import Combine
import LumaCore
import SwiftUI
import SwiftyPharo

struct NotebookView: View {
    let engine: Engine
    @Binding var selection: SidebarItemID?

    #if canImport(UIKit)
    @Environment(\.horizontalSizeClass) private var horizontalSizeClass
    private var horizontalInset: CGFloat { horizontalSizeClass == .compact ? 6 : 16 }
    #else
    private var horizontalInset: CGFloat { 16 }
    #endif

    private var entries: [LumaCore.NotebookEntry] {
        engine.notebookEntries.sorted { a, b in
            if a.position != b.position { return a.position < b.position }
            return a.id.uuidString < b.id.uuidString
        }
    }

    @State private var drillPath = PharoColumnPath()
    @State private var inspected: UUID?
    @State private var centers: [UUID: CGFloat] = [:]
    @State private var drillWidth: CGFloat = 520
    @State private var resizingFrom: CGFloat?

    private let runtime = PharoRuntime.shared

    var body: some View {
        GeometryReader { page in
            HStack(spacing: 0) {
                self.page
                    .frame(maxWidth: .infinity)

                if !drillPath.objects.isEmpty {
                    let widestDrillLeavingAPageToRead = page.size.width / 2
                    let width = min(drillWidth, widestDrillLeavingAPageToRead)

                    Divider()
                    drillSide(width: width).frame(width: width)
                }
            }
        }
        .coordinateSpace(name: pharoPageSpace)
        .background(.pharoGutter)
        .pharoMaximizedPane(runtime: runtime, path: drillPath, onCloseAll: closeDrill)
    }

    private var page: some View {
        Group {
            if entries.isEmpty {
                NotebookEmptyStateView(
                    engine: engine,
                    onAddNote: { addEntry(kind: .note, after: nil) },
                    onAddPharoCell: { addEntry(kind: .pharo, after: nil) })
            } else {
                content
            }
        }
    }

    private var content: some View {
        ZStack(alignment: .bottomTrailing) {
            ScrollViewReader { proxy in
                ScrollView {
                    LazyVStack(alignment: .leading, spacing: 16) {
                        let ordered = entries
                        TopDropZone(engine: engine, firstEntry: ordered.first)
                            .padding(.horizontal, horizontalInset)
                        ForEach(Array(ordered.enumerated()), id: \.element.id) { index, entry in
                            NotebookEntryRow(
                                entry: entry,
                                previous: index > 0 ? ordered[index - 1] : nil,
                                next: index < ordered.count - 1 ? ordered[index + 1] : nil,
                                engine: engine,
                                selection: $selection,
                                autoBeginEditing: entry.id == lastInsertedID,
                                drillPath: drillPath,
                                inspected: $inspected,
                                centers: $centers,
                                onEditingChanged: { editing in
                                    if editing {
                                        editingEntryIDs.insert(entry.id)
                                    } else {
                                        editingEntryIDs.remove(entry.id)
                                    }
                                },
                                addNoteBelow: { addEntry(kind: .note, after: entry) },
                                addPharoCellBelow: { addEntry(kind: .pharo, after: entry) },
                                deleteAction: { engine.deleteNotebookEntry(entry) }
                            )
                            .id(entry.id)
                        }
                        .padding(.horizontal, horizontalInset)
                        Color.clear
                            .frame(height: 80)
                            .id("notebook-bottom-anchor")
                    }
                }
                .onChange(of: lastInsertedID) { _, newID in
                    guard newID != nil else { return }
                    withAnimation(.easeInOut(duration: 0.2)) {
                        proxy.scrollTo("notebook-bottom-anchor", anchor: .bottom)
                    }
                }
                .onChange(of: entries.map(\.id)) { _, newIDs in
                    editingEntryIDs.formIntersection(Set(newIDs))
                }
            }

            HStack(spacing: 8) {
                Button {
                    addEntry(kind: .note, after: nil)
                } label: {
                    Label("New Note", systemImage: "plus")
                        .font(.callout.weight(.medium))
                        .padding(.horizontal, 10)
                        .padding(.vertical, 4)
                }
                .accessibilityIdentifier("notebook.newNote")
                .buttonStyle(.borderedProminent)

