(**
 * 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 Result = Core_result
open Flow_ast_visitor

type t = {
  module_sig: module_sig;
  declare_modules: (Loc.t * module_sig) SMap.t;
  tolerable_errors: tolerable_error list;
}

and module_sig = {
  requires: require list;
  module_kind: module_kind;
  type_exports_named: type_export SMap.t;
  type_exports_star: export_star SMap.t;
}

and require =
  | Require of {
    source: ident;
    require_loc: Loc.t;
    bindings: require_bindings option;
  }
  | ImportDynamic of { source: ident; import_loc: Loc.t }
  | Import0 of ident
  | Import of {
    source: ident;
    named: Loc.t Nel.t SMap.t SMap.t;
    ns: Loc.t Nel.t SMap.t;
    types: Loc.t Nel.t SMap.t SMap.t;
    typesof: Loc.t Nel.t SMap.t SMap.t;
    typesof_ns: Loc.t Nel.t SMap.t;
  }

and require_bindings =
  | BindIdent of ident
  | BindNamed of (Loc.t * ident) SMap.t

and module_kind =
  | CommonJS of {
    exports: cjs_exports option;
  }
  | ES of {
    named: export SMap.t;
    star: export_star SMap.t;
  }

and cjs_exports =
  | CJSExportIdent of ident
  | CJSExportProps of cjs_export SMap.t
  | CJSExportOther

and cjs_export =
  | CJSExport of {
    loc: Loc.t;
    local: ident option;
  }

and export =
  | ExportDefault of { default_loc: Loc.t; local: ident option }
  | ExportNamed of {
    loc: Loc.t;
    local: ident option;
    source: ident option;
  }
  | ExportNs of {
    loc: Loc.t;
    source: ident;
  }

and export_star =
  | ExportStar of { star_loc: Loc.t; source_loc: Loc.t }

and type_export =
  | TypeExportNamed of {
    loc: Loc.t;
    local: ident option;
    source: ident option;
  }

and ident = Loc.t * string

and tolerable_error =
  (* e.g. `module.exports.foo = 4` when not at the top level *)
  | BadExportPosition of Loc.t
  (* e.g. `foo(module)`, dangerous because `module` is aliased *)
  | BadExportContext of string (* offending identifier *) * Loc.t

type error =
  | IndeterminateModuleType of Loc.t

let empty_module_sig = {
  requires = [];
  module_kind = CommonJS { exports = None };
  type_exports_named = SMap.empty;
  type_exports_star = SMap.empty;
}

let empty_file_sig = {
  module_sig = empty_module_sig;
  declare_modules = SMap.empty;
  tolerable_errors = [];
}

let to_string t =
  let string_of_option f = function
  | None -> "None"
  | Some x -> Printf.sprintf "Some (%s)" (f x)
  in
  let items_to_collection_string indent open_ close items =
    let indent_str = String.make (indent * 2) ' ' in
    let items_str =
      items
      |> List.map (Printf.sprintf "%s%s;\n" (indent_str ^ "  "))
      |> String.concat ""
    in
    Printf.sprintf "%s\n%s%s%s" open_ items_str indent_str close
  in
  let items_to_list_string indent items =
    items_to_collection_string indent "[" "]" items
  in
  let items_to_record_string indent items =
    let items = items |> List.map (fun (label, value) ->
      Printf.sprintf "%s: %s" label value
    ) in
    items_to_collection_string indent "{" "}" items
  in
  let string_of_module_sig module_sig =
    let string_of_require_list require_list =
      let string_of_require_bindings = function
      | BindIdent (_, name) -> "BindIdent: " ^ name
      | BindNamed _ -> "BindNamed"
      in
      let string_of_require = function
      | Require {source=(_, name); bindings; _} ->
        Printf.sprintf "Require (%s, %s)"
          name
          (string_of_option string_of_require_bindings bindings)
      | ImportDynamic _ -> "ImportDynamic"
      | Import0 _ -> "Import0"
      | Import _ -> "Import"
      in
      items_to_list_string 2 (List.map string_of_require require_list)
    in
    let string_of_module_kind _ = "TODO" in
    let string_of_type_export_map _ = "TODO" in
    let string_of_export_star_map _ = "TODO" in
    items_to_record_string 1 [
      "requires", string_of_require_list module_sig.requires;
      "module_kind", string_of_module_kind module_sig.module_kind;
      "type_exports_named", string_of_type_export_map module_sig.type_exports_named;
      "type_exports_star", string_of_export_star_map module_sig.type_exports_star;
    ]
  in
  let string_of_declare_modules _ = "TODO" in
  let string_of_tolerable_errors _ = "TODO" in
  items_to_record_string 0 [
    "module_sig", string_of_module_sig t.module_sig;
    "declare_modules", string_of_declare_modules t.declare_modules;
    "tolerable_errors", string_of_tolerable_errors t.tolerable_errors;
  ]

