/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.transition;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ObjectAnimator;
import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;

import com.android.internal.R;

This transition tracks changes to the visibility of target views in the start and end scenes and fades views in or out when they become visible or non-visible. Visibility is determined by both the View.setVisibility(int) state of the view as well as whether it is parented in the current view hierarchy. 
The ability of this transition to fade out a particular view, and the way that that fading operation takes place, is based on the situation of the view in the view hierarchy. For example, if a view was simply removed from its parent, then the view will be added into a ViewGroupOverlay while fading. If a visible view is changed to be View.GONE or View.INVISIBLE, then the visibility will be changed to View.VISIBLE for the duration of the animation. However, if a view is in a hierarchy which is also altering its visibility, the situation can be more complicated. In general, if a view that is no longer in the hierarchy in the end scene still has a parent (so its parent hierarchy was removed, but it was not removed from its parent), then it will be left alone to avoid side-effects from improperly removing it from its parent. The only exception to this is if the previous Scene was 
created from a layout resource file, then it is considered safe to un-parent the starting scene view in order to fade it out.
A Fade transition can be described in a resource file by using the
tag fade, along with the standard attributes of Fade.Fade and Transition.Transition.
/**
 * This transition tracks changes to the visibility of target views in the
 * start and end scenes and fades views in or out when they become visible
 * or non-visible. Visibility is determined by both the
 * {@link View#setVisibility(int)} state of the view as well as whether it
 * is parented in the current view hierarchy.
 *
 * <p>The ability of this transition to fade out a particular view, and the
 * way that that fading operation takes place, is based on
 * the situation of the view in the view hierarchy. For example, if a view was
 * simply removed from its parent, then the view will be added into a {@link
 * android.view.ViewGroupOverlay} while fading. If a visible view is
 * changed to be {@link View#GONE} or {@link View#INVISIBLE}, then the
 * visibility will be changed to {@link View#VISIBLE} for the duration of
 * the animation. However, if a view is in a hierarchy which is also altering
 * its visibility, the situation can be more complicated. In general, if a
 * view that is no longer in the hierarchy in the end scene still has a
 * parent (so its parent hierarchy was removed, but it was not removed from
 * its parent), then it will be left alone to avoid side-effects from
 * improperly removing it from its parent. The only exception to this is if
 * the previous {@link Scene} was
 * {@link Scene#getSceneForLayout(android.view.ViewGroup, int, android.content.Context)
 * created from a layout resource file}, then it is considered safe to un-parent
 * the starting scene view in order to fade it out.</p>
 *
 * <p>A Fade transition can be described in a resource file by using the
 * tag <code>fade</code>, along with the standard
 * attributes of {@link android.R.styleable#Fade} and
 * {@link android.R.styleable#Transition}.</p>
 */
public class Fade extends Visibility {
    static final String PROPNAME_TRANSITION_ALPHA = "android:fade:transitionAlpha";

    private static boolean DBG = Transition.DBG && false;

    private static final String LOG_TAG = "Fade";

    
Fading mode used in Fade(int) to make the transition operate on targets that are appearing. Maybe be combined with OUT to fade both in and out. Equivalent to Visibility.MODE_IN. /**
     * Fading mode used in {@link #Fade(int)} to make the transition
     * operate on targets that are appearing. Maybe be combined with
     * {@link #OUT} to fade both in and out. Equivalent to
     * {@link Visibility#MODE_IN}.
     */
    public static final int IN = Visibility.MODE_IN;

    
Fading mode used in Fade(int) to make the transition operate on targets that are disappearing. Maybe be combined with IN to fade both in and out. Equivalent to Visibility.MODE_OUT. /**
     * Fading mode used in {@link #Fade(int)} to make the transition
     * operate on targets that are disappearing. Maybe be combined with
     * {@link #IN} to fade both in and out. Equivalent to
     * {@link Visibility#MODE_OUT}.
     */
    public static final int OUT = Visibility.MODE_OUT;

