tts-extractor/src/google-tts-api/splitLongText.ts

A text-to-speech extractor for discord-player

// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim
const SPACE_REGEX = "\\s\\uFEFF\\xA0";

// https://remarkablemark.org/blog/2019/09/28/javascript-remove-punctuation/
const DEFAULT_PUNCTUATION_REGEX = "!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~";

interface Option {
  maxLength?: number;
  splitPunct?: string;
}

/**
 * split the long text to short texts
 * Time Complexity: O(n)
 *
 * @param {string}  text
 * @param {object?} option
 * @param {number?} option.maxLength  default is 200
 * @param {string?} option.splitPunct default is ''
 * @returns {string[]} short text list
 */
const splitLongText = (
    text: string,
    { maxLength = 200, splitPunct = "" }: Option = {},
): string[] => {
    const isSpaceOrPunct = (s: string, i: number) => {
        const regex = new RegExp("[" + SPACE_REGEX + DEFAULT_PUNCTUATION_REGEX + splitPunct + "]");
        return regex.test(s.charAt(i));
    };

    const lastIndexOfSpaceOrPunct = (s: string, left: number, right: number): number => {
        for (let i = right; i >= left; i--) 
            if (isSpaceOrPunct(s, i)) return i;
    
        return -1; // not found
    };

    const result: string[] = [];
    // eslint-disable-next-line no-shadow
    const addResult = (text: string, start: number, end: number) => {
        result.push(text.slice(start, end + 1));
    };

    let start = 0;
    for (;;) {
    // check text's length
        if (text.length - start <= maxLength) {
            addResult(text, start, text.length - 1);
            break; // end of text
        }

        // check whether the word is cut in the middle.
        let end = start + maxLength - 1;
        if (isSpaceOrPunct(text, end) || isSpaceOrPunct(text, end + 1)) {
            addResult(text, start, end);
            start = end + 1;
            continue;
        }

        // find last index of space
        end = lastIndexOfSpaceOrPunct(text, start, end);
        if (end === -1) {
            const str = text.slice(start, start + maxLength);
            throw new Error(
                "The word is too long to split into a short text:" +
          `\n${str} ...` +
          "\n\nTry the option \"splitPunct\" to split the text by punctuation.",
            );
        }

        // add result
        addResult(text, start, end);
        start = end + 1;
    }

    return result;
};

export default splitLongText;