Build shadow_dom package in dart/pkg

pkg/shadow_dom/lib/src/platform/ShadowCSS.js

+/*
+ * Copyright 2012 The Polymer Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file.
+ */
+
+/*
+  This is a limited shim for ShadowDOM css styling.
+  https://dvcs.w3.org/hg/webcomponents/raw-file/tip/spec/shadow/index.html#styles
+
+  The intention here is to support only the styling features which can be
+  relatively simply implemented. The goal is to allow users to avoid the
+  most obvious pitfalls and do so without compromising performance significantly.
+  For ShadowDOM styling that's not covered here, a set of best practices
+  can be provided that should allow users to accomplish more complex styling.
+
+  The following is a list of specific ShadowDOM styling features and a brief
+  discussion of the approach used to shim.
+
+  Shimmed features:
+
+  * @host: ShadowDOM allows styling of the shadowRoot's host element using the
+  @host rule. To shim this feature, the @host styles are reformatted and
+  prefixed with a given scope name and promoted to a document level stylesheet.
+  For example, given a scope name of .foo, a rule like this:
+
+    @host {
+      * {
+        background: red;
+      }
+    }
+
+  becomes:
+
+    .foo {
+      background: red;
+    }
+
+  * encapsultion: Styles defined within ShadowDOM, apply only to
+  dom inside the ShadowDOM. Polymer uses one of two techniques to imlement
+  this feature.
+
+  By default, rules are prefixed with the host element tag name
+  as a descendant selector. This ensures styling does not leak out of the 'top'
+  of the element's ShadowDOM. For example,
+
+  div {
+      font-weight: bold;
+    }
+
+  becomes:
+
+  x-foo div {
+      font-weight: bold;
+    }
+
+  becomes:
+
+
+  Alternatively, if Platform.ShadowCSS.strictStyling is set to true then
+  selectors are scoped by adding an attribute selector suffix to each
+  simple selector that contains the host element tag name. Each element
+  in the element's ShadowDOM template is also given the scope attribute.
+  Thus, these rules match only elements that have the scope attribute.
+  For example, given a scope name of x-foo, a rule like this:
+
+    div {
+      font-weight: bold;
+    }
+
+  becomes:
+
+    div[x-foo] {
+      font-weight: bold;
+    }
+
+  Note that elements that are dynamically added to a scope must have the scope
+  selector added to them manually.
+
+  * ::pseudo: These rules are converted to rules that take advantage of the
+  pseudo attribute. For example, a shadowRoot like this inside an x-foo
+
+    <div pseudo="x-special">Special</div>
+
+  with a rule like this:
+
+    x-foo::x-special { ... }
+
+  becomes:
+
+    x-foo [pseudo=x-special] { ... }
+
+  Unaddressed ShadowDOM styling features:
+
+  * upper/lower bound encapsulation: Styles which are defined outside a
+  shadowRoot should not cross the ShadowDOM boundary and should not apply
+  inside a shadowRoot.
+
+  This styling behavior is not emulated. Some possible ways to do this that
+  were rejected due to complexity and/or performance concerns include: (1) reset
+  every possible property for every possible selector for a given scope name;
+  (2) re-implement css in javascript.
+
+  As an alternative, users should make sure to use selectors
+  specific to the scope in which they are working.
+
+  * ::distributed: This behavior is not emulated. It's often not necessary
+  to style the contents of a specific insertion point and instead, descendants
+  of the host element can be styled selectively. Users can also create an
+  extra node around an insertion point and style that node's contents
+  via descendent selectors. For example, with a shadowRoot like this:
+
+    <style>
+      content::-webkit-distributed(div) {
+        background: red;
+      }
+    </style>
+    <content></content>
+
+  could become:
+
+    <style>
+      / *@polyfill .content-container div * /
+      content::-webkit-distributed(div) {
+        background: red;
+      }
+    </style>
+    <div class="content-container">
+      <content></content>
+    </div>
+
+  Note the use of @polyfill in the comment above a ShadowDOM specific style
+  declaration. This is a directive to the styling shim to use the selector
+  in comments in lieu of the next selector when running under polyfill.