let combine_nel _ a b = Some (Nel.concat (a, [b]))

let require_loc_map msig =
  let acc = SMap.empty in
  (* requires *)
  let acc = List.fold_left (fun acc require ->
    match require with
    | Require { source = (loc, mref); _ }
    | ImportDynamic { source = (loc, mref); _ }
    | Import0 (loc, mref)
    | Import { source = (loc, mref); _ } ->
      SMap.add mref (Nel.one loc) acc ~combine:Nel.rev_append
  ) acc msig.requires in
  (* export type {...} from 'foo' *)
  let acc = SMap.fold (fun _ type_export acc ->
    match type_export with
    | TypeExportNamed { source = Some (loc, mref); _ } ->
      SMap.add mref (Nel.one loc) acc ~combine:Nel.rev_append
    | _ -> acc
  ) msig.type_exports_named acc in
  (* export type * from 'foo' *)
  let acc = SMap.fold (fun mref export_star acc ->
    match export_star with
    | ExportStar { source_loc; _ } ->
      SMap.add mref (Nel.one source_loc) acc ~combine:Nel.rev_append
  ) msig.type_exports_star acc in
  let acc = match msig.module_kind with
  | CommonJS _ -> acc
  | ES { named; star } ->
    (* export {...} from 'foo' *)
    let acc = SMap.fold (fun _ export acc ->
      match export with
      | ExportNamed { source = Some (loc, mref); _ }
      | ExportNs { source = (loc, mref); _ } ->
        SMap.add mref (Nel.one loc) acc ~combine:Nel.rev_append
      | _ -> acc
    ) named acc in
    (* export * from 'foo' *)
    let acc = SMap.fold (fun mref export_star acc ->
      match export_star with
      | ExportStar { source_loc; _ } ->
        SMap.add mref (Nel.one source_loc) acc ~combine:Nel.rev_append
    ) star acc in
    acc
  in
  acc

let add_declare_module name m loc fsig = {
  fsig with
  declare_modules = SMap.add name (loc, m) fsig.declare_modules;
}

let add_require require msig =
  let requires = require :: msig.requires in
  Ok ({ msig with requires })

let add_type_exports named star msig =
  let type_exports_named = List.fold_left (fun acc (export, name) ->
    let type_export = match export with
    | ExportNamed { loc; local; source } -> TypeExportNamed { loc; local; source }
    | ExportDefault _ -> failwith "export default type"
    | ExportNs _ -> failwith "export type * as X"
    in
    SMap.add name type_export acc
  ) msig.type_exports_named named in
  let type_exports_star = List.fold_left (fun acc (export_star, mref) ->
    SMap.add mref export_star acc
  ) msig.type_exports_star star in
  Ok { msig with type_exports_named; type_exports_star }

let add_es_exports loc named star msig =
  let result = match msig.module_kind with
  | CommonJS { exports = Some _ } -> Error (IndeterminateModuleType loc)
  | CommonJS { exports = None } -> Ok (SMap.empty, SMap.empty)
  | ES { named; star } -> Ok (named, star)
  in
  match result with
  | Error e -> Error e
  | Ok (named0, star0) ->
    let named = List.fold_left (fun acc (export, name) ->
      SMap.add name export acc
    ) named0 named in
    let star = List.fold_left (fun acc (export_star, mref) ->
      SMap.add mref export_star acc
    ) star0 star in
    let module_kind = ES { named; star } in
    Ok ({ msig with module_kind })

let assert_cjs ~update_exports mod_exp_loc msig =
  match msig.module_kind with
  | CommonJS { exports } ->
    let exports = Some (update_exports @@ Option.value exports ~default:(CJSExportProps SMap.empty)) in
    let module_kind = CommonJS { exports } in
    Ok { msig with module_kind }
  | ES _ -> Error (IndeterminateModuleType mod_exp_loc)

let set_cjs_exports exports mod_exp_loc msig =
  assert_cjs mod_exp_loc msig ~update_exports:(Fn.const exports)

let add_cjs_export name loc local mod_exp_loc msig =
  assert_cjs mod_exp_loc msig ~update_exports:(function
    | CJSExportProps exports -> CJSExportProps (SMap.add name (CJSExport { loc; local }) exports)
    (* TODO: What do we do if we see `module.exports = ...` and then
     * 'module.exports.foo = ...'? *)
    | x -> x
  )

