/**
 * Copyright (c) 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule getCharacterRemovalRange
 * @format
 * @flow
 */

'use strict';

import type { BlockNodeRecord } from './BlockNodeRecord';
import type { DraftRemovalDirection } from './DraftRemovalDirection';
import type { EntityMap } from './EntityMap';
import type SelectionState from './SelectionState';

var DraftEntitySegments = require('./DraftEntitySegments');

var getRangesForDraftEntity = require('./getRangesForDraftEntity');
var invariant = require('fbjs/lib/invariant');

/**
 * Given a SelectionState and a removal direction, determine the entire range
 * that should be removed from a ContentState. This is based on any entities
 * within the target, with their `mutability` values taken into account.
 *
 * For instance, if we are attempting to remove part of an "immutable" entity
 * range, the entire entity must be removed. The returned `SelectionState`
 * will be adjusted accordingly.
 */
function getCharacterRemovalRange(entityMap: EntityMap, startBlock: BlockNodeRecord, endBlock: BlockNodeRecord, selectionState: SelectionState, direction: DraftRemovalDirection): SelectionState {
  var start = selectionState.getStartOffset();
  var end = selectionState.getEndOffset();
  var startEntityKey = startBlock.getEntityAt(start);
  var endEntityKey = endBlock.getEntityAt(end - 1);
  if (!startEntityKey && !endEntityKey) {
    return selectionState;
  }
  var newSelectionState = selectionState;
  if (startEntityKey && startEntityKey === endEntityKey) {
    newSelectionState = getEntityRemovalRange(entityMap, startBlock, newSelectionState, direction, startEntityKey, true, true);
  } else if (startEntityKey && endEntityKey) {
    const startSelectionState = getEntityRemovalRange(entityMap, startBlock, newSelectionState, direction, startEntityKey, false, true);
    const endSelectionState = getEntityRemovalRange(entityMap, endBlock, newSelectionState, direction, endEntityKey, false, false);
    newSelectionState = newSelectionState.merge({
      anchorOffset: startSelectionState.getAnchorOffset(),
      focusOffset: endSelectionState.getFocusOffset(),
      isBackward: false
    });
  } else if (startEntityKey) {
    const startSelectionState = getEntityRemovalRange(entityMap, startBlock, newSelectionState, direction, startEntityKey, false, true);
    newSelectionState = newSelectionState.merge({
      anchorOffset: startSelectionState.getStartOffset(),
      isBackward: false
    });
  } else if (endEntityKey) {
    const endSelectionState = getEntityRemovalRange(entityMap, endBlock, newSelectionState, direction, endEntityKey, false, false);
    newSelectionState = newSelectionState.merge({
      focusOffset: endSelectionState.getEndOffset(),
      isBackward: false
    });
  }
  return newSelectionState;
}

function getEntityRemovalRange(entityMap: EntityMap, block: BlockNodeRecord, selectionState: SelectionState, direction: DraftRemovalDirection, entityKey: string, isEntireSelectionWithinEntity: boolean, isEntityAtStart: boolean): SelectionState {
  var start = selectionState.getStartOffset();
  var end = selectionState.getEndOffset();
  var entity = entityMap.__get(entityKey);
  var mutability = entity.getMutability();
  const sideToConsider = isEntityAtStart ? start : end;

  // `MUTABLE` entities can just have the specified range of text removed
  // directly. No adjustments are needed.
  if (mutability === 'MUTABLE') {
    return selectionState;
  }

  // Find the entity range that overlaps with our removal range.
  var entityRanges = getRangesForDraftEntity(block, entityKey).filter(range => sideToConsider <= range.end && sideToConsider >= range.start);

  invariant(entityRanges.length == 1, 'There should only be one entity range within this removal range.');

  var entityRange = entityRanges[0];

  // For `IMMUTABLE` entity types, we will remove the entire entity range.
  if (mutability === 'IMMUTABLE') {
    return selectionState.merge({
      anchorOffset: entityRange.start,
      focusOffset: entityRange.end,
      isBackward: false
    });
  }

  // For `SEGMENTED` entity types, determine the appropriate segment to
  // remove.
  if (!isEntireSelectionWithinEntity) {
    if (isEntityAtStart) {
      end = entityRange.end;
    } else {
      start = entityRange.start;
    }
  }

  var removalRange = DraftEntitySegments.getRemovalRange(start, end, block.getText().slice(entityRange.start, entityRange.end), entityRange.start, direction);

  return selectionState.merge({
    anchorOffset: removalRange.start,
    focusOffset: removalRange.end,
    isBackward: false
  });
}

module.exports = getCharacterRemovalRange;