alternate buffer support (#12471)

packages/cli/src/ui/utils/input.ts

@@ -0,0 +1,58 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+export const ESC = '\u001B';
+export const SGR_EVENT_PREFIX = `${ESC}[<`;
+export const X11_EVENT_PREFIX = `${ESC}[M`;
+
+// eslint-disable-next-line no-control-regex
+export const SGR_MOUSE_REGEX = /^\x1b\[<(\d+);(\d+);(\d+)([mM])/; // SGR mouse events
+// X11 is ESC [ M followed by 3 bytes.
+// eslint-disable-next-line no-control-regex
+export const X11_MOUSE_REGEX = /^\x1b\[M([\s\S]{3})/;
+
+export function couldBeSGRMouseSequence(buffer: string): boolean {
+  if (buffer.length === 0) return true;
+  // Check if buffer is a prefix of a mouse sequence starter
+  if (SGR_EVENT_PREFIX.startsWith(buffer)) return true;
+  // Check if buffer is a mouse sequence prefix
+  if (buffer.startsWith(SGR_EVENT_PREFIX)) return true;
+
+  return false;
+}
+
+export function couldBeMouseSequence(buffer: string): boolean {
+  if (buffer.length === 0) return true;
+
+  // Check SGR prefix
+  if (
+    SGR_EVENT_PREFIX.startsWith(buffer) ||
+    buffer.startsWith(SGR_EVENT_PREFIX)
+  )
+    return true;
+  // Check X11 prefix
+  if (
+    X11_EVENT_PREFIX.startsWith(buffer) ||
+    buffer.startsWith(X11_EVENT_PREFIX)
+  )
+    return true;
+
+  return false;
+}
+
+/**
+ * Checks if the buffer *starts* with a complete mouse sequence.
+ * Returns the length of the sequence if matched, or 0 if not.
+ */
+export function getMouseSequenceLength(buffer: string): number {
+  const sgrMatch = buffer.match(SGR_MOUSE_REGEX);
+  if (sgrMatch) return sgrMatch[0].length;
+
+  const x11Match = buffer.match(X11_MOUSE_REGEX);
+  if (x11Match) return x11Match[0].length;
+
+  return 0;
+}