1 files changed, 163 insertions, 0 deletions
diff --git a/packages/core/src/tools/modifiable-tool.ts b/packages/core/src/tools/modifiable-tool.ts
new file mode 100644
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--- /dev/null
+++ b/packages/core/src/tools/modifiable-tool.ts
@@ -0,0 +1,163 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { EditorType } from '../utils/editor.js';
+import os from 'os';
+import path from 'path';
+import fs from 'fs';
+import * as Diff from 'diff';
+import { openDiff } from '../utils/editor.js';
+import { DEFAULT_DIFF_OPTIONS } from './diffOptions.js';
+import { isNodeError } from '../utils/errors.js';
+import { Tool } from './tools.js';
+
+/**
+ * A tool that supports a modify operation.
+ */
+export interface ModifiableTool<ToolParams> extends Tool<ToolParams> {
+  getModifyContext(abortSignal: AbortSignal): ModifyContext<ToolParams>;
+}
+
+export interface ModifyContext<ToolParams> {
+  getFilePath: (params: ToolParams) => string;
+
+  getCurrentContent: (params: ToolParams) => Promise<string>;
+
+  getProposedContent: (params: ToolParams) => Promise<string>;
+
+  createUpdatedParams: (
+    modifiedProposedContent: string,
+    originalParams: ToolParams,
+  ) => ToolParams;
+}
+
+export interface ModifyResult<ToolParams> {
+  updatedParams: ToolParams;
+  updatedDiff: string;
+}
+
+export function isModifiableTool<TParams>(
+  tool: Tool<TParams>,
+): tool is ModifiableTool<TParams> {
+  return 'getModifyContext' in tool;
+}
+
+function createTempFilesForModify(
+  currentContent: string,
+  proposedContent: string,
+  file_path: string,
+): { oldPath: string; newPath: string } {
+  const tempDir = os.tmpdir();
+  const diffDir = path.join(tempDir, 'gemini-cli-tool-modify-diffs');
+
+  if (!fs.existsSync(diffDir)) {
+    fs.mkdirSync(diffDir, { recursive: true });
+  }
+
+  const fileName = path.basename(file_path);
+  const timestamp = Date.now();
+  const tempOldPath = path.join(
+    diffDir,
+    `gemini-cli-modify-${fileName}-old-${timestamp}`,
+  );
+  const tempNewPath = path.join(
+    diffDir,
+    `gemini-cli-modify-${fileName}-new-${timestamp}`,
+  );
+
+  fs.writeFileSync(tempOldPath, currentContent, 'utf8');
+  fs.writeFileSync(tempNewPath, proposedContent, 'utf8');
+
+  return { oldPath: tempOldPath, newPath: tempNewPath };
+}
+
+function getUpdatedParams<ToolParams>(
+  tmpOldPath: string,
+  tempNewPath: string,
+  originalParams: ToolParams,
+  modifyContext: ModifyContext<ToolParams>,
+): { updatedParams: ToolParams; updatedDiff: string } {
+  let oldContent = '';
+  let newContent = '';
+
+  try {
+    oldContent = fs.readFileSync(tmpOldPath, 'utf8');
+  } catch (err) {
+    if (!isNodeError(err) || err.code !== 'ENOENT') throw err;
+    oldContent = '';
+  }
+
+  try {
+    newContent = fs.readFileSync(tempNewPath, 'utf8');
+  } catch (err) {
+    if (!isNodeError(err) || err.code !== 'ENOENT') throw err;
+    newContent = '';
+  }
+
+  const updatedParams = modifyContext.createUpdatedParams(
+    newContent,
+    originalParams,
+  );
+  const updatedDiff = Diff.createPatch(
+    path.basename(modifyContext.getFilePath(originalParams)),
+    oldContent,
+    newContent,
+    'Current',
+    'Proposed',
+    DEFAULT_DIFF_OPTIONS,
+  );
+
+  return { updatedParams, updatedDiff };
+}
+
+function deleteTempFiles(oldPath: string, newPath: string): void {
+  try {
+    fs.unlinkSync(oldPath);
+  } catch {
+    console.error(`Error deleting temp diff file: ${oldPath}`);
+  }
+
+  try {
+    fs.unlinkSync(newPath);
+  } catch {
+    console.error(`Error deleting temp diff file: ${newPath}`);
+  }
+}
+
+/**
+ * Triggers an external editor for the user to modify the proposed content,
+ * and returns the updated tool parameters and the diff after the user has modified the proposed content.
+ */
+export async function modifyWithEditor<ToolParams>(
+  originalParams: ToolParams,
+  modifyContext: ModifyContext<ToolParams>,
+  editorType: EditorType,
+  _abortSignal: AbortSignal,
+): Promise<ModifyResult<ToolParams>> {
+  const currentContent = await modifyContext.getCurrentContent(originalParams);
+  const proposedContent =
+    await modifyContext.getProposedContent(originalParams);
+
+  const { oldPath, newPath } = createTempFilesForModify(
+    currentContent,
+    proposedContent,
+    modifyContext.getFilePath(originalParams),
+  );
+
+  try {
+    await openDiff(oldPath, newPath, editorType);
+    const result = getUpdatedParams(
+      oldPath,
+      newPath,
+      originalParams,
+      modifyContext,
+    );
+
+    return result;
+  } finally {
+    deleteTempFiles(oldPath, newPath);
+  }
+}