/*
 * Copyright (C) 2010 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.widget;

import android.annotation.ColorInt;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.view.animation.AnimationUtils;
import android.view.animation.DecelerateInterpolator;
import android.view.animation.Interpolator;

This class performs the graphical effect used at the edges of scrollable widgets
when the user scrolls beyond the content bounds in 2D space.
EdgeEffect is stateful. Custom widgets using EdgeEffect should create an instance for each edge that should show the effect, feed it input data using the methods onAbsorb(int), onPull(float), and onRelease(), and draw the effect using draw(Canvas) in the widget's overridden View.draw(Canvas) method. If isFinished() returns false after drawing, the edge effect's animation is not yet complete and the widget should schedule another drawing pass to continue the animation.
When drawing, widgets should draw their main content and child views first,
usually by invoking super.draw(canvas) from an overridden draw method. (This will invoke onDraw and dispatch drawing to child views as needed.) The edge effect may then be drawn on top of the view's content using the draw(Canvas) method.
/**
 * This class performs the graphical effect used at the edges of scrollable widgets
 * when the user scrolls beyond the content bounds in 2D space.
 *
 * <p>EdgeEffect is stateful. Custom widgets using EdgeEffect should create an
 * instance for each edge that should show the effect, feed it input data using
 * the methods {@link #onAbsorb(int)}, {@link #onPull(float)}, and {@link #onRelease()},
 * and draw the effect using {@link #draw(Canvas)} in the widget's overridden
 * {@link android.view.View#draw(Canvas)} method. If {@link #isFinished()} returns
 * false after drawing, the edge effect's animation is not yet complete and the widget
 * should schedule another drawing pass to continue the animation.</p>
 *
 * <p>When drawing, widgets should draw their main content and child views first,
 * usually by invoking <code>super.draw(canvas)</code> from an overridden <code>draw</code>
 * method. (This will invoke onDraw and dispatch drawing to child views as needed.)
 * The edge effect may then be drawn on top of the view's content using the
 * {@link #draw(Canvas)} method.</p>
 */
public class EdgeEffect {
    @SuppressWarnings("UnusedDeclaration")
    private static final String TAG = "EdgeEffect";

    // Time it will take the effect to fully recede in ms
    private static final int RECEDE_TIME = 600;

    // Time it will take before a pulled glow begins receding in ms
    private static final int PULL_TIME = 167;

    // Time it will take in ms for a pulled glow to decay to partial strength before release
    private static final int PULL_DECAY_TIME = 2000;

    private static final float MAX_ALPHA = 0.15f;
    private static final float GLOW_ALPHA_START = .09f;

    private static final float MAX_GLOW_SCALE = 2.f;

    private static final float PULL_GLOW_BEGIN = 0.f;

    // Minimum velocity that will be absorbed
    private static final int MIN_VELOCITY = 100;
    // Maximum velocity, clamps at this value
    private static final int MAX_VELOCITY = 10000;

    private static final float EPSILON = 0.001f;

    private static final double ANGLE = Math.PI / 6;
    private static final float SIN = (float) Math.sin(ANGLE);
    private static final float COS = (float) Math.cos(ANGLE);
    private static final float RADIUS_FACTOR = 0.6f;

    private float mGlowAlpha;
    private float mGlowScaleY;

    private float mGlowAlphaStart;
    private float mGlowAlphaFinish;
    private float mGlowScaleYStart;
    private float mGlowScaleYFinish;

    private long mStartTime;
    private float mDuration;

    private final Interpolator mInterpolator;

    private static final int STATE_IDLE = 0;
    private static final int STATE_PULL = 1;
    private static final int STATE_ABSORB = 2;
    private static final int STATE_RECEDE = 3;
    private static final int STATE_PULL_DECAY = 4;

    private static final float PULL_DISTANCE_ALPHA_GLOW_FACTOR = 0.8f;

    private static final int VELOCITY_GLOW_FACTOR = 6;

    private int mState = STATE_IDLE;

    private float mPullDistance;

    private final Rect mBounds = new Rect();
    private final Paint mPaint = new Paint();
    private float mRadius;
    private float mBaseGlowScale;
    private float mDisplacement = 0.5f;
    private float mTargetDisplacement = 0.5f;

