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(* SPDX-License-Identifier: AGPL-3.0-or-later *)
(* Copyright © 2021-2026 OCamlPro *)
(* Written by the Owi programmers *)

module Func = struct
  module Make (Value : sig
    type i32

    type i64

    type f32

    type f64

    type v128
  end) (M : sig
    (** The monad type *)
    type 'a t
  end) (Memory : sig
    (** The memory type *)
    type t
  end) : sig
    val fresh : unit -> int

    include
      Extern_intf.T
        with type i32 := Value.i32
         and type i64 := Value.i64
         and type f32 := Value.f32
         and type f64 := Value.f64
         and type v128 := Value.v128
         and type 'a m := 'a M.t
         and type memory := Memory.t
  end = struct
    type 'a m = 'a M.t

    type memory = Memory.t

    type _ telt =
      | I32 : Value.i32 telt
      | I64 : Value.i64 telt
      | F32 : Value.f32 telt
      | F64 : Value.f64 telt
      | V128 : Value.v128 telt
      | Externref : 'a Type.Id.t -> 'a telt

    type _ rtype =
      | R0 : unit rtype
      | R1 : 'a telt -> 'a rtype
      | R2 : 'a telt * 'b telt -> ('a * 'b) rtype
      | R3 : 'a telt * 'b telt * 'c telt -> ('a * 'b * 'c) rtype
      | R4 : 'a telt * 'b telt * 'c telt * 'd telt -> ('a * 'b * 'c * 'd) rtype

    type (_, _) atype =
      | Mem : int * ('b, 'r) atype -> (memory -> 'b, 'r) atype
      | UArg : ('b, 'r) atype -> (unit -> 'b, 'r) atype
      | Arg : 'a telt * ('b, 'r) atype -> ('a -> 'b, 'r) atype
      | Res : ('r, 'r) atype

    type _ func_type = Func : ('f, 'r m) atype * 'r rtype -> 'f func_type

    type t = Extern_func : 'a func_type * 'a -> t

    let elt_type (type t) (e : t telt) : Binary.val_type =
      match e with
      | I32 -> Num_type I32
      | I64 -> Num_type I64
      | F32 -> Num_type F32
      | F64 -> Num_type F64
      | V128 -> Num_type V128
      | Externref _ -> Ref_type (Null, Extern_ht)

    let res_type (type t) (r : t rtype) : Binary.result_type =
      match r with
      | R0 -> []
      | R1 a -> [ elt_type a ]
      | R2 (a, b) -> [ elt_type a; elt_type b ]
      | R3 (a, b, c) -> [ elt_type a; elt_type b; elt_type c ]
      | R4 (a, b, c, d) -> [ elt_type a; elt_type b; elt_type c; elt_type d ]

    let arg_type =
      let rec aux : type t r. (t, r) atype -> Binary.param_type = function
        | Mem (_, tl) -> aux tl
        | UArg tl -> aux tl
        | Arg (hd, tl) -> (None, elt_type hd) :: aux tl
        | Res -> []
      in
      aux

    (* TODO: we could move this out, as it does not really depend on the functor's parameters *)
    let to_func_type (Extern_func (Func (arg, res), _)) : Binary.func_type =
      (arg_type arg, res_type res)

    let fresh =
      let r = ref ~-1 in
      fun () ->
        incr r;
        !r

    module Syntax = struct
      type l = private [ `L ]

      type lr = private [ `Lr ]

      type elt = private [ `Elt ]

      type (_, _, _) t =
        | Unit : (lr, unit, unit) t
        | Memory : int -> (l, memory, memory) t
        | Elt : 'a telt -> (lr, elt, 'a) t

      let return r = Func (Res, r)

      let r0 = R0 |> return

      let r1 (Elt a) = R1 a |> return

      let r2 (Elt a) (Elt b) = R2 (a, b) |> return

      let r3 (Elt a) (Elt b) (Elt c) = R3 (a, b, c) |> return

      let r4 (Elt a) (Elt b) (Elt c) (Elt d) = R4 (a, b, c, d) |> return

      let i32 = Elt I32

      let i64 = Elt I64

      let f32 = Elt F32

      let f64 = Elt F64

      let v128 = Elt V128

      let externref id = Elt (Externref id)

      let unit = Unit

      let memory id = Memory id

      let ( ^-> ) =
        let aux : type lr k a b.
          (lr, k, a) t -> b func_type -> (a -> b) func_type =
         fun a (Func (b, r)) ->
          match a with
          | Elt a -> Func (Arg (a, b), r)
          | Unit -> Func (UArg b, r)
          | Memory id -> Func (Mem (id, b), r)
        in
        aux

      let ( ^->. ) =
        let aux : type ll k kk a b.
          (ll, k, a) t -> (lr, kk, b) t -> (a -> b m) func_type =
         fun a b -> match b with Elt _ -> a ^-> r1 b | Unit -> a ^-> r0
        in
        aux

      let ( ^->.. ) : type ll k a b1 b2.
           (ll, k, a) t
        -> (lr, elt, b1) t * (lr, elt, b2) t
        -> (a -> (b1 * b2) m) func_type =
       fun a (b1, b2) -> a ^-> r2 b1 b2

      let ( ^->... ) : type ll k a b1 b2 b3.
           (ll, k, a) t
        -> (lr, elt, b1) t * (lr, elt, b2) t * (lr, elt, b3) t
        -> (a -> (b1 * b2 * b3) m) func_type =
       fun a (b1, b2, b3) -> a ^-> r3 b1 b2 b3

      let ( ^->.... ) : type ll k a b1 b2 b3 b4.
           (ll, k, a) t
        -> (lr, elt, b1) t * (lr, elt, b2) t * (lr, elt, b3) t * (lr, elt, b4) t
        -> (a -> (b1 * b2 * b3 * b4) m) func_type =
       fun a (b1, b2, b3, b4) -> a ^-> r4 b1 b2 b3 b4
    end
  end
end