                Button {
                    addEntry(kind: .pharo, after: nil)
                } label: {
                    Label("New Pharo Cell", systemImage: "chevron.left.forwardslash.chevron.right")
                        .font(.callout.weight(.medium))
                        .padding(.horizontal, 10)
                        .padding(.vertical, 4)
                }
                .accessibilityIdentifier("notebook.newPharoCell")
                .buttonStyle(.bordered)
            }
            .buttonBorderShape(.capsule)
            #if canImport(UIKit)
            .controlSize(.regular)
            #else
            .controlSize(.small)
            #endif
            .shadow(radius: 3, y: 1)
            .padding()
            .opacity(isAnyEditing ? 0 : 1)
            .allowsHitTesting(!isAnyEditing)
            .animation(.easeInOut(duration: 0.15), value: isAnyEditing)
        }
    }

    @State private var editingEntryIDs: Set<UUID> = []

    private var isAnyEditing: Bool { !editingEntryIDs.isEmpty }

    @State private var lastInsertedID: UUID?

    private func addEntry(kind: LumaCore.NotebookEntry.Kind, after entry: LumaCore.NotebookEntry?) {
        let added = LumaCore.NotebookEntry(
            kind: kind,
            title: "",
            details: "",
            binaryData: nil,
            processName: entry?.processName
        )
        engine.addNotebookEntry(added, after: entry)
        lastInsertedID = added.id
    }

    /// A cell drills into the pane beside the page, its columns riding a scroller
    /// of their own with the arrow that points across from the cell they came
    /// from. It is here only while a drill is open, so the page is the whole
    /// width the rest of the time.
    private func drillSide(width: CGFloat) -> some View {
        VStack(spacing: 0) {
            PharoOverviewStrip(path: drillPath)
            Divider()

            ScrollView(.horizontal) {
                HStack(spacing: 0) {
                    if !drillPath.isFirstColumnCollapsed {
                        PharoPointingArrow(pointsFrom: inspected.flatMap { centers[$0] })
                    }
                    pharoColumns(
                        runtime: runtime,
                        path: drillPath,
                        width: pharoColumnWidth(fitting: width),
                        onCloseAll: closeDrill)
                }
                .scrollTargetLayout()
            }
            .contentMargins(8, for: .scrollContent)
            .pharoColumnScrolling(drillPath)
        }
        .overlay(alignment: .leading) { drillResizeHandle }
    }

    private func closeDrill() {
        drillPath.clear()
        inspected = nil
    }

    private var drillResizeHandle: some View {
        Rectangle()
            .fill(.clear)
            .frame(width: 8)
            .contentShape(Rectangle())
            .platformPointer(.columnResize)
            .gesture(
                // Global, since the handle rides the pane's edge as it resizes.
                DragGesture(coordinateSpace: .global)
                    .onChanged { drag in
                        let base = resizingFrom ?? drillWidth
                        resizingFrom = base
                        drillWidth = min(max(base - drag.translation.width, 320), 1000)
                    }
                    .onEnded { _ in resizingFrom = nil })
    }
}

/// Thin drop strip above the first entry so drags can actually land at
/// position 0. The per-row `.dropDestination` only fires inside the
/// row's frame; drops into the empty space above the first row used
/// to fall on the floor.
private struct TopDropZone: View {
    let engine: Engine
    let firstEntry: LumaCore.NotebookEntry?
    @State private var isTargeted = false

    var body: some View {
        Rectangle()
            .fill(Color.clear)
            .frame(height: 6)
            .overlay(alignment: .bottom) {
                if isTargeted {
                    Color.accentColor.frame(height: 2)
                }
            }
            .dropDestination(for: String.self) { items, _ in
                guard let first = items.first,
                      let sourceID = UUID(uuidString: first),
                      let source = engine.notebookEntries.first(where: { $0.id == sourceID })
                else { return false }
                if source.id == firstEntry?.id { return false }
                engine.reorderNotebookEntry(
                    source,
                    between: nil,
                    and: firstEntry,
                )
                return true
            } isTargeted: { isTargeted = $0 }
    }
}

struct NotebookEntryRow: View {
    let entry: LumaCore.NotebookEntry
    let previous: LumaCore.NotebookEntry?
    let next: LumaCore.NotebookEntry?
    let engine: Engine
    @Binding var selection: SidebarItemID?
    let autoBeginEditing: Bool
    let drillPath: PharoColumnPath
    @Binding var inspected: UUID?
    @Binding var centers: [UUID: CGFloat]

    let onEditingChanged: (Bool) -> Void
    let addNoteBelow: () -> Void
    let addPharoCellBelow: () -> Void
    let deleteAction: () -> Void

