implement parser for new pagination algorithm

java/org/chromium/distiller/PageParameterParser.java

Index: java/org/chromium/distiller/PageParameterParser.java
diff --git a/java/org/chromium/distiller/PageParameterParser.java b/java/org/chromium/distiller/PageParameterParser.java
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+++ b/java/org/chromium/distiller/PageParameterParser.java
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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.
+
+package org.chromium.distiller;
+
+import org.chromium.distiller.proto.DomDistillerProtos;
+import org.chromium.distiller.proto.DomDistillerProtos.TimingInfo;
+
+import com.google.gwt.dom.client.AnchorElement;
+import com.google.gwt.dom.client.Document;
+import com.google.gwt.dom.client.Element;
+import com.google.gwt.dom.client.Node;
+import com.google.gwt.dom.client.NodeList;
+import com.google.gwt.dom.client.Style;
+import com.google.gwt.regexp.shared.MatchResult;
+import com.google.gwt.regexp.shared.RegExp;
+
+/**
+ * Background:
+ *   The long article/news/forum thread/blog document may be partitioned into several partial pages
+ *   by webmaster.  Each partial page has outlinks pointing to the adjacent partial pages.  The
+ *   anchor text of those outlinks is numeric.
+ *
+ * This class parses the document to collect groups of adjacent plain text numbers and outlinks with
+ * digital anchor text.  These are then passed to PageParameterParser which would spit out the
+ * pagination URLs if available.
+ */
+public class PageParameterParser {
+    // If the numeric value of a link's anchor text is greater than this number, we don't think it
+    // represents the page number of the link.
+    private static final int MAX_NUM_FOR_PAGE_PARAM = 100;
+
+    /**
+     * Stores PageParamInfo.PageInfo and the anchor's text, specifically returned by
+     * getPageInfoAndText().
+     */
+    private static class PageInfoAndText {
+        private final PageParamInfo.PageInfo mPageInfo;
+        private final String mText;
+
+        PageInfoAndText(int number, String url, String text) {
+            mPageInfo = new PageParamInfo.PageInfo(number, url);
+            mText = text;
+        }
+    }
+
+    /**
+     * Entry point for PageParameterParser.
+     * Parses the document to collect outlinks with numeric anchor text and numeric text around
+     * them.  These are then passed to PageParameterParser to detect pagination URLs.
+     *
+     * @return PageParamInfo (see PageParamInfo.java), always.  If no page parameter is detected or
+     * determined to be best, its mType is PageParamInfo.Type.UNSET.
+     *
+     * @param originalUrl the original URL of the document to be parsed.
+     * @param timingInfo for tracking performance.
+     */
+    public static PageParamInfo parse(String originalUrl, TimingInfo timingInfo) {
+        PageParameterParser parser = new PageParameterParser(timingInfo);
+        return parser.parseDocument(Document.get().getDocumentElement(), originalUrl);
+    }
+
+    private final TimingInfo mTimingInfo;
+    private String mDocUrl = "";
+    private ParsedUrl mParsedUrl = null;
+    private final MonotonicPageInfosGroups mAdjacentNumbersGroups = new MonotonicPageInfosGroups();
+    private int mNumForwardLinksProcessed = 0;
+
+    private static RegExp sHrefCleaner = RegExp.compile("\\/$");
+    private static RegExp sInvalidParentWrapper = null;
+
+    private PageParameterParser(TimingInfo timingInfo) {
+        mTimingInfo = timingInfo;
+    }
+
+    /**
+     * Acutually implements PageParameterParser.parse(), see above description for parse().
+     */
+    private PageParamInfo parseDocument(Element root, String originalUrl) {
+        double startTime = DomUtil.getTime();
+
+        mDocUrl = sHrefCleaner.replace(originalUrl, "");
+        mParsedUrl = ParsedUrl.create(mDocUrl);
+        if (mParsedUrl == null) return new PageParamInfo();  // Invalid document URL.
