Add feature extraction for distillability to Blink

third_party/WebKit/Source/core/dom/DocumentStatisticsCollector.cpp

Index: third_party/WebKit/Source/core/dom/DocumentStatisticsCollector.cpp
diff --git a/third_party/WebKit/Source/core/dom/DocumentStatisticsCollector.cpp b/third_party/WebKit/Source/core/dom/DocumentStatisticsCollector.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..695cecacf91063c9cf9df59f066948ce7c75d934
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+++ b/third_party/WebKit/Source/core/dom/DocumentStatisticsCollector.cpp
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+// Copyright 2015 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 "DocumentStatisticsCollector.h"
+
+#include "core/HTMLNames.h"
+#include "core/InputTypeNames.h"
+#include "core/dom/ElementTraversal.h"
+#include "core/dom/NodeComputedStyle.h"
+#include "core/dom/Text.h"
+#include "core/frame/FrameHost.h"
+#include "core/html/HTMLHeadElement.h"
+#include "core/html/HTMLInputElement.h"
+#include "core/html/HTMLMetaElement.h"
+#include "public/platform/Platform.h"
+#include "public/platform/WebDistillability.h"
+
+namespace blink {
+
+using namespace HTMLNames;
+
+namespace {
+
+// Saturate the length of a paragraph to save time.
+const int kTextContentLengthSaturation = 1000;
+
+// Filter out short P elements. The threshold is set to around 2 English sentences.
+const unsigned kParagraphLengthThreshold = 140;
+
+// Saturate the scores to save time. The max is the score of 6 long paragraphs.
+const double kMozScoreSaturation = 175.954539583; // 6 * sqrt(kTextContentLengthSaturation - kParagraphLengthThreshold)
+const double kMozScoreAllSqrtSaturation = 189.73665961; // 6 * sqrt(kTextContentLengthSaturation);
+const double kMozScoreAllLinearSaturation = 6 * kTextContentLengthSaturation;
+
+unsigned textContentLengthSaturated(Element& root)
+{
+    unsigned length = 0;
+    // This skips shadow DOM intentionally, to match the JavaScript implementation.
+    // We would like to use the same statistics extracted by the JavaScript implementation
+    // on iOS, and JavaScript cannot peek deeply into shadow DOM except on modern Chrome
+    // versions.
+    // Given shadow DOM rarely appears in <P> elements in long-form articles, the overall
+    // accuracy should not be largely affected.
+    for (Node& node : NodeTraversal::inclusiveDescendantsOf(root)) {
+        if (!node.isTextNode()) {
+            continue;
+        }
+        length += toText(node).length();
+        if (length > kTextContentLengthSaturation) {
+            return kTextContentLengthSaturation;
+        }
+    }
+    return length;
+}
+
+bool isVisible(const Element& element)
+{
+    const ComputedStyle* style = element.computedStyle();
+    if (!style)
+        return false;
+    return (
+        style->display() != NONE
+        && style->visibility() != HIDDEN
+        && style->opacity() != 0
+    );
+}
+
+bool matchAttributes(const Element& element, const Vector<String>& words)
+{
+    const String& classes = element.getClassAttribute();
+    const String& id = element.getIdAttribute();
+    for (const String& word : words) {
+        if (classes.findIgnoringCase(word) != WTF::kNotFound
+            || id.findIgnoringCase(word) != WTF::kNotFound) {
+            return true;
+        }
+    }
+    return false;
+}
+
+bool isGoodForScoring(const WebDistillabilityFeatures& features, const Element& element)
+{
+    DEFINE_STATIC_LOCAL(Vector<String>, unlikelyCandidates, ());
+    if (unlikelyCandidates.isEmpty()) {
+        auto words = {
+            "banner",
+            "combx",
+            "comment",
+            "community",
+            "disqus",
+            "extra",
+            "foot",
+            "header",
+            "menu",
+            "related",
+            "remark",
+            "rss",
+            "share",
+            "shoutbox",
+            "sidebar",
+            "skyscraper",
+            "sponsor",
+            "ad-break",
+            "agegate",
+            "pagination",
+            "pager",
+            "popup"
+        };
+        for (auto word : words) {
+            unlikelyCandidates.append(word);
+        }
+    }
+    DEFINE_STATIC_LOCAL(Vector<String>, highlyLikelyCandidates, ());
+    if (highlyLikelyCandidates.isEmpty()) {
+        auto words = {
+            "and",
+            "article",
+            "body",
+            "column",
+            "main",
+            "shadow"
+        };
+        for (auto word : words) {
+            highlyLikelyCandidates.append(word);
+        }
+    }
+
+    if (!isVisible(element))
+        return false;
+    if (features.mozScore >= kMozScoreSaturation
+        && features.mozScoreAllSqrt >= kMozScoreAllSqrtSaturation
+        && features.mozScoreAllLinear >= kMozScoreAllLinearSaturation)
+        return false;
+    if (matchAttributes(element, unlikelyCandidates)
+        && !matchAttributes(element, highlyLikelyCandidates))
+        return false;
+    return true;
+}
+
+// underListItem denotes that at least one of the ancesters is <li> element.