+*/
+(function(scope) {
+
+var ShadowCSS = {
+  strictStyling: false,
+  registry: {},
+  // Shim styles for a given root associated with a name and extendsName
+  // 1. cache root styles by name
+  // 2. optionally tag root nodes with scope name
+  // 3. shim polyfill directives /* @polyfill */
+  // 4. shim @host and scoping
+  shimStyling: function(root, name, extendsName) {
+    if (root) {
+      // use caching to make working with styles nodes easier and to facilitate
+      // lookup of extendee
+      var def = this.registerDefinition(root, name, extendsName);
+      // find styles and apply shimming...
+      if (this.strictStyling) {
+        this.applyScopeToContent(root, name);
+      }
+      this.shimPolyfillDirectives(def.rootStyles, name);
+      this.applyShimming(def.scopeStyles, name);
+    }
+  },
+  // Shim styles to be placed inside a shadowRoot.
+  // 1. shim polyfill directives /* @polyfill */
+  // 2. shim @host and scoping
+  shimShadowDOMStyling: function(styles, name) {
+    this.shimPolyfillDirectives(styles, name);
+    this.applyShimming(styles, name);
+  },
+  registerDefinition: function(root, name, extendsName) {
+    var def = this.registry[name] = {
+      root: root,
+      name: name,
+      extendsName: extendsName
+    }
+    var styles = root.querySelectorAll('style');
+    styles = styles ? Array.prototype.slice.call(styles, 0) : [];
+    def.rootStyles = styles;
+    def.scopeStyles = def.rootStyles;
+    var extendee = this.registry[def.extendsName];
+    if (extendee) {
+      def.scopeStyles = def.scopeStyles.concat(extendee.scopeStyles);
+    }
+    return def;
+  },
+  applyScopeToContent: function(root, name) {
+    if (root) {
+      // add the name attribute to each node in root.
+      Array.prototype.forEach.call(root.querySelectorAll('*'),
+          function(node) {
+            node.setAttribute(name, '');
+          });
+      // and template contents too
+      Array.prototype.forEach.call(root.querySelectorAll('template'),
+          function(template) {
+            this.applyScopeToContent(template.content, name);
+          },
+          this);
+    }
+  },
+  /*
+   * Process styles to convert native ShadowDOM rules that will trip
+   * up the css parser; we rely on decorating the stylesheet with comments.
+   *
+   * For example, we convert this rule:
+   *
+   * (comment start) @polyfill @host g-menu-item (comment end)
+   * shadow::-webkit-distributed(g-menu-item) {
+   *
+   * to this:
+   *
+   * scopeName g-menu-item {
+   *
+  **/
+  shimPolyfillDirectives: function(styles, name) {
+    if (styles) {
+      Array.prototype.forEach.call(styles, function(s) {
+        s.textContent = this.convertPolyfillDirectives(s.textContent, name);
+      }, this);
+    }
+  },
+  convertPolyfillDirectives: function(cssText, name) {
+    var r = '', l = 0, matches, selector;
+    while (matches = cssPolyfillCommentRe.exec(cssText)) {
+      r += cssText.substring(l, matches.index);
+      // remove end comment delimiter (*/)
+      selector = matches[1].slice(0, -2).replace(hostRe, name);
+      r += this.scopeSelector(selector, name) + '{';
+      l = cssPolyfillCommentRe.lastIndex;
+    }
+    r += cssText.substring(l, cssText.length);
+    return r;
+  },
+  // apply @host and scope shimming
+  applyShimming: function(styles, name) {
+    var cssText = this.shimAtHost(styles, name);
+    cssText += this.shimScoping(styles, name);
+    addCssToDocument(cssText);
+  },
+  // form: @host { .foo { declarations } }
+  // becomes: scopeName.foo { declarations }
+  shimAtHost: function(styles, name) {
+    if (styles) {
