/*
 * Copyright 2020 Adobe. All rights reserved.
 * This file is licensed to you 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 REPRESENTATIONS
 * OF ANY KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

// Portions of the code in this file are based on code from react.
// Original licensing for the following can be found in the
// NOTICE file in the root directory of this source tree.
// See https://github.com/facebook/react/tree/cc7c1aece46a6b69b41958d731e0fd27c94bfc6c/packages/react-interactions

import {DOMAttributes} from '@react-types/shared';
import {FocusEvent, useCallback, useRef} from 'react';
import {useSyntheticBlurEvent} from './utils';

export interface FocusWithinProps {
  /** Whether the focus within events should be disabled. */
  isDisabled?: boolean,
  /** Handler that is called when the target element or a descendant receives focus. */
  onFocusWithin?: (e: FocusEvent) => void,
  /** Handler that is called when the target element and all descendants lose focus. */
  onBlurWithin?: (e: FocusEvent) => void,
  /** Handler that is called when the the focus within state changes. */
  onFocusWithinChange?: (isFocusWithin: boolean) => void
}

export interface FocusWithinResult {
  /** Props to spread onto the target element. */
  focusWithinProps: DOMAttributes
}

/**
 * Handles focus events for the target and its descendants.
 */
export function useFocusWithin(props: FocusWithinProps): FocusWithinResult {
  let {
    isDisabled,
    onBlurWithin,
    onFocusWithin,
    onFocusWithinChange
  } = props;
  let state = useRef({
    isFocusWithin: false
  });

  let onBlur = useCallback((e: FocusEvent) => {
    // We don't want to trigger onBlurWithin and then immediately onFocusWithin again
    // when moving focus inside the element. Only trigger if the currentTarget doesn't
    // include the relatedTarget (where focus is moving).
    if (state.current.isFocusWithin && !(e.currentTarget as Element).contains(e.relatedTarget as Element)) {
      state.current.isFocusWithin = false;

      if (onBlurWithin) {
        onBlurWithin(e);
      }

      if (onFocusWithinChange) {
        onFocusWithinChange(false);
      }
    }
  }, [onBlurWithin, onFocusWithinChange, state]);

  let onSyntheticFocus = useSyntheticBlurEvent(onBlur);
  let onFocus = useCallback((e: FocusEvent) => {
    // Double check that document.activeElement actually matches e.target in case a previously chained
    // focus handler already moved focus somewhere else.
    if (!state.current.isFocusWithin && document.activeElement === e.target) {
      if (onFocusWithin) {
        onFocusWithin(e);
      }

      if (onFocusWithinChange) {
        onFocusWithinChange(true);
      }

      state.current.isFocusWithin = true;
      onSyntheticFocus(e);
    }
  }, [onFocusWithin, onFocusWithinChange, onSyntheticFocus]);

  if (isDisabled) {
    return {
      focusWithinProps: {
        // These should not have been null, that would conflict in mergeProps
        onFocus: undefined,
        onBlur: undefined
      }
    };
  }

  return {
    focusWithinProps: {
      onFocus,
      onBlur
    }
  };
}