source: frontend/node_modules/webpack/lib/util/URLAbsoluteSpecifier.js

/*
        MIT License http://www.opensource.org/licenses/mit-license.php
        Author Ivan Kopeykin @vankop
*/

"use strict";

/** @typedef {(error: Error | null, result?: Buffer) => void} ErrorFirstCallback */

const backSlashCharCode = "\\".charCodeAt(0);
const slashCharCode = "/".charCodeAt(0);
const aLowerCaseCharCode = "a".charCodeAt(0);
const zLowerCaseCharCode = "z".charCodeAt(0);
const aUpperCaseCharCode = "A".charCodeAt(0);
const zUpperCaseCharCode = "Z".charCodeAt(0);
const _0CharCode = "0".charCodeAt(0);
const _9CharCode = "9".charCodeAt(0);
const plusCharCode = "+".charCodeAt(0);
const hyphenCharCode = "-".charCodeAt(0);
const colonCharCode = ":".charCodeAt(0);
const hashCharCode = "#".charCodeAt(0);
const queryCharCode = "?".charCodeAt(0);
/**
 * Get scheme if specifier is an absolute URL specifier
 * e.g. Absolute specifiers like 'file:///user/webpack/index.js'
 * https://tools.ietf.org/html/rfc3986#section-3.1
 * @param {string} specifier specifier
 * @returns {string | undefined} scheme if absolute URL specifier provided
 */
function getScheme(specifier) {
        const start = specifier.charCodeAt(0);

        // First char maybe only a letter
        if (
                (start < aLowerCaseCharCode || start > zLowerCaseCharCode) &&
                (start < aUpperCaseCharCode || start > zUpperCaseCharCode)
        ) {
                return;
        }

        let i = 1;
        let ch = specifier.charCodeAt(i);

        while (
                (ch >= aLowerCaseCharCode && ch <= zLowerCaseCharCode) ||
                (ch >= aUpperCaseCharCode && ch <= zUpperCaseCharCode) ||
                (ch >= _0CharCode && ch <= _9CharCode) ||
                ch === plusCharCode ||
                ch === hyphenCharCode
        ) {
                if (++i === specifier.length) return;
                ch = specifier.charCodeAt(i);
        }

        // Scheme must end with colon
        if (ch !== colonCharCode) return;

        // Check for Windows absolute path
        // https://url.spec.whatwg.org/#url-miscellaneous
        if (i === 1) {
                const nextChar = i + 1 < specifier.length ? specifier.charCodeAt(i + 1) : 0;
                if (
                        nextChar === 0 ||
                        nextChar === backSlashCharCode ||
                        nextChar === slashCharCode ||
                        nextChar === hashCharCode ||
                        nextChar === queryCharCode
                ) {
                        return;
                }
        }

        return specifier.slice(0, i).toLowerCase();
}

/**
 * Returns protocol if absolute URL specifier provided.
 * @param {string} specifier specifier
 * @returns {string | null | undefined} protocol if absolute URL specifier provided
 */
function getProtocol(specifier) {
        const scheme = getScheme(specifier);
        return scheme === undefined ? undefined : `${scheme}:`;
}

module.exports.getProtocol = getProtocol;
module.exports.getScheme = getScheme;