A sizes attribute parser

Source/core/css/parser/SizesAttributeParser.cpp

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "SizesAttributeParser.h"
+
+#include "MediaTypeNames.h"
+#include "core/css/MediaQueryEvaluator.h"
+#include "core/css/parser/MediaQueryTokenizer.h"
+
+namespace WebCore {
+
+unsigned SizesAttributeParser::findEffectiveSize(const String& attribute, PassRefPtr<MediaValues> mediaValues)
+{
+    Vector<MediaQueryToken> tokens;
+    SizesAttributeParser parser(mediaValues);
+
+    MediaQueryTokenizer::tokenize(attribute, tokens);
+    if (!parser.parse(tokens))
+        return parser.effectiveSizeDefaultValue();
+    return parser.effectiveSize();
+}
+
+bool SizesAttributeParser::calculateLengthInPixels(TokenIterator startToken, TokenIterator endToken, unsigned& result)
+{
+    MediaQueryTokenType type = startToken->type();
+    if (type == NumberToken || type == PercentageToken || type == DimensionToken) {

[eseidel, 2014/04/14 23:10:13]

Would this be clearer returning early instead of a long if block?

+        int length;

[eseidel, 2014/04/14 23:10:13]

Can this be negative?

+        RefPtr<CSSPrimitiveValue> primitiveValue = CSSPrimitiveValue::create(startToken->numericValue(), startToken->unitType());

[eseidel, 2014/04/14 23:10:13]

Presumably this only ever runs on the main thread?  I'm not sure if
CSSPrimitiveValue is safe to use from multipel threads.

+        if (!primitiveValue->isLength())
+            return false;
+        if (m_mediaValues->computeLength(*primitiveValue, length)) {
+            if (length > 0) {
+                result = (unsigned)length;
+                return true;
+            }
+        }
+    }
+    // FIXME - Handle calc() functions here!
+    return false;
+}
+
+static void reverseSkipIrrelevantTokens(TokenIterator& token, TokenIterator startToken)
+{
+    TokenIterator endToken = token;
+    while (token != startToken && (token->type() == WhitespaceToken || token->type() == CommentToken || token->type() == EOFToken))
+        --token;
+    if (token != endToken)
+        ++token;
+}
+
+static void reverseSkipUntilComponentStart(TokenIterator& token, TokenIterator startToken)
+{
+    if (token == startToken)
+        return;
+    --token;
+    if (token->blockType() != MediaQueryToken::BlockEnd)
+        return;
+    unsigned blockLevel = 0;
+    while (token != startToken) {
+        if (token->blockType() == MediaQueryToken::BlockEnd) {
+            ++blockLevel;
+        } else if (token->blockType() == MediaQueryToken::BlockStart) {
+            --blockLevel;
+            if (!blockLevel)
+                break;
+        }
+
+        --token;
+    }
+}
+
+bool SizesAttributeParser::mediaConditionMatches(PassRefPtr<MediaQuerySet> mediaCondition)
+{
+    // FIXME: How do I handle non-screen media types here?
+    MediaQueryEvaluator mediaQueryEvaluator(MediaTypeNames::screen, *m_mediaValues);
+    return mediaQueryEvaluator.eval(mediaCondition.get());
+}
+
+bool SizesAttributeParser::parseMediaConditionAndLength(TokenIterator startToken, TokenIterator endToken)
+{
+    TokenIterator lengthTokenStart;
+    TokenIterator lengthTokenEnd;
+
+    reverseSkipIrrelevantTokens(endToken, startToken);
+    lengthTokenEnd = endToken;
+    reverseSkipUntilComponentStart(endToken, startToken);
+    lengthTokenStart = endToken;
+    unsigned length;
+    if (!calculateLengthInPixels(lengthTokenStart, lengthTokenEnd, length))
+        return false;
+    RefPtr<MediaQuerySet> mediaCondition = MediaQueryParser::parseMediaCondition(startToken, endToken);
+    if (mediaCondition && mediaConditionMatches(mediaCondition)) {
+        m_length = length;
+        return true;
+    }
+    return false;
+}
+
+bool SizesAttributeParser::parse(Vector<MediaQueryToken>& tokens)
+{
+    TokenIterator startToken = tokens.begin();
+    TokenIterator endToken;
+    // Split on a comma token, and send the result tokens to be parsed as (media-condition, length) pairs
+    for (TokenIterator token = tokens.begin(); token != tokens.end(); ++token) {
+        if (token->type() == CommaToken) {
+            endToken = token;
+            if (parseMediaConditionAndLength(startToken, endToken))
+                return true;
+            startToken = token;
+            ++startToken;
+        }
+    }
+    endToken = tokens.end();
+    return parseMediaConditionAndLength(startToken, --endToken);
+}
+
+unsigned SizesAttributeParser::effectiveSize()
+{
+    if (m_length)
+        return m_length;
+    return effectiveSizeDefaultValue();
+}
+
+unsigned SizesAttributeParser::effectiveSizeDefaultValue()
+{
+    // Returning the equivalent of "100%"
+    return m_mediaValues->viewportWidth();
+}
+
+} // namespace
+