feat(editor): implement document loading and saving

Sources/SaplingApp/SaplingApp.swift

@@ -1,4 +1,5 @@
 import SwiftUI
+import UniformTypeIdentifiers
 import SaplingCore
 import SaplingWorkspace
 import SaplingGit
@@ -40,6 +41,7 @@ private final class SaplingAppModel: ObservableObject {
     @Published var editorViewModel: HybridMarkdownEditorViewModel?
     @Published var gitStatuses: [GitFileStatus] = []
     @Published var configuration: SaplingConfiguration
+    @Published var editorErrorMessage: String?
 
     private let gitProvider: any GitProvider
     private let configurationStore: any ConfigurationStore
@@ -71,11 +73,40 @@ private final class SaplingAppModel: ObservableObject {
         if file.url == SaplingSampleData.document.url {
             setSelectedDocument(SaplingSampleData.document)
         } else {
-            setSelectedDocument(MarkdownDocument(
-                url: file.url,
-                title: file.name,
-                content: "# \(file.name)\n\nTODO: Load document contents from disk."
-            ))
+            openDocument(at: file.url)
+        }
+    }
+
+    func openDocument(at url: URL) {
+        let didStartAccessing = url.startAccessingSecurityScopedResource()
+        defer {
+            if didStartAccessing {
+                url.stopAccessingSecurityScopedResource()
+            }
+        }
+
+        do {
+            let document = try HybridMarkdownEditorViewModel.loadDocument(at: url)
+            setSelectedDocument(document)
+            editorErrorMessage = nil
+            logger.info("Opened document: \(document.title)", category: .editor)
+        } catch {
+            editorErrorMessage = "Unable to open \(url.lastPathComponent): \(error.localizedDescription)"
+            logger.error("Failed to open document: \(error)", category: .editor)
+        }
+    }
+
+    func saveSelectedDocument() {
+        guard let editorViewModel else { return }
+
+        do {
+            try editorViewModel.save()
+            selectedDocument = editorViewModel.document
+            editorErrorMessage = nil
+            logger.info("Saved document: \(editorViewModel.document.title)", category: .editor)
+        } catch {
+            editorErrorMessage = "Unable to save \(editorViewModel.document.title): \(error.localizedDescription)"
+            logger.error("Failed to save document: \(error)", category: .editor)
         }
     }
 
@@ -123,6 +154,7 @@ private final class SaplingAppModel: ObservableObject {
 
 private struct MainWindow: View {
     @ObservedObject var model: SaplingAppModel
+    @State private var isImportingMarkdown = false
 
     var body: some View {
         NavigationSplitView {
@@ -138,18 +170,73 @@ private struct MainWindow: View {
                     viewModel: editorViewModel,
                     renderer: MarkdownRenderer()
                 )
-                .navigationTitle(editorViewModel.document.title)
+                .navigationTitle(navigationTitle(for: editorViewModel))
             } else {
                 EmptyEditorPlaceholder()
             }
         } detail: {
             SaplingInspectorView(
                 project: model.selectedProject,
-                document: model.selectedDocument,
+                document: model.editorViewModel?.document ?? model.selectedDocument,
                 statuses: model.gitStatuses
             )
             .frame(minWidth: 260)
         }
+        .toolbar {
+            ToolbarItemGroup {
+                Button {
+                    isImportingMarkdown = true
+                } label: {
+                    Label("Open Markdown", systemImage: "doc.badge.plus")
+                }
+                .help("Open Markdown")
+
+                Button {
+                    model.saveSelectedDocument()
+                } label: {
+                    Label("Save", systemImage: "square.and.arrow.down")
+                }
+                .help("Save")
+                .disabled(model.editorViewModel?.hasUnsavedChanges != true)
+                .keyboardShortcut("s", modifiers: .command)
+            }
+        }
+        .fileImporter(
+            isPresented: $isImportingMarkdown,
+            allowedContentTypes: [.saplingMarkdown, .plainText],
+            allowsMultipleSelection: false
+        ) { result in
+            switch result {
+            case .success(let urls):
+                guard let url = urls.first else { return }
+                model.openDocument(at: url)
+            case .failure(let error):
+                model.editorErrorMessage = "Unable to open document: \(error.localizedDescription)"
+            }
+        }
+        .alert(
+            "Editor Error",
+            isPresented: Binding(
+                get: { model.editorErrorMessage != nil },
+                set: { if !$0 { model.editorErrorMessage = nil } }
+            )
+        ) {
+            Button("OK", role: .cancel) {
+                model.editorErrorMessage = nil
+            }
+        } message: {
+            Text(model.editorErrorMessage ?? "")
+        }
+    }
+
+    private func navigationTitle(for viewModel: HybridMarkdownEditorViewModel) -> String {
+        viewModel.hasUnsavedChanges ? "\(viewModel.document.title) *" : viewModel.document.title
+    }
+}
+
+private extension UTType {
+    static var saplingMarkdown: UTType {
+        UTType(filenameExtension: "md") ?? .plainText
     }
 }