    
Construct a new EdgeEffect with a theme appropriate for the provided context.
Params:
context – Context used to provide theming and resource information for the EdgeEffect/**
     * Construct a new EdgeEffect with a theme appropriate for the provided context.
     * @param context Context used to provide theming and resource information for the EdgeEffect
     */
    public EdgeEffect(Context context) {
        mPaint.setAntiAlias(true);
        final TypedArray a = context.obtainStyledAttributes(
                com.android.internal.R.styleable.EdgeEffect);
        final int themeColor = a.getColor(
                com.android.internal.R.styleable.EdgeEffect_colorEdgeEffect, 0xff666666);
        a.recycle();
        mPaint.setColor((themeColor & 0xffffff) | 0x33000000);
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_ATOP));
        mInterpolator = new DecelerateInterpolator();
    }

    
Set the size of this edge effect in pixels.
Params:
width – Effect width in pixels
height – Effect height in pixels/**
     * Set the size of this edge effect in pixels.
     *
     * @param width Effect width in pixels
     * @param height Effect height in pixels
     */
    public void setSize(int width, int height) {
        final float r = width * RADIUS_FACTOR / SIN;
        final float y = COS * r;
        final float h = r - y;
        final float or = height * RADIUS_FACTOR / SIN;
        final float oy = COS * or;
        final float oh = or - oy;

        mRadius = r;
        mBaseGlowScale = h > 0 ? Math.min(oh / h, 1.f) : 1.f;

        mBounds.set(mBounds.left, mBounds.top, width, (int) Math.min(height, h));
    }

    
Reports if this EdgeEffect's animation is finished. If this method returns false after a call to draw(Canvas) the host widget should schedule another drawing pass to continue the animation. 
Returns:
true if animation is finished, false if drawing should continue on the next frame./**
     * Reports if this EdgeEffect's animation is finished. If this method returns false
     * after a call to {@link #draw(Canvas)} the host widget should schedule another
     * drawing pass to continue the animation.
     *
     * @return true if animation is finished, false if drawing should continue on the next frame.
     */
    public boolean isFinished() {
        return mState == STATE_IDLE;
    }

    
Immediately finish the current animation. After this call isFinished() will return true. /**
     * Immediately finish the current animation.
     * After this call {@link #isFinished()} will return true.
     */
    public void finish() {
        mState = STATE_IDLE;
    }

    
A view should call this when content is pulled away from an edge by the user. This will update the state of the current visual effect and its associated animation. The host view should always View.invalidate() after this and draw the results accordingly. 
Views using EdgeEffect should favor onPull(float, float) when the displacement of the pull point is known.
Params:
deltaDistance – Change in distance since the last call. Values may be 0 (no change) to
                     1.f (full length of the view) or negative values to express change
                     back toward the edge reached to initiate the effect./**
     * A view should call this when content is pulled away from an edge by the user.
     * This will update the state of the current visual effect and its associated animation.
     * The host view should always {@link android.view.View#invalidate()} after this
     * and draw the results accordingly.
     *
     * <p>Views using EdgeEffect should favor {@link #onPull(float, float)} when the displacement
     * of the pull point is known.</p>
     *
     * @param deltaDistance Change in distance since the last call. Values may be 0 (no change) to
     *                      1.f (full length of the view) or negative values to express change
     *                      back toward the edge reached to initiate the effect.
     */
    public void onPull(float deltaDistance) {
        onPull(deltaDistance, 0.5f);
    }

    
A view should call this when content is pulled away from an edge by the user. This will update the state of the current visual effect and its associated animation. The host view should always View.invalidate() after this and draw the results accordingly. 
Params:
deltaDistance – Change in distance since the last call. Values may be 0 (no change) to
                     1.f (full length of the view) or negative values to express change
                     back toward the edge reached to initiate the effect.
displacement – The displacement from the starting side of the effect of the point
                    initiating the pull. In the case of touch this is the finger position.
                    Values may be from 0-1./**
     * A view should call this when content is pulled away from an edge by the user.
     * This will update the state of the current visual effect and its associated animation.
     * The host view should always {@link android.view.View#invalidate()} after this
     * and draw the results accordingly.
     *
     * @param deltaDistance Change in distance since the last call. Values may be 0 (no change) to
     *                      1.f (full length of the view) or negative values to express change
     *                      back toward the edge reached to initiate the effect.
     * @param displacement The displacement from the starting side of the effect of the point
     *                     initiating the pull. In the case of touch this is the finger position.
     *                     Values may be from 0-1.
     */
    public void onPull(float deltaDistance, float displacement) {
        final long now = AnimationUtils.currentAnimationTimeMillis();
        mTargetDisplacement = displacement;
        if (mState == STATE_PULL_DECAY && now - mStartTime < mDuration) {
            return;
        }
        if (mState != STATE_PULL) {
            mGlowScaleY = Math.max(PULL_GLOW_BEGIN, mGlowScaleY);
        }
        mState = STATE_PULL;

