feat: add image diff viewer

Sources/GitKit/CLIGitService.swift

@@ -461,6 +461,12 @@ public struct CLIGitService: GitService {
         try? String(contentsOf: root.appendingPathComponent(path), encoding: .utf8)
     }
 
+    public func fileData(at path: String, revision: String) async throws -> Data {
+        try Self.requireSafe(path, "path")
+        if !revision.isEmpty { try Self.requireSafe(revision, "revision") }
+        return try await runner.run(["show", "\(revision):\(path)"])
+    }
+
     public func resolveFile(path: String, contents: String) async throws {
         try Self.requireSafe(path, "path")
         try contents.write(to: root.appendingPathComponent(path), atomically: true, encoding: .utf8)

Sources/GitKit/GitService.swift

@@ -234,6 +234,10 @@ public protocol GitService: Sendable {
     /// The working-tree contents of `path` (including any conflict markers).
     func fileContents(path: String) async -> String?
 
+    /// Raw file content at `revision` (e.g. `"HEAD"`, a SHA, or `""` for the index).
+    /// Used for binary file previews such as image diffs.
+    func fileData(at path: String, revision: String) async throws -> Data
+
     /// Writes `contents` to `path` and stages it (marking a conflict resolved).
     func resolveFile(path: String, contents: String) async throws
 }

Sources/GitKit/Models/Diff.swift

@@ -78,7 +78,27 @@ public struct FileDiff: Sendable {
         self.header = header
     }
 
+    /// Whether the file has a recognised image extension.
+    public var isImage: Bool {
+        Self.imageExtensions.contains((path as NSString).pathExtension.lowercased())
+    }
+
+    private static let imageExtensions: Set<String> = [
+        "png", "jpg", "jpeg", "gif", "webp", "tiff", "tif", "bmp", "svg", "ico", "heic", "heif",
+    ]
+
     public static func empty(path: String) -> FileDiff {
         FileDiff(path: path, oldPath: nil, isBinary: false, isNew: false, isDeleted: false, hunks: [])
     }
 }
+
+/// The old and new image data for a binary image diff.
+public struct ImageDiffData: Sendable {
+    public let oldImage: Data?
+    public let newImage: Data?
+
+    public init(oldImage: Data?, newImage: Data?) {
+        self.oldImage = oldImage
+        self.newImage = newImage
+    }
+}

Sources/Gitify/Model/RepositoryViewModel.swift

@@ -42,6 +42,7 @@ final class RepositoryViewModel {
     var selectedPath: String?
     private(set) var selectedStaged = false
     private(set) var currentDiff: FileDiff?
+    private(set) var imageDiffData: ImageDiffData?
     var commitMessage: String = ""
     var amendMode: Bool = false
     private(set) var isCommitting = false
@@ -132,7 +133,28 @@ final class RepositoryViewModel {
 
     private func loadDiff(path: String, staged: Bool) async {
         guard let service else { return }
-        currentDiff = (try? await service.diff(path: path, staged: staged)) ?? .empty(path: path)
+        let diff = (try? await service.diff(path: path, staged: staged)) ?? .empty(path: path)
+        currentDiff = diff
+        if diff.isBinary && diff.isImage {
+            imageDiffData = await loadImageDiffData(diff: diff, staged: staged)
+        } else {
+            imageDiffData = nil
+        }
+    }
+
+    private func loadImageDiffData(diff: FileDiff, staged: Bool) async -> ImageDiffData {
+        guard let service else { return ImageDiffData(oldImage: nil, newImage: nil) }
+        let oldPath = diff.oldPath ?? diff.path
+        let oldImage: Data? = diff.isNew ? nil : (try? await service.fileData(at: oldPath, revision: "HEAD"))
+        let newImage: Data?
+        if diff.isDeleted {
+            newImage = nil
+        } else if staged {
+            newImage = try? await service.fileData(at: diff.path, revision: "")
+        } else {
+            newImage = try? Data(contentsOf: service.root.appendingPathComponent(diff.path))
+        }
+        return ImageDiffData(oldImage: oldImage, newImage: newImage)
     }
 
     /// Stages or unstages a single hunk of the currently-displayed diff. The direction is
@@ -280,6 +302,7 @@ final class RepositoryViewModel {
             } else {
                 selectedPath = nil
                 currentDiff = nil
+                imageDiffData = nil
             }
         }
         // Refresh history so amend/commit changes are reflected.
@@ -511,6 +534,18 @@ final class RepositoryViewModel {
         return try? await service.commitFileDiff(sha: sha, path: path)
     }
 
