Domain Entities: Unit 2 — Document Management

class MarkdownDocument: NSDocument {
    var sourceText: String                      // Raw Markdown source
    var viewModel: EditorViewModel?             // Attached editor (created on makeWindowControllers)

    // NSDocument overrides
    override func read(from data: Data, ofType typeName: String) throws
    override func data(ofType typeName: String) throws -> Data
    override func defaultDraftName() -> String

    // Asset management
    func assetsDirectoryURL() -> URL?           // .md file's sibling assets/ directory
    func ensureAssetsDirectory() throws         // Create assets/ if needed
}

enum DocumentState: Equatable {
    case blank                                  // New untitled document, never saved
    case saved(url: URL)                        // Saved to disk at known URL
    case edited                                 // Has unsaved changes (NSDocument.isDocumentEdited)
    case conflict                               // Save conflict detected (NSDocument ubiquity)
}

@Observable
final class EditorSettings {
    static let shared = EditorSettings()

    var fontFamily: String                      // e.g., "SF Mono", "Menlo"
    var fontSize: CGFloat                       // Points, e.g., 14.0
    var lineSpacing: CGFloat                    // Multiplier, e.g., 1.4
    var appearanceOverride: AppearanceMode      // .system, .light, .dark
    var defaultFocusMode: Bool                  // Default state for new documents
    var defaultTypewriterScroll: Bool           // Default state for new documents

    private init()                              // Singleton — load from UserDefaults
    func save()                                 // Persist to UserDefaults
    func reset()                                // Restore factory defaults
}

enum AppearanceMode: String, CaseIterable, Codable {
    case system                                 // Follow macOS appearance
    case light                                  // Force light
    case dark                                   // Force dark
}

enum EditorSettingsKey: String {
    case fontFamily         = "editor.fontFamily"
    case fontSize           = "editor.fontSize"
    case lineSpacing        = "editor.lineSpacing"
    case appearanceOverride = "editor.appearanceOverride"
    case defaultFocusMode   = "editor.defaultFocusMode"
    case defaultTypewriterScroll = "editor.defaultTypewriterScroll"
}

@Observable
class EditorViewModel {
    // State
    var sourceText: String                      // Synced with MarkdownDocument.sourceText
    var nodeModel: EditorNodeModel              // Block tree from Unit 1 parser
    var cursorPosition: Int                     // UTF-16 offset
    var activeBlockID: EditorNode.ID?           // Currently active block
    var isFocusModeEnabled: Bool
    var isTypewriterScrollEnabled: Bool

    // Document binding
    weak var document: MarkdownDocument?        // Back-reference for save coordination

    // Methods
    func textDidChange(_ newText: String, editedRange: NSRange)
    func cursorDidMove(to position: Int)
    func attributedStringForDisplay() -> NSAttributedString
    func rerenderBlock(_ blockID: EditorNode.ID)
    func toggleFocusMode()
    func toggleTypewriterScroll()
    func insertImage(url: URL)
    func exportHTML() -> String
    func exportPDF() -> Data
}

struct RecentFileEntry: Identifiable, Codable {
    let id: UUID
    var url: URL                                // File URL
    var lastOpened: Date                        // Last access timestamp
    var displayName: String                     // File name without extension
}

actor FileService {
    func createDirectoryIfNeeded(at url: URL) throws
    func fileExists(at url: URL) -> Bool
    func safeWrite(data: Data, to url: URL) throws   // Atomic write via temporary file
}

struct ToolbarItem: Identifiable {
    let id: String                              // e.g., "bold", "heading1"
    var label: String                           // Display label
    var systemImage: String                     // SF Symbol name
    var shortcutHint: String?                   // e.g., "Cmd+B"
    var action: () -> Void                      // Callback
}

struct FontDescriptor: Identifiable, Hashable {
    let id: String                              // Font family name
    var displayName: String                     // Localized display name
    var isMonospaced: Bool                      // For code-friendly fonts
    var sampleText: String                      // Preview string
}