(**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *)

module S = Ast.Statement;;
module E = Ast.Expression;;
module T = Ast.Type;;
module P = Ast.Pattern;;
module Utils = Flowtestgen_utils;;

(* ESSENTIAL: Syntax type and related functions *)
module Syntax = Syntax_base;;
open Ruleset_base;;

class ruleset_func = object(self)
  inherit Ruleset_base.ruleset_base

  method! get_name () : string = "func"

  method! weak_assert b = self#backtrack_on_false b

  method! is_subtype_func
      (f1 : Loc.t T.Function.t)
      (f2 : Loc.t T.Function.t) : bool =
    let open T.Function in
    let get_type_list (f : Loc.t T.Function.t) : Loc.t T.t' list =
      let open T.Function.Param in
      let (_, { T.Function.Params.params; rest = _ }) = f.params in
      List.map
        (fun param -> (snd param).typeAnnotation |> snd)
        params @ [f.returnType |> snd] in

    let rec func_subtype_helper l1 l2 = match l1, l2 with
      | [], [] -> true
      (* checking the return type *)
      | hd1 :: [], hd2 :: [] -> self#is_subtype hd1 hd2
      (* checking the param type *)
      | hd1 :: tl1, hd2 :: tl2 ->
        (* BAD subtyping check. Please look at ruleset_base
           for the correct subtyping check *)
        (match hd1, hd2 with
         | T.Object _, T.Object _
         | T.Number, T.Number
         | T.String, T.String
         | T.Function _, T.Function _ ->
           func_subtype_helper tl1 tl2
         | _ -> false)
      | _ -> false in

    let p1_list = get_type_list f1 in
    let p2_list = get_type_list f2 in
    if (not ((List.length p1_list) = (List.length p2_list))) then false
    else func_subtype_helper p1_list p2_list

  (* A rule for generating function definitions *)
  method! rule_funcdef (env : env_t) : (Syntax.t * env_t) =
    let mk_func_type (ptype : Loc.t T.t') (rtype : Loc.t T.t') : Loc.t T.t' =
      let param_type =
        (Loc.none, T.Function.Param.({name = None;
                                      typeAnnotation = (Loc.none, ptype);
                                      optional = false})) in
      let ret_type = (Loc.none, rtype) in

      T.Function.(T.Function {params = (Loc.none, { Params.params = [param_type]; rest = None });
                              returnType = ret_type;
                              typeParameters = None}) in

    (* parameter type *)
    let param_type =
      match self#choose 0 (fun () -> self#require_type env) with
      | Type t -> t
      | _ -> failwith "has to be a type" in
    self#backtrack_on_false (match param_type with
        | T.Object _ | T.Function _ -> true
        | _ -> false);

    (* We are assuming we only have one parameter for now *)
    let pname = "param" in

    (* make a new environment to account for parameters

       TODO: This is a hacky way to account for parameters. The
       correct way to do this is to change every expression
       that has the variable occurrences whose type is the super
       type of the parameter *)
    let fenv = (Expr (E.Identifier (Loc.none, pname), param_type)) ::
               (let open T.Function in
                match param_type with
                (* If the parameter is a function, we create new function calls *)
                | T.Function {params = _;
                              returnType = _, rt;
                              typeParameters = _;} ->
                  let open E.Call in
                  List.fold_right (fun elt acc ->
                      match elt with
                      | Expr (E.Call {callee = _, fid;
                                      arguments = args}, _) ->
                        let ftype = self#get_type_from_expr fid env in
                        if self#is_subtype param_type ftype then begin
                          (Expr (E.Call {callee = (Loc.none, E.Identifier (Loc.none, pname));
                                         arguments = args}, rt)) :: elt :: acc
                        end else elt :: acc
                      | _ -> elt :: acc) env []
                (* If the parameter is an object, we create new property read *)
                | T.Object _ ->
                  let open E.Member in
                  List.fold_right (fun elt acc ->
                      match elt with
                      | Expr (E.Member {_object = _, obj;
                                        property = prop;
                                        computed = c}, t) ->
                        let otype = self#get_type_from_expr obj env in
                        if self#is_subtype param_type otype then begin
                          (Expr (E.Member {_object = (Loc.none, E.Identifier (Loc.none, pname));
                                           property = prop;
                                           computed = c}, t)) :: elt :: acc
                        end else elt :: acc
                      | _ -> elt :: acc) env []
                | _ -> env) in

