/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.geckoview;

import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.BlendMode;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.os.Build;
import android.widget.EdgeEffect;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.annotation.UiThread;
import java.lang.reflect.Field;
import org.mozilla.gecko.util.ThreadUtils;

@UiThread
public final class OverscrollEdgeEffect {
  // Used to index particular edges in the edges array
  private static final int TOP = 0;
  private static final int BOTTOM = 1;
  private static final int LEFT = 2;
  private static final int RIGHT = 3;

  /* package */ static final int AXIS_X = 0;
  /* package */ static final int AXIS_Y = 1;

  // All four edges of the screen
  private final EdgeEffect[] mEdges = new EdgeEffect[4];

  private GeckoSession mSession;
  private Runnable mInvalidationCallback;
  private int mWidth;
  private int mHeight;

  /* package */ OverscrollEdgeEffect() {}

  private static Field sPaintField;

  @SuppressLint("DiscouragedPrivateApi")
  private void setBlendMode(final EdgeEffect edgeEffect) {
    if (Build.VERSION.SDK_INT < 29) {
      // setBlendMode is only supported on SDK_INT >= 29 and above.

      if (sPaintField == null) {
        try {
          sPaintField = EdgeEffect.class.getDeclaredField("mPaint");
          sPaintField.setAccessible(true);
        } catch (final NoSuchFieldException e) {
          // Cannot get the field, nothing we can do here
          return;
        }
      }

      try {
        final Paint paint = (Paint) sPaintField.get(edgeEffect);
        final PorterDuffXfermode mode = new PorterDuffXfermode(PorterDuff.Mode.SRC);
        paint.setXfermode(mode);
      } catch (final IllegalAccessException ex) {
        // Nothing we can do
      }

      return;
    }

    edgeEffect.setBlendMode(BlendMode.SRC);
  }

  /**
   * Set the theme to use for overscroll from a given Context.
   *
   * @param context Context to use for the overscroll theme.
   */
  public void setTheme(final @NonNull Context context) {
    ThreadUtils.assertOnUiThread();

    for (int i = 0; i < mEdges.length; i++) {
      final EdgeEffect edgeEffect = new EdgeEffect(context);
      if (mWidth != 0 || mHeight != 0) {
        edgeEffect.setSize(mWidth, mHeight);
      }
      setBlendMode(edgeEffect);
      mEdges[i] = edgeEffect;
    }
  }

  /* package */ void setSession(final @Nullable GeckoSession session) {
    mSession = session;
  }

  /**
   * Set a Runnable that acts as a callback to invalidate the overscroll effect (for example, as a
   * response to user fling for example). The Runnbale should schedule a future call to {@link
   * #draw(Canvas)} as a result of the invalidation.
   *
   * @param runnable Invalidation Runnable.
   * @see #getInvalidationCallback()
   */
  public void setInvalidationCallback(final @Nullable Runnable runnable) {
    ThreadUtils.assertOnUiThread();
    mInvalidationCallback = runnable;
  }

  /**
   * Get the current invalidatation Runnable.
   *
   * @return Invalidation Runnable.
   * @see #setInvalidationCallback(Runnable)
   */
  public @Nullable Runnable getInvalidationCallback() {
    ThreadUtils.assertOnUiThread();
    return mInvalidationCallback;
  }

  /* package */ void setSize(final int width, final int height) {
    mEdges[LEFT].setSize(height, width);
    mEdges[RIGHT].setSize(height, width);
    mEdges[TOP].setSize(width, height);
    mEdges[BOTTOM].setSize(width, height);

    mWidth = width;
    mHeight = height;
  }

  private EdgeEffect getEdgeForAxisAndSide(final int axis, final float side) {
    if (axis == AXIS_Y) {
      if (side < 0) {
        return mEdges[TOP];
      } else {
        return mEdges[BOTTOM];
      }
    } else {
      if (side < 0) {
        return mEdges[LEFT];
      } else {
        return mEdges[RIGHT];
      }
    }
  }

  /* package */ void setVelocity(final float velocity, final int axis) {
    if (velocity == 0.0f) {
      if (axis == AXIS_Y) {
        mEdges[TOP].onRelease();
        mEdges[BOTTOM].onRelease();
      } else {
        mEdges[LEFT].onRelease();
        mEdges[RIGHT].onRelease();
      }

      if (mInvalidationCallback != null) {
        mInvalidationCallback.run();
      }
      return;
    }

    final EdgeEffect edge = getEdgeForAxisAndSide(axis, velocity);

    // If we're showing overscroll already, start fading it out.
    if (!edge.isFinished()) {
      edge.onRelease();
    } else {
      // Otherwise, show an absorb effect
      edge.onAbsorb((int) velocity);
    }

    if (mInvalidationCallback != null) {
      mInvalidationCallback.run();
    }
  }

  /* package */ void setDistance(final float distance, final int axis) {
    // The first overscroll event often has zero distance. Throw it out
    if (distance == 0.0f) {
      return;
    }

    final EdgeEffect edge = getEdgeForAxisAndSide(axis, (int) distance);
    edge.onPull(distance / (axis == AXIS_X ? mWidth : mHeight));

    if (mInvalidationCallback != null) {
      mInvalidationCallback.run();
    }
  }

  /**
   * Draw the overscroll effect on a Canvas.
   *
   * @param canvas Canvas to draw on.
   */
  public void draw(final @NonNull Canvas canvas) {
    ThreadUtils.assertOnUiThread();

    if (mSession == null) {
      return;
    }

    final Rect pageRect = new Rect();
    mSession.getSurfaceBounds(pageRect);

    // If we're pulling an edge, or fading it out, draw!
    boolean invalidate = false;
    if (!mEdges[TOP].isFinished()) {
      invalidate |= draw(mEdges[TOP], canvas, pageRect.left, pageRect.top, 0);
    }

    if (!mEdges[BOTTOM].isFinished()) {
      invalidate |= draw(mEdges[BOTTOM], canvas, pageRect.right, pageRect.bottom, 180);
    }

    if (!mEdges[LEFT].isFinished()) {
      invalidate |= draw(mEdges[LEFT], canvas, pageRect.left, pageRect.bottom, 270);
    }

    if (!mEdges[RIGHT].isFinished()) {
      invalidate |= draw(mEdges[RIGHT], canvas, pageRect.right, pageRect.top, 90);
    }

    // If the edge effect is animating off screen, invalidate.
    if (invalidate && mInvalidationCallback != null) {
      mInvalidationCallback.run();
    }
  }

  private static boolean draw(
      final EdgeEffect edge,
      final Canvas canvas,
      final float translateX,
      final float translateY,
      final float rotation) {
    final int state = canvas.save();
    canvas.translate(translateX, translateY);
    canvas.rotate(rotation);
    final boolean invalidate = edge.draw(canvas);
    canvas.restoreToCount(state);

    return invalidate;
  }
}
