// Copyright (c) 2026, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:async';

extension Keys on Stream<List<int>> {
  /// Listens for terminal byte sequences and maps them to key commands.
  Stream<Key> get keys {
    // Note that we cannot use async* here because the returned stream will not
    // actually complete when cancelled if the user hits ctrl+c.
    final streamController = StreamController<Key>();

    final subscription = listen((bytes) {
      for (var b = 0; b < bytes.length; b++) {
        final byte = bytes[b];
        Key? key;
        // Check for an escape sequence (starts with "esc [").
        if (byte == 27 && b + 1 < bytes.length && bytes[b + 1] == 91) {
          b += 2;
          key = switch (bytes[b]) {
            65 => Key.up, // A
            66 => Key.down, // B
            49 || 72 => Key.home, // 1, H
            52 || 70 => Key.end, // 4, F
            53 when b + 1 < bytes.length && bytes[b + 1] == 126 =>
              Key.pageUp, // 5 ~
            54 when b + 1 < bytes.length && bytes[b + 1] == 126 =>
              Key.pageDown, // 6 ~
            _ => null,
          };
        } else {
          // handle normal keys
          key = switch (bytes[b]) {
            10 || 13 => Key.enter, // newline/carraige return
            32 => Key.space,
            3 || 4 => Key.quit, // End of text/end of transmission
            27 => Key.quit, // Escape key but not escape sequence
            1 => Key.selectAll, // Ctrl+A
            _ => null,
          };
        }
        if (key != null) {
          streamController.add(key);
        }
      }
    });
    streamController.onCancel = subscription.cancel;
    return streamController.stream;
  }
}

enum Key {
  up,
  down,
  pageUp,
  pageDown,
  home,
  end,
  space,
  enter,
  quit,
  selectAll,
}