flutter/examples/flutter_gallery/lib/gallery/example_code_parser.dart

// Copyright 2014 The Flutter Authors. 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';

import 'package:flutter/services.dart';

const String _kStartTag = '// START ';
const String _kEndTag = '// END';

Map<String, String> _exampleCode;

Future<String> getExampleCode(String tag, AssetBundle bundle) async {
  if (_exampleCode == null)
    await _parseExampleCode(bundle);
  return _exampleCode[tag];
}

Future<void> _parseExampleCode(AssetBundle bundle) async {
  final String code = await bundle.loadString('lib/gallery/example_code.dart') ??
    '// lib/gallery/example_code.dart not found\n';
  _exampleCode = <String, String>{};

  final List<String> lines = code.split('\n');

  List<String> codeBlock;
  String codeTag;

  for (final String line in lines) {
    if (codeBlock == null) {
      // Outside a block.
      if (line.startsWith(_kStartTag)) {
        // Starting a new code block.
        codeBlock = <String>[];
        codeTag = line.substring(_kStartTag.length).trim();
      } else {
        // Just skipping the line.
      }
    } else {
      // Inside a block.
      if (line.startsWith(_kEndTag)) {
        // Add the block.
        _exampleCode[codeTag] = codeBlock.join('\n');
        codeBlock = null;
        codeTag = null;
      } else {
        // Add to the current block
        // trimRight() to remove any \r on Windows
        // without removing any useful indentation
        codeBlock.add(line.trimRight());
      }
    }
  }
}