+
+        AnchorElement baseAnchor = PagingLinksFinder.createAnchorWithBase(
+                PagingLinksFinder.getBaseUrlForRelative(root, originalUrl));
+
+        NodeList<Element> allLinks = root.getElementsByTagName("A");
+        int idx = 0;
+        while (idx < allLinks.getLength()) {
+            final AnchorElement link = AnchorElement.as(allLinks.getItem(idx));
+            PageInfoAndText pageInfoAndText = getPageInfoAndText(link, baseAnchor);
+            if (pageInfoAndText == null) {
+                idx++;
+                continue;
+            }
+
+            // This link is a good candidate for pagination.
+
+            // Close current group of adjacent numbers, add a new group if necessary.
+            mAdjacentNumbersGroups.addGroup();
+
+            // Before we append the link to the new group of adjacent numbers, check if it's
+            // preceded by a text node with numeric text; if so, add it before the link.
+            findAndAddClosestValidLeafNodes(link, false, true, null);
+
+            // Add the link to the current group of adjacent numbers.
+            mAdjacentNumbersGroups.addPageInfo(pageInfoAndText.mPageInfo);
+
+            // Add all following text nodes and links with numeric text.
+            mNumForwardLinksProcessed = 0;
+            findAndAddClosestValidLeafNodes(link, false, false, baseAnchor);
+
+            // Skip the current link and links already processed in the forward
+            // findandAddClosestValidLeafNodes().
+            idx += 1 + mNumForwardLinksProcessed;
+        }  // while there're links.
+
+        mAdjacentNumbersGroups.cleanup();
+
+        LogUtil.addTimingInfo(startTime, mTimingInfo, "PageParameterParser");
+
+        startTime = DomUtil.getTime();
+        PageParamInfo info = PageParameterDetector.detect(mAdjacentNumbersGroups, mDocUrl);
+        LogUtil.addTimingInfo(startTime, mTimingInfo, "PageParameterDetector");
+        return info;
+    }
+
+    /**
+     * @return a populated PageInfoAndText if given link is to be added to mAdjacentNumbersGroups.
+     * Otherwise, returns null if link is to be ignored.
+     * "javascript:" links with numeric text are considered valid links to be added.
+     *
+     * @param link to process.
+     * @param baseAnchor created for the current document.
+     */
+    private PageInfoAndText getPageInfoAndText(AnchorElement link, AnchorElement baseAnchor) {
+        // Ignore invisible links.
+        if (!DomUtil.isVisible(link)) return null;
+
+        // Use javascript innerText (instead of javascript textContent) to only get visible text.
+        String linkText = StringUtil.jsTrim(DomUtil.getInnerText(link));
+        int number = linkTextToNumber(linkText);
+        if (!isPlainPageNumber(number)) return null;
+
+        String linkHref = resolveLinkHref(link, baseAnchor);
+        final boolean isEmptyHref = linkHref.isEmpty();
+        boolean isJavascriptLink = false;
+        ParsedUrl url = null;
+        if (!isEmptyHref) {
+            isJavascriptLink = isJavascriptHref(linkHref);
+            url = ParsedUrl.create(linkHref);
+            if (url == null ||
+                    (!isJavascriptLink && !url.getHost().equalsIgnoreCase(mParsedUrl.getHost()))) {
+                return null;
+            }
+            url.setHash("");
+        }
+
+        if (isEmptyHref || isJavascriptLink || isDisabledLink(link)) {
+            return new PageInfoAndText(number, "", linkText);
+        }
+
+        return new PageInfoAndText(number, sHrefCleaner.replace(url.toString(), ""), linkText);
+    }
+
+    /**
+     * Finds and adds the leaf node(s) closest to the given start node.
+     * This recurses and keeps finding and, if necessary, adding the numeric text of valid nodes,
+     * collecting the PageParamInfo.PageInfo's for the current adjacency group. 