+      return this.convertAtHostStyles(styles, name);
+    }
+  },
+  convertAtHostStyles: function(styles, name) {
+    var cssText = stylesToCssText(styles);
+    var r = '', l=0, matches;
+    while (matches = hostRuleRe.exec(cssText)) {
+      r += cssText.substring(l, matches.index);
+      r += this.scopeHostCss(matches[1], name);
+      l = hostRuleRe.lastIndex;
+    }
+    r += cssText.substring(l, cssText.length);
+    var re = new RegExp('^' + name + selectorReSuffix, 'm');
+    var cssText = rulesToCss(this.findAtHostRules(cssToRules(r),
+      re));
+    return cssText;
+  },
+  scopeHostCss: function(cssText, name) {
+    var r = '', matches;
+    while (matches = selectorRe.exec(cssText)) {
+      r += this.scopeHostSelector(matches[1], name) +' ' + matches[2] + '\n\t';
+    }
+    return r;
+  },
+  // supports scopig by name and  [is=name] syntax
+  scopeHostSelector: function(selector, name) {
+    var r = [], parts = selector.split(','), is = '[is=' + name + ']';
+    parts.forEach(function(p) {
+      p = p.trim();
+      // selector: *|:scope -> name
+      if (p.match(hostElementRe)) {
+        p = p.replace(hostElementRe, name + '$1$3, ' + is + '$1$3');
+      // selector: .foo -> name.foo, [bar] -> name[bar]
+      } else if (p.match(hostFixableRe)) {
+        p = name + p + ', ' + is + p;
+      }
+      r.push(p);
+    }, this);
+    return r.join(', ');
+  },
+  // consider styles that do not include component name in the selector to be
+  // unscoped and in need of promotion;
+  // for convenience, also consider keyframe rules this way.
+  findAtHostRules: function(cssRules, matcher) {
+    return Array.prototype.filter.call(cssRules,
+      this.isHostRule.bind(this, matcher));
+  },
+  isHostRule: function(matcher, cssRule) {
+    return (cssRule.selectorText && cssRule.selectorText.match(matcher)) ||
+      (cssRule.cssRules && this.findAtHostRules(cssRule.cssRules, matcher).length) ||
+      (cssRule.type == CSSRule.WEBKIT_KEYFRAMES_RULE);
+  },
+  /* Ensure styles are scoped. Pseudo-scoping takes a rule like:
+   *
+   *  .foo {... }
+   *
+   *  and converts this to
+   *
+   *  scopeName .foo { ... }
+  */
+  shimScoping: function(styles, name) {
+    if (styles) {
+      return this.convertScopedStyles(styles, name);
+    }
+  },
+  convertScopedStyles: function(styles, name) {
+    Array.prototype.forEach.call(styles, function(s) {
+      if (s.parentNode) {
+        s.parentNode.removeChild(s);
+      }
+    });
+    var cssText = stylesToCssText(styles).replace(hostRuleRe, '');
+    cssText = this.convertPseudos(cssText);
+    var rules = cssToRules(cssText);
+    cssText = this.scopeRules(rules, name);
+    return cssText;
+  },
+  convertPseudos: function(cssText) {
+    return cssText.replace(cssPseudoRe, ' [pseudo=$1]');
+  },
+  // change a selector like 'div' to 'name div'
+  scopeRules: function(cssRules, name) {
+    var cssText = '';
+    Array.prototype.forEach.call(cssRules, function(rule) {
+      if (rule.selectorText && (rule.style && rule.style.cssText)) {
+        cssText += this.scopeSelector(rule.selectorText, name,
+          this.strictStyling) + ' {\n\t';
+        cssText += this.propertiesFromRule(rule) + '\n}\n\n';
+      } else if (rule.media) {
+        cssText += '@media ' + rule.media.mediaText + ' {\n';
+        cssText += this.scopeRules(rule.cssRules, name);
+        cssText += '\n}\n\n';
+      } else if (rule.cssText) {
+        cssText += rule.cssText + '\n\n';
+      }
+    }, this);
+    return cssText;
+  },
+  scopeSelector: function(selector, name, strict) {
+    var r = [], parts = selector.split(',');