(* Subclass of the AST visitor class that calculates requires. Initializes with
   the scope builder class.
*)
class requires_calculator ~ast = object(this)
  inherit [(t, error) result] visitor ~init:(Ok empty_file_sig) as super

  val scope_info = Scope_builder.program ast

  val mutable curr_declare_module: module_sig option = None;

  (* This ensures that we do not add `require`s to `module_sig.requires` twice:
   * once in `variable_declarator`/`assignment` and once in `call`. *)
  val mutable visited_requires: Utils_js.LocSet.t = Utils_js.LocSet.empty;

  method private update_module_sig f =
    match curr_declare_module with
    | Some m ->
      (match f m with
      | Error e -> this#set_acc (Error e)
      | Ok msig -> curr_declare_module <- Some msig)
    | None ->
      this#update_acc (function
        | Error _ as acc -> acc
        | Ok fsig ->
          match f fsig.module_sig with
          | Error e -> Error e
          | Ok module_sig -> Ok ({ fsig with module_sig })
      )

  method private add_require require =
    this#update_module_sig (add_require require)

  method private add_exports loc kind named batch =
    let add = Ast.Statement.(match kind with
    | ExportType -> add_type_exports
    | ExportValue -> (add_es_exports loc)
    ) in
    this#update_module_sig (add named batch)

  method private set_cjs_exports exports mod_exp_loc =
    this#update_module_sig (set_cjs_exports exports mod_exp_loc)

  method private add_cjs_export name loc local mod_exp_loc =
    this#update_module_sig (add_cjs_export name loc local mod_exp_loc)

  method private add_tolerable_error (err: tolerable_error) =
    this#update_acc (Result.map ~f:(fun fsig ->
        { fsig with tolerable_errors=err::fsig.tolerable_errors }
    ))

  method! expression (expr: Loc.t Ast.Expression.t) =
    let open Ast.Expression in
    begin match expr with
    (* Disallow expressions consisting of `module` or `exports`. These are dangerous because they
     * can allow aliasing and mutation. *)
    | _, Identifier (loc, (("module" | "exports") as name))
        when not (Scope_api.is_local_use scope_info loc) ->
      this#add_tolerable_error (BadExportContext (name, loc))
    | _ -> ()
    end;
    super#expression expr

  method! binary (expr: Loc.t Ast.Expression.Binary.t) =
    let open Ast.Expression in
    let open Ast.Expression.Binary in
    let is_module_or_exports = function
      | _, Identifier (_, ("module" | "exports")) -> true
      | _ -> false
    in
    let is_legal_operator = function
      | StrictEqual | StrictNotEqual -> true
      | _ -> false
    in
    let identify_or_recurse subexpr =
      if not (is_module_or_exports subexpr) then
        ignore (this#expression subexpr)
    in
    let { operator; left; right } = expr in
    (* Whitelist e.g. `require.main === module` by avoiding the recursive calls (where the errors
     * are generated) if the AST matches specific patterns. *)
    if is_legal_operator operator then begin
      identify_or_recurse left;
      identify_or_recurse right;
      expr
    end else
      super#binary expr

  method! member (expr: Loc.t Ast.Expression.Member.t) =
    let open Ast.Expression in
    let open Ast.Expression.Member in
    let { _object; property; computed = _ } = expr in
    (* Strip the loc to simplify the patterns *)
    let _, _object = _object in
    (* This gets called when patterns like `module.id` appear on the LHS of an
     * assignment, in addition to when they appear in ordinary expression
     * locations. Therefore we have to prevent anything that would be dangerous
     * if it appeared on the LHS side of an assignment. Ordinary export
     * statements are handled by handle_assignment, which stops recursion so we
     * don't arrive here in those cases. *)
    begin match _object, property with
      (* Allow `module.anythingButExports` *)
      | Identifier (_, "module"), PropertyIdentifier (_, prop) when prop <> "exports" -> ()
      (* Allow `module.exports.whatever` -- this is safe because handle_assignment has already
       * looked for assignments to it before recursing down here. *)
      | Member {
          _object=(_, Identifier (_, "module"));
          property = PropertyIdentifier (_, "exports");
          _;
        },
        PropertyIdentifier _
      (* Allow `exports.whatever`, for the same reason as above *)
      | Identifier (_, "exports"), PropertyIdentifier _ ->
        (* In these cases we don't know much about the property so we should recurse *)
        ignore (this#member_property property)
      | _ -> ignore (super#member expr)
    end;
    expr

