// @flow
import PromiseMiddlewareLayer from './PromiseMiddlewareLayer';
import InternalServerError from './InternalServerError';

const middlewareLayer = new PromiseMiddlewareLayer();

export type Resp<T> = {
    originalResponse: Response
} & T;

type Middleware = {
    before?: () => Promise<*>,
    after?: () => Promise<*>,
    catch?: () => Promise<*>
};

export default {
    /**
     * @param {string} url
     * @param {object} [data] - request data
     * @param {object} [options] - additional options for fetch or middlewares
     *
     * @return {Promise}
     */
    post<T>(url: string, data?: Object, options: Object = {}): Promise<Resp<T>> {
        return doFetch(url, {
            method: 'POST',
            headers: {
                'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8'
            },
            body: buildQuery(data),
            ...options
        });
    },

    /**
     * @param {string} url
     * @param {object} [data] - request data
     * @param {object} [options] - additional options for fetch or middlewares
     *
     * @return {Promise}
     */
    get<T>(url: string, data?: Object, options: Object = {}): Promise<Resp<T>> {
        if (typeof data === 'object' && Object.keys(data).length) {
            const separator = url.indexOf('?') === -1 ? '?' : '&';
            url += separator + buildQuery(data);
        }

        return doFetch(url, options);
    },

    /**
     * Serializes object into encoded key=value presentation
     *
     * @param {object} data
     *
     * @return {string}
     */
    buildQuery,

    /**
     * @param {object} middleware
     * @param {function} [middleware.before] - a function({url, options}), that will be called before executing request.
     *                                         It will get data object {url, options} as an argument and should return
     *                                         Promise, that will resolve into new data object
     * @param {function} [middleware.then] - a function(resp), that will be called on successful request result. It will
     *                                       get response as an argument and should return a Promise that resolves to
     *                                       the new response
     * @param {function} [middleware.catch] - a function(resp, restart), that will be called on request fail. It will
     *                                        get response and callback to restart request as an arguments and should
     *                                        return a Promise that resolves to the new response.
     */
    addMiddleware(middleware: Middleware) {
        middlewareLayer.add(middleware);
    }
};


const checkStatus = (resp) => resp.status >= 200 && resp.status < 300
    ? Promise.resolve(resp)
    : Promise.reject(resp);
const toJSON = (resp = {}) => {
    if (!resp.json) {
        // e.g. 'TypeError: Failed to fetch' due to CORS
        throw new InternalServerError(resp);
    }

    return resp.json().then((json) => {
        json.originalResponse = resp;

        return json;
    }, (error) => Promise.reject(
        new InternalServerError(error, resp)
    ));
};
const rejectWithJSON = (resp) => toJSON(resp).then((resp) => {
    if (resp.originalResponse.status >= 500) {
        throw new InternalServerError(resp, resp.originalResponse);
    }

    throw resp;
});
const handleResponseSuccess = (resp) => resp.success || typeof resp.success === 'undefined'
    ? Promise.resolve(resp)
    : Promise.reject(resp);

function doFetch(url, options = {}) {
    // NOTE: we are wrapping fetch, because it is returning
    // Promise instance that can not be pollyfilled with Promise.prototype.finally

    options.headers = options.headers || {};
    options.headers.Accept = 'application/json';

    return middlewareLayer.run('before', {url, options})
        .then(({url, options}) => fetch(url, options))
        .then(checkStatus)
        .then(toJSON, rejectWithJSON)
        .then(handleResponseSuccess)
        .then((resp) => middlewareLayer.run('then', resp, {url, options}))
        .catch((resp) => middlewareLayer.run('catch', resp, {url, options}, () => doFetch(url, options)));
}

/**
 * Converts specific js values to query friendly values
 *
 * @param {any} value
 *
 * @return {string}
 */
function convertQueryValue(value) {
    if (typeof value === 'undefined' || value === null) {
        return '';
    }

    if (value === true) {
        return '1';
    }

    if (value === false) {
        return '0';
    }

    return value;
}

/**
 * Serializes object into encoded key=value presentation
 *
 * @param {object} data
 *
 * @return {string}
 */
function buildQuery(data: Object = {}): string {
    return Object.keys(data)
        .map(
            (keyName) =>
                [keyName, convertQueryValue(data[keyName])]
                    .map(encodeURIComponent)
                    .join('=')
        )
        .join('&');
}