module-name-mapper-helper.js

const path = require('path');

/**
 * Resolve a Sass @import or @use rule.
 *
 * @param {String} to - The path to the current file
 * @param {String} importPath - The path to resolve
 * @param {String} fileType - The filetype of the current file
 */
function resolveSass(to, importPath, fileType) {
    // Mimic Sass-loader's `~` syntax for bare imports.
    const matchModuleImport = /^~/;

    if (path.isAbsolute(importPath)) {
        return importPath;
    } if (matchModuleImport.test(importPath)) {
        const dirname = path.dirname(importPath).replace(matchModuleImport, '');
        const basename = path.basename(importPath);

        const filenames = [];

        if (!/\.(sc|sa|c)ss/.test(basename)) {
            const extensions = ['scss', 'sass', 'css'].filter((e) => e !== fileType);
            extensions.unshift(fileType);
            extensions.forEach((ext) => {
                filenames.push(`${basename}.${ext}`, `_${basename}.${ext}`);
            });
        } else {
            filenames.push(basename, `_${basename}`);
        }

        for (const filename of filenames) {
            try {
                return require.resolve(path.join(dirname, filename));
            } catch (_) {}
        }
    }

    return path.join(path.dirname(to), importPath);
}

/**
 * Applies the moduleNameMapper substitution from the jest config
 *
 * @param {String} source - the original string
 * @param {String} filePath - the path of the current file (where the source originates)
 * @param {Object} jestConfig - the jestConfig holding the moduleNameMapper settings
 * @param {Object} fileType - extn of the file to be resolved
 * @returns {String} path - the final path to import (including replacements via moduleNameMapper)
 */
module.exports = function applyModuleNameMapper(
    source,
    filePath,
    jestConfig = {},
    fileType = '',
) {
    if (!jestConfig.moduleNameMapper) return source;
    // Extract the moduleNameMapper settings from the jest config. TODO: In case of development via babel@7, somehow the jestConfig.moduleNameMapper might end up being an Array. After a proper upgrade to babel@7 we should probably fix this.
    const module = Array.isArray(jestConfig.moduleNameMapper) ?
        jestConfig.moduleNameMapper :
        Object.entries(jestConfig.moduleNameMapper);

    const importPath = module.reduce((acc, [regex, replacement]) => {
        const matches = acc.match(regex);

        if (matches === null) {
            return acc;
        }

        return replacement.replace(
            /\$([0-9]+)/g,
            (_, index) => matches[parseInt(index, 10)],
        );
    }, source);

    return resolveSass(filePath, importPath, fileType);
};