        mStartTime = now;
        mDuration = PULL_TIME;

        mPullDistance += deltaDistance;

        final float absdd = Math.abs(deltaDistance);
        mGlowAlpha = mGlowAlphaStart = Math.min(MAX_ALPHA,
                mGlowAlpha + (absdd * PULL_DISTANCE_ALPHA_GLOW_FACTOR));

        if (mPullDistance == 0) {
            mGlowScaleY = mGlowScaleYStart = 0;
        } else {
            final float scale = (float) (Math.max(0, 1 - 1 /
                    Math.sqrt(Math.abs(mPullDistance) * mBounds.height()) - 0.3d) / 0.7d);

            mGlowScaleY = mGlowScaleYStart = scale;
        }

        mGlowAlphaFinish = mGlowAlpha;
        mGlowScaleYFinish = mGlowScaleY;
    }

    
Call when the object is released after being pulled. This will begin the "decay" phase of the effect. After calling this method the host view should View.invalidate() and thereby draw the results accordingly. /**
     * Call when the object is released after being pulled.
     * This will begin the "decay" phase of the effect. After calling this method
     * the host view should {@link android.view.View#invalidate()} and thereby
     * draw the results accordingly.
     */
    public void onRelease() {
        mPullDistance = 0;

        if (mState != STATE_PULL && mState != STATE_PULL_DECAY) {
            return;
        }

        mState = STATE_RECEDE;
        mGlowAlphaStart = mGlowAlpha;
        mGlowScaleYStart = mGlowScaleY;

        mGlowAlphaFinish = 0.f;
        mGlowScaleYFinish = 0.f;

        mStartTime = AnimationUtils.currentAnimationTimeMillis();
        mDuration = RECEDE_TIME;
    }

    
Call when the effect absorbs an impact at the given velocity.
Used when a fling reaches the scroll boundary.
When using a Scroller or OverScroller, the method getCurrVelocity will provide a reasonable approximation
to use here.
Params:
velocity – Velocity at impact in pixels per second./**
     * Call when the effect absorbs an impact at the given velocity.
     * Used when a fling reaches the scroll boundary.
     *
     * <p>When using a {@link android.widget.Scroller} or {@link android.widget.OverScroller},
     * the method <code>getCurrVelocity</code> will provide a reasonable approximation
     * to use here.</p>
     *
     * @param velocity Velocity at impact in pixels per second.
     */
    public void onAbsorb(int velocity) {
        mState = STATE_ABSORB;
        velocity = Math.min(Math.max(MIN_VELOCITY, Math.abs(velocity)), MAX_VELOCITY);

        mStartTime = AnimationUtils.currentAnimationTimeMillis();
        mDuration = 0.15f + (velocity * 0.02f);

        // The glow depends more on the velocity, and therefore starts out
        // nearly invisible.
        mGlowAlphaStart = GLOW_ALPHA_START;
        mGlowScaleYStart = Math.max(mGlowScaleY, 0.f);


        // Growth for the size of the glow should be quadratic to properly
        // respond
        // to a user's scrolling speed. The faster the scrolling speed, the more
        // intense the effect should be for both the size and the saturation.
        mGlowScaleYFinish = Math.min(0.025f + (velocity * (velocity / 100) * 0.00015f) / 2, 1.f);
        // Alpha should change for the glow as well as size.
        mGlowAlphaFinish = Math.max(
                mGlowAlphaStart, Math.min(velocity * VELOCITY_GLOW_FACTOR * .00001f, MAX_ALPHA));
        mTargetDisplacement = 0.5f;
    }