  method! call call_loc (expr: Loc.t Ast.Expression.Call.t) =
    let open Ast.Expression in
    let { Call.callee; targs = _; arguments } = expr in
    this#handle_call call_loc callee arguments None;
    super#call call_loc expr

  method! import import_loc (expr: Loc.t Ast.Expression.t) =
    let open Ast.Expression in
    begin match expr with
    | loc, (
        Literal { Ast.Literal.value = Ast.Literal.String name; _ } |
        TemplateLiteral { TemplateLiteral.
          quasis = [_, { TemplateLiteral.Element.
            value = { TemplateLiteral.Element.cooked = name; _ }; _
          }]; _
        }
      ) ->
      this#add_require (ImportDynamic {
        source = (loc, name);
        import_loc;
      })
    | _ -> ()
    end;
    super#expression expr

  method! import_declaration stmt_loc (decl: Loc.t Ast.Statement.ImportDeclaration.t) =
    let open Ast.Statement.ImportDeclaration in
    let { importKind; source; specifiers; default } = decl in
    let source = match source with
    | loc, { Ast.StringLiteral.value = name; _ } -> loc, name
    in
    let import = match default, specifiers with
    | None, None -> Import0 source
    | _ ->
      let named = ref SMap.empty in
      let ns = ref SMap.empty in
      let types = ref SMap.empty in
      let typesof = ref SMap.empty in
      let typesof_ns = ref SMap.empty in
      let ref_of_kind = function
        | ImportType -> types
        | ImportTypeof -> typesof
        | ImportValue -> named
      in
      let add_named remote local loc ref =
        let locals = SMap.singleton local (Nel.one loc) in
        let combine_nel_smap a b = SMap.union a b ~combine:combine_nel in
        ref := SMap.add remote locals !ref ~combine:combine_nel_smap
      in
      let add_ns local loc ref =
        let locs = Nel.one loc in
        ref := SMap.add local locs !ref ~combine:Nel.rev_append
      in
      Option.iter ~f:(fun (loc, local) ->
        add_named "default" local loc (ref_of_kind importKind)
      ) default;
      Option.iter ~f:(function
        | ImportNamespaceSpecifier (loc, (_, local)) ->
          (match importKind with
          | ImportType -> failwith "import type * is a parse error"
          | ImportTypeof -> add_ns local loc typesof_ns
          | ImportValue -> add_ns local loc ns)
        | ImportNamedSpecifiers named_specifiers ->
          List.iter (function {local; remote; kind} ->
            let importKind = match kind with Some k -> k | None -> importKind in
            let loc, local_name = match local with Some x -> x | None -> remote in
            let _, remote_name = remote in
            add_named remote_name local_name loc (ref_of_kind importKind)
          ) named_specifiers
      ) specifiers;
      Import {
        source;
        named = !named;
        ns = !ns;
        types = !types;
        typesof = !typesof;
        typesof_ns = !typesof_ns;
      }
    in
    this#add_require import;
    super#import_declaration stmt_loc decl

  method! export_default_declaration stmt_loc (decl: Loc.t Ast.Statement.ExportDefaultDeclaration.t) =
    let open Ast.Statement in
    let open Ast.Statement.ExportDefaultDeclaration in
    let { default = default_loc; declaration } = decl in
    let local =  match declaration with
    | Declaration (_, FunctionDeclaration { Ast.Function.id; _ }) -> id
    | Declaration (_, ClassDeclaration { Ast.Class.id; _ }) -> id
    | _ -> None
    in
    let export = ExportDefault { default_loc; local } in
    this#add_exports stmt_loc ExportValue [export, "default"] [];
    super#export_default_declaration stmt_loc decl

