/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @format
 * @flow strict-local
 * @emails oncall+draft_js
 */
'use strict';

const Immutable = require("immutable");

const insertIntoList = require("./insertIntoList");

const invariant = require("fbjs/lib/invariant");

const {
  Repeat
} = Immutable;
import type CharacterMetadata from "./CharacterMetadata";
import type ContentState from "./ContentState";
import type SelectionState from "./SelectionState";

function insertTextIntoContentState(contentState: ContentState, selectionState: SelectionState, text: string, characterMetadata: CharacterMetadata): ContentState {
  invariant(selectionState.isCollapsed(), '`insertText` should only be called with a collapsed range.');
  let len: ?number = null;

  if (text != null) {
    len = text.length;
  }

  if (len == null || len === 0) {
    return contentState;
  }

  const blockMap = contentState.getBlockMap();
  const key = selectionState.getStartKey();
  const offset = selectionState.getStartOffset();
  const block = blockMap.get(key);
  const blockText = block.getText();
  const newBlock = block.merge({
    text: blockText.slice(0, offset) + text + blockText.slice(offset, block.getLength()),
    characterList: insertIntoList(block.getCharacterList(), Repeat(characterMetadata, len).toList(), offset)
  });
  const newOffset = offset + len;
  return contentState.merge({
    blockMap: blockMap.set(key, newBlock),
    selectionAfter: selectionState.merge({
      anchorOffset: newOffset,
      focusOffset: newOffset
    })
  });
}

module.exports = insertTextIntoContentState;