/**
 * Internal dependencies
 */

import { normaliseFormats } from './normalise-formats';

/** @typedef {import('./types').RichTextValue} RichTextValue */
/** @typedef {import('./types').RichTextFormat} RichTextFormat */

function replace(array, index, value) {
  array = array.slice();
  array[index] = value;
  return array;
}

/**
 * Apply a format object to a Rich Text value from the given `startIndex` to the
 * given `endIndex`. Indices are retrieved from the selection if none are
 * provided.
 *
 * @param {RichTextValue}  value        Value to modify.
 * @param {RichTextFormat} format       Format to apply.
 * @param {number}         [startIndex] Start index.
 * @param {number}         [endIndex]   End index.
 *
 * @return {RichTextValue} A new value with the format applied.
 */
export function applyFormat(value, format, startIndex = value.start, endIndex = value.end) {
  const {
    formats,
    activeFormats
  } = value;
  const newFormats = formats.slice();

  // The selection is collapsed.
  if (startIndex === endIndex) {
    const startFormat = newFormats[startIndex]?.find(({
      type
    }) => type === format.type);

    // If the caret is at a format of the same type, expand start and end to
    // the edges of the format. This is useful to apply new attributes.
    if (startFormat) {
      const index = newFormats[startIndex].indexOf(startFormat);
      while (newFormats[startIndex] && newFormats[startIndex][index] === startFormat) {
        newFormats[startIndex] = replace(newFormats[startIndex], index, format);
        startIndex--;
      }
      endIndex++;
      while (newFormats[endIndex] && newFormats[endIndex][index] === startFormat) {
        newFormats[endIndex] = replace(newFormats[endIndex], index, format);
        endIndex++;
      }
    }
  } else {
    // Determine the highest position the new format can be inserted at.
    let position = +Infinity;
    for (let index = startIndex; index < endIndex; index++) {
      if (newFormats[index]) {
        newFormats[index] = newFormats[index].filter(({
          type
        }) => type !== format.type);
        const length = newFormats[index].length;
        if (length < position) {
          position = length;
        }
      } else {
        newFormats[index] = [];
        position = 0;
      }
    }
    for (let index = startIndex; index < endIndex; index++) {
      newFormats[index].splice(position, 0, format);
    }
  }
  return normaliseFormats({
    ...value,
    formats: newFormats,
    // Always revise active formats. This serves as a placeholder for new
    // inputs with the format so new input appears with the format applied,
    // and ensures a format of the same type uses the latest values.
    activeFormats: [...(activeFormats?.filter(({
      type
    }) => type !== format.type) || []), format]
  });
}
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