    @FocusState private var isTitleFocused: Bool
    @FocusState private var isBodyFocused: Bool
    @State private var isEditingUserNote: Bool = false
    @State private var editTitle: String = ""
    @State private var editDetails: String = ""
    @State private var dropHighlight: DropHighlight = .none
    @State private var rowHeight: CGFloat = 0

    private enum DropHighlight { case none, above, below }
    private struct RowHeightKey: PreferenceKey {
        static var defaultValue: CGFloat = 0
        static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
            value = nextValue()
        }
    }

    private var isNote: Bool { entry.kind == .note }

    private var isPharo: Bool { entry.kind == .pharo }

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

            if isNote {
                if isEditingUserNote {
                    editableUserNoteBody
                } else {
                    readOnlyUserNoteBody
                }
            } else if isPharo {
                PharoNotebookCell(
                    entry: entry,
                    engine: engine,
                    autoFocus: autoBeginEditing,
                    drillPath: drillPath,
                    inspected: $inspected,
                    centers: $centers)
            } else {
                systemEntryBody
            }

            if let data = entry.binaryData, !data.isEmpty {
                HexView(data: data)
                    .font(.system(.footnote, design: .monospaced))
                    .fixedSize(horizontal: false, vertical: true)
            }
        }
        .padding(10)
        .background(Color.secondary.opacity(0.06))
        .clipShape(RoundedRectangle(cornerRadius: 8))
        .background(
            GeometryReader { proxy in
                Color.clear.preference(key: RowHeightKey.self, value: proxy.size.height)
            }
        )
        .onPreferenceChange(RowHeightKey.self) { rowHeight = $0 }
        .overlay(alignment: .top) {
            if dropHighlight == .above {
                Color.accentColor.frame(height: 2)
            }
        }
        .overlay(alignment: .bottom) {
            if dropHighlight == .below {
                Color.accentColor.frame(height: 2)
            }
        }
        .draggable(entry.id.uuidString)
        .dropDestination(for: String.self) { items, location in
            handleDrop(items: items, location: location)
        } isTargeted: { targeted in
            if !targeted { dropHighlight = .none }
        }
        .contextMenu {
            if isNote {
                Button {
                    beginEditing()
                } label: {
                    Label("Edit Note", systemImage: "pencil")
                }
            }

            Button {
                addNoteBelow()
            } label: {
                Label("Insert Note Below", systemImage: "plus")
            }

            Button {
                addPharoCellBelow()
            } label: {
                Label("Insert Pharo Cell Below", systemImage: "chevron.left.forwardslash.chevron.right")
            }

            Divider()

            Button(role: .destructive) {
                deleteAction()
            } label: {
                Label("Delete Entry", systemImage: "trash")
            }
        }
        .onAppear {
            editTitle = entry.title
            editDetails = entry.details
            if autoBeginEditing && isNote && entry.details.isEmpty && entry.title.isEmpty {
                isEditingUserNote = true
                DispatchQueue.main.async {
                    isTitleFocused = true
                }
            }
        }
        .onChange(of: isEditingUserNote) { _, newValue in
            onEditingChanged(newValue)
        }
        .onDisappear {
            if isEditingUserNote {
                onEditingChanged(false)
            }
        }
        .onTapGesture(count: 2) {
            guard isNote else { return }
            beginEditing(focusBody: true)
        }
    }

    @ViewBuilder
    private var header: some View {
        HStack(alignment: .center, spacing: 10) {
            editorStack

            if let processName = entry.processName {
                Text(processName)
                    .font(.caption2)
                    .padding(.horizontal, 6)
                    .padding(.vertical, 2)
                    .background(Color.accentColor.opacity(0.12))
                    .clipShape(RoundedRectangle(cornerRadius: 4))
            }

            if !(isNote && isEditingUserNote) {
                Text(isNote && entry.title.isEmpty ? "Note" : entry.title)
                    .font(.headline)
                    .lineLimit(1)
                    .textSelection(.enabled)
                    .frame(maxWidth: .infinity, alignment: .leading)
            } else {
                Spacer(minLength: 0)
            }

