import { YError } from '../yerror.js';
let previouslyVisitedConfigs = [];
let shim;
export function applyExtends(config, cwd, mergeExtends, _shim) {
    shim = _shim;
    let defaultConfig = {};
    if (Object.prototype.hasOwnProperty.call(config, 'extends')) {
        if (typeof config.extends !== 'string')
            return defaultConfig;
        const isPath = /\.json|\..*rc$/.test(config.extends);
        let pathToDefault = null;
        if (!isPath) {
            try {
                pathToDefault = require.resolve(config.extends);
            }
            catch (_err) {
                return config;
            }
        }
        else {
            pathToDefault = getPathToDefaultConfig(cwd, config.extends);
        }
        checkForCircularExtends(pathToDefault);
        previouslyVisitedConfigs.push(pathToDefault);
        defaultConfig = isPath
            ? JSON.parse(shim.readFileSync(pathToDefault, 'utf8'))
            : require(config.extends);
        delete config.extends;
        defaultConfig = applyExtends(defaultConfig, shim.path.dirname(pathToDefault), mergeExtends, shim);
    }
    previouslyVisitedConfigs = [];
    return mergeExtends
        ? mergeDeep(defaultConfig, config)
        : Object.assign({}, defaultConfig, config);
}
function checkForCircularExtends(cfgPath) {
    if (previouslyVisitedConfigs.indexOf(cfgPath) > -1) {
        throw new YError(`Circular extended configurations: '${cfgPath}'.`);
    }
}
function getPathToDefaultConfig(cwd, pathToExtend) {
    return shim.path.resolve(cwd, pathToExtend);
}
function mergeDeep(config1, config2) {
    const target = {};
    function isObject(obj) {
        return obj && typeof obj === 'object' && !Array.isArray(obj);
    }
    Object.assign(target, config1);
    for (const key of Object.keys(config2)) {
        if (isObject(config2[key]) && isObject(target[key])) {
            target[key] = mergeDeep(config1[key], config2[key]);
        }
        else {
            target[key] = config2[key];
        }
    }
    return target;
}