Add CSS Specificity score system to WebvttCssStyle

This CL provides the necessary infrastructure to add styling by class. This was separated
into two different CLs to ease reviewing.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120336976

library/src/androidTest/java/com/google/android/exoplayer/text/webvtt/CssParserTest.java

@@ -178,6 +178,36 @@ public final class CssParserTest extends InstrumentationTestCase {
     assertEquals(CssParser.parseNextToken(input, builder), null);
   }
 
+  public void testStyleScoreSystem() {
+    WebvttCssStyle style = new WebvttCssStyle();
+    // Universal selector.
+    assertEquals(1, style.getSpecificityScore(null, null, new String[0], null));
+    // Class match without tag match.
+    style.setTargetClasses(new String[] { "class1", "class2"});
+    assertEquals(8, style.getSpecificityScore(null, null,
+        new String[] { "class1", "class2", "class3" }, null));
+    // Class and tag match
+    style.setTargetTagName("b");
+    assertEquals(10, style.getSpecificityScore(null, "b",
+        new String[] { "class1", "class2", "class3" }, null));
+    // Class insufficiency.
+    assertEquals(0, style.getSpecificityScore(null, "b", new String[] { "class1", "class" }, null));
+    // Voice, classes and tag match.
+    style.setTargetVoice("Manuel Cráneo");
+    assertEquals(14, style.getSpecificityScore(null, "b",
+        new String[] { "class1", "class2", "class3" }, "Manuel Cráneo"));
+    // Voice mismatch.
+    assertEquals(0, style.getSpecificityScore(null, "b",
+        new String[] { "class1", "class2", "class3" }, "Manuel Craneo"));
+    // Id, voice, classes and tag match.
+    style.setTargetId("id");
+    assertEquals(0x40000000 + 14, style.getSpecificityScore("id", "b",
+        new String[] { "class1", "class2", "class3" }, "Manuel Cráneo"));
+    // Id mismatch.
+    assertEquals(0, style.getSpecificityScore("id1", "b",
+        new String[] { "class1", "class2", "class3" }, null));
+  }
+
   // Utility methods.
 
   private void assertSkipsToEndOfSkip(String expectedLine, String s) {

library/src/main/java/com/google/android/exoplayer/text/webvtt/WebvttCssStyle.java

@@ -20,6 +20,10 @@ import com.google.android.exoplayer.util.Util;
 import android.graphics.Typeface;
 import android.text.Layout;
 
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
 /**
  * Style object of a Css style block in a Webvtt file.
  *
@@ -42,6 +46,13 @@ import android.text.Layout;
   private static final int OFF = 0;
   private static final int ON = 1;
 
+  // Selector properties.
+  private String targetId;
+  private String targetTag;
+  private List<String> targetClasses;
+  private String targetVoice;
+
+  // Style properties.
   private String fontFamily;
   private int fontColor;
   private boolean hasFontColor;
@@ -60,6 +71,10 @@ import android.text.Layout;
   }
 
   public void reset() {
+    targetId = "";
+    targetTag = "";
+    targetClasses = Collections.emptyList();
+    targetVoice = "";
     fontFamily = null;
     hasFontColor = false;
     hasBackgroundColor = false;
@@ -71,6 +86,59 @@ import android.text.Layout;
     textAlign = null;
   }
 
+  public void setTargetId(String targetId) {
+    this.targetId  = targetId;
+  }
+
+  public void setTargetTagName(String targetTag) {
+    this.targetTag = targetTag;
+  }
+
+  public void setTargetClasses(String[] targetClasses) {
+    this.targetClasses = Arrays.asList(targetClasses);
+  }
+
+  public void setTargetVoice(String targetVoice) {
+    this.targetVoice = targetVoice;
+  }
+
+  /**
+   * Returns a value in a score system compliant with the CSS Specificity rules.
+   *
+   * @see <a href="https://www.w3.org/TR/CSS2/cascade.html">CSS Cascading</a>
+   *
+   * The score works as follows:
+   * <ul>
+   * <li> Id match adds 0x40000000 to the score.
+   * <li> Each class and voice match adds 4 to the score.
+   * <li> Tag matching adds 2 to the score.
+   * <li> Universal selector matching scores 1.
+   * </ul>
+   *
+   * @param id The id of the cue if present, {@code null} otherwise.
+   * @param tag Name of the tag, {@code null} if it refers to the entire cue.
+   * @param classes An array containing the classes the tag belongs to. Must not be null.
+   * @param voice Annotated voice if present, {@code null} otherwise.
+   * @return The score of the match, zero if there is no match.
+   */
+  public int getSpecificityScore(String id, String tag, String[] classes, String voice) {
+    if (targetId.isEmpty() && targetTag.isEmpty() && targetClasses.isEmpty()
+        && targetVoice.isEmpty()) {
+      // The selector is universal. It matches with the minimum score.
+      return 1;
+    }
+    int score = 0;
+    score = updateScoreForMatch(score, targetId, id, 0x40000000);
+    score = updateScoreForMatch(score, targetTag, tag, 2);
+    score = updateScoreForMatch(score, targetVoice, voice, 4);
+    if (score == -1 || !Arrays.asList(classes).containsAll(targetClasses)) {
+      return 0;
+    } else {
+      score += targetClasses.size() * 4;
+    }
+    return score;
+  }
+
   /**
    * Returns the style or {@link #UNSPECIFIED} when no style information is given.
    *
@@ -214,5 +282,12 @@ import android.text.Layout;
     }
   }
 
+  private static int updateScoreForMatch(int currentScore, String target, String actual,
+      int score) {
+    if (target.isEmpty() || currentScore == -1) {
+      return currentScore;
+    }
+    return target.equals(actual) ? currentScore + score : -1;
+  }
 
 }

library/src/main/java/com/google/android/exoplayer/text/webvtt/WebvttCueParser.java

@@ -211,10 +211,10 @@ import java.util.regex.Pattern;
       }
     }
     // apply unclosed tags
+    applyStyleToText(spannedText, styleMap.get(UNIVERSAL_CUE_ID), 0, spannedText.length());
     while (!startTagStack.isEmpty()) {
       applySpansForTag(startTagStack.pop(), spannedText, styleMap);
     }
-    applyStyleToText(spannedText, styleMap.get(UNIVERSAL_CUE_ID), 0, spannedText.length());
     applyStyleToText(spannedText, styleMap.get(CUE_ID_PREFIX + id), 0, spannedText.length());
     builder.setText(spannedText);
   }