pdf-lib/src/utils/strings.ts

Create and modify PDF files with JavaScript

export const toCharCode = (character: string) => character.charCodeAt(0);

export const toCodePoint = (character: string) => character.codePointAt(0);

export const toHexStringOfMinLength = (num: number, minLength: number) =>
  padStart(num.toString(16), minLength, '0').toUpperCase();

export const toHexString = (num: number) => toHexStringOfMinLength(num, 2);

export const charFromCode = (code: number) => String.fromCharCode(code);

export const charFromHexCode = (hex: string) => charFromCode(parseInt(hex, 16));

export const padStart = (value: string, length: number, padChar: string) => {
  let padding = '';
  for (let idx = 0, len = length - value.length; idx < len; idx++) {
    padding += padChar;
  }
  return padding + value;
};

export const copyStringIntoBuffer = (
  str: string,
  buffer: Uint8Array,
  offset: number,
): number => {
  const length = str.length;
  for (let idx = 0; idx < length; idx++) {
    buffer[offset++] = str.charCodeAt(idx);
  }
  return length;
};

export const addRandomSuffix = (prefix: string, suffixLength = 4) =>
  `${prefix}-${Math.floor(Math.random() * 10 ** suffixLength)}`;

export const escapeRegExp = (str: string) =>
  str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');

export const cleanText = (text: string) =>
  text.replace(/\t|\u0085|\u2028|\u2029/g, '    ').replace(/[\b\v]/g, '');

export const escapedNewlineChars = ['\\n', '\\f', '\\r', '\\u000B'];

export const newlineChars = ['\n', '\f', '\r', '\u000B'];

export const isNewlineChar = (text: string) => /^[\n\f\r\u000B]$/.test(text);

export const lineSplit = (text: string) => text.split(/[\n\f\r\u000B]/);

export const mergeLines = (text: string) =>
  text.replace(/[\n\f\r\u000B]/g, ' ');

// JavaScript's String.charAt() method doesn work on strings containing UTF-16
// characters (with high and low surrogate pairs), such as 💩 (poo emoji). This
// `charAtIndex()` function does.
//
// Credit: https://github.com/mathiasbynens/String.prototype.at/blob/master/at.js#L14-L48
export const charAtIndex = (text: string, index: number): [string, number] => {
  // Get the first code unit and code unit value
  const cuFirst = text.charCodeAt(index);
  let cuSecond: number;
  const nextIndex = index + 1;
  let length = 1;
  if (
    // Check if it's the start of a surrogate pair.
    cuFirst >= 0xd800 &&
    cuFirst <= 0xdbff && // high surrogate
    text.length > nextIndex // there is a next code unit
  ) {
    cuSecond = text.charCodeAt(nextIndex);
    if (cuSecond >= 0xdc00 && cuSecond <= 0xdfff) length = 2; // low surrogate
  }
  return [text.slice(index, index + length), length];
};

export const charSplit = (text: string) => {
  const chars: string[] = [];

  for (let idx = 0, len = text.length; idx < len; ) {
    const [c, cLen] = charAtIndex(text, idx);
    chars.push(c);
    idx += cLen;
  }

  return chars;
};

const buildWordBreakRegex = (wordBreaks: string[]) => {
  const newlineCharUnion = escapedNewlineChars.join('|');

  const escapedRules: string[] = ['$'];
  for (let idx = 0, len = wordBreaks.length; idx < len; idx++) {
    const wordBreak = wordBreaks[idx];
    if (isNewlineChar(wordBreak)) {
      throw new TypeError(`\`wordBreak\` must not include ${newlineCharUnion}`);
    }
    escapedRules.push(wordBreak === '' ? '.' : escapeRegExp(wordBreak));
  }

  const breakRules = escapedRules.join('|');
  return new RegExp(`(${newlineCharUnion})|((.*?)(${breakRules}))`, 'gm');
};

export const breakTextIntoLines = (
  text: string,
  wordBreaks: string[],
  maxWidth: number,
  computeWidthOfText: (t: string) => number,
): string[] => {
  const regex = buildWordBreakRegex(wordBreaks);

  const words = cleanText(text).match(regex)!;

  let currLine = '';
  let currWidth = 0;
  const lines: string[] = [];

  const pushCurrLine = () => {
    if (currLine !== '') lines.push(currLine);
    currLine = '';
    currWidth = 0;
  };

  for (let idx = 0, len = words.length; idx < len; idx++) {
    const word = words[idx];
    if (isNewlineChar(word)) {
      pushCurrLine();
    } else {
      const width = computeWidthOfText(word);
      if (currWidth + width > maxWidth) pushCurrLine();
      currLine += word;
      currWidth += width;
    }
  }
  pushCurrLine();

  return lines;
};

// See section "7.9.4 Dates" of the PDF specification
const dateRegex = /^D:(\d\d\d\d)(\d\d)?(\d\d)?(\d\d)?(\d\d)?(\d\d)?([+\-Z])?(\d\d)?'?(\d\d)?'?$/;

export const parseDate = (dateStr: string): Date | undefined => {
  const match = dateStr.match(dateRegex);

  if (!match) return undefined;

  const [
    ,
    year,
    month = '01',
    day = '01',
    hours = '00',
    mins = '00',
    secs = '00',
    offsetSign = 'Z',
    offsetHours = '00',
    offsetMins = '00',
  ] = match;

  // http://www.ecma-international.org/ecma-262/5.1/#sec-15.9.1.15
  const tzOffset =
    offsetSign === 'Z' ? 'Z' : `${offsetSign}${offsetHours}:${offsetMins}`;
  const date = new Date(
    `${year}-${month}-${day}T${hours}:${mins}:${secs}${tzOffset}`,
  );

  return date;
};

export const findLastMatch = (value: string, regex: RegExp) => {
  let position = 0;
  let lastMatch: RegExpMatchArray | undefined;
  while (position < value.length) {
    const match = value.substring(position).match(regex);
    if (!match) return { match: lastMatch, pos: position };
    lastMatch = match;
    position += (match.index ?? 0) + match[0].length;
  }
  return { match: lastMatch, pos: position };
};