/* 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_example;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import androidx.core.view.NestedScrollingChild;
import androidx.core.view.NestedScrollingChildHelper;
import androidx.core.view.ViewCompat;
import org.mozilla.geckoview.GeckoView;
import org.mozilla.geckoview.PanZoomController;

/**
 * GeckoView that supports nested scrolls (for using in a CoordinatorLayout).
 *
 * <p>This code is a simplified version of the NestedScrollView implementation which can be found in
 * the support library: [android.support.v4.widget.NestedScrollView]
 *
 * <p>Based on: https://github.com/takahirom/webview-in-coordinatorlayout
 */
public class NestedGeckoView extends GeckoView implements NestedScrollingChild {

  private int mLastY;
  private final int[] mScrollOffset = new int[2];
  private final int[] mScrollConsumed = new int[2];
  private int mNestedOffsetY;
  private NestedScrollingChildHelper mChildHelper;

  /**
   * Integer indicating how user's MotionEvent was handled.
   *
   * <p>There must be a 1-1 relation between this values and [EngineView.InputResult]'s.
   */
  private int mInputResult = PanZoomController.INPUT_RESULT_UNHANDLED;

  public NestedGeckoView(final Context context) {
    this(context, null);
  }

  public NestedGeckoView(final Context context, final AttributeSet attrs) {
    super(context, attrs);
    mChildHelper = new NestedScrollingChildHelper(this);
    setNestedScrollingEnabled(true);
  }

  @Override
  public boolean onTouchEvent(MotionEvent ev) {
    MotionEvent event = MotionEvent.obtain(ev);
    final int action = event.getActionMasked();
    int eventY = (int) event.getY();

    switch (action) {
      case MotionEvent.ACTION_MOVE:
        final boolean allowScroll =
            !shouldPinOnScreen() && mInputResult == PanZoomController.INPUT_RESULT_HANDLED;
        int deltaY = mLastY - eventY;

        if (allowScroll && dispatchNestedPreScroll(0, deltaY, mScrollConsumed, mScrollOffset)) {
          deltaY -= mScrollConsumed[1];
          event.offsetLocation(0f, -mScrollOffset[1]);
          mNestedOffsetY += mScrollOffset[1];
        }

        mLastY = eventY - mScrollOffset[1];

        if (allowScroll && dispatchNestedScroll(0, mScrollOffset[1], 0, deltaY, mScrollOffset)) {
          mLastY -= mScrollOffset[1];
          event.offsetLocation(0f, mScrollOffset[1]);
          mNestedOffsetY += mScrollOffset[1];
        }
        break;

      case MotionEvent.ACTION_DOWN:
        // A new gesture started. Reset handled status and ask GV if it can handle this.
        mInputResult = PanZoomController.INPUT_RESULT_UNHANDLED;
        updateInputResult(event);

        mNestedOffsetY = 0;
        mLastY = eventY;

        // The event should be handled either by onTouchEvent,
        // either by onTouchEventForResult, never by both.
        // Early return if we sent it to updateInputResult(..) which calls onTouchEventForResult.
        event.recycle();
        return true;

        // We don't care about other touch events
      case MotionEvent.ACTION_UP:
      case MotionEvent.ACTION_CANCEL:
        stopNestedScroll();
        break;
    }

    // Execute event handler from parent class in all cases
    final boolean eventHandled = callSuperOnTouchEvent(event);

    // Recycle previously obtained event
    event.recycle();

    return eventHandled;
  }

  private boolean callSuperOnTouchEvent(MotionEvent event) {
    return super.onTouchEvent(event);
  }

  private void updateInputResult(MotionEvent event) {
    super.onTouchEventForDetailResult(event)
        .accept(
            inputResult -> {
              mInputResult = inputResult.handledResult();
              startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
            });
  }

  public int getInputResult() {
    return mInputResult;
  }

  @Override
  public void setNestedScrollingEnabled(boolean enabled) {
    mChildHelper.setNestedScrollingEnabled(enabled);
  }

  @Override
  public boolean isNestedScrollingEnabled() {
    return mChildHelper.isNestedScrollingEnabled();
  }

  @Override
  public boolean startNestedScroll(int axes) {
    return mChildHelper.startNestedScroll(axes);
  }

  @Override
  public void stopNestedScroll() {
    mChildHelper.stopNestedScroll();
  }

  @Override
  public boolean hasNestedScrollingParent() {
    return mChildHelper.hasNestedScrollingParent();
  }

  @Override
  public boolean dispatchNestedScroll(
      int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {
    return mChildHelper.dispatchNestedScroll(
        dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, offsetInWindow);
  }

  @Override
  public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
    return mChildHelper.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow);
  }

  @Override
  public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed) {
    return mChildHelper.dispatchNestedFling(velocityX, velocityY, consumed);
  }

  @Override
  public boolean dispatchNestedPreFling(float velocityX, float velocityY) {
    return mChildHelper.dispatchNestedPreFling(velocityX, velocityY);
  }
}