#30 feat: add social media export presets

BifcodePackage/Sources/BifcodeFeature/ContentView.swift

@@ -91,6 +91,7 @@ public struct ContentView: View {
     @AppStorage("fontSize") private var fontSize: Double = 14
     @AppStorage("selectedTheme") private var selectedThemeRaw: String = EditorThemeOption.atomOneDark.rawValue
     @AppStorage("themeMode") private var themeModeRaw: String = ThemeMode.dark.rawValue
+    @AppStorage("exportPreset") private var exportPresetRaw: String = ExportPreset.auto.rawValue
 
     private var layout: WindowLayout {
         WindowLayout(rawValue: windowLayoutRaw) ?? .horizontal
@@ -112,6 +113,10 @@ public struct ContentView: View {
         ThemeMode(rawValue: themeModeRaw) ?? .dark
     }
 
+    private var exportPreset: ExportPreset {
+        ExportPreset(rawValue: exportPresetRaw) ?? .auto
+    }
+
     public init() {}
 
     /// Check if both code panels are empty (export should be disabled)
@@ -445,8 +450,59 @@ public struct ContentView: View {
         let finalImage = NSImage(size: size)
         finalImage.addRepresentation(scaledBitmapRep)
 
+        // Apply export preset scaling if not auto
+        if let presetSize = exportPreset.size {
+            return scaleImageToPreset(finalImage, targetSize: presetSize)
+        }
+
         return finalImage
     }
+
+    /// Scales an image to fit within the target preset size while maintaining aspect ratio.
+    ///
+    /// The image is scaled down to fit within the preset dimensions, centered on a transparent background.
+    /// If the content is smaller than the preset, it's centered without scaling up.
+    ///
+    /// - Parameters:
+    ///   - image: The source image to scale.
+    ///   - targetSize: The target dimensions from the export preset.
+    /// - Returns: A new image at the exact preset dimensions.
+    @MainActor
+    private func scaleImageToPreset(_ image: NSImage, targetSize: CGSize) -> NSImage {
+        let sourceSize = image.size
+
+        // Calculate scale to fit within target while maintaining aspect ratio
+        let widthRatio = targetSize.width / sourceSize.width
+        let heightRatio = targetSize.height / sourceSize.height
+        let scale = min(widthRatio, heightRatio, 1.0) // Don't scale up, only down
+
+        let scaledWidth = sourceSize.width * scale
+        let scaledHeight = sourceSize.height * scale
+
+        // Center the scaled content within the target size
+        let xOffset = (targetSize.width - scaledWidth) / 2
+        let yOffset = (targetSize.height - scaledHeight) / 2
+
+        // Create the final image at preset dimensions
+        let presetImage = NSImage(size: targetSize)
+        presetImage.lockFocus()
+
+        // Clear background (transparent)
+        NSColor.clear.setFill()
+        NSRect(origin: .zero, size: targetSize).fill()
+
+        // Draw the scaled image centered
+        image.draw(
+            in: NSRect(x: xOffset, y: yOffset, width: scaledWidth, height: scaledHeight),
+            from: .zero,
+            operation: .copy,
+            fraction: 1.0
+        )
+
+        presetImage.unlockFocus()
+
+        return presetImage
+    }
 }
 
 // MARK: - Preview

BifcodePackage/Sources/BifcodeFeature/Models/SettingsTypes.swift

@@ -286,6 +286,86 @@ public enum ThemeMode: String, CaseIterable, Sendable {
     }
 }
 
+// MARK: - Export Preset
+
+/// Preset export dimensions for different platforms.
+///
+/// Provides optimized dimensions for sharing code comparisons on
+/// various social media platforms and messaging apps.
+///
+/// ## Usage
+///
+/// ```swift
+/// @AppStorage("exportPreset") private var exportPreset = ExportPreset.auto.rawValue
+/// ```
+///
+/// ## Topics
+///
+/// ### Presets
+///
+/// - ``auto``
+/// - ``twitter``
+/// - ``linkedin``
+/// - ``slack``
+public enum ExportPreset: String, CaseIterable, Sendable {
+    /// Automatic sizing based on content.
+    ///
+    /// The default behavior that calculates dimensions from the
+    /// actual code content and settings.
+    case auto
+
+    /// Twitter/X optimized dimensions (1200×675).
+    ///
+    /// Optimal for Twitter image cards and timeline display.
+    case twitter
+
+    /// LinkedIn optimized dimensions (1200×627).
+    ///
+    /// Matches LinkedIn's recommended image dimensions for posts.
+    case linkedin
+
+    /// Slack optimized dimensions (800×600).
+    ///
+    /// Works well in Slack messages and previews.
+    case slack
+
+    /// A human-readable label for display in pickers.
+    public var label: String {
+        switch self {
+        case .auto: "Auto"
+        case .twitter: "Twitter"
+        case .linkedin: "LinkedIn"
+        case .slack: "Slack"
+        }
+    }
+
+    /// The target width for this preset, or nil for auto.
+    public var width: CGFloat? {
+        switch self {
+        case .auto: nil
+        case .twitter: 1200
+        case .linkedin: 1200
+        case .slack: 800
+        }
+    }
+
+    /// The target height for this preset, or nil for auto.
+    public var height: CGFloat? {
+        switch self {
+        case .auto: nil
+        case .twitter: 675
+        case .linkedin: 627
+        case .slack: 600
+        }
+    }
+
+    /// The target size for this preset, or nil for auto.
+    public var size: CGSize? {
+        guard let width, let height else { return nil }
+        return CGSize(width: width, height: height)
+    }
+}
+
 // MARK: - Editor Themes
 
 /// Available syntax highlighting themes for the code editor.

BifcodePackage/Sources/BifcodeFeature/Views/ToolBarView.swift

@@ -60,6 +60,7 @@ public struct ToolBarView: View {
     @AppStorage("fontSize") private var fontSize: Double = 14
     @AppStorage("selectedTheme") private var selectedThemeRaw: String = EditorThemeOption.atomOneDark.rawValue
     @AppStorage("themeMode") private var themeModeRaw: String = ThemeMode.dark.rawValue
+    @AppStorage("exportPreset") private var exportPresetRaw: String = ExportPreset.auto.rawValue
 
     @AppStorage("selectedLanguage") private var selectedLanguageRaw: String = "swift"
 
@@ -546,6 +547,8 @@ public struct ToolBarView: View {
 
             // Secondary Actions
             VStack(spacing: 8) {
+                exportPresetPicker
+
                 Button {
                     chooseSaveLocation()
                 } label: {
@@ -561,7 +564,19 @@ public struct ToolBarView: View {
                     .padding(.top, 32)
             }
         }
-        .frame(minWidth: 80)
+        .frame(minWidth: 100)
+    }
+
+    private var exportPresetPicker: some View {
+        Picker("", selection: $exportPresetRaw) {
+            ForEach(ExportPreset.allCases, id: \.self) { preset in
+                Text(preset.label).tag(preset.rawValue)
+            }
+        }
+        .pickerStyle(.menu)
+        .fixedSize()
+        .accessibilityLabel("Export Size")
+        .accessibilityHint("Choose preset dimensions for social media")
     }
 
     private var storeButton: some View {