pkg/analyzer/lib/src/source/package_map_resolver.dart

// Copyright (c) 2014, 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 'package:analyzer/file_system/file_system.dart';
import 'package:analyzer/source/file_source.dart';
import 'package:analyzer/source/source.dart';
import 'package:analyzer/src/generated/source.dart' show UriResolver;
import 'package:analyzer/src/utilities/uri_cache.dart';
import 'package:path/path.dart' as pathos;

/// A [UriResolver] implementation for the `package:` scheme that uses a map of
/// package names to their directories.
class PackageMapUriResolver extends UriResolver {
  /// The name of the `package` scheme.
  static const String _packageScheme = "package";

  /// A table mapping package names to the path of the directories containing
  /// the package.
  final Map<String, List<Folder>> packageMap;

  /// The [ResourceProvider] for this resolver.
  final ResourceProvider resourceProvider;

  /// Create a new [PackageMapUriResolver].
  ///
  /// [packageMap] is a table mapping package names to the paths of the
  /// directories containing the package
  PackageMapUriResolver(this.resourceProvider, this.packageMap) {
    packageMap.forEach((name, folders) {
      if (folders.length != 1) {
        throw ArgumentError(
          'Exactly one folder must be specified for a package. '
          'Found $name = $folders',
        );
      }
    });
  }

  @override
  Uri? pathToUri(String path) {
    // TODO(jensj): There should be an index on this instead of trying all entries.
    // When analyzing rwf-materials (562 contexts) with a filled cache this
    // function is called 624,750 times and a combined 39,352,289 iterations
    // are done in the loop below.
    // See for instance https://github.com/dart-lang/package_config/pull/117
    // for inspiration, but also, maybe just use package:package_config?
    pathos.Context pathContext = resourceProvider.pathContext;
    for (var packageEntry in packageMap.entries) {
      String pkgName = packageEntry.key;
      Folder pkgFolder = packageEntry.value[0];
      String pkgFolderPath = pkgFolder.path;
      if (path.length >= pkgFolderPath.length + pathContext.separator.length &&
          path.startsWith(pkgFolderPath) &&
          path.startsWith(pathContext.separator, pkgFolderPath.length)) {
        String relPath = path.substring(pkgFolderPath.length + 1);
        List<String> relPathComponents = pathContext.split(relPath);
        String relUriPath = pathos.posix.joinAll(relPathComponents);
        return uriCache.parse('$_packageScheme:$pkgName/$relUriPath');
      }
    }
    return null;
  }

  @override
  Source? resolveAbsolute(Uri uri) {
    if (!isPackageUri(uri)) {
      return null;
    }

    var pathSegments = uri.pathSegments;
    if (pathSegments.length < 2) {
      return null;
    }

    // <pkgName>/<relPath>
    String pkgName = pathSegments[0];

    // If the package is known, return the corresponding file.
    var packageDirs = packageMap[pkgName];
    if (packageDirs != null) {
      Folder packageDir = packageDirs.single;
      String relPath = pathSegments.skip(1).join('/');
      File file = packageDir.getChildAssumingFile(relPath);
      return FileSource(file, uri);
    }
    return null;
  }

  /// Returns `true` if [uri] is a `package` URI.
  static bool isPackageUri(Uri uri) {
    return uri.isScheme(_packageScheme);
  }
}