omni-tools/src/pages/string/extract-substring/service.ts

import { reverseString } from 'utils/string'

export function extractSubstring(
    input: string,
    start: number,
    length: number,
    multiLine: boolean,
    reverse: boolean
): string {
    if (!input) return '';
    // edge Cases
    if (start <= 0) throw new Error("Start index must be greater than zero.");
    if (length < 0) throw new Error("Length value must be greater than or equal to zero.");
    if (length === 0) return '';

    let array: string[];
    let result: string[] = [];

    const extract = (str: string, start: number, length: number): string => {
        const end = start - 1 + length;
        if (start - 1 >= str.length) return '';
        return str.substring(start - 1, Math.min(end, str.length));
    };

    if (!multiLine) {
        result.push(extract(input, start, length));
    }
    else {
        array = input.split('\n');
        for (const word of array) {
            result.push(extract(word, start, length));
        }
    }
    result = reverse ? result.map(word => reverseString(word)) : result;
    return result.join('\n');
}