {
                ForEach(Array(rows.enumerated()), id: \.offset) { _, row in
                    if let taskId, let anchor = row.anchor, let drafts = store.drafts {
                        let comment = drafts.lineComment(taskId, anchor)
                        DiffLineRow(row: row, mark: comment != nil, hoverable: true)
                            .simultaneousGesture(TapGesture().onEnded {
                                drafts.toggleLineComment(taskId, anchor)
                            })
                        if comment != nil {
                            LineCommentBox(drafts: drafts, taskId: taskId, anchor: anchor)
                                .frame(width: max(0, width - 20))
                                .padding(.horizontal, 10)
                                .padding(.vertical, 4)
                                .frame(maxWidth: .infinity, alignment: .leading)
                        }
                    } else {
                        DiffLineRow(row: row, mark: row.mark, hoverable: false)
                    }
                }
            }
            .font(Fonts.font(11))
            .padding(.vertical, 4)
            .textSelection(.enabled)
        }
        .scrollBounceBehavior(.basedOnSize)
        .onGeometryChange(for: CGFloat.self) { g in
            g.size.width
        } action: { w in
            width = w
        }
    }
}

private struct DiffLineRow: View {
    let row: DiffRow
    let mark: Bool
    let hoverable: Bool
    @ViewState private var hover = false

    var body: some View {
        HStack(spacing: 0) {
            if let n = row.lineno {
                Text(n)
                    .foregroundStyle(Palette.muted)
                    .frame(minWidth: 30, alignment: .trailing)
                    .padding(.trailing, 8)
            }
            Text(verbatim: row.text.isEmpty ? " " : row.text)
                .foregroundStyle(row.kind.color)
        }
        .fixedSize()
        .padding(.horizontal, 10)
        .frame(maxWidth: .infinity, alignment: .leading)
        .background(row.kind.background)
        .background(hover ? Palette.accent.opacity(0.08) : .clear)
        .overlay(alignment: .leading) {
            if mark {
                Rectangle().fill(Palette.accent).frame(width: 3)
            }
        }
        .contentShape(Rectangle())
        .help(hoverable ? "Click to comment on this line" : "")
        .onHover { on in
            hover = hoverable && on
        }
    }
}

private struct LineCommentBox: View {
    let drafts: Drafts
    let taskId: String
    let anchor: LineAnchor
    @FocusState private var focused: Bool

    var body: some View {
        let text = Binding(get: { drafts.lineComment(taskId, anchor)?.text ?? "" }, set: { drafts.setLineComment(taskId, anchor, $0) })
        VStack(alignment: .trailing, spacing: 4) {
            TextEditor(text: text)
                .font(Fonts.font(12))
                .scrollContentBackground(.hidden)
                .focused($focused)
                .padding(.horizontal, 5)
                .padding(.vertical, 4)
                .frame(height: 64)
                .background(Palette.surface, in: RoundedRectangle(cornerRadius: 6))
                .overlay(alignment: .topLeading) {
                    if text.wrappedValue.isEmpty {
                        Text("Comment on line \(anchor.line)…")
                            .foregroundStyle(Palette.muted)
                            .padding(.horizontal, 10)
                            .padding(.vertical, 4)
                            .allowsHitTesting(false)
                    }
                }
                .overlay(RoundedRectangle(cornerRadius: 6).stroke(focused ? Palette.accent : Palette.border))
            Button("remove") {
                drafts.dropLineComment(taskId, anchor)
            }
            .buttonStyle(SmallLinkButtonStyle())
        }
        .onAppear {
            if text.wrappedValue.isEmpty {
                focused = true
            }
        }
    }
}