+     * For backward search, i.e. nodes before start node, search terminates (i.e. recursion stops)
+     * once a text node or anchor is encountered.  If the text node contains numeric text, it's
+     * added to the current adjacency group.  Otherwise, a new group is created to break the
+     * adjacency.
+     * For forward search, i.e. nodes after start node, search continues (i.e. recursion continues)
+     * until a text node or anchor with non-numeric text is encountered.  In the process, text nodes
+     * and anchors with numeric text are added to the current adjaency group.  When a non-numeric
+     * text node or anchor is encountered, a new group is started to break the adjacency, and search
+     * ends.
+     *
+     * @return true to continue search, false to stop.
+     *
+     * @param start node to work on.
+     * @param checkStart true to check start node.  Otherwise, the previous or next sibling of the
+     * start node is checked.
+     * @param backward true to search backward (i.e. nodes before start node), false to search
+     * forward (i.e. nodes after start node).
+     * @param baseAnchor created for the current document, only needed for forward search.
+     */
+    private boolean findAndAddClosestValidLeafNodes(Node start, boolean checkStart,
+            boolean backward, AnchorElement baseAnchor) {
+        Node node = checkStart ? start :
+                (backward ? start.getPreviousSibling() : start.getNextSibling());
+        if (node == null) {  // No sibling, try parent.
+            node = start.getParentNode();
+            if (sInvalidParentWrapper == null) {
+                sInvalidParentWrapper = RegExp.compile("(BODY)|(HTML)");
+            }
+            if (sInvalidParentWrapper.test(node.getNodeName())) return false;
+            return findAndAddClosestValidLeafNodes(node, false, backward, baseAnchor);
+        }
+
+        checkStart = false;
+        switch (node.getNodeType()) {
+            case Node.TEXT_NODE:
+                String text = node.getNodeValue();
+                // Text must contain words.
+                if (text.isEmpty() || StringUtil.countWords(text) == 0) break;
+                boolean added = addNonLinkTextIfValid(node.getNodeValue());
+                // For backward search, we're done regardless if text was added.
+                // For forward search, we're done only if text was invalid, otherwise continue.
+                if (backward || !added) return false;
+                break;
+
+            case Node.ELEMENT_NODE:
+                Element e = Element.as(node);
+                if (e.hasTagName("A")) {
+                    // For backward search, we're done because we've already processed the anchor.
+                    if (backward) return false;
+                    // For forward search, we're done only if link was invalid, otherwise continue.
+                    mNumForwardLinksProcessed++;
+                    if (!addLinkIfValid(AnchorElement.as(e), baseAnchor)) return false;
+                    break;
+                }
+                // Intentionally fall through.
+
+            default:
+                // Check children nodes.
+                if (!node.hasChildNodes()) break;
+                checkStart = true;  // We want to check the child node.
+                if (backward) {
+                    // Start the backward search with the rightmost child i.e. last and closest to
+                    // given node.
+                    node = node.getLastChild();
+                } else {
+                    // Start the forward search with the leftmost child i.e. first and closest to
+                    // given node.
+                    node = node.getFirstChild();
+                }
+                break;
+        }
+
+        return findAndAddClosestValidLeafNodes(node, checkStart, backward, baseAnchor);
+    }
+
+    private static RegExp sTermsRegExp = null;  // Match terms i.e. words.
+    private static RegExp sSurroundingDigitsRegExp = null;  // Match term with only digits.
+
+    /**
+     * Handle the text for a non-link node.  Each numeric term in the text that is a valid plain
+     * page number adds a PageParamInfo.PageInfo into the current adjacent group.  All other terms
+     * break the adjacency in the current group, adding a new group instead.
+     *
+     * @Return true if text was added to current group of adjacent numbers.  Otherwise, false with
+     * a new group created to break the current adjacency.
+     */
+    private boolean addNonLinkTextIfValid(String text) {
+        if (!StringUtil.containsDigit(text)) {
+            // The text does not contain valid number(s); if necessary, current group of adjacent
+            // numbers should be closed, adding a new group if possible.
