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code_transformers/lib/assets.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.
-
-/// Common methods used by transfomers for dealing with asset IDs.
-library code_transformers.assets;
-
-import 'dart:math' show min, max;
-
-import 'package:barback/barback.dart';
-import 'package:path/path.dart' as path;
-import 'package:source_span/source_span.dart';
-
-import 'messages/build_logger.dart';
-import 'src/messages.dart';
-
-/// Create an [AssetId] for a [url] seen in the [source] asset.
-///
-/// By default this is used to resolve relative urls that occur in HTML assets,
-/// including cross-package urls of the form "packages/foo/bar.html". Dart
-/// "package:" urls are not resolved unless [source] is Dart file (has a .dart
-/// extension).
-///
-/// This function returns null if [url] can't be resolved. We log a warning
-/// message in [logger] if we know the reason why resolution failed. This
-/// happens, for example, when using incorrect paths to reach into another
-/// package, or when [errorsOnAbsolute] is true and the url seems to be
-/// absolute. If [span] is not `null` it is used to provide context for any
-/// warning message(s) generated.
-// TODO(sigmund): delete once this is part of barback (dartbug.com/12610)
-AssetId uriToAssetId(
-    AssetId source, String url, TransformLogger logger, SourceSpan span,
-    {bool errorOnAbsolute: true}) {
-  if (url == null || url == '') return null;
-  var uri = Uri.parse(url);
-  var urlBuilder = path.url;
-  if (uri.host != '' || uri.scheme != '' || urlBuilder.isAbsolute(url)) {
-    if (source.extension == '.dart' && uri.scheme == 'package') {
-      var index = uri.path.indexOf('/');
-      if (index != -1) {
-        return new AssetId(
-            uri.path.substring(0, index), 'lib${uri.path.substring(index)}');
-      }
-    }
-
-    if (errorOnAbsolute) {
-      var msg = NO_ABSOLUTE_PATHS.create({'url': url});
-      logger.warning(logger is BuildLogger ? msg : msg.snippet, span: span);
-    }
-    return null;
-  }
-
-  var targetPath = urlBuilder
-      .normalize(urlBuilder.join(urlBuilder.dirname(source.path), url));
-  var segments = urlBuilder.split(targetPath);
-  var sourceSegments = urlBuilder.split(source.path);
-  assert(sourceSegments.length > 0);
-  var topFolder = sourceSegments[0];
-  var entryFolder = topFolder != 'lib' && topFolder != 'asset';
-
-  // Find the first 'packages/'  or 'assets/' segment:
-  var packagesIndex = segments.indexOf('packages');
-  var assetsIndex = segments.indexOf('assets');
-  var index = (packagesIndex >= 0 && assetsIndex >= 0)
-      ? min(packagesIndex, assetsIndex)
-      : max(packagesIndex, assetsIndex);
-  if (index > -1) {
-    if (entryFolder) {
-      // URLs of the form "packages/foo/bar" seen under entry folders (like
-      // web/, test/, example/, etc) are resolved as an asset in another
-      // package. 'packages' can be used anywhere, there is no need to walk up
-      // where the entrypoint file was.
-      // TODO(sigmund): this needs to change: Only resolve when index == 1 &&
-      // topFolder == segment[0], otherwise give a warning (dartbug.com/17596).
-      return _extractOtherPackageId(index, segments, logger, span);
-    } else if (index == 1 && segments[0] == '..') {
-      // Relative URLs of the form "../../packages/foo/bar" in an asset under
-      // lib/ or asset/ are also resolved as an asset in another package, but we
-      // check that the relative path goes all the way out where the packages
-      // folder lives (otherwise the app would not work in Dartium). Since
-      // [targetPath] has been normalized, "packages" or "assets" should be at
-      // index 1.
-      return _extractOtherPackageId(1, segments, logger, span);
-    } else {
-      var prefix = segments[index];
-      var fixedSegments = [];
-      fixedSegments.addAll(sourceSegments.map((_) => '..'));
-      fixedSegments.addAll(segments.sublist(index));
-      var fixedUrl = urlBuilder.joinAll(fixedSegments);
-      var msg = INVALID_URL_TO_OTHER_PACKAGE
-          .create({'url': url, 'prefix': prefix, 'fixedUrl': fixedUrl});
-      logger.warning(logger is BuildLogger ? msg : msg.snippet, span: span);
-      return null;
-    }
-  }
-
-  // Otherwise, resolve as a path in the same package.
-  return new AssetId(source.package, targetPath);
-}
-
-AssetId _extractOtherPackageId(
-    int index, List segments, TransformLogger logger, SourceSpan span) {
-  if (index >= segments.length) return null;
-  var prefix = segments[index];
-  if (prefix != 'packages' && prefix != 'assets') return null;
-  var folder = prefix == 'packages' ? 'lib' : 'asset';
-  if (segments.length < index + 3) {
-    var msg = INVALID_PREFIX_PATH.create({'prefix': prefix, 'folder': folder});
-    logger.warning(logger is BuildLogger ? msg : msg.snippet, span: span);
-    return null;
-  }
-  return new AssetId(segments[index + 1],
-      path.url.join(folder, path.url.joinAll(segments.sublist(index + 2))));
-}
-
-/// Gets a URI which would be appropriate for importing the file represented by
-/// [assetId].
-///
-/// This function returns null if we cannot determine a uri for [assetId].
-///
-/// Note that [assetId] may represent a non-importable file such as a part.
-String assetIdToUri(AssetId assetId,
-    {TransformLogger logger, SourceSpan span, AssetId from}) {
-  if (!assetId.path.startsWith('lib/')) {
-    // Cannot do absolute imports of non lib-based assets.
-    if (from == null) {
-      if (logger != null) {
-        var msg = UNSPECIFIED_FROM_IN_NON_LIB_ASSET.create({'id': '$assetId'});
-        logger.warning(logger is BuildLogger ? msg : msg.snippet, span: span);
-      }
-      return null;
-    }
-
-    if (assetId.package != from.package) {
-      if (logger != null) {
-        var msg = IMPORT_FROM_DIFFERENT_PACKAGE
-            .create({'toId': '$assetId', 'fromId': '$from'});
-        logger.warning(logger is BuildLogger ? msg : msg.snippet, span: span);
-      }
-      return null;
-    }
-    return new Uri(
-            path: path.url.relative(assetId.path, from: path.url.dirname(from.path)))
-        .toString();
-  }
-
-  return Uri
-      .parse('package:${assetId.package}/${assetId.path.substring(4)}')
-      .toString();
-}