+    func commitImageDiffData(sha: String, parentSHA: String?, diff: FileDiff) async -> ImageDiffData? {
+        guard let service, diff.isBinary, diff.isImage else { return nil }
+        let oldPath = diff.oldPath ?? diff.path
+        let oldImage: Data? = if let parentSHA, !diff.isNew {
+            try? await service.fileData(at: oldPath, revision: parentSHA)
+        } else {
+            nil
+        }
+        let newImage: Data? = diff.isDeleted ? nil : (try? await service.fileData(at: diff.path, revision: sha))
+        return ImageDiffData(oldImage: oldImage, newImage: newImage)
+    }
+
     func merge(branch: String, squash: Bool, noFastForward: Bool, noCommit: Bool, skipHooks: Bool) async {
         await runIntegration("Merge") {
             try await $0.merge(branch: branch, squash: squash, noFastForward: noFastForward,
@@ -650,6 +685,7 @@ final class RepositoryViewModel {
         } else {
             selectedPath = nil
             currentDiff = nil
+            imageDiffData = nil
         }
     }
 }

Sources/Gitify/Views/CommitDetailView.swift

@@ -11,7 +11,7 @@ struct CommitDetailView: View {
         VStack(alignment: .leading, spacing: 0) {
             metadata
             Divider()
-            ChangesetDiffPane(ref: commit.id, viewModel: viewModel)
+            ChangesetDiffPane(ref: commit.id, parentSHA: commit.parents.first, viewModel: viewModel)
         }
         .frame(maxWidth: .infinity, maxHeight: .infinity)
     }
@@ -46,11 +46,13 @@ struct CommitDetailView: View {
 /// changed files with +/- counts on top, and the selected file's diff below.
 struct ChangesetDiffPane: View {
     let ref: String
+    var parentSHA: String? = nil
     let viewModel: RepositoryViewModel
 
     @State private var changes: [FileChange] = []
     @State private var selectedFile: String?
     @State private var fileDiff: FileDiff?
+    @State private var imageDiffData: ImageDiffData?
     @State private var loading = false
 
     var body: some View {
@@ -64,14 +66,23 @@ struct ChangesetDiffPane: View {
             }
             .frame(maxWidth: .infinity, minHeight: 140)
 
-            CommitFileDiffPane(fileDiff: fileDiff)
+            CommitFileDiffPane(fileDiff: fileDiff, imageDiffData: imageDiffData)
                 .frame(maxWidth: .infinity, minHeight: 120)
         }
         .frame(maxWidth: .infinity, maxHeight: .infinity)
         .task(id: ref) { await load() }
         .onChange(of: selectedFile) { _, path in
-            guard let path else { fileDiff = nil; return }
-            Task { fileDiff = await viewModel.commitFileDiff(ref, path: path) }
+            guard let path else { fileDiff = nil; imageDiffData = nil; return }
+            Task {
+                let diff = await viewModel.commitFileDiff(ref, path: path)
+                fileDiff = diff
+                if let diff {
+                    imageDiffData = await viewModel.commitImageDiffData(
+                        sha: ref, parentSHA: parentSHA, diff: diff)
+                } else {
+                    imageDiffData = nil
+                }
+            }
         }
     }
 
@@ -122,13 +133,14 @@ struct ChangesetDiffPane: View {
 /// Concrete (not an inline if/else) so selecting a changed file doesn't reset the dragged divider.
 private struct CommitFileDiffPane: View {
     let fileDiff: FileDiff?
+    var imageDiffData: ImageDiffData? = nil
 
     var body: some View {
         // GeometryReader so the pane keeps a constant (greedy) size whether the diff or the
         // placeholder is shown — otherwise VSplitView shifts the divider on file selection.
         GeometryReader { _ in
             if let fileDiff {
-                DiffView(diff: fileDiff)
+                DiffView(diff: fileDiff, imageDiffData: imageDiffData)
             } else {
                 ContentUnavailableView("No File Selected", systemImage: "doc.text.magnifyingglass",
                                        description: Text("Select a changed file to view its diff."))

Sources/Gitify/Views/DiffView.swift

@@ -9,6 +9,7 @@ private struct LineRef: Hashable { let hunk: Int; let index: Int }
 /// `onApplyLines` is provided, individual added/removed lines can be selected and staged.
 struct DiffView: View {
     let diff: FileDiff
+    var imageDiffData: ImageDiffData? = nil
     var actionLabel: String = "Stage Hunk"
     var lineActionLabel: String = "Stage Lines"
     var onApplyHunk: ((DiffHunk) -> Void)? = nil
@@ -21,9 +22,11 @@ struct DiffView: View {
     private var language: String { (diff.path as NSString).pathExtension.lowercased() }
 
     var body: some View {
-        if diff.isBinary {
+        if diff.isBinary, let imageDiffData {
+            ImageDiffView(data: imageDiffData, isNew: diff.isNew, isDeleted: diff.isDeleted)
+        } else if diff.isBinary {
             ContentUnavailableView("Binary File", systemImage: "doc.badge.gearshape",
-                                   description: Text("Binary content can't be displayed."))
+                                   description: Text("Binary content can\u{2019}t be displayed."))
                 .frame(maxWidth: .infinity, maxHeight: .infinity)
         } else if diff.hunks.isEmpty {
             ContentUnavailableView("No Changes", systemImage: "doc.plaintext",