% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License. You may obtain a copy of
% the License at
%
%   http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.

-module(chttpd_view).
-include_lib("couch/include/couch_db.hrl").
-include_lib("couch_mrview/include/couch_mrview.hrl").

-export([handle_view_req/3, handle_temp_view_req/2]).

multi_query_view(Req, Db, DDoc, ViewName, Queries) ->
    Args0 = couch_mrview_http:parse_params(Req, undefined),
    {ok, #mrst{views=Views}} = couch_mrview_util:ddoc_to_mrst(Db, DDoc),
    Args1 = couch_mrview_util:set_view_type(Args0, ViewName, Views),
    ArgQueries = lists:map(fun({Query}) ->
        QueryArg = couch_mrview_http:parse_params(Query, undefined, Args1),
        couch_mrview_util:validate_args(QueryArg)
    end, Queries),
    {ok, Resp2} = couch_httpd:etag_maybe(Req, fun() ->
        VAcc0 = #vacc{db=Db, req=Req, prepend="\r\n"},
        %% TODO: proper calculation of etag
        Etag = couch_uuids:new(),
        Headers = [{"ETag", Etag}],
        FirstChunk = "{\"results\":[",
        {ok, Resp0} = chttpd:start_delayed_json_response(VAcc0#vacc.req, 200, Headers, FirstChunk),
        VAcc1 = VAcc0#vacc{resp=Resp0},
        VAcc2 = lists:foldl(fun(Args, Acc0) ->
            {ok, Acc1} = fabric:query_view(Db, DDoc, ViewName, fun couch_mrview_http:view_cb/2, Acc0, Args),
            Acc1
        end, VAcc1, ArgQueries),
        {ok, Resp1} = chttpd:send_delayed_chunk(VAcc2#vacc.resp, "\r\n]}"),
        {ok, Resp2} = chttpd:end_delayed_json_response(Resp1),
        {ok, VAcc2#vacc{resp=Resp2}}
    end),
    case is_record(Resp2, vacc) of
        true -> {ok, Resp2#vacc.resp};
        _ -> {ok, Resp2}
    end.


design_doc_view(Req, Db, DDoc, ViewName, Keys) ->
    Args0 = couch_mrview_http:parse_params(Req, Keys),
    ETagFun = fun(Sig, Acc0) ->
        couch_mrview_http:check_view_etag(Sig, Acc0, Req)
    end,
    Args = Args0#mrargs{preflight_fun=ETagFun},
    {ok, Resp} = couch_httpd:etag_maybe(Req, fun() ->
        VAcc0 = #vacc{db=Db, req=Req},
        fabric:query_view(Db, DDoc, ViewName, fun couch_mrview_http:view_cb/2, VAcc0, Args)
    end),
    case is_record(Resp, vacc) of
        true -> {ok, Resp#vacc.resp};
        _ -> {ok, Resp}
    end.

handle_view_req(#httpd{method='GET',
        path_parts=[_, _, _, _, ViewName]}=Req, Db, DDoc) ->
    couch_stats:increment_counter([couchdb, httpd, view_reads]),
    Keys = chttpd:qs_json_value(Req, "keys", undefined),
    design_doc_view(Req, Db, DDoc, ViewName, Keys);

handle_view_req(#httpd{method='POST',
        path_parts=[_, _, _, _, ViewName]}=Req, Db, DDoc) ->
    Props = couch_httpd:json_body_obj(Req),
    Keys = couch_mrview_util:get_view_keys(Props),
    Queries = couch_mrview_util:get_view_queries(Props),
    case {Queries, Keys} of
        {Queries, undefined} when is_list(Queries) ->
            [couch_stats:increment_counter([couchdb, httpd, view_reads]) || _I <- Queries],
            multi_query_view(Req, Db, DDoc, ViewName, Queries);
        {undefined, Keys} when is_list(Keys) ->
            couch_stats:increment_counter([couchdb, httpd, view_reads]),
            design_doc_view(Req, Db, DDoc, ViewName, Keys);
        {undefined, undefined} ->
            throw({
                bad_request,
                "POST body must contain `keys` or `queries` field"
            });
        {_, _} ->
            throw({bad_request, "`keys` and `queries` are mutually exclusive"})
    end;

handle_view_req(Req, _Db, _DDoc) ->
    chttpd:send_method_not_allowed(Req, "GET,POST,HEAD").

handle_temp_view_req(Req, _Db) ->
    Msg = <<"Temporary views are not supported in CouchDB">>,
    chttpd:send_error(Req, 403, forbidden, Msg).