open Async
open Core
open Websocket_async

exception Invalid_Payload
exception Failure_to_Establish_Heartbeat

module Shard = struct
    type shard = {
        hb: unit Ivar.t option;
        seq: int;
        session: string option;
        pipe: Frame.t Pipe.Reader.t * Frame.t Pipe.Writer.t;
        ready: unit Ivar.t;
        token: string;
        url: string;
        id: int * int;
    }

    type 'a t = {
        mutable shard: 'a;
        mutable binds: ('a -> unit) list;
    }

    let identify_lock = Mutex.create ()

    let bind ~f t =
        t.binds <- f :: t.binds

    let parse (frame:[`Ok of Frame.t | `Eof]) =
        match frame with
        | `Ok s -> begin
            let open Frame.Opcode in
            match s.opcode with
            | Text -> Some (Yojson.Basic.from_string s.content)
            | _ -> None
        end
        | `Eof -> None

    let push_frame ?payload ~ev shard =
        print_endline @@ "Pushing frame. OP: " ^ Opcode.to_string @@ ev;
        let content = match payload with
        | None -> ""
        | Some p ->
            Yojson.Basic.to_string @@ `Assoc [
            ("op", `Int (Opcode.to_int ev));
            ("d", p);
            ]
        in
        let (_, write) = shard.pipe in
        Pipe.write_if_open write @@ Frame.create ~content ()
        >>| fun () ->
        shard

    let heartbeat shard =
        let payload = match shard.seq with
        | 0 -> `Null
        | i -> `Int i
        in
        push_frame ~payload ~ev:HEARTBEAT shard

    let dispatch ~payload shard =
        let module J = Yojson.Basic.Util in
        let seq = J.(member "s" payload |> to_int) in
        let t = J.(member "t" payload |> to_string) in
        let data = J.member "d" payload in
        let session = J.(member "session_id" data |> to_string_option) in
        if t = "READY" then begin
            Ivar.fill_if_empty shard.ready ();
        end;
        return { shard with
            seq = seq;
            session = session;
        }

    let set_status ~status shard =
        let payload = match status with
        | `Assoc [("name", `String name); ("type", `Int t)] ->
            `Assoc [
                ("status", `String "online");
                ("afk", `Bool false);
                ("since", `Null);
                ("game", `Assoc [
                    ("name", `String name);
                    ("type", `Int t)
                ])
            ]
        | `String name ->
            `Assoc [
                ("status", `String "online");
                ("afk", `Bool false);
                ("since", `Null);
                ("game", `Assoc [
                    ("name", `String name);
                    ("type", `Int 0)
                ])
            ]
        | _ -> raise Invalid_Payload
        in
        Ivar.read shard.ready >>= fun _ ->
        push_frame ~payload ~ev:STATUS_UPDATE shard

    let request_guild_members ~guild ?(query="") ?(limit=0) shard =
        let payload = `Assoc [
            ("guild_id", `String (string_of_int guild));
            ("query", `String query);
            ("limit", `Int limit);
        ] in
        Ivar.read shard.ready >>= fun _ ->
        push_frame ~payload ~ev:REQUEST_GUILD_MEMBERS shard

    let initialize ?data shard =
        let module J = Yojson.Basic.Util in
        let hb = match shard.hb with
        | None -> begin
            match data with
            | Some data ->
                let hb_interval = J.(member "heartbeat_interval" data |> to_int) in
                let finished = Ivar.create () in
                Clock.every'
                ~continue_on_error:true
                ~finished
                (Core.Time.Span.create ~ms:hb_interval ())
                (fun () -> heartbeat shard >>= fun _ -> return ());
                finished
            | None -> raise Failure_to_Establish_Heartbeat
        end
        | Some s -> s
        in
        let shard = { shard with hb = Some hb; } in
        let (cur, max) = shard.id in
        let shards = [`Int cur; `Int max] in
        match shard.session with
        | None -> begin
            Mutex.lock identify_lock;
            let payload = `Assoc [
                ("token", `String shard.token);
                ("properties", `Assoc [
                    ("$os", `String Sys.os_type);
                    ("$device", `String "dis.ml");
                    ("$browser", `String "dis.ml")
                ]);
                ("compress", `Bool false); (* TODO add compression handling*)
                ("large_threshold", `Int 250);
                ("shard", `List shards);
            ] in
            push_frame ~payload ~ev:IDENTIFY shard
            >>| fun s -> begin
            Clock.after (Core.Time.Span.create ~sec:5 ())
            >>> (fun _ -> Mutex.unlock identify_lock);
            s
            end
        end
        | Some s ->
            let payload = `Assoc [
                ("token", `String shard.token);
                ("session_id", `String s);
                ("seq", `Int shard.seq)
            ] in
            push_frame ~payload ~ev:RESUME shard

