import SwiftUI
import AppKit

private struct NoteCollection: Identifiable, Hashable {
    enum Kind: Hashable {
        case notes
        case archive
        case recentlyDeleted
    }

    let id: UUID
    let name: String
    let kind: Kind
}

struct Note: Identifiable, Equatable, Hashable, Codable {
    let id: UUID
    var title: String
    var body: String
    var updatedAt: Date
    var isArchived: Bool
    var isDeleted: Bool
    var deletedAt: Date?
}

struct NotesAppRootView: View {
    fileprivate enum EditorFocusField: Hashable {
        case title
        case body
    }

    @State private var searchText: String = ""
    private static let defaultCollectionID: UUID = UUID(uuidString: "2E6A2D4E-0B3D-4E8A-A5B7-8D9E0C9E2A01")!
    private static let archiveCollectionID: UUID = UUID(uuidString: "2E6A2D4E-0B3D-4E8A-A5B7-8D9E0C9E2A03")!
    private static let recentlyDeletedCollectionID: UUID = UUID(uuidString: "2E6A2D4E-0B3D-4E8A-A5B7-8D9E0C9E2A04")!
    @State private var selectedCollectionID: UUID? = NotesAppRootView.defaultCollectionID
    @State private var selectedNoteID: UUID? = nil
    @State private var editorFocus: EditorFocusField? = nil
    @State private var showPermanentDeleteConfirmation = false

    @StateObject private var store = NotesStore()

    private var collections: [NoteCollection] = [
        NoteCollection(id: NotesAppRootView.defaultCollectionID, name: "Notes", kind: .notes),
        NoteCollection(id: NotesAppRootView.archiveCollectionID, name: "Archive", kind: .archive),
        NoteCollection(id: NotesAppRootView.recentlyDeletedCollectionID, name: "Recently Deleted", kind: .recentlyDeleted)
    ]

    private var selectedCollection: NoteCollection? {
        collections.first { $0.id == selectedCollectionID }
    }

    private var filteredNotes: [Note] {
        guard let selectedCollection else { return [] }

        let scoped: [Note]
        switch selectedCollection.kind {
        case .notes:
            scoped = store.notes.filter { !$0.isDeleted && !$0.isArchived }
        case .archive:
            scoped = store.notes.filter { !$0.isDeleted && $0.isArchived }
        case .recentlyDeleted:
            scoped = store.notes.filter { $0.isDeleted }
        }

        let trimmed = searchText.trimmingCharacters(in: .whitespacesAndNewlines).lowercased()
        if trimmed.isEmpty { return scoped }

        return scoped.filter {
            $0.title.lowercased().contains(trimmed) || $0.body.lowercased().contains(trimmed)
        }
    }

    private func addNote() {
        let now = Date()
        let newNote = Note(
            id: UUID(),
            title: "New Note",
            body: "",
            updatedAt: now,
            isArchived: false,
            isDeleted: false,
            deletedAt: nil
        )

        selectedCollectionID = NotesAppRootView.defaultCollectionID
        store.notes.insert(newNote, at: 0)
        selectedNoteID = newNote.id
        editorFocus = .title
    }

    private var canDeleteSelectedNote: Bool {
        guard let selectedNoteID else { return false }
        return store.notes.contains { $0.id == selectedNoteID }
    }

    private var canMoveToRecentlyDeleted: Bool {
        guard let selectedCollection else { return false }
        guard let selectedNoteID else { return false }
        guard let note = store.notes.first(where: { $0.id == selectedNoteID }) else { return false }
        if note.isDeleted { return false }
        return selectedCollection.kind == .notes || selectedCollection.kind == .archive
    }

    private func moveSelectedNoteToRecentlyDeleted() {
        guard let selectedNoteID else { return }
        guard let index = store.notes.firstIndex(where: { $0.id == selectedNoteID }) else { return }

        store.notes[index].isDeleted = true
        store.notes[index].deletedAt = Date()

        // Stay on the current sidebar section (e.g. Notes); clear selection since the note left this list.
        self.selectedNoteID = nil
        editorFocus = nil
    }

    private var canPermanentlyDeleteSelectedNote: Bool {
        guard let selectedCollection else { return false }
        guard let selectedNoteID else { return false }
        guard let note = store.notes.first(where: { $0.id == selectedNoteID }) else { return false }
        return selectedCollection.kind == .recentlyDeleted && note.isDeleted
    }

    private func permanentlyDeleteSelectedNote() {
        guard let selectedNoteID else { return }
        store.notes.removeAll { $0.id == selectedNoteID }
        self.selectedNoteID = nil
        editorFocus = nil
    }

