-module(forward_handler).
-behavior(cowboy_rest).

-export([init/2]).
-export([allowed_methods/2]).
-export([content_types_accepted/2]).
-export([content_types_provided/2]).
-export([resource_exists/2]).
-export([from_json/2]).
-export([to_json/2]).

init(Req, State) ->
  {cowboy_rest, Req, State}.

allowed_methods(Req, State) ->
  {[<<"POST">>, <<"OPTIONS">>], Req, State}.

content_types_accepted(Req, State) ->
  {[
    {<<"application/json">>, from_json}
  ],
  Req, State}.

content_types_provided(Req, State) ->
  {[
    {<<"application/json">>, to_json}
  ], Req, State}.

resource_exists(Req, State) ->
  {false, Req, State}.

from_json(Req, State) ->
  {ok, Body, Req1} = cowboy_req:read_body(Req),
  {ok, Data} = thoas:decode(Body),
  Result = forward(Data),
  ResultJSON = thoas:encode(Result),
  Req2 = cowboy_req:set_resp_body(ResultJSON, Req1),
  {true, Req2, State}.

to_json(Req, State) ->
  % Not used but required by content_types_provided/2
  {true, Req, State}.

forward(Data) ->
  forward(Data, []).

forward([], Result) ->
  Result;

forward([#{<<"uri">> := URI,
           <<"payload">> := Payload}|Tail], Result) ->
  JSONBody = thoas:encode(Payload),
  case httpc:request(post, {URI, [], "application/json", JSONBody}, [], []) of
    {ok, {{_, 200, _}, _Headers, Response}} ->
      {ok, ResponseMap} = thoas:decode(list_to_binary(Response)),
      forward(Tail, [#{uri => URI, payload => Payload, result => ResponseMap}|Result]);
    {ok, {_StatusLine, _Headers, _Response}} ->
      forward(Tail, [#{uri => URI, payload => Payload, result => failed}|Result])
  end.