    
Set the color of this edge effect in argb.
Params:
color – Color in argb/**
     * Set the color of this edge effect in argb.
     *
     * @param color Color in argb
     */
    public void setColor(@ColorInt int color) {
        mPaint.setColor(color);
    }

    
Return the color of this edge effect in argb.
Returns:
The color of this edge effect in argb/**
     * Return the color of this edge effect in argb.
     * @return The color of this edge effect in argb
     */
    @ColorInt
    public int getColor() {
        return mPaint.getColor();
    }

    
Draw into the provided canvas. Assumes that the canvas has been rotated
accordingly and the size has been set. The effect will be drawn the full
width of X=0 to X=width, beginning from Y=0 and extending to some factor <
1.f of height.
Params:
canvas – Canvas to draw into
Returns:
true if drawing should continue beyond this frame to continue the
        animation/**
     * Draw into the provided canvas. Assumes that the canvas has been rotated
     * accordingly and the size has been set. The effect will be drawn the full
     * width of X=0 to X=width, beginning from Y=0 and extending to some factor <
     * 1.f of height.
     *
     * @param canvas Canvas to draw into
     * @return true if drawing should continue beyond this frame to continue the
     *         animation
     */
    public boolean draw(Canvas canvas) {
        update();

        final int count = canvas.save();

        final float centerX = mBounds.centerX();
        final float centerY = mBounds.height() - mRadius;

        canvas.scale(1.f, Math.min(mGlowScaleY, 1.f) * mBaseGlowScale, centerX, 0);

        final float displacement = Math.max(0, Math.min(mDisplacement, 1.f)) - 0.5f;
        float translateX = mBounds.width() * displacement / 2;

        canvas.clipRect(mBounds);
        canvas.translate(translateX, 0);
        mPaint.setAlpha((int) (0xff * mGlowAlpha));
        canvas.drawCircle(centerX, centerY, mRadius, mPaint);
        canvas.restoreToCount(count);

        boolean oneLastFrame = false;
        if (mState == STATE_RECEDE && mGlowScaleY == 0) {
            mState = STATE_IDLE;
            oneLastFrame = true;
        }

        return mState != STATE_IDLE || oneLastFrame;
    }

    
Return the maximum height that the edge effect will be drawn at given the original input size. 
Returns:
The maximum height of the edge effect/**
     * Return the maximum height that the edge effect will be drawn at given the original
     * {@link #setSize(int, int) input size}.
     * @return The maximum height of the edge effect
     */
    public int getMaxHeight() {
        return (int) (mBounds.height() * MAX_GLOW_SCALE + 0.5f);
    }

    private void update() {
        final long time = AnimationUtils.currentAnimationTimeMillis();
        final float t = Math.min((time - mStartTime) / mDuration, 1.f);

        final float interp = mInterpolator.getInterpolation(t);

        mGlowAlpha = mGlowAlphaStart + (mGlowAlphaFinish - mGlowAlphaStart) * interp;
        mGlowScaleY = mGlowScaleYStart + (mGlowScaleYFinish - mGlowScaleYStart) * interp;
        mDisplacement = (mDisplacement + mTargetDisplacement) / 2;

        if (t >= 1.f - EPSILON) {
            switch (mState) {
                case STATE_ABSORB:
                    mState = STATE_RECEDE;
                    mStartTime = AnimationUtils.currentAnimationTimeMillis();
                    mDuration = RECEDE_TIME;

                    mGlowAlphaStart = mGlowAlpha;
                    mGlowScaleYStart = mGlowScaleY;

                    // After absorb, the glow should fade to nothing.
                    mGlowAlphaFinish = 0.f;
                    mGlowScaleYFinish = 0.f;
                    break;
                case STATE_PULL:
                    mState = STATE_PULL_DECAY;
                    mStartTime = AnimationUtils.currentAnimationTimeMillis();
                    mDuration = PULL_DECAY_TIME;

                    mGlowAlphaStart = mGlowAlpha;
                    mGlowScaleYStart = mGlowScaleY;

                    // After pull, the glow should fade to nothing.
                    mGlowAlphaFinish = 0.f;
                    mGlowScaleYFinish = 0.f;
                    break;
                case STATE_PULL_DECAY:
                    mState = STATE_RECEDE;
                    break;
                case STATE_RECEDE:
                    mState = STATE_IDLE;
                    break;
            }
        }
    }
}