    private var canRestoreSelectedNote: Bool {
        guard let selectedCollection else { return false }
        guard let selectedNoteID else { return false }
        guard let note = store.notes.first(where: { $0.id == selectedNoteID }) else { return false }
        return selectedCollection.kind == .recentlyDeleted && note.isDeleted
    }

    private func restoreSelectedNote() {
        guard let selectedNoteID else { return }
        guard let index = store.notes.firstIndex(where: { $0.id == selectedNoteID }) else { return }

        store.notes[index].isDeleted = false
        store.notes[index].deletedAt = nil

        if store.notes[index].isArchived {
            selectedCollectionID = NotesAppRootView.archiveCollectionID
        } else {
            selectedCollectionID = NotesAppRootView.defaultCollectionID
        }

        self.selectedNoteID = store.notes[index].id
    }

    private var canArchiveSelectedNote: Bool {
        guard let selectedNoteID else { return false }
        guard let note = store.notes.first(where: { $0.id == selectedNoteID }) else { return false }
        guard let selectedCollection else { return false }
        if note.isDeleted { return false }
        return selectedCollection.kind == .notes && !note.isArchived
    }

    private func archiveSelectedNote() {
        guard let selectedNoteID else { return }
        guard let index = store.notes.firstIndex(where: { $0.id == selectedNoteID }) else { return }

        store.notes[index].isArchived = true
        // Stay on Notes; clear selection since archived notes no longer appear in this list.
        self.selectedNoteID = nil
        editorFocus = nil
    }

    private var canUnarchiveSelectedNote: Bool {
        guard let selectedNoteID else { return false }
        guard let note = store.notes.first(where: { $0.id == selectedNoteID }) else { return false }
        guard let selectedCollection else { return false }
        if note.isDeleted { return false }
        return selectedCollection.kind == .archive && note.isArchived
    }

    private func unarchiveSelectedNote() {
        guard let selectedNoteID else { return }
        guard let index = store.notes.firstIndex(where: { $0.id == selectedNoteID }) else { return }

        store.notes[index].isArchived = false
        selectedCollectionID = NotesAppRootView.defaultCollectionID
        self.selectedNoteID = store.notes[index].id
        editorFocus = nil
    }

    var body: some View {
        NavigationSplitView {
            SidebarView(
                collections: collections,
                notes: store.notes,
                selectedCollectionID: $selectedCollectionID
            )
        } content: {
            VStack(spacing: 0) {
                HStack(spacing: 10) {
                    SearchBar(text: $searchText)

                    Button(action: addNote) {
                        Image(systemName: "square.and.pencil")
                            .font(.system(size: 14, weight: .semibold))
                    }
                    .buttonStyle(.borderless)
                    .keyboardShortcut("n", modifiers: [.command])
                    .help("New Note")

                    Button(action: moveSelectedNoteToRecentlyDeleted) {
                        Image(systemName: "trash")
                            .font(.system(size: 14, weight: .semibold))
                    }
                    .buttonStyle(.borderless)
                    .keyboardShortcut(.delete, modifiers: [.command])
                    .help("Delete Note")
                    .disabled(!canMoveToRecentlyDeleted)

                    Button(action: restoreSelectedNote) {
                        Image(systemName: "arrow.uturn.left")
                            .font(.system(size: 14, weight: .semibold))
                    }
                    .buttonStyle(.borderless)
                    .keyboardShortcut("z", modifiers: [.command, .shift])
                    .help("Restore Note")
                    .disabled(!canRestoreSelectedNote)

                    Button(action: { showPermanentDeleteConfirmation = true }) {
                        Image(systemName: "trash.slash")
                            .font(.system(size: 14, weight: .semibold))
                    }
                    .buttonStyle(.borderless)
                    .keyboardShortcut(.delete, modifiers: [.command, .option])
                    .help("Delete Permanently")
                    .disabled(!canPermanentlyDeleteSelectedNote)

                    Button(action: archiveSelectedNote) {
                        Image(systemName: "archivebox")
                            .font(.system(size: 14, weight: .semibold))
                    }
                    .buttonStyle(.borderless)
                    .keyboardShortcut("a", modifiers: [.command, .shift])
                    .help("Archive Note")
                    .disabled(!canArchiveSelectedNote)

                    Button(action: unarchiveSelectedNote) {
                        Image(systemName: "tray.and.arrow.up")
                            .font(.system(size: 14, weight: .semibold))
                    }
                    .buttonStyle(.borderless)
                    .keyboardShortcut("u", modifiers: [.command, .shift])
                    .help("Unarchive Note")
                    .disabled(!canUnarchiveSelectedNote)
                    .padding(.trailing, 12)
                }