            NotebookTimestampLabel(date: entry.timestamp)
                .help(entry.timestamp.formatted())
        }
    }

    @ViewBuilder
    private var editorStack: some View {
        AuthorAvatarStack(authors: entry.editors)
    }

    private func handleDrop(items: [String], location: CGPoint) -> Bool {
        defer { dropHighlight = .none }
        guard let first = items.first,
            let sourceID = UUID(uuidString: first),
            sourceID != entry.id
        else { return false }
        guard let source = engine.notebookEntries.first(where: { $0.id == sourceID })
        else { return false }

        let ordered = engine.notebookEntries.sorted { a, b in
            if a.position != b.position { return a.position < b.position }
            return a.id.uuidString < b.id.uuidString
        }
        guard let targetIndex = ordered.firstIndex(where: { $0.id == entry.id }) else { return false }

        let midpoint = rowHeight > 0 ? rowHeight / 2 : 0
        let dropAbove = location.y < midpoint
        let neighborA: LumaCore.NotebookEntry?
        let neighborB: LumaCore.NotebookEntry?
        if dropAbove {
            neighborA = targetIndex > 0 ? ordered[targetIndex - 1] : nil
            neighborB = ordered[targetIndex]
        } else {
            neighborA = ordered[targetIndex]
            neighborB = targetIndex < ordered.count - 1 ? ordered[targetIndex + 1] : nil
        }
        if neighborA?.id == source.id || neighborB?.id == source.id { return false }

        engine.reorderNotebookEntry(source, between: neighborA, and: neighborB)
        return true
    }

    @ViewBuilder
    private var editableUserNoteBody: some View {
        VStack(alignment: .leading, spacing: 6) {
            TextField("Title", text: $editTitle)
                .font(.subheadline.weight(.semibold))
                .focused($isTitleFocused)
                .onSubmit { saveEdits() }
                .accessibilityIdentifier("notebook.note.title")

            TextEditor(text: $editDetails)
                .font(.system(.body, design: .default))
                .frame(minHeight: 80)
                .focused($isBodyFocused)
                .accessibilityIdentifier("notebook.note.body")
                .overlay(alignment: .topLeading) {
                    if editDetails.isEmpty {
                        Text("Write something\u{2026}")
                            .font(.body)
                            .foregroundStyle(.secondary)
                            .padding(.horizontal, 5)
                            .padding(.vertical, 8)
                            .allowsHitTesting(false)
                    }
                }
                .overlay(
                    RoundedRectangle(cornerRadius: 6)
                        .stroke(Color.secondary.opacity(0.2))
                )

            HStack(spacing: 8) {
                Spacer()
                Button("Cancel") { cancelEdits() }
                Button("Save") { saveEdits() }
                    .buttonStyle(.borderedProminent)
                    .keyboardShortcut(.defaultAction)
            }
        }
    }

    @ViewBuilder
    private var readOnlyUserNoteBody: some View {
        if !entry.details.isEmpty {
            MarkdownView(entry.details)
        }
    }

    @ViewBuilder
    private var systemEntryBody: some View {
        if let jsValue = entry.jsValue {
            JSInspectValueView(
                value: jsValue,
                sessionID: entry.sessionID ?? UUID(),
                engine: engine,
                selection: $selection
            )
            .font(.system(.footnote, design: .monospaced))
        } else if let styled = entry.styledDetails {
            Text(styled.attributed)
                .font(.system(.body, design: .monospaced))
                .textSelection(.enabled)
        } else if !entry.details.isEmpty {
            Text(entry.details)
                .font(.system(.body, design: .monospaced))
                .textSelection(.enabled)
        }
    }

    private func saveEdits() {
        var updated = entry
        updated.title = editTitle
        updated.details = editDetails
        withAnimation(.easeOut(duration: 0.15)) {
            isEditingUserNote = false
        }
        engine.updateNotebookEntry(updated)
    }