  method! export_named_declaration stmt_loc (decl: Loc.t Ast.Statement.ExportNamedDeclaration.t) =
    let open Ast.Statement.ExportNamedDeclaration in
    let { exportKind; source; specifiers; declaration} = decl in
    let source = match source with
    | Some (loc, { Ast.StringLiteral.value = mref; raw = _ }) -> Some (loc, mref)
    | None -> None
    in
    begin match declaration with
    | None -> () (* assert specifiers <> None *)
    | Some (loc, stmt) ->
      let open Ast.Statement in
      assert (source = None);
      match stmt with
      | FunctionDeclaration { Ast.Function.id = Some (loc, name); _ }
      | ClassDeclaration { Ast.Class.id = Some (loc, name); _ } ->
        let export = ExportNamed { loc; local = None; source } in
        this#add_exports stmt_loc ExportValue [export, name] []
      | VariableDeclaration { VariableDeclaration.declarations = decls; _ } ->
        let bindings = Ast_utils.bindings_of_variable_declarations decls in
        let bindings = List.map (fun (loc, name) ->
          let export = ExportNamed { loc; local = None; source } in
          (export, name)
        ) bindings in
        this#add_exports stmt_loc ExportValue bindings []
      | TypeAlias { TypeAlias.id; _ }
      | OpaqueType { OpaqueType.id; _ }
      | InterfaceDeclaration { Interface.id; _ } ->
        let export = ExportNamed { loc; local = None; source } in
        this#add_exports stmt_loc ExportType [export, (snd id)] [];
      | _ -> failwith "unsupported declaration"
    end;
    begin match specifiers with
    | None -> () (* assert declaration <> None *)
    | Some specifiers ->
      this#export_specifiers stmt_loc exportKind source specifiers
    end;
    super#export_named_declaration stmt_loc decl

  method! declare_module_exports loc (annot: Loc.t Ast.Type.annotation) =
    this#set_cjs_exports (CJSExportProps SMap.empty) loc;
    super#declare_module_exports loc annot

  method! declare_export_declaration stmt_loc (decl: Loc.t Ast.Statement.DeclareExportDeclaration.t) =
    let open Ast.Statement.DeclareExportDeclaration in
    let { default; source; specifiers; declaration } = decl in
    let source = match source with
    | Some (loc, { Ast.StringLiteral.value = mref; raw = _ }) ->
      assert (Option.is_none default); (* declare export default from not supported *)
      Some (loc, mref)
    | _ -> None
    in
    begin match declaration with
    | None -> () (* assert specifiers <> None *)
    | Some declaration ->
      let open Ast.Statement in
      assert (source = None);
      match declaration with
      | Variable (_, { DeclareVariable.id; _ })
      | Function (_, { DeclareFunction.id; _ })
      | Class (_, { DeclareClass.id; _ }) ->
        let name, export =
          match default with
          | Some default_loc ->
            "default", ExportDefault { default_loc; local = Some id }
          | None ->
            snd id, ExportNamed { loc = fst id; local = None; source }
        in
        this#add_exports stmt_loc ExportValue [export, name] []
      | DefaultType _ ->
        let default_loc = match default with
        | Some loc -> loc
        | None -> failwith "declare export default must have a default loc"
        in
        let export = ExportDefault { default_loc; local = None } in
        this#add_exports stmt_loc ExportValue [export, "default"] []
      | NamedType (_, { TypeAlias.id; _ })
      | NamedOpaqueType (_, { OpaqueType.id; _ })
      | Interface (_, { Interface.id; _ }) ->
        assert (Option.is_none default);
        let export = ExportNamed { loc = fst id; local = None; source } in
        this#add_exports stmt_loc ExportType [export, snd id] []
    end;
    begin match specifiers with
    | None -> () (* assert declaration <> None *)
    | Some specifiers ->
      assert (Option.is_none default);
      (* declare export type unsupported *)
      let exportKind = Ast.Statement.ExportValue in
      this#export_specifiers stmt_loc exportKind source specifiers
    end;
    super#declare_export_declaration stmt_loc decl

  method! assignment (expr: Loc.t Ast.Expression.Assignment.t) =
    this#handle_assignment ~is_toplevel:false expr;
    expr

  method handle_assignment ~(is_toplevel: bool) (expr: Loc.t Ast.Expression.Assignment.t) =
    let open Ast.Expression in
    let open Ast.Expression.Assignment in
    let { operator; left; right } = expr in

