{
    This file is part of the Free Pascal run time library.
    Copyright (c) 2017 by the Free Pascal development team

    RTTI Function Call Manager