ConfigGroup.js

const { existsSync } = require('fs');
const { resolve, extname } = require('path');
const webpackMerge = require('webpack-merge');
const { extensions, jsVariants } = require('interpret');
const rechoir = require('rechoir');
const logger = require('../utils/logger');

// Order defines the priority, in increasing order
// example - config file lookup will be in order of .webpack/webpack.config.development.js -> webpack.config.development.js -> webpack.config.js
const DEFAULT_CONFIG_LOC = [
    'webpack.config',
    'webpack.config.dev',
    'webpack.config.development',
    'webpack.config.prod',
    'webpack.config.production',
    '.webpack/webpack.config',
    '.webpack/webpack.config.none',
    '.webpack/webpack.config.dev',
    '.webpack/webpack.config.development',
    '.webpack/webpack.config.prod',
    '.webpack/webpack.config.production',
    '.webpack/webpackfile',
];

const modeAlias = {
    production: 'prod',
    development: 'dev',
};

let opts = {
    outputOptions: {},
    options: {},
};

// Return a list of default configs in various formats
const getDefaultConfigFiles = () => {
    return DEFAULT_CONFIG_LOC.map((filename) => {
        // Since .cjs is not available on interpret side add it manually to default config extension list
        return [...Object.keys(extensions), '.cjs'].map((ext) => {
            return {
                path: resolve(filename + ext),
                ext: ext,
                module: extensions[ext],
            };
        });
    }).reduce((a, i) => a.concat(i), []);
};

const getConfigInfoFromFileName = (filename) => {
    const ext = extname(filename);
    // since we support only one config for now
    const allFiles = [filename];
    // return all the file metadata
    return allFiles
        .map((file) => {
            return {
                path: resolve(file),
                ext: ext,
                module: extensions[ext] || null,
            };
        })
        .filter((e) => existsSync(e.path));
};

// Reads a config file given the config metadata
const requireConfig = (configModule) => {
    const extension = Object.keys(jsVariants).find((t) => configModule.ext.endsWith(t));

    if (extension) {
        rechoir.prepare(extensions, configModule.path, process.cwd());
    }

    let config = require(configModule.path);

    if (config.default) {
        config = config.default;
    }

    return { config, path: configModule.path };
};

// Responsible for reading user configuration files
// else does a default config lookup and resolves it.
const resolveConfigFiles = async (args) => {
    const { config, mode } = args;

    if (config && config.length > 0) {
        const resolvedOptions = [];
        const finalizedConfigs = config.map(async (webpackConfig) => {
            const configPath = resolve(webpackConfig);
            const configFiles = getConfigInfoFromFileName(configPath);

            if (!configFiles.length) {
                logger.error(`The specified config file doesn't exist in ${configPath}`);
                process.exit(2);
            }

            const foundConfig = configFiles[0];
            const resolvedConfig = requireConfig(foundConfig);

            return finalize(resolvedConfig, args);
        });

        // resolve all the configs
        for await (const resolvedOption of finalizedConfigs) {
            if (Array.isArray(resolvedOption.options)) {
                resolvedOptions.push(...resolvedOption.options);
            } else {
                resolvedOptions.push(resolvedOption.options);
            }
        }

        opts['options'] = resolvedOptions.length > 1 ? resolvedOptions : resolvedOptions[0] || {};

        return;
    }

    // When no config is supplied, lookup for default configs
    const defaultConfigFiles = getDefaultConfigFiles();
    const tmpConfigFiles = defaultConfigFiles.filter((file) => {
        return existsSync(file.path);
    });

    const configFiles = tmpConfigFiles.map(requireConfig);
    if (configFiles.length) {
        const defaultConfig = configFiles.find((p) => p.path.includes(mode) || p.path.includes(modeAlias[mode]));

        if (defaultConfig) {
            opts = await finalize(defaultConfig, args);
            return;
        }

        const foundConfig = configFiles.pop();

        opts = await finalize(foundConfig, args);

        return;
    }
};

// Given config data, determines the type of config and
// returns final config
const finalize = async (moduleObj, args) => {
    const { env, configName } = args;
    const newOptionsObject = {
        outputOptions: {},
        options: {},
    };

    if (!moduleObj) {
        return newOptionsObject;
    }

    const config = moduleObj.config;

    const isMultiCompilerMode = Array.isArray(config);
    const rawConfigs = isMultiCompilerMode ? config : [config];

    let configs = await Promise.all(
        rawConfigs.map(async (rawConfig) => {
            const isPromise = typeof rawConfig.then === 'function';

            if (isPromise) {
                rawConfig = await rawConfig;
            }

            // `Promise` may return `Function`
            if (typeof rawConfig === 'function') {
                // when config is a function, pass the env from args to the config function
                let envs;

                if (Array.isArray(env)) {
                    envs = env.reduce((envObject, envOption) => {
                        envObject[envOption] = true;

                        return envObject;
                    }, {});
                }

                rawConfig = await rawConfig(envs, args);
            }

            return rawConfig;
        }),
    );

    if (configName) {
        const foundConfigNames = [];

        configs = configs.filter((options) => {
            const found = configName.includes(options.name);

            if (found) {
                foundConfigNames.push(options.name);
            }

            return found;
        });

        if (foundConfigNames.length !== configName.length) {
            // Configuration with name "test" was not found.
            logger.error(
                configName
                    .filter((name) => !foundConfigNames.includes(name))
                    .map((configName) => `Configuration with name "${configName}" was not found.`)
                    .join('\n'),
            );
            process.exit(2);
        }
    }

    if (configs.length === 0) {
        logger.error('No configurations found');
        process.exit(2);
    }

    newOptionsObject['options'] = isMultiCompilerMode ? configs : configs[0];

    return newOptionsObject;
};

const resolveConfigMerging = async (args) => {
    const { merge } = args;

    if (merge) {
        // Get the current configuration options
        const { options: configOptions } = opts;

        // we can only merge when there are multiple configurations
        // either by passing multiple configs by flags or passing a
        // single config exporting an array
        if (!Array.isArray(configOptions)) {
            logger.error('At least two configurations are required for merge.');
            process.exit(2);
        }

        // We return a single config object which is passed to the compiler
        opts['options'] = configOptions.reduce((currentConfig, mergedConfig) => webpackMerge(currentConfig, mergedConfig), {});
    }
};

module.exports = async (args) => {
    await resolveConfigFiles(args);
    await resolveConfigMerging(args);

    return opts;
};