From 7faedcc5ceecc78a015b9cb33d042a5c79f0558a Mon Sep 17 00:00:00 2001
From: Mark Wei <markwei@google.com>
Date: Wed, 7 Dec 2016 18:09:10 -0800
Subject: [PATCH] Implement map() for android.

Summary: Fixes https://github.com/material-motion/streams-android/issues/2

Reviewers: featherless, O2 Material Motion, O6 Material Motion Android platform reviewers

Reviewed By: featherless, O2 Material Motion, O6 Material Motion Android platform reviewers

Subscribers: featherless

Tags: #material_motion

Differential Revision: http://codereview.cc/D2157
---
 .../motion/streams/MotionObservable.java      | 43 +++++++++++++++----
 .../motion/streams/sample/MainActivity.java   | 11 +++--
 2 files changed, 40 insertions(+), 14 deletions(-)

diff --git a/library/src/main/java/com/google/android/material/motion/streams/MotionObservable.java b/library/src/main/java/com/google/android/material/motion/streams/MotionObservable.java
index 633383b..6b64579 100644
--- a/library/src/main/java/com/google/android/material/motion/streams/MotionObservable.java
+++ b/library/src/main/java/com/google/android/material/motion/streams/MotionObservable.java
@@ -74,36 +74,49 @@ public interface MotionObserver<T> extends Observer<T> {
     void next(T value);
 
     /**
-     * A method to handle new state values from upstream.
+     * A method to handle new incoming state values.
      */
     void state(@MotionState int state);
   }
 
   /**
    * An operation is able to transform incoming values before choosing whether or not to pass them
-   * downstream.
+   * to the observer.
    *
    * @param <T> The incoming value type.
-   * @param <U> The downstream value type.
+   * @param <U> The observer value type.
    */
   public interface Operation<T, U> {
 
     /**
-     * Modifies the given value before passing it downstream, or blocks the value.
+     * Transforms the incoming value before passing it to the observer, or blocks the value.
      *
-     * @param observer Downstream.
-     * @param value The value from upstream.
+     * @param value The incoming value.
      */
     void next(MotionObserver<U> observer, T value);
   }
 
+  /**
+   * A transformation transforms incoming values before they are passed downstream.
+   *
+   * @param <T> The incoming value type.
+   * @param <U> The downstream value type.
+   */
+  public interface Transformation<T, U> {
+
+    /**
+     * Transforms the given value.
+     */
+    U transform(T value);
+  }
+
   /**
    * A predicate evaluates whether to pass a value downstream.
    */
   public interface Predicate<T> {
 
     /**
-     * Evaluates whether to pass the value downstream.
+     * Evaluates whether to pass the value.
      */
     boolean evaluate(T value);
   }
@@ -147,6 +160,21 @@ public void unsubscribe() {
     });
   }
 
+  /**
+   * Transform the items emitted by an Observable by applying a function to each item.
+   *
+   * @see <a href="https://material-motion.github.io/material-motion/starmap/specifications/streams/operators/$._map">The
+   * filter() specification</a>
+   */
+  public <U> MotionObservable<U> map(final Transformation<T, U> transformation) {
+    return operator(new Operation<T, U>() {
+      @Override
+      public void next(MotionObserver<U> observer, T value) {
+        observer.next(transformation.transform(value));
+      }
+    });
+  }
+
   /**
    * Only emit those values from an Observable that satisfy a predicate.
    *
@@ -155,7 +183,6 @@ public void unsubscribe() {
    */
   public MotionObservable<T> filter(final Predicate<T> predicate) {
     return operator(new Operation<T, T>() {
-
       @Override
       public void next(MotionObserver<T> observer, T value) {
         if (predicate.evaluate(value)) {
diff --git a/sample/src/main/java/com/google/android/material/motion/streams/sample/MainActivity.java b/sample/src/main/java/com/google/android/material/motion/streams/sample/MainActivity.java
index eaa170d..6bc7080 100644
--- a/sample/src/main/java/com/google/android/material/motion/streams/sample/MainActivity.java
+++ b/sample/src/main/java/com/google/android/material/motion/streams/sample/MainActivity.java
@@ -33,7 +33,6 @@
 import com.google.android.material.motion.streams.MotionObservable;
 import com.google.android.material.motion.streams.MotionObservable.MotionObserver;
 import com.google.android.material.motion.streams.MotionObservable.MotionState;
-import com.google.android.material.motion.streams.MotionObservable.Operation;
 
 import static com.google.android.material.motion.streams.MotionObservable.ACTIVE;
 import static com.google.android.material.motion.streams.MotionObservable.AT_REST;
@@ -85,14 +84,14 @@ public boolean evaluate(String value) {
           return value != "skip";
         }
       })
-      .operator(new Operation<String, CharSequence>() {
+      .map(new MotionObservable.Transformation<String, CharSequence>() {
 
         @Override
-        public void next(MotionObserver<CharSequence> observer, String value) {
-          CharSequence charSequence = italicizeAndCapitalize(value);
-          observer.next(charSequence);
+        public CharSequence transform(String value) {
+          return italicizeAndCapitalize(value);
         }
-      }).subscribe(new MotionObserver<CharSequence>() {
+      })
+      .subscribe(new MotionObserver<CharSequence>() {
 
         @Override
         public void next(CharSequence value) {