    let handle_frame ~f shard =
        let module J = Yojson.Basic.Util in
        let op = J.(member "op" f |> to_int)
            |> Opcode.from_int
        in
        match op with
        | DISPATCH -> dispatch ~payload:f shard
        | HEARTBEAT -> heartbeat shard
        | INVALID_SESSION -> begin
            if J.(member "d" f |> to_bool) then
                initialize shard
            else begin
                initialize { shard with session = None; }
            end
        end
        | RECONNECT -> initialize shard
        | HELLO -> initialize ~data:(J.member "d" f) shard
        | HEARTBEAT_ACK -> return shard
        | opcode ->
            print_endline @@ "Invalid Opcode: " ^ Opcode.to_string opcode;
            return shard

    let rec create ~url ~shards ~token () =
        let open Core in
        let uri = (url ^ "?v=6&encoding=json") |> Uri.of_string in
        let extra_headers = Http.Base.process_request_headers () in
        let host = Option.value_exn ~message:"no host in uri" Uri.(host uri) in
        let port =
            match Uri.port uri, Uri_services.tcp_port_of_uri uri with
            | Some p, _ -> p
            | None, Some p -> p
            | _ -> 443 in
        let scheme = Option.value_exn ~message:"no scheme in uri" Uri.(scheme uri) in
        let tcp_fun (net_to_ws, ws_to_net) =
            let (app_to_ws, write) = Pipe.create () in
            let (read, ws_to_app) = Pipe.create () in
            let initialized = Ivar.create () in
            client
                ~initialized
                ~extra_headers
                ~app_to_ws
                ~ws_to_app
                ~net_to_ws
                ~ws_to_net
                uri
            >>> ignore; (* TODO this needs to error check and retry with backoff *)
            Ivar.read initialized >>| fun () ->
            {
                pipe = (read, write);
                ready = Ivar.create ();
                hb = None;
                seq = 0;
                id = shards;
                session = None;
                token;
                url;
            }
        in
        match Unix.getaddrinfo host (string_of_int port) [] with
        | [] -> failwithf "DNS resolution failed for %s" host ()
        | { ai_addr; _ } :: _ ->
            let addr =
            match scheme, ai_addr with
            | _, ADDR_UNIX path -> `Unix_domain_socket path
            | "https", ADDR_INET (h, p)
            | "wss", ADDR_INET (h, p) ->
                let h = Ipaddr_unix.of_inet_addr h in
                `OpenSSL (h, p, Conduit_async.V2.Ssl.Config.create ())
            | _, ADDR_INET (h, p) ->
                let h = Ipaddr_unix.of_inet_addr h in
                `TCP (h, p)
            in
            Conduit_async.V2.connect addr >>= tcp_fun
    and recreate shard =
        print_endline "Reconnecting...";
        (match shard.hb with
        | Some hb -> Ivar.fill_if_empty hb ()
        | None -> ()
        );
        create ~url:(shard.url) ~shards:(shard.id) ~token:(shard.token) ()
end

type t = {
    shards: (Shard.shard Shard.t) list;
}

let start ?count token =
    let module J = Yojson.Basic.Util in
    Http.get_gateway_bot () >>= fun data ->
    let url = J.(member "url" data |> to_string) in
    let count = match count with
    | Some c -> c
    | None -> J.(member "shards" data |> to_int)
    in
    let shard_list = (0, count) in
    let rec gen_shards l a =
        match l with
        | (id, total) when id >= total -> return a
        | (id, total) ->
            Shard.create ~url ~shards:(id, total) ~token ()
            >>= fun shard ->
            let rec ev_loop t =
                let (read, _) = t.shard.pipe in
                Pipe.read read
                >>= fun frame ->
                (match parse frame with
                | Some f -> begin
                    handle_frame ~f t.shard
                    >>| fun shard ->
                    t.shard <- shard;
                    t
                end
                | None -> recreate t.shard)
                >>= fun t ->
                List.iter ~f:(fun f -> f t.shard) t.binds;
                ev_loop t
            in
            let t = { shard; binds = []; } in
            ev_loop t >>> ignore;
            let a = t :: a in
            gen_shards (id+1, total) a
    in
    gen_shards shard_list []
    >>| fun shards ->
    { shards; }

let set_status sharder status =
    Deferred.all @@ List.map ~f:(fun t ->
        Shard.set_status ~status t.shard
    ) sharder.shards

let set_status_with sharder f =
    Deferred.all @@ List.map ~f:(fun t ->
        Shard.set_status ~status:(f t.shard) t.shard
    ) sharder.shards

let request_guild_members ~guild ?query ?limit sharder =
    Deferred.all @@ List.map ~f:(fun t ->
        Shard.request_guild_members ~guild ?query ?limit t.shard
    ) sharder.shards