+            mAdjacentNumbersGroups.addGroup();
+            return false;
+        }
+
+        if (sTermsRegExp == null) {
+            sTermsRegExp = RegExp.compile("(\\S*[\\w\u00C0-\u1FFF\u2C00-\uD7FF]\\S*)", "gi");
+        } else {
+            sTermsRegExp.setLastIndex(0);
+        }
+        if (sSurroundingDigitsRegExp == null) {
+            sSurroundingDigitsRegExp = RegExp.compile("^[\\W_]*(\\d+)[\\W_]*$", "i");
+        }
+
+        // Extract terms from the text, differentiating between those that contain only digits and
+        // those that contain non-digits.
+        boolean added = false;
+        while (true) {
+            MatchResult match = sTermsRegExp.exec(text);
+            if (match == null) break;
+            if (match.getGroupCount() <= 1) continue;
+
+            String term = match.getGroup(1);
+            MatchResult termWithDigits = sSurroundingDigitsRegExp.exec(term);
+            int number = -1;
+            if (termWithDigits != null && termWithDigits.getGroupCount() > 1) {
+                number = StringUtil.toNumber(termWithDigits.getGroup(1));
+            }
+            if (isPlainPageNumber(number)) {
+                // This text is a valid candidate of plain text page number, add it to last group of
+                // adjacent numbers.
+                mAdjacentNumbersGroups.addNumber(number, "");
+                added = true;
+            } else {
+                // The text is not a valid number, so current group of adjacent numbers should be
+                // closed, adding a new group if possible.
+               mAdjacentNumbersGroups.addGroup();
+            }
+        }  // while there're matches
+
+        return added;
+    }
+
+    /**
+     * Adds PageParamInfo.PageInfo to the current adjacent group for a link if its text is numeric.
+     * Otherwise, add a new group to break the adjacency.
+     *
+     * @Return true if link was added, false otherwise.
+     */
+    private boolean addLinkIfValid(AnchorElement link, AnchorElement baseAnchor) {
+        PageInfoAndText pageInfoAndText = getPageInfoAndText(link, baseAnchor);
+        if (pageInfoAndText != null) {
+            mAdjacentNumbersGroups.addPageInfo(pageInfoAndText.mPageInfo);
+            return true;
+        }
+        mAdjacentNumbersGroups.addGroup();
+        return false;
+    }
+
+    /**
+     * @return true if link is disabled i.e. not clickable because it has a text cursor.
+     */
+    private static boolean isDisabledLink(AnchorElement link) {
+        Style style = DomUtil.getComputedStyle(link);
+        return Style.Cursor.valueOf(style.getCursor().toUpperCase()) == Style.Cursor.TEXT;
+    }
+
+    /**
+     * @return true if href starts with "javascript:".
+     */
+    private static boolean isJavascriptHref(String href) {
+        return href.startsWith("javascript:");
+    }
+
+    private static String resolveLinkHref(AnchorElement link, AnchorElement baseAnchor) {
+        // Anchors without "href" attribute are not considered potential pagination links.
+        String linkHref = link.getAttribute("href");
+        if (linkHref.isEmpty()) return "";
+        baseAnchor.setAttribute("href", linkHref);
+        return baseAnchor.getHref();
+    }
+
+    private static int linkTextToNumber(String linkText) {
+        linkText = linkText.replaceAll("[()\\[\\]{}]", "");
+        linkText = linkText.trim();  // Remove leading and trailing whitespaces.
+        return StringUtil.toNumber(linkText);
+    }
+
+    /**
+     * @returns true if number is >= 0 && < MAX_NUM_FOR_PAGE_PARAM.
+     */
+    private static boolean isPlainPageNumber(int number) {
+        return number >= 0 && number <= MAX_NUM_FOR_PAGE_PARAM;
+    }
+
+}