Created GreedyContents to clean up merge path handling (airbnb#362)

lottie/src/main/java/com/airbnb/lottie/ContentGroup.java

@@ -8,7 +8,6 @@
 import android.support.annotation.Nullable;
 
 import java.util.ArrayList;
-import java.util.Iterator;
 import java.util.List;
 
 class ContentGroup implements DrawingContent, PathContent,
@@ -38,32 +37,19 @@ class ContentGroup implements DrawingContent, PathContent,
       transformAnimation.addListener(this);
     }
 
+    List<GreedyContent> greedyContents = new ArrayList<>();
     for (int i = 0; i < items.size(); i++) {
       Content content = items.get(i).toContent(lottieDrawable, layer);
       if (content != null) {
         contents.add(content);
+        if (content instanceof GreedyContent) {
+          greedyContents.add((GreedyContent) content);
+        }
       }
     }
 
-    List<Content> contentsToRemove = new ArrayList<>();
-    MergePathsContent currentMergePathsContent = null;
-    for (int i = contents.size() - 1; i >= 0; i--) {
-      Content content = contents.get(i);
-      if (content instanceof MergePathsContent) {
-        currentMergePathsContent = (MergePathsContent) content;
-      }
-      if (currentMergePathsContent != null && content != currentMergePathsContent) {
-        currentMergePathsContent.addContentIfNeeded(content);
-        contentsToRemove.add(content);
-      }
-    }
-
-    Iterator<Content> it = contents.iterator();
-    while (it.hasNext()) {
-      Content content = it.next();
-      if (contentsToRemove.contains(content)) {
-        it.remove();
-      }
+    for (int i = greedyContents.size() - 1; i >= 0; i--) {
+      greedyContents.get(i).absorbContent(contents.listIterator(contents.size()));
     }
   }
 

lottie/src/main/java/com/airbnb/lottie/GreedyContent.java

@@ -0,0 +1,19 @@
+package com.airbnb.lottie;
+
+import java.util.ListIterator;
+
+/**
+ * Content that may want to absorb and take ownership of the content around it.
+ * For example, merge paths will absorb the shapes above it and repeaters will absorb the content
+ * above it.
+ */
+interface GreedyContent {
+  /**
+   * An iterator of contents that can be used to take ownership of contents. If ownership is taken,
+   * the content should be removed from the iterator.
+   *
+   * The contents should be iterated by calling hasPrevious() and previous() so that the list of
+   * contents is traversed from bottom to top which is the correct order for handling AE logic.
+   */
+  void absorbContent(ListIterator<Content> contents);
+}

lottie/src/main/java/com/airbnb/lottie/MergePathsContent.java

@@ -6,9 +6,10 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.ListIterator;
 
 @TargetApi(Build.VERSION_CODES.KITKAT)
-class MergePathsContent implements PathContent {
+class MergePathsContent implements PathContent, GreedyContent {
   private final Path firstPath = new Path();
   private final Path remainderPath = new Path();
   private final Path path = new Path();
@@ -25,9 +26,16 @@ class MergePathsContent implements PathContent {
     this.mergePaths = mergePaths;
   }
 
-  void addContentIfNeeded(Content content) {
-    if (content instanceof PathContent) {
-      pathContents.add((PathContent) content);
+  @Override public void absorbContent(ListIterator<Content> contents) {
+    // Fast forward the iterator until after this content.
+    //noinspection StatementWithEmptyBody
+    while (contents.hasPrevious() && contents.previous() != this) {}
+    while (contents.hasPrevious()) {
+      Content content = contents.previous();
+      if (content instanceof PathContent) {
+        pathContents.add((PathContent) content);
+        contents.remove();
+      }
     }
   }