ptt-client/src/utils/char.ts

A Node client for fetching data from ptt.cc.

import wcwidth from 'wcwidth';

export function dbcswidth(str: string): number {
    return str.split('').reduce(function(sum, c) {
        return sum + (c.charCodeAt(0) > 255 ? 2 : 1);
    }, 0);
}
/**
* calculate width of string.
* @params {string} widthType - calculate width by wcwidth or String.length
* @params {string} str - string to calculate
*/
export function getWidth(widthType: string, str: string): number {
    switch (widthType) {
        case 'length':
            return str.length;
        case 'wcwidth':
            return wcwidth(str);
        case 'dbcs':
            return dbcswidth(str);
        default:
            throw new Error(`Invalid widthType "${widthType}"`);
    }
}

/**
* calculate the position that the prefix of string is a specific width
* @params {string} widthType - calculate width by wcwidth or String.length
* @params {string} str - string to calculate
* @params {number} width - the width of target string
*/
export function indexOfWidth(widthType: string, str: string, width?: number): number {
    if (widthType === 'length') {
        return getWidth(widthType, str);
    }
    for (let i = 0; i <= str.length; i++) {
        if (getWidth(widthType, str.substr(0, i)) > width) {
            return i - 1;
        }
    }
    return str.length;
}

/**
* extract parts of string, beginning at the character at the specified position,
* and returns the specified width of characters. if the character is incomplete,
* it will be replaced by space.
* @params {string} widthType - calculate width by wcwidth or String.length
* @params {string} str - string to calculate
* @params {number} startWidth - the beginning position of string
* @params {number} width - the width of target string
*/
export function substrWidth(widthType: string, str: string, startWidth: number, width?: number): string {
    const ignoreWidth = typeof width === 'undefined';
    let length = width;
    let start = startWidth;
    let prefixSpace = 0, suffixSpace = 0;
    if (widthType !== 'length') {
        start = indexOfWidth(widthType, str, startWidth);
        if (getWidth(widthType, str.substr(0, start)) < startWidth) {
            start += 1;
            prefixSpace = Math.max(getWidth(widthType, str.substr(0, start)) - startWidth, 0);
        }
        if (!ignoreWidth) {
            length = indexOfWidth(widthType, str.substr(start), width - prefixSpace);
            suffixSpace = Math.min(width, getWidth(widthType, str.substr(start))) -
                (prefixSpace + getWidth(widthType, str.substr(start, length)));
        }
    }
    const substr = ignoreWidth ? str.substr(start) : str.substr(start, length);
    return ' '.repeat(prefixSpace) + substr + ' '.repeat(suffixSpace);
}