Add New Diagram command with starter templates

- Archify: New Diagram… (Explorer folder menu, File > New File…, Command
  Palette) creates a .archify file from a template and opens the diagram
- Six YAML templates: architecture, workflow, sequence, dataflow,
  lifecycle and an everyday plan; connections carry ids, workflows use
  schema 2
- Title and meta.output follow the file name; template comments are kept
- Tests: every template passes archify validate; integration check for
  the command

Closes #2

src/extension.ts

@@ -7,6 +7,7 @@ import { HTML_VIEW_TYPE, HtmlViewerProvider } from './htmlViewer';
 import { DIAGRAM_EDITOR_VIEW_TYPE, PreviewManager } from './preview';
 import { isEvidenceError, renderDiagram, renderToFile } from './renderer';
 import { clearGitRootCache, evidenceMode, log, readText, runtimeFor } from './runtime';
+import { diagramFromTemplate, diagramName, invalidNameReason, TEMPLATES } from './templates';
 
 const JSON_LANGUAGES = new Set(['json', 'jsonc']);
 
@@ -61,6 +62,26 @@ export function activate(context: vscode.ExtensionContext): void {
   const openHtmlViewer = (uri: vscode.Uri, viewColumn?: vscode.ViewColumn) =>
     vscode.commands.executeCommand('vscode.openWith', uri, HTML_VIEW_TYPE, viewColumn);
 
+  const exists = async (uri: vscode.Uri) => {
+    try {
+      await vscode.workspace.fs.stat(uri);
+      return true;
+    } catch {
+      return false;
+    }
+  };
+
+  /** Folder for a new diagram: the clicked folder (or a file's folder), else a workspace folder. */
+  async function newDiagramFolder(arg?: unknown): Promise<vscode.Uri | undefined> {
+    if (arg instanceof vscode.Uri) {
+      const stat = await vscode.workspace.fs.stat(arg);
+      return stat.type & vscode.FileType.Directory ? arg : vscode.Uri.joinPath(arg, '..');
+    }
+    const folders = vscode.workspace.workspaceFolders ?? [];
+    if (folders.length <= 1) return folders[0]?.uri;
+    return (await vscode.window.showWorkspaceFolderPick({ placeHolder: 'Folder for the new diagram' }))?.uri;
+  }
+
   context.subscriptions.push(
     vscode.commands.registerCommand('archify.showPreview', (arg?: unknown) => {
       const uri = sourceUri(arg);
@@ -88,6 +109,44 @@ export function activate(context: vscode.ExtensionContext): void {
       if (uri) return openHtmlViewer(uri);
     }),
 
+    vscode.commands.registerCommand('archify.newDiagram', async (arg?: unknown) => {
+      const template = await vscode.window.showQuickPick(
+        TEMPLATES.map((item) => ({ label: item.label, description: item.description, template: item })),
+        { title: 'New Archify Diagram', placeHolder: 'Kind of diagram' },
+      );
+      if (!template) return;
+      const { file, defaultName } = template.template;
+
+      const folder = await newDiagramFolder(arg);
+      let target: vscode.Uri | undefined;
+      if (folder) {
+        const name = await vscode.window.showInputBox({
+          title: 'New Archify Diagram',
+          prompt: `File name in ${vscode.workspace.asRelativePath(folder, true)}`,
+          value: defaultName,
+          validateInput: async (value) =>
+            invalidNameReason(value) ??
+            ((await exists(vscode.Uri.joinPath(folder, `${diagramName(value)}.archify`))) ? `${diagramName(value)}.archify already exists.` : undefined),
+        });
+        if (name === undefined) return;
+        target = vscode.Uri.joinPath(folder, `${diagramName(name)}.archify`);
+      } else {
+        // No workspace: let the user choose where to save.
+        target = await vscode.window.showSaveDialog({
+          title: 'New Archify Diagram',
+          filters: { 'Archify Diagram': ['archify'] },
+          saveLabel: 'Create',
+        });
+        if (!target) return;
+        if (!isArchifyFile(target.path)) target = target.with({ path: `${target.path}.archify` });
+      }
+
+      const templateText = await readText(vscode.Uri.joinPath(context.extensionUri, 'templates', file));
+      const text = diagramFromTemplate(templateText, diagramBaseName(target.path));
+      await vscode.workspace.fs.writeFile(target, Buffer.from(text, 'utf8'));
+      await vscode.commands.executeCommand('vscode.openWith', target, DIAGRAM_EDITOR_VIEW_TYPE);
+    }),
+
     vscode.commands.registerCommand('archify.refreshPreview', () => previews.activePreview?.update(true)),
 
     vscode.commands.registerCommand('archify.showSource', async () => {