Add utility to collect headers from google/mediapipe (#10)

* adds cmd to pull header files from google/mediapipe

* polish and missing parts from git surgery

* More comments and touch ups

* Apply suggestions from code review

* moves build command into `tool/` directory

and renames folder `build_cmd` -> `builder`

* complete build_cmd -> builder rename

* Update readme

* Added licenses

* Adds DownloadModelCommand

---------

Co-authored-by: Kate Lovett <katelovett@google.com>

.flutter-mediapipe-root

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+// Used to normalize the paths of commands.
+// The contents of this file do not matter.

tool/builder/.gitignore

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+# https://dart.dev/guides/libraries/private-files
+# Created by `dart pub`
+.dart_tool/

tool/builder/CHANGELOG.md

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+## 1.0.0
+
+- Initial version with headers command to sync C headers from `google/mediapipe`.

tool/builder/README.md

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+# Flutter MediaPipe builder
+
+Helper utility which performs build or CI/CD step operations necessary to develop, release, and use `flutter-mediapipe`.
+
+### Usage:
+
+Usage depends on which task you need to accomplish. All supported workflows are described below.
+
+#### Header aggregation
+
+Header files across all tasks in `google/flutter-mediapipe` have to stay in sync with their origin, `google/mediapipe`. To
+resync these files, check out both repositories on the same machine (ideally next to each other on the file system) and run:
+
+```sh
+$ dart tool/builder/bin/main.dart headers
+```
+
+--
+
+Check back in the future for any additional development workflows this command may support.

tool/builder/analysis_options.yaml

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+include: package:lints/recommended.yaml
+

tool/builder/bin/main.dart

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+// 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:io' as io;
+import 'package:args/command_runner.dart';
+import 'package:builder/download_model.dart';
+import 'package:builder/sync_headers.dart';
+import 'package:logging/logging.dart';
+
+final runner = CommandRunner(
+  'build',
+  'Performs build operations for google/flutter-mediapipe that '
+      'depend on contents in this repository',
+)
+  ..addCommand(SyncHeadersCommand())
+  ..addCommand(DownloadModelCommand());
+
+void main(List<String> arguments) {
+  Logger.root.onRecord.listen((LogRecord record) {
+    io.stdout
+        .writeln('${record.level.name}: ${record.time}: ${record.message}');
+  });
+  runner.run(arguments);
+}

tool/builder/lib/download_model.dart

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+// 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:io' as io;
+import 'package:args/command_runner.dart';
+import 'package:builder/repo_finder.dart';
+import 'package:http/http.dart' as http;
+import 'package:logging/logging.dart';
+import 'package:path/path.dart' as path;
+
+final _log = Logger('DownloadModelCommand');
+
+enum Models {
+  textclassification,
+  languagedetection,
+}
+
+class DownloadModelCommand extends Command with RepoFinderMixin {
+  @override
+  String description = 'Downloads a given MediaPipe model and places it in '
+      'the designated location.';
+  @override
+  String name = 'model';
+
+  DownloadModelCommand() {
+    argParser
+      ..addOption(
+        'model',
+        abbr: 'm',
+        allowed: [
+          // Values will be added to this as the repository gets more
+          // integration tests that require new models.
+          Models.textclassification.name,
+          Models.languagedetection.name,
+        ],
+        help: 'The desired model to download. Use this option if you want the '
+            'standard model for a given task. Using this option also removes any '
+            'need to use the `destination` option, as a value here implies a '
+            'destination. However, you still can specify a destination to '
+            'override the default location where the model is placed.\n'
+            '\n'
+            'Note: Either this or `custommodel` must be used. If both are '
+            'supplied, `model` is used.',
+      )
+      ..addOption(
+        'custommodel',
+        abbr: 'c',
+        help: 'The desired model to download. Use this option if you want to '
+            'specify a specific and nonstandard model. Using this option means '
+            'you *must* use the `destination` option.\n'
+            '\n'
+            'Note: Either this or `model` must be used. If both are supplied, '
+            '`model` is used.',
+      )
+      ..addOption(
+        'destination',
+        abbr: 'd',
+        help:
+            'The location to place the downloaded model. This value is required '
+            'if you use the `custommodel` option, but optional if you use the '
+            '`model` option.',
+      );
+  }
+
+  static final Map<String, String> _standardModelSources = {
+    Models.textclassification.name:
+        'https://storage.googleapis.com/mediapipe-models/text_classifier/bert_classifier/float32/1/bert_classifier.tflite',
+    Models.languagedetection.name:
+        'https://storage.googleapis.com/mediapipe-models/language_detector/language_detector/float32/1/language_detector.tflite',
+  };
+
+  static final Map<String, String> _standardModelDestinations = {
+    Models.textclassification.name:
+        'packages/mediapipe-task-text/example/assets/',
+    Models.languagedetection.name:
+        'packages/mediapipe-task-text/example/assets/',
+  };
+
+  @override
+  Future<void> run() async {
+    final io.Directory flutterMediaPipeDirectory = findFlutterMediaPipeRoot();
+
+    late final String modelSource;
+    late final String modelDestination;
+
+    if (argResults!['model'] != null) {
+      modelSource = _standardModelSources[argResults!['model']]!;
+      modelDestination = (_isArgProvided(argResults!['destination']))
+          ? argResults!['destination']
+          : _standardModelDestinations[argResults!['model']]!;
+    } else {
+      if (argResults!['custommodel'] == null) {
+        throw Exception(
+          'You must use either the `model` or `custommodel` option.',
+        );
+      }
+      if (argResults!['destination'] == null) {
+        throw Exception(
+          'If you do not use the `model` option, then you must supply a '
+          '`destination`, as a "standard" destination cannot be used.',
+        );
+      }
+      modelSource = argResults!['custommodel'];
+      modelDestination = argResults!['destination'];
+    }
+
+    io.File destinationFile = io.File(
+      path.joinAll([
+        flutterMediaPipeDirectory.absolute.path,
+        modelDestination,
+        modelSource.split('/').last,
+      ]),
+    );
+    ensureFolders(destinationFile);
+    await downloadModel(modelSource, destinationFile);
+  }
+
+  Future<void> downloadModel(
+    String modelSource,
+    io.File destinationFile,
+  ) async {
+    _log.info('Downloading $modelSource');
+
+    // TODO(craiglabenz): Convert to StreamedResponse
+    final response = await http.get(Uri.parse(modelSource));
+
+    if (response.statusCode != 200) {
+      throw Exception('${response.statusCode} ${response.reasonPhrase} :: '
+          '$modelSource');
+    }
+
+    if (!(await destinationFile.exists())) {
+      _log.fine('Creating file at ${destinationFile.absolute.path}');
+      await destinationFile.create();
+    }
+
+    _log.fine('Downloaded ${response.contentLength} bytes');
+    _log.info('Saving to ${destinationFile.absolute.path}');
+    await destinationFile.writeAsBytes(response.bodyBytes);
+  }
+}
+
+bool _isArgProvided(String? val) => val != null && val != '';

