1 files changed, 228 insertions, 0 deletions
diff --git a/packages/vscode-ide-companion/src/diff-manager.ts b/packages/vscode-ide-companion/src/diff-manager.ts
new file mode 100644
index 00000000..159a6101
--- /dev/null
+++ b/packages/vscode-ide-companion/src/diff-manager.ts
@@ -0,0 +1,228 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as vscode from 'vscode';
+import * as path from 'node:path';
+import { DIFF_SCHEME } from './extension.js';
+import { type JSONRPCNotification } from '@modelcontextprotocol/sdk/types.js';
+
+export class DiffContentProvider implements vscode.TextDocumentContentProvider {
+  private content = new Map<string, string>();
+  private onDidChangeEmitter = new vscode.EventEmitter<vscode.Uri>();
+
+  get onDidChange(): vscode.Event<vscode.Uri> {
+    return this.onDidChangeEmitter.event;
+  }
+
+  provideTextDocumentContent(uri: vscode.Uri): string {
+    return this.content.get(uri.toString()) ?? '';
+  }
+
+  setContent(uri: vscode.Uri, content: string): void {
+    this.content.set(uri.toString(), content);
+    this.onDidChangeEmitter.fire(uri);
+  }
+
+  deleteContent(uri: vscode.Uri): void {
+    this.content.delete(uri.toString());
+  }
+
+  getContent(uri: vscode.Uri): string | undefined {
+    return this.content.get(uri.toString());
+  }
+}
+
+// Information about a diff view that is currently open.
+interface DiffInfo {
+  originalFilePath: string;
+  newContent: string;
+  rightDocUri: vscode.Uri;
+}
+
+/**
+ * Manages the state and lifecycle of diff views within the IDE.
+ */
+export class DiffManager {
+  private readonly onDidChangeEmitter =
+    new vscode.EventEmitter<JSONRPCNotification>();
+  readonly onDidChange = this.onDidChangeEmitter.event;
+  private diffDocuments = new Map<string, DiffInfo>();
+
+  constructor(
+    private readonly logger: vscode.OutputChannel,
+    private readonly diffContentProvider: DiffContentProvider,
+  ) {}
+
+  /**
+   * Creates and shows a new diff view.
+   */
+  async showDiff(filePath: string, newContent: string) {
+    const fileUri = vscode.Uri.file(filePath);
+
+    const rightDocUri = vscode.Uri.from({
+      scheme: DIFF_SCHEME,
+      path: filePath,
+      // cache busting
+      query: `rand=${Math.random()}`,
+    });
+    this.diffContentProvider.setContent(rightDocUri, newContent);
+
+    this.addDiffDocument(rightDocUri, {
+      originalFilePath: filePath,
+      newContent,
+      rightDocUri,
+    });
+
+    const diffTitle = `${path.basename(filePath)} ↔ Modified`;
+    await vscode.commands.executeCommand(
+      'setContext',
+      'gemini.diff.isVisible',
+      true,
+    );
+
+    let leftDocUri;
+    try {
+      await vscode.workspace.fs.stat(fileUri);
+      leftDocUri = fileUri;
+    } catch {
+      // We need to provide an empty document to diff against.
+      // Using the 'untitled' scheme is one way to do this.
+      leftDocUri = vscode.Uri.from({
+        scheme: 'untitled',
+        path: filePath,
+      });
+    }
+
+    await vscode.commands.executeCommand(
+      'vscode.diff',
+      leftDocUri,
+      rightDocUri,
+      diffTitle,
+      {
+        preview: false,
+      },
+    );
+    await vscode.commands.executeCommand(
+      'workbench.action.files.setActiveEditorWriteableInSession',
+    );
+  }
+
+  /**
+   * Closes an open diff view for a specific file.
+   */
+  async closeDiff(filePath: string) {
+    let uriToClose: vscode.Uri | undefined;
+    for (const [uriString, diffInfo] of this.diffDocuments.entries()) {
+      if (diffInfo.originalFilePath === filePath) {
+        uriToClose = vscode.Uri.parse(uriString);
+        break;
+      }
+    }
+
+    if (uriToClose) {
+      const rightDoc = await vscode.workspace.openTextDocument(uriToClose);
+      const modifiedContent = rightDoc.getText();
+      await this.closeDiffEditor(uriToClose);
+      this.onDidChangeEmitter.fire({
+        jsonrpc: '2.0',
+        method: 'ide/diffClosed',
+        params: {
+          filePath,
+          content: modifiedContent,
+        },
+      });
+      vscode.window.showInformationMessage(`Diff for ${filePath} closed.`);
+    } else {
+      vscode.window.showWarningMessage(`No open diff found for ${filePath}.`);
+    }
+  }
+
+  /**
+   * User accepts the changes in a diff view. Does not apply changes.
+   */
+  async acceptDiff(rightDocUri: vscode.Uri) {
+    const diffInfo = this.diffDocuments.get(rightDocUri.toString());
+    if (!diffInfo) {
+      this.logger.appendLine(
+        `No diff info found for ${rightDocUri.toString()}`,
+      );
+      return;
+    }
+
+    const rightDoc = await vscode.workspace.openTextDocument(rightDocUri);
+    const modifiedContent = rightDoc.getText();
+    await this.closeDiffEditor(rightDocUri);
+
+    this.onDidChangeEmitter.fire({
+      jsonrpc: '2.0',
+      method: 'ide/diffAccepted',
+      params: {
+        filePath: diffInfo.originalFilePath,
+        content: modifiedContent,
+      },
+    });
+  }
+
+  /**
+   * Called when a user cancels a diff view.
+   */
+  async cancelDiff(rightDocUri: vscode.Uri) {
+    const diffInfo = this.diffDocuments.get(rightDocUri.toString());
+    if (!diffInfo) {
+      this.logger.appendLine(
+        `No diff info found for ${rightDocUri.toString()}`,
+      );
+      // Even if we don't have diff info, we should still close the editor.
+      await this.closeDiffEditor(rightDocUri);
+      return;
+    }
+
+    const rightDoc = await vscode.workspace.openTextDocument(rightDocUri);
+    const modifiedContent = rightDoc.getText();
+    await this.closeDiffEditor(rightDocUri);
+
+    this.onDidChangeEmitter.fire({
+      jsonrpc: '2.0',
+      method: 'ide/diffClosed',
+      params: {
+        filePath: diffInfo.originalFilePath,
+        content: modifiedContent,
+      },
+    });
+  }
+
+  private addDiffDocument(uri: vscode.Uri, diffInfo: DiffInfo) {
+    this.diffDocuments.set(uri.toString(), diffInfo);
+  }
+
+  private async closeDiffEditor(rightDocUri: vscode.Uri) {
+    const diffInfo = this.diffDocuments.get(rightDocUri.toString());
+    await vscode.commands.executeCommand(
+      'setContext',
+      'gemini.diff.isVisible',
+      false,
+    );
+
+    if (diffInfo) {
+      this.diffDocuments.delete(rightDocUri.toString());
+      this.diffContentProvider.deleteContent(rightDocUri);
+    }
+
+    // Find and close the tab corresponding to the diff view
+    for (const tabGroup of vscode.window.tabGroups.all) {
+      for (const tab of tabGroup.tabs) {
+        const input = tab.input as {
+          modified?: vscode.Uri;
+          original?: vscode.Uri;
+        };
+        if (input && input.modified?.toString() === rightDocUri.toString()) {
+          await vscode.window.tabGroups.close(tab);
+          return;
+        }
+      }
+    }
+  }
+}