    (* return expression and its type *)
    let func_return_type =
      match self#choose 1 (fun () -> self#require_type fenv) with
      | Type t -> t
      | _ -> failwith "Has to be a type" in
    self#backtrack_on_false (match func_return_type with
        | T.Object _ -> true
        | _ -> false);

    let fname = Utils.mk_func () in

    (* return expression and its type *)
    let ret_expr = self#choose 2 (fun () -> self#require_expr fenv) in
    let ret_expr_expr, ret_expr_type = match ret_expr with
        | Expr (e, t) -> e, t
        | _ -> failwith "This has to be an expression" in
    self#backtrack_on_false (self#is_subtype ret_expr_type func_return_type);
    let ret_stmt = Syntax.mk_ret_stmt ret_expr_expr in

    let func_def =
      Syntax.mk_func_def
        fname
        pname
        param_type
        [ret_stmt]
        func_return_type in

    let ret_type = mk_func_type param_type func_return_type in
    let new_env =
      self#add_binding
        env
        (Expr ((E.Identifier (Loc.none, fname)), ret_type)) in
    let new_env = self#add_binding new_env (Type ret_type) in
    func_def, new_env

  (* A rule for generating function calls *)
  method! rule_func_call (env : env_t) : (Syntax.t * env_t) =
    (* require a function from the environment.*)
    let func = self#choose 0 (fun () -> self#require_expr env) in
    let func_expr, func_type = match func with
        | Expr (e, t) -> e, t
        | _ -> failwith "This has to be an expression" in
    self#backtrack_on_false (match func_type with
        | T.Function _ -> true
        | _ -> false);

    (* get the type of the parameter assuming we only have one param *)
    let f_ptype =
      let open T.Function in
      match func_type with
      | T.Function {params = (_, { Params.params = plist; rest = _ });
                    returnType = _;
                    typeParameters = _} ->
        T.Function.Param.((plist |> List.hd |> snd).typeAnnotation)
      | _ -> failwith "This has to a function type" in

    (* parameter *)
    let param = self#choose 1 (fun () -> self#require_expr env) in
    let param_expr, param_type = match param with
        | Expr (e, t) -> e, t
        | _ -> failwith "This has to be an expression" in
    self#backtrack_on_false (match param_type with
        | T.Function _ -> true
        | T.Object _ -> true
        | _ -> false);
    self#weak_assert (self#is_subtype param_type (snd f_ptype));

    let func_call = Syntax.mk_func_call func_expr param_expr in

    let ret_type = T.Function.(match func_type with
        | T.Function {params = _;
                      returnType = (_, rt);
                      typeParameters =_} -> rt
        | _ -> failwith "This has to be a function type") in
    let new_env =
      self#add_binding
        env
        (Expr ((match func_call with
             | Syntax.Expr e -> e
             | _ -> failwith "This has to be an expression"),
               ret_type)) in

    let new_env = self#add_binding new_env (Type ret_type) in
    func_call, new_env

  method! get_all_rules () =
    [|self#rule_num_lit;
      self#rule_obj_lit 1 0;
      self#rule_obj_lit 2 0;
      self#rule_funcdef;
      self#rule_funcdef;
      self#rule_func_call;
      self#rule_funcdef;
      self#rule_func_call;
    |]
end


class ruleset_random_func = object
  inherit ruleset_func
  method! weak_assert b =
    if (not b) && ((Random.int 3) > 0) then raise Engine.Backtrack
end