tool/builder/lib/repo_finder.dart

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+// 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:io' as io;
+import 'package:args/args.dart';
+import 'package:args/command_runner.dart';
+import 'package:path/path.dart' as path;
+import 'package:io/ansi.dart';
+
+/// Mixin to help [Command] subclasses locate both `google/mediapipe` and
+/// the root of `google/flutter-mediapipe` (this repository).
+///
+/// The primary methods are [findFlutterMediaPipeRoot] and [findMediaPipeRoot].
+///
+/// By default, the root for `google/flutter-mediapipe` is determined by the
+/// firest ancestor directory which contains a `.flutter-mediapipe-root` file
+/// (whose contents are irrelevant), and the root of `google/mediapipe` is
+/// expected to be a sibling of that. However, the `--source` flag can overwrite
+/// this expectation and specify an absolute path where to find `google/mediapipe`.
+///
+/// Note that it is not possible to override the method of locating the root of
+/// `google/flutter-mediapipe`.
+mixin RepoFinderMixin on Command {
+  /// Name of the file which, when found, indicates the root of this repository.
+  static String sentinelFileName = '.flutter-mediapipe-root';
+
+  void addSourceOption(ArgParser argParser) {
+    argParser.addOption(
+      'source',
+      abbr: 's',
+      help: 'The location of google/mediapipe. Defaults to being '
+          'adjacent to google/flutter-mediapipe.',
+    );
+  }
+
+  /// Looks upward for the root of the `google/mediapipe` repository. This assumes
+  /// the `dart build` command is executed from within said repository. If it is
+  /// not executed from within, then this searching algorithm will reach the root
+  /// of the file system, log the error, and exit.
+  io.Directory findFlutterMediaPipeRoot() {
+    final placesChecked = <io.Directory>[];
+    io.Directory dir = io.Directory(path.current);
+    while (true) {
+      if (_isFlutterMediaPipeRoot(dir)) {
+        return dir;
+      }
+      placesChecked.add(dir);
+      dir = dir.parent;
+      if (dir.parent.path == dir.path) {
+        io.stderr.writeln(
+          wrapWith(
+            'Failed to find google/flutter-mediapipe root directory. '
+            'Did you execute this command from within the repository?\n'
+            'Looked in:',
+            [red],
+          ),
+        );
+        io.stderr.writeln(
+          wrapWith(
+            placesChecked
+                .map<String>((dir) => ' - ${dir.absolute.path}')
+                .toList()
+                .join('\n'),
+            [red],
+          ),
+        );
+        io.exit(1);
+      }
+    }
+  }
+
+  /// Finds the `google/mediapipe` checkout where artifacts built in this
+  /// repository should be sourced. By default, this command assumes the two
+  /// repositories are siblings on the file system, but the `--source` flag
+  /// allows for this assumption to be overridden.
+  io.Directory findMediaPipeRoot(
+    io.Directory flutterMediaPipeDir,
+    String? source,
+  ) {
+    final mediaPipeDirectory = io.Directory(
+      source ??
+          path.joinAll([flutterMediaPipeDir.parent.absolute.path, 'mediapipe']),
+    );
+
+    if (!mediaPipeDirectory.existsSync()) {
+      io.stderr.writeln(
+        'Could not find ${mediaPipeDirectory.absolute.path}. '
+        'Folder does not exist.',
+      );
+      io.exit(1);
+    }
+    return mediaPipeDirectory;
+  }
+
+  /// Looks for the sentinel file of this repository's root directory. This allows
+  /// the `dart build` command to be run from various locations within the
+  /// `google/mediapipe` repository and still correctly set paths for all of its
+  /// operations.
+  bool _isFlutterMediaPipeRoot(io.Directory dir) {
+    return io.File(
+      path.joinAll(
+        [dir.absolute.path, sentinelFileName],
+      ),
+    ).existsSync();
+  }
+
+  /// Builds any missing folders between the file and the root of the repository
+  void ensureFolders(io.File file) {
+    io.Directory parent = file.parent;
+    List<io.Directory> dirsToCreate = [];
+    while (!parent.existsSync()) {
+      dirsToCreate.add(parent);
+      parent = parent.parent;
+    }
+    for (io.Directory dir in dirsToCreate.reversed) {
+      dir.createSync();
+    }
+  }
+}