refactor(transformer): precompile stylesheets

Part of #3605

modules/angular2/src/core/dom/emulated_css.dart

@@ -0,0 +1,102 @@
+/**
+ * Emulates browser CSS API.
+ *
+ * WARNING: this is a very incomplete emulation; it only has enough to support
+ *          Angular's CSS scoping (a.k.a. shimming).
+ */
+library angular2.dom.emulated_css;
+
+import 'package:csslib/parser.dart' as cssp;
+import 'package:csslib/visitor.dart' as cssv;
+
+/// Parses [css] string and emits the list of top-level CSS rules in it via
+/// data structures that mimick browser CSS APIs.
+List<EmulatedCssRule> parseAndEmulateCssRules(String css) {
+  var stylesheet = cssp.parse(css);
+  return emulateRules(stylesheet.topLevels);
+}
+
+/// Converts `csslib` [rules] to their emulated counterparts.
+List<EmulatedCssRule> emulateRules(Iterable<cssv.TreeNode> rules) {
+  return rules
+    .map((cssv.TreeNode node) {
+      if (node is cssv.RuleSet) {
+        if (node.declarationGroup.span.text.isEmpty) {
+          // Skip CSS matchers with no bodies
+          return null;
+        }
+        return new EmulatedCssStyleRule(node);
+      } else if (node is cssv.MediaDirective) {
+        return new EmulatedCssMedialRule(node);
+      }
+    })
+    .where((r) => r != null)
+    .toList();
+}
+
+/// Emulates [CSSRule](https://developer.mozilla.org/en-US/docs/Web/API/CSSRule)
+abstract class EmulatedCssRule {
+  int type;
+  String cssText;
+}
+
+/// Emulates [CSSStyleRule](https://developer.mozilla.org/en-US/docs/Web/API/CSSStyleRule)
+class EmulatedCssStyleRule extends EmulatedCssRule {
+  String selectorText;
+  EmulatedCssStyleDeclaration style;
+
+  EmulatedCssStyleRule(cssv.RuleSet ruleSet) {
+    final declarationText = new StringBuffer();
+    ruleSet.declarationGroup.declarations.forEach((d) {
+      if (d is! cssv.Declaration) {
+        // Nested selectors not supported
+        return;
+      }
+      // TODO: expression spans are currently broken in csslib; see:
+      //       https://github.com/dart-lang/csslib/pull/14
+      var declarationSpan = d.span.text;
+      var colonIdx = declarationSpan.indexOf(':');
+      var expression = declarationSpan.substring(colonIdx + 1);
+      declarationText.write('${d.property}: ${expression};');
+    });
+
+    final style = new EmulatedCssStyleDeclaration()
+      ..cssText = declarationText.toString();
+
+    this
+      ..type = 1
+      ..cssText = ruleSet.span.text
+      ..selectorText = ruleSet.selectorGroup.span.text
+      ..style = style;
+  }
+}
+
+/// Emulates [CSSStyleDeclaration](https://developer.mozilla.org/en-US/docs/Web/API/CSSStyleDeclaration)
+class EmulatedCssStyleDeclaration {
+  final String content = '';
+  String cssText;
+}
+
+/// Emulates [CSSMediaRule](https://developer.mozilla.org/en-US/docs/Web/API/CSSMediaRule)
+class EmulatedCssMedialRule extends EmulatedCssRule {
+  List<EmulatedCssStyleRule> cssRules;
+  EmulatedMediaList media;
+
+  EmulatedCssMedialRule(cssv.MediaDirective directive) {
+    this
+      ..type = 4
+      ..media = new EmulatedMediaList(directive)
+      ..cssText = directive.span.text
+      ..cssRules = emulateRules(directive.rulesets);
+  }
+}
+
+/// Emulates [MediaList](https://developer.mozilla.org/en-US/docs/Web/API/MediaList)
+class EmulatedMediaList {
+  String mediaText;
+
+  EmulatedMediaList(cssv.MediaDirective directive) {
+    this.mediaText = directive.mediaQueries
+        .map((q) => q.span.text).join(' and ');
+  }
+}