    private func cancelEdits() {
        if isFreshPlaceholder {
            engine.deleteNotebookEntry(entry)
            return
        }

        editTitle = entry.title
        editDetails = entry.details
        withAnimation(.easeOut(duration: 0.15)) {
            isEditingUserNote = false
        }
    }

    private var isFreshPlaceholder: Bool {
        entry.title.isEmpty && entry.details.isEmpty
    }

    private func beginEditing(focusBody: Bool = false) {
        guard isNote else { return }
        editTitle = entry.title
        editDetails = entry.details

        withAnimation(.easeInOut(duration: 0.15)) {
            isEditingUserNote = true
        }

        DispatchQueue.main.async {
            if focusBody {
                isBodyFocused = true
            } else {
                isTitleFocused = true
            }
        }
    }
}

private let instructionsMaxWidth: CGFloat = 440

struct NotebookEmptyStateView: View {
    let engine: Engine
    let onAddNote: () -> Void
    let onAddPharoCell: () -> Void

    #if canImport(UIKit)
    @Environment(\.horizontalSizeClass) private var horizontalSizeClass
    private var isCompact: Bool { horizontalSizeClass == .compact }
    #else
    private var isCompact: Bool { false }
    #endif

    var body: some View {
        GeometryReader { geo in
            VStack {
                Spacer(minLength: 0)

                if engine.collaboration.status == .connecting {
                    joiningContent
                } else {
                    defaultContent
                }

                Spacer(minLength: 0)
            }
            .frame(width: geo.size.width, height: geo.size.height)
        }
    }

    private var joiningContent: some View {
        VStack(spacing: 16) {
            ProgressView()
                .controlSize(.large)
            Text("Joining lab\u{2026}")
                .font(.title3.weight(.semibold))
            Text("Syncing this project's shared state.")
                .font(.subheadline)
                .foregroundStyle(.secondary)
                .multilineTextAlignment(.center)
        }
        .padding(.horizontal, 24)
    }

    private var defaultContent: some View {
        VStack(spacing: 24) {
            EmptyStateHeading(
                title: "Notebook",
                systemImage: "book.pages",
                subtitle: "Capture interesting findings here."
            )

            if !isCompact {
                walkthrough
            }

            HStack(spacing: 8) {
                Button(action: onAddNote) {
                    Label("New Note", systemImage: "plus")
                }
                .buttonStyle(.borderedProminent)

                Button(action: onAddPharoCell) {
                    Label("New Pharo Cell", systemImage: "chevron.left.forwardslash.chevron.right")
                }
                .buttonStyle(.bordered)
            }
            .controlSize(.large)
        }
        .padding(.horizontal, 24)
    }

    private var walkthrough: some View {
        HStack {
            Spacer(minLength: 0)

            VStack(alignment: .leading, spacing: 8) {
                walkthroughStep(
                    number: 1,
                    text: Text("Use the \(Image(systemName: "target")) button to attach to a running app or process.")
                )
                walkthroughStep(
                    number: 2,
                    text: Text("Then use the \(Image(systemName: "waveform.path.ecg")) button to add instruments.")
                )
                walkthroughStep(
                    number: 3,
                    text: Text("Pin any event from the bottom event stream to save it here.")
                )
            }
            .font(.callout)
            .frame(maxWidth: instructionsMaxWidth, alignment: .leading)
            .padding(.leading, 72)

            Spacer(minLength: 0)
        }
    }

    @ViewBuilder
    private func walkthroughStep(number: Int, text: Text) -> some View {
        HStack(alignment: .firstTextBaseline, spacing: 8) {
            Text("\(number).")
                .monospacedDigit()
                .foregroundStyle(.secondary)
                .frame(width: 18, alignment: .trailing)
            text
                .fixedSize(horizontal: false, vertical: true)
        }
    }
}

struct NotebookTimestampLabel: View {
    let date: Date

    var body: some View {
        TimelineView(.periodic(from: .now, by: 60)) { context in
            Text(NotebookTimestamp.string(from: date, now: context.date))
                .font(.caption2)
                .foregroundStyle(.tertiary)
                .monospacedDigit()
        }
    }
}