1 files changed, 92 insertions, 0 deletions
diff --git a/packages/vscode-ide-companion/src/recent-files-manager.ts b/packages/vscode-ide-companion/src/recent-files-manager.ts
new file mode 100644
index 00000000..84316363
--- /dev/null
+++ b/packages/vscode-ide-companion/src/recent-files-manager.ts
@@ -0,0 +1,92 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as vscode from 'vscode';
+
+export const MAX_FILES = 10;
+export const MAX_FILE_AGE_MINUTES = 5;
+
+interface RecentFile {
+  uri: vscode.Uri;
+  timestamp: number;
+}
+
+/**
+ * Keeps track of the 10 most recently-opened files
+ * opened less than 5 ago. If a file is closed or deleted,
+ * it will be removed. If the length is maxxed out,
+ * the now-removed file will not be replaced by an older file.
+ */
+export class RecentFilesManager {
+  private readonly files: RecentFile[] = [];
+  private readonly onDidChangeEmitter = new vscode.EventEmitter<void>();
+  readonly onDidChange = this.onDidChangeEmitter.event;
+
+  constructor(private readonly context: vscode.ExtensionContext) {
+    const editorWatcher = vscode.window.onDidChangeActiveTextEditor(
+      (editor) => {
+        if (editor) {
+          this.add(editor.document.uri);
+        }
+      },
+    );
+    const fileWatcher = vscode.workspace.onDidDeleteFiles((event) => {
+      for (const uri of event.files) {
+        this.remove(uri);
+      }
+    });
+    const closeWatcher = vscode.workspace.onDidCloseTextDocument((document) => {
+      this.remove(document.uri);
+    });
+    const renameWatcher = vscode.workspace.onDidRenameFiles((event) => {
+      for (const { oldUri, newUri } of event.files) {
+        this.remove(oldUri, false);
+        this.add(newUri);
+      }
+    });
+    context.subscriptions.push(
+      editorWatcher,
+      fileWatcher,
+      closeWatcher,
+      renameWatcher,
+    );
+  }
+
+  private remove(uri: vscode.Uri, fireEvent = true) {
+    const index = this.files.findIndex(
+      (file) => file.uri.fsPath === uri.fsPath,
+    );
+    if (index !== -1) {
+      this.files.splice(index, 1);
+      if (fireEvent) {
+        this.onDidChangeEmitter.fire();
+      }
+    }
+  }
+
+  add(uri: vscode.Uri) {
+    // Remove if it already exists to avoid duplicates and move it to the top.
+    this.remove(uri, false);
+
+    this.files.unshift({ uri, timestamp: Date.now() });
+
+    if (this.files.length > MAX_FILES) {
+      this.files.pop();
+    }
+    this.onDidChangeEmitter.fire();
+  }
+
+  get recentFiles(): Array<{ filePath: string; timestamp: number }> {
+    const now = Date.now();
+    const maxAgeInMs = MAX_FILE_AGE_MINUTES * 60 * 1000;
+    return this.files
+      .filter((file) => now - file.timestamp < maxAgeInMs)
+      .map((file) => ({
+        filePath: file.uri.fsPath,
+        timestamp: file.timestamp,
+      }));
+  }
+}