    (* Handle exports *)
    begin match operator, left with
    (* module.exports = ... *)
    | Assign, (mod_exp_loc, Ast.Pattern.Expression (_, Member { Member.
        _object = module_loc, Identifier (_, "module");
        property = Member.PropertyIdentifier (_, "exports"); _
      })) when not (Scope_api.is_local_use scope_info module_loc) ->
      this#handle_cjs_default_export mod_exp_loc module_loc right;
      ignore (this#expression right);
      if not is_toplevel then
        this#add_tolerable_error (BadExportPosition mod_exp_loc)
    (* exports.foo = ... *)
    | Assign, (_, Ast.Pattern.Expression (_, Member { Member.
        _object = mod_exp_loc as module_loc, Identifier (_, "exports");
        property = Member.PropertyIdentifier (loc, name); _
      }))
    (* module.exports.foo = ... *)
    | Assign, (_, Ast.Pattern.Expression (_, Member { Member.
        _object = mod_exp_loc, Member { Member.
          _object = module_loc, Identifier (_, "module");
          property = Member.PropertyIdentifier (_, "exports"); _
        };
        property = Member.PropertyIdentifier (loc, name); _
      })) when not (Scope_api.is_local_use scope_info module_loc) ->
      (* expressions not allowed in declare module body *)
      assert (curr_declare_module = None);
      begin match right with
      | _, Identifier id ->
        this#add_cjs_export name loc (Some id) mod_exp_loc
      | _ ->
        this#add_cjs_export name loc None mod_exp_loc
      end;
      ignore (this#expression right);
      if not is_toplevel then
        this#add_tolerable_error (BadExportPosition mod_exp_loc)
    (* module = ... *)
    | Assign, (_, Ast.Pattern.Identifier {
        Ast.Pattern.Identifier.name=(loc, ("exports" | "module" as id)); _
      }) when not (Scope_api.is_local_use scope_info loc) ->
      ignore (this#expression right);
      this#add_tolerable_error (BadExportContext (id, loc))
    | _ ->
      ignore (super#assignment expr)
    end;

    (* Handle imports *)
    begin match operator with
    | Assign -> this#handle_require left right
    | _ -> ()
    end

  method handle_cjs_default_export
      (mod_exp_loc: Loc.t)
      (module_loc: Loc.t)
      (right: Loc.t Ast.Expression.t) =
    let open Ast.Expression in
    (* expressions not allowed in declare module body *)
    assert (curr_declare_module = None);
    if not (Scope_api.is_local_use scope_info module_loc)
    then this#set_cjs_exports (CJSExportProps SMap.empty) mod_exp_loc;
    begin match right with
    | _, Identifier id -> this#set_cjs_exports (CJSExportIdent id) mod_exp_loc
    | _, Object { Object.properties } ->
      List.iter (function
        | Object.Property (_, Object.Property.Init { key; value; _ }) ->
          begin match key with
          | Object.Property.Identifier (loc, name) ->
            begin match value with
            | _, Identifier id -> this#add_cjs_export name loc (Some id) mod_exp_loc
            | _ -> this#add_cjs_export name loc None mod_exp_loc
            end
          | _ -> ()
          end
        | _ -> ()
      ) properties
    | _ -> this#set_cjs_exports CJSExportOther mod_exp_loc
    end

  method! variable_declarator ~kind (decl: Loc.t Ast.Statement.VariableDeclaration.Declarator.t) =
    begin match decl with
    | _, { Ast.Statement.VariableDeclaration.Declarator.id; init = Some init } ->
      this#handle_require id init
    | _ -> ()
    end;
    super#variable_declarator ~kind decl

  method private handle_require (left: Loc.t Ast.Pattern.t) (right: Loc.t Ast.Expression.t) =
    let open Ast.Expression in
    let bindings = begin match left with
    | _, Ast.Pattern.Identifier { Ast.Pattern.Identifier.name; _ } -> Some (BindIdent name)
    | _, Ast.Pattern.Object { Ast.Pattern.Object.properties; _ } ->
      Some (BindNamed (List.fold_left (fun acc prop ->
        match prop with
        | Ast.Pattern.Object.Property (_, {
            Ast.Pattern.Object.Property.key = Ast.Pattern.Object.Property.Identifier remote;
            pattern = _, Ast.Pattern.Identifier { Ast.Pattern.Identifier.name = (local_loc, local_name); _ };
            _
          }) ->
          SMap.add local_name (local_loc, remote) acc
        | _ -> acc
      ) SMap.empty properties))
    | _ -> None
    end in
    begin match right with
    | call_loc, Call { Call.callee; targs = _; arguments } ->
      this#handle_call call_loc callee arguments bindings
    | _ -> ()
    end