+void collectFeatures(Element& root, WebDistillabilityFeatures& features, bool underListItem = false)
+{
+    for (Node& node : NodeTraversal::childrenOf(root)) {
+        if (!node.isElementNode()) {
+            continue;
+        }
+
+        features.elementCount++;
+        Element& element = toElement(node);
+        if (element.hasTagName(aTag)) {
+            features.anchorCount++;
+        } else if (element.hasTagName(formTag)) {
+            features.formCount++;
+        } else if (element.hasTagName(inputTag)) {
+            const HTMLInputElement& input = toHTMLInputElement(element);
+            if (input.type() == InputTypeNames::text) {
+                features.textInputCount++;
+            } else if (input.type() == InputTypeNames::password) {
+                features.passwordInputCount++;
+            }
+        } else if (element.hasTagName(pTag) || element.hasTagName(preTag)) {
+            if (element.hasTagName(pTag)) {
+                features.pCount++;
+            } else {
+                features.preCount++;
+            }
+            if (!underListItem && isGoodForScoring(features, element)) {
+                unsigned length = textContentLengthSaturated(element);
+                if (length >= kParagraphLengthThreshold) {
+                    features.mozScore += sqrt(length - kParagraphLengthThreshold);
+                    features.mozScore = std::min(features.mozScore, kMozScoreSaturation);
+                }
+                features.mozScoreAllSqrt += sqrt(length);
+                features.mozScoreAllSqrt = std::min(features.mozScoreAllSqrt, kMozScoreAllSqrtSaturation);
+
+                features.mozScoreAllLinear += length;
+                features.mozScoreAllLinear = std::min(features.mozScoreAllLinear, kMozScoreAllLinearSaturation);
+            }
+        } else if (element.hasTagName(liTag)) {
+            underListItem = true;
+        }
+        collectFeatures(element, features, underListItem);
+    }
+}
+
+bool hasOpenGraphArticle(const Element& head)
+{
+    DEFINE_STATIC_LOCAL(AtomicString, ogType, ("og:type"));
+    DEFINE_STATIC_LOCAL(AtomicString, propertyAttr, ("property"));
+    for (const Element* child = ElementTraversal::firstChild(head); child; child = ElementTraversal::nextSibling(*child)) {
+        if (!isHTMLMetaElement(*child))
+            continue;
+        const HTMLMetaElement& meta = toHTMLMetaElement(*child);
+
+        if (meta.name() == ogType || meta.getAttribute(propertyAttr) == ogType) {
+            if (equalIgnoringCase(meta.content(), "article")) {
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
+bool isMobileFriendly(Document& document)
+{
+    if (FrameHost* frameHost = document.frameHost())
+        return frameHost->visualViewport().shouldDisableDesktopWorkarounds();
+    return false;
+}
+
+} // namespace
+
+WebDistillabilityFeatures DocumentStatisticsCollector::collectStatistics(Document& document)
+{
+    TRACE_EVENT0("blink", "DocumentStatisticsCollector::collectStatistics");
+
+    WebDistillabilityFeatures features = WebDistillabilityFeatures();
+
+    if (!document.frame() || !document.frame()->isMainFrame())
+        return features;
+
+    ASSERT(document.hasFinishedParsing());
+
+    HTMLElement* body = document.body();
+    HTMLElement* head = document.head();
+
+    if (!body || !head)
+        return features;
+
+    if (isMobileFriendly(document)) {
+        features.isMobileFriendly = true;
+        // We only trigger Reader Mode on non-mobile-friendly pages for now.
+        return features;
+    }
+
+    double startTime = monotonicallyIncreasingTime();
+
+    // This should be cheap since collectStatistics is only called right after layout.
+    document.updateLayoutTreeIfNeeded();
+
+    // Traverse the DOM tree and collect statistics.
+    collectFeatures(*body, features);
+    features.openGraph = hasOpenGraphArticle(*head);
+
+    double elapsedTime = monotonicallyIncreasingTime() - startTime;
+    Platform::current()->histogramCustomCounts("WebCore.DistillabilityUs", static_cast<int>(1e6 * elapsedTime), 1, 1000000, 50);
+
+    return features;
+}
+
+}