                Group {
                    if filteredNotes.isEmpty {
                        EmptyListView(text: "No Notes")
                    } else {
                        NotesListView(
                            notes: filteredNotes,
                            selectedNoteID: $selectedNoteID
                        )
                    }
                }
                .frame(maxWidth: .infinity, maxHeight: .infinity)
            }
            .background(Color(nsColor: .textBackgroundColor))
        } detail: {
            NoteEditorView(
                notes: $store.notes,
                selectedNoteID: selectedNoteID,
                focusField: $editorFocus
            )
            .background(Color(nsColor: .textBackgroundColor))
        }
        .preferredColorScheme(.dark)
        .onAppear {
            store.purgeExpiredRecentlyDeletedIfNeeded()
        }
        .alert("Delete permanently?", isPresented: $showPermanentDeleteConfirmation) {
            Button("Cancel", role: .cancel) {}
            Button("Delete Permanently", role: .destructive) {
                permanentlyDeleteSelectedNote()
            }
        } message: {
            Text("This note will be permanently removed from this device. Notes in Recently Deleted are also removed automatically after 30 days. You cannot undo this action.")
        }
    }
}

private struct SidebarView: View {
    let collections: [NoteCollection]
    let notes: [Note]

    @Binding var selectedCollectionID: UUID?

    private func notesCount(for collection: NoteCollection) -> Int {
        switch collection.kind {
        case .notes:
            return notes.filter { !$0.isDeleted && !$0.isArchived }.count
        case .archive:
            return notes.filter { !$0.isDeleted && $0.isArchived }.count
        case .recentlyDeleted:
            return notes.filter { $0.isDeleted }.count
        }
    }

    var body: some View {
        List(selection: $selectedCollectionID) {
            Section(header: Text("Keep Notebook")) {
                ForEach(collections) { collection in
                    HStack(spacing: 8) {
                        Text(collection.name)
                            .foregroundStyle(.primary)
                        Spacer(minLength: 8)
                        Text("\(notesCount(for: collection))")
                            .foregroundStyle(.secondary)
                            .font(.system(size: 12, weight: .semibold))
                    }
                    .tag(collection.id)
                }
            }
        }
        .listStyle(.sidebar)
        .frame(minWidth: 210)
    }
}

private struct SearchBar: View {
    @Binding var text: String

    var body: some View {
        HStack(spacing: 8) {
            Image(systemName: "magnifyingglass")
                .foregroundStyle(.secondary)
            TextField("Search", text: $text)
                .textFieldStyle(.plain)
                .foregroundStyle(.primary)
        }
        .padding(10)
        .background(Color(nsColor: .windowBackgroundColor))
        .overlay(
            RoundedRectangle(cornerRadius: 10)
                .stroke(Color(nsColor: .separatorColor).opacity(0.35), lineWidth: 1)
        )
        .padding(12)
    }
}

private struct EmptyListView: View {
    let text: String

    var body: some View {
        VStack {
            Spacer()
            Text(text)
                .foregroundStyle(.secondary)
                .font(.system(size: 16, weight: .semibold))
            Spacer()
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }
}

private struct NotesListView: View {
    let notes: [Note]
    @Binding var selectedNoteID: UUID?

    var body: some View {
        List(selection: $selectedNoteID) {
            ForEach(notes) { note in
                HStack(spacing: 8) {
                    Text(note.title)
                        .lineLimit(1)
                    Spacer(minLength: 8)
                }
                .tag(note.id)
            }
        }
        .listStyle(.inset)
    }
}

private struct NoteEditorView: View {
    @Binding var notes: [Note]
    let selectedNoteID: UUID?
    @Binding var focusField: NotesAppRootView.EditorFocusField?

    @FocusState private var focusedField: NotesAppRootView.EditorFocusField?

    var body: some View {
        VStack(spacing: 10) {
            if let selectedNoteID,
               let index = notes.firstIndex(where: { $0.id == selectedNoteID }) {
                TextField("Title", text: $notes[index].title)
                    .textFieldStyle(.plain)
                    .font(.system(size: 22, weight: .semibold))
                    .padding(.horizontal, 14)
                    .focused($focusedField, equals: .title)

                Divider()
                    .padding(.horizontal, 14)

                TextEditor(text: $notes[index].body)
                    .font(.system(size: 14))
                    .foregroundStyle(.primary)
                    .padding(14)
                    .background(Color(nsColor: .textBackgroundColor))
                    .focused($focusedField, equals: .body)
            } else {
                // Keep the editor empty to match the screenshot's "nothing selected" state.
                Spacer()
            }
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .top)
        .onChange(of: focusField) { _, newValue in
            guard let newValue else { return }
            focusedField = newValue
            focusField = nil
        }
    }
}