    
Constructs a Fade transition that will fade targets in and out.
/**
     * Constructs a Fade transition that will fade targets in and out.
     */
    public Fade() {
    }

    
Constructs a Fade transition that will fade targets in
and/or out, according to the value of fadingMode.
Params:
fadingMode – The behavior of this transition, a combination of IN and OUT./**
     * Constructs a Fade transition that will fade targets in
     * and/or out, according to the value of fadingMode.
     *
     * @param fadingMode The behavior of this transition, a combination of
     * {@link #IN} and {@link #OUT}.
     */
    public Fade(int fadingMode) {
        setMode(fadingMode);
    }

    public Fade(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.Fade);
        int fadingMode = a.getInt(R.styleable.Fade_fadingMode, getMode());
        setMode(fadingMode);
        a.recycle();
    }

    @Override
    public void captureStartValues(TransitionValues transitionValues) {
        super.captureStartValues(transitionValues);
        transitionValues.values.put(PROPNAME_TRANSITION_ALPHA,
                transitionValues.view.getTransitionAlpha());
    }

    
Utility method to handle creating and running the Animator.
/**
     * Utility method to handle creating and running the Animator.
     */
    private Animator createAnimation(final View view, float startAlpha, final float endAlpha) {
        if (startAlpha == endAlpha) {
            return null;
        }
        view.setTransitionAlpha(startAlpha);
        final ObjectAnimator anim = ObjectAnimator.ofFloat(view, "transitionAlpha", endAlpha);
        if (DBG) {
            Log.d(LOG_TAG, "Created animator " + anim);
        }
        final FadeAnimatorListener listener = new FadeAnimatorListener(view);
        anim.addListener(listener);
        addListener(new TransitionListenerAdapter() {
            @Override
            public void onTransitionEnd(Transition transition) {
                view.setTransitionAlpha(1);
                transition.removeListener(this);
            }
        });
        return anim;
    }

    @Override
    public Animator onAppear(ViewGroup sceneRoot, View view,
            TransitionValues startValues,
            TransitionValues endValues) {
        if (DBG) {
            View startView = (startValues != null) ? startValues.view : null;
            Log.d(LOG_TAG, "Fade.onAppear: startView, startVis, endView, endVis = " +
                    startView + ", " + view);
        }
        float startAlpha = getStartAlpha(startValues, 0);
        if (startAlpha == 1) {
            startAlpha = 0;
        }
        return createAnimation(view, startAlpha, 1);
    }

    @Override
    public Animator onDisappear(ViewGroup sceneRoot, final View view, TransitionValues startValues,
            TransitionValues endValues) {
        float startAlpha = getStartAlpha(startValues, 1);
        return createAnimation(view, startAlpha, 0);
    }

    private static float getStartAlpha(TransitionValues startValues, float fallbackValue) {
        float startAlpha = fallbackValue;
        if (startValues != null) {
            Float startAlphaFloat = (Float) startValues.values.get(PROPNAME_TRANSITION_ALPHA);
            if (startAlphaFloat != null) {
                startAlpha = startAlphaFloat;
            }
        }
        return startAlpha;
    }

    private static class FadeAnimatorListener extends AnimatorListenerAdapter {
        private final View mView;
        private boolean mLayerTypeChanged = false;

        public FadeAnimatorListener(View view) {
            mView = view;
        }

        @Override
        public void onAnimationStart(Animator animator) {
            if (mView.hasOverlappingRendering() && mView.getLayerType() == View.LAYER_TYPE_NONE) {
                mLayerTypeChanged = true;
                mView.setLayerType(View.LAYER_TYPE_HARDWARE, null);
            }
        }

        @Override
        public void onAnimationEnd(Animator animator) {
            mView.setTransitionAlpha(1);
            if (mLayerTypeChanged) {
                mView.setLayerType(View.LAYER_TYPE_NONE, null);
            }
        }
    }
}