let src = Logs.Src.create "requests.headers" ~doc:"HTTP Headers"
module Log = (val Logs.src_log src : Logs.LOG)

(* Use a map with lowercase keys for case-insensitive lookup *)
module StringMap = Map.Make(String)

type t = (string * string list) StringMap.t

let empty = StringMap.empty

let normalize_key k = String.lowercase_ascii k

let add key value t =
  let nkey = normalize_key key in
  Log.debug (fun m -> m "Adding header %s: %s" key value);
  let existing =
    match StringMap.find_opt nkey t with
    | Some (_, values) -> values
    | None -> []
  in
  StringMap.add nkey (key, value :: existing) t

let set key value t =
  let nkey = normalize_key key in
  StringMap.add nkey (key, [value]) t

let get key t =
  let nkey = normalize_key key in
  match StringMap.find_opt nkey t with
  | Some (_, values) -> List.nth_opt values 0
  | None -> None

let get_all key t =
  let nkey = normalize_key key in
  match StringMap.find_opt nkey t with
  | Some (_, values) -> List.rev values
  | None -> []

let remove key t =
  let nkey = normalize_key key in
  StringMap.remove nkey t

let mem key t =
  let nkey = normalize_key key in
  StringMap.mem nkey t

let of_list lst =
  List.fold_left (fun acc (k, v) -> add k v acc) empty lst

let to_list t =
  StringMap.fold (fun _ (orig_key, values) acc ->
    List.fold_left (fun acc v -> (orig_key, v) :: acc) acc (List.rev values)
  ) t []

let merge t1 t2 =
  StringMap.union (fun _ _ v2 -> Some v2) t1 t2

(* Common header builders *)

let content_type mime t =
  set "Content-Type" (Mime.to_string mime) t

let content_length len t =
  set "Content-Length" (Int64.to_string len) t

let accept mime t =
  set "Accept" (Mime.to_string mime) t

let authorization value t =
  set "Authorization" value t

let bearer token t =
  set "Authorization" (Printf.sprintf "Bearer %s" token) t

let basic ~username ~password t =
  let credentials = Printf.sprintf "%s:%s" username password in
  let encoded = Base64.encode_exn credentials in
  set "Authorization" (Printf.sprintf "Basic %s" encoded) t

let user_agent ua t =
  set "User-Agent" ua t

let host h t =
  set "Host" h t

let cookie name value t =
  add "Cookie" (Printf.sprintf "%s=%s" name value) t

let range ~start ?end_ () t =
  let range_value = match end_ with
    | None -> Printf.sprintf "bytes=%Ld-" start
    | Some e -> Printf.sprintf "bytes=%Ld-%Ld" start e
  in
  set "Range" range_value t

(* Additional helper for getting multiple header values *)
let get_multi key t = get_all key t

(* Pretty printer for headers *)
let pp ppf t =
  Format.fprintf ppf "@[<v>Headers:@,";
  let headers = to_list t in
  List.iter (fun (k, v) ->
    Format.fprintf ppf "  %s: %s@," k v
  ) headers;
  Format.fprintf ppf "@]"

let pp_brief ppf t =
  let headers = to_list t in
  let count = List.length headers in
  Format.fprintf ppf "Headers(%d entries)" count