import { fromJS, List, Map } from 'immutable';
import { curry, flow, isString } from "lodash";

const decodeParams = paramsString => List(paramsString.split("&"))
  .map(s => List(s.split("=")).map(decodeURIComponent))
  .update(Map);

const fromURL = wholeURL => {
  const [url, allParamsString] = wholeURL.split("?");
  return Map({ url, ...(allParamsString ? { params: decodeParams(allParamsString) } : {}) });
};

const encodeParams = params => params.entrySeq()
  .map(([k, v]) => `${ encodeURIComponent(k) }=${ encodeURIComponent(v) }`)
  .join("&");

const toURL = req => `${ req.get("url") }${ req.get("params") ? `?${ encodeParams(req.get("params")) }` : "" }`;

const toFetchArguments = req => [toURL(req), req.delete("url").delete("params").toJS()];

const maybeRequestArg = req => {
  if (isString(req)) { return fromURL(req); }
  if (req) { return fromJS(req); }
  return Map();
};
const ensureRequestArg = func => req => func(maybeRequestArg(req));
const ensureRequestArg2 = func => (arg, req) => func(arg, maybeRequestArg(req));

// This actually performs the built request object
const performRequest = ensureRequestArg(req => fetch(...toFetchArguments(req)));

// Each of the following functions takes options and returns another
// function that performs the requested action on a request. They each
// default to containing an empty object, so you can simply call them
// without arguments to generate a request with only those properties.
const getCurriedRequestProcessor = flow([ensureRequestArg2, curry]);
const getPropSetFunctions = path => [
  getCurriedRequestProcessor((val, req) => req.setIn(path, val)),
  getCurriedRequestProcessor((val, req) => (req.getIn(path) ? req : req.setIn(path, val))),
];
const getPropMergeFunctions = path => [
  getCurriedRequestProcessor((obj, req) => req.updateIn(path, (p=Map()) => p.merge(obj))),
  getCurriedRequestProcessor((obj, req) => req.updateIn(path, (p=Map()) => Map(obj).merge(p))),
];

const [withMethod, withDefaultMethod] = getPropSetFunctions(["method"]);
const [withBody, withDefaultBody] = getPropSetFunctions(["method"]);
const [withParams, withDefaultParams] = getPropMergeFunctions(["params"]);
const [withHeaders, withDefaultHeaders] = getPropMergeFunctions(["headers"]);

// withRoot sets a root URL, unless the URL is already absolute
const absolutePath = new RegExp('^(?:[a-z]+:)?//', 'i');
const withRoot = getCurriedRequestProcessor((root, req) => req.update("url", p => {
  if (absolutePath.test(p)) { return p; }
  return (root && p && p[0] !== "/" && root[root.length - 1] !== "/")
    ? `${ root }/${ p }`
    : `${ root }${ p }`;
}));

// withTimestamp needs no argument and has to run as late as possible,
// so it calls `withParams` only when it's actually called with a
// request.
const withTimestamp = ensureRequestArg(req => withParams({ ts: new Date().getTime() }, req));

export default {
  toURL,
  fromURL,
  performRequest,
  withMethod,
  withDefaultMethod,
  withBody,
  withDefaultBody,
  withHeaders,
  withDefaultHeaders,
  withParams,
  withDefaultParams,
  withRoot,
  withTimestamp,
};