+    parts.forEach(function(p) {
+      p = p.trim();
+      if (this.selectorNeedsScoping(p, name)) {
+        p = strict ? this.applyStrictSelectorScope(p, name) :
+          this.applySimpleSelectorScope(p, name);
+      }
+      r.push(p);
+    }, this);
+    return r.join(', ');
+  },
+  selectorNeedsScoping: function(selector, name) {
+    var matchScope = '(' + name + '|\\[is=' + name + '\\])';
+    var re = new RegExp('^' + matchScope + selectorReSuffix, 'm');
+    return !selector.match(re);
+  },
+  // scope via name and [is=name]
+  applySimpleSelectorScope: function(selector, name) {
+    return name + ' ' + selector + ', ' + '[is=' + name + '] ' + selector;
+  },
+  // return a selector with [name] suffix on each simple selector
+  // e.g. .foo.bar > .zot becomes .foo[name].bar[name] > .zot[name]
+  applyStrictSelectorScope: function(selector, name) {
+    var splits = [' ', '>', '+', '~'],
+      scoped = selector,
+      attrName = '[' + name + ']';
+    splits.forEach(function(sep) {
+      var parts = scoped.split(sep);
+      scoped = parts.map(function(p) {
+        var t = p.trim();
+        if (t && (splits.indexOf(t) < 0) && (t.indexOf(attrName) < 0)) {
+          p = t.replace(/([^:]*)(:*)(.*)/, '$1' + attrName + '$2$3')
+        }
+        return p;
+      }).join(sep);
+    });
+    return scoped;
+  },
+  propertiesFromRule: function(rule) {
+    var properties = rule.style.cssText;
+    // TODO(sorvell): Chrome cssom incorrectly removes quotes from the content
+    // property. (https://code.google.com/p/chromium/issues/detail?id=247231)
+    if (rule.style.content && !rule.style.content.match(/['"]+/)) {
+      properties = 'content: \'' + rule.style.content + '\';\n' +
+        rule.style.cssText.replace(/content:[^;]*;/g, '');
+    }
+    return properties;
+  }
+};
+
+var hostRuleRe = /@host[^{]*{(([^}]*?{[^{]*?}[\s\S]*?)+)}/gim,
+    selectorRe = /([^{]*)({[\s\S]*?})/gim,
+    hostElementRe = /(.*)((?:\*)|(?:\:scope))(.*)/,
+    hostFixableRe = /^[.\[:]/,
+    cssCommentRe = /\/\*[^*]*\*+([^/*][^*]*\*+)*\//gim,
+    cssPolyfillCommentRe = /\/\*\s*@polyfill ([^*]*\*+([^/*][^*]*\*+)*\/)([^{]*?){/gim,
+    cssPseudoRe = /::(x-[^\s{,(]*)/gim,
+    selectorReSuffix = '([>\\s~+\[.,{:][\\s\\S]*)?$',
+    hostRe = /@host/gim;
+
+function stylesToCssText(styles, preserveComments) {
+  var cssText = '';
+  Array.prototype.forEach.call(styles, function(s) {
+    cssText += s.textContent + '\n\n';
+  });
+  // strip comments for easier processing
+  if (!preserveComments) {
+    cssText = cssText.replace(cssCommentRe, '');
+  }
+  return cssText;
+}
+
+function cssToRules(cssText) {
+  var style = document.createElement('style');
+  style.textContent = cssText;
+  document.head.appendChild(style);
+  var rules = style.sheet.cssRules;
+  style.parentNode.removeChild(style);
+  return rules;
+}
+
+function rulesToCss(cssRules) {
+  for (var i=0, css=[]; i < cssRules.length; i++) {
+    css.push(cssRules[i].cssText);
+  }
+  return css.join('\n\n');
+}
+
+function addCssToDocument(cssText) {
+  if (cssText) {
+    getSheet().appendChild(document.createTextNode(cssText));
+  }
+}
+
+var sheet;
+function getSheet() {
+  if (!sheet) {
+    sheet = document.createElement("style");
+    sheet.setAttribute('ShadowCSSShim', '');
+  }
+  return sheet;
+}
+
+// add polyfill stylesheet to document
+if (window.ShadowDOMPolyfill) {
+  addCssToDocument('style { display: none !important; }\n');
+  var head = document.querySelector('head');
+  head.insertBefore(getSheet(), head.childNodes[0]);
+}
+
+// exports
+scope.ShadowCSS = ShadowCSS;
+
+})(window.Platform);