(* Ocsigen
 * http://www.ocsigen.org
 * Module outputfilter.ml
 * Copyright (C) 2008 Vincent Balat
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, with linking exception;
 * either version 2.1 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *)

(* This module enables rewritting the server output *)

type header_filter =
  [ `Rewrite of Ocsigen_header.Name.t * Re.Pcre.regexp * string
  | `Add of Ocsigen_header.Name.t * string * bool option ]

let gen filter = function
  | Ocsigen_extensions.Req_not_found (code, _) ->
      Lwt.return (Ocsigen_extensions.Ext_next code)
  | Ocsigen_extensions.Req_found (_ri, res) ->
      Lwt.return
      @@ Ocsigen_extensions.Ext_found
           (fun () ->
             Lwt.return
             @@
             match filter with
             | `Rewrite (header, regexp, dest) -> (
               try
                 let l =
                   List.map
                     (Ocsigen_lib.Netstring_pcre.global_replace regexp dest)
                     (Ocsigen_response.header_multi res header)
                 and a = Ocsigen_response.remove_header res header in
                 Ocsigen_response.add_header_multi a header l
               with Not_found -> res)
             | `Add (header, dest, replace) -> (
               match replace with
               | None -> (
                 match Ocsigen_response.header res header with
                 | Some _ -> res
                 | None -> Ocsigen_response.add_header res header dest)
               | Some false -> Ocsigen_response.add_header res header dest
               | Some true -> Ocsigen_response.replace_header res header dest))

let gen_code code = function
  | Ocsigen_extensions.Req_not_found (code, _) ->
      Lwt.return (Ocsigen_extensions.Ext_next code)
  | Ocsigen_extensions.Req_found (_ri, res) ->
      Lwt.return
      @@ Ocsigen_extensions.Ext_found
           (fun () -> Lwt.return (Ocsigen_response.set_status res code))

let parse_config config_elem =
  let header = ref None in
  let regexp = ref None in
  let dest = ref None in
  let replace = ref None in
  let code = ref None in
  Ocsigen_extensions.(
    Configuration.process_element ~in_tag:"host"
      ~other_elements:(fun t _ _ -> raise (Bad_config_tag_for_extension t))
      ~elements:
        [ Configuration.element ~name:"outputfilter"
            ~attributes:
              [ Configuration.attribute ~name:"header" (fun s ->
                    header := Some s)
              ; Configuration.attribute ~name:"regexp" (fun s ->
                    regexp := Some (Ocsigen_lib.Netstring_pcre.regexp s))
              ; Configuration.attribute ~name:"dest" (fun s -> dest := Some s)
              ; Configuration.attribute ~name:"replace" (fun s ->
                    try replace := Some (bool_of_string s)
                    with Invalid_argument _ ->
                      badconfig
                        "Wrong value for attribute replace of <outputfilter/>: %s. It should be true or false"
                        s) ]
            ()
        ; Configuration.element ~name:"sethttpcode"
            ~attributes:
              [ Configuration.attribute ~name:"code" (fun s ->
                    try
                      match Cohttp.Code.status_of_code (int_of_string s) with
                      | #Cohttp.Code.status as status -> code := Some status
                      | `Code _ -> failwith "Invalid code"
                    with Failure _ ->
                      badconfig "Invalid code attribute in <sethttpcode>") ]
            () ]
      config_elem);
  match !code with
  | None -> (
    match !header, !regexp, !dest, !replace with
    | _, Some _, _, Some _ ->
        Ocsigen_extensions.badconfig
          "Wrong attributes for <outputfilter/>: attributes regexp and replace can't be set simultaneously"
    | Some h, Some r, Some d, None ->
        gen (`Rewrite (Ocsigen_header.Name.of_string h, r, d))
    | Some h, None, Some d, rep ->
        gen (`Add (Ocsigen_header.Name.of_string h, d, rep))
    | _ ->
        Ocsigen_extensions.badconfig
          "Wrong attributes for <outputfilter header=... dest=... (regexp=... / replace=...)/>"
    )
  | Some code -> gen_code code

let () =
  Ocsigen_extensions.register ~name:"outputfilter"
    ~fun_site:(fun _ _ _ _ _ _ -> parse_config)
    ()

let mode = Ocsigen_server.Site.Config.key ()

let extension =
  Ocsigen_server.Site.create_extension
    (fun {Ocsigen_server.Site.Config.accessor} ->
      match accessor mode with
      | Some (`Code c) -> gen_code c
      | Some (#header_filter as f) -> gen f
      | None -> failwith "Outputfilter.mode not set")