  method private handle_call call_loc callee arguments bindings =
    let open Ast.Expression in
    if not (Utils_js.LocSet.mem call_loc visited_requires) then begin
      visited_requires <- Utils_js.LocSet.add call_loc visited_requires;
      match callee, arguments with
      | ((_, Identifier (loc, "require")), [Expression (source_loc, (
          Literal { Ast.Literal.value = Ast.Literal.String name; _ } |
          TemplateLiteral { TemplateLiteral.
            quasis = [_, { TemplateLiteral.Element.
              value = { TemplateLiteral.Element.cooked = name; _ }; _
            }]; _
          }
        ))]) ->
        if not (Scope_api.is_local_use scope_info loc)
        then
          this#add_require (Require {
            source = (source_loc, name);
            require_loc = call_loc;
            bindings;
          })
      | ((_, Identifier (loc, "requireLazy")),
         [Expression (_, Array ({ Array.elements })); Expression (_);])
        ->
        let element = function
          | Some (Expression (source_loc, Literal { Ast.Literal.value = Ast.Literal.String name; _ })) ->
            if not (Scope_api.is_local_use scope_info loc)
            then
              this#add_require (Require {
                source = (source_loc, name);
                require_loc = call_loc;
                bindings;
              })
          | _ -> () in
        List.iter element elements
      | _ -> ()
    end

  method! declare_module loc (m: Loc.t Ast.Statement.DeclareModule.t) =
    let name = Ast.Statement.DeclareModule.(match m.id with
    | Identifier (_, name) -> name
    | Literal (_, { Ast.StringLiteral.value; _ }) -> value
    ) in
    curr_declare_module <- Some (empty_module_sig);
    let ret = super#declare_module loc m in
    begin match curr_declare_module with
    | None -> failwith "lost curr_declare_module"
    | Some m ->
      this#update_acc (function
        | Error _ as acc -> acc
        | Ok fsig -> Ok (add_declare_module name m loc fsig)
      )
    end;
    curr_declare_module <- None;
    ret

  method private export_specifiers stmt_loc kind source =
    let open Ast.Statement.ExportNamedDeclaration in
    function
    | ExportBatchSpecifier (_, Some (loc, name)) ->
      (* export type * as X from "foo" unsupported *)
      assert (kind = Ast.Statement.ExportValue);
      let mref = match source with
      | Some mref -> mref
      | None -> failwith "export batch without source"
      in
      this#add_exports stmt_loc kind [ExportNs { loc; source = mref }, name] []
    | ExportBatchSpecifier (star_loc, None) ->
      let source_loc, mref = match source with
      | Some (source_loc, mref) -> source_loc, mref
      | _ -> failwith "batch export missing source"
      in
      this#add_exports stmt_loc kind [] [ExportStar { star_loc; source_loc }, mref]
    | ExportSpecifiers specs ->
      let bindings = List.fold_left ExportSpecifier.(fun acc (_, spec) ->
        let name, loc, local = match spec.exported with
        | None -> snd spec.local, fst spec.local, None
        | Some remote -> snd remote, fst remote, Some spec.local
        in
        let export = ExportNamed { loc; local; source } in
        (export, name) :: acc
      ) [] specs in
      this#add_exports stmt_loc kind bindings []

  method! toplevel_statement_list (stmts: Loc.t Ast.Statement.t list) =
    let open Ast in
    let id = Flow_ast_mapper.id in
    let map_expression (expr: Loc.t Expression.t) =
      let open Expression in
      match expr with
      | _, Assignment assg ->
          this#handle_assignment ~is_toplevel:true assg;
          expr
      | _ -> this#expression expr
    in
    let map_expression_statement (stmt: Loc.t Statement.Expression.t) =
      let open Statement.Expression in
      let {expression; _} = stmt in
      id map_expression expression stmt (fun expr -> { stmt with expression=expr })
    in
    let map_statement (stmt: Loc.t Statement.t) =
      let open Statement in
      match stmt with
      | loc, Expression expr ->
        id map_expression_statement expr stmt (fun expr -> loc, Expression expr)
      | _ -> this#statement stmt
    in
    ListUtils.ident_map map_statement stmts
end

let program ~ast =
  let walk = new requires_calculator ~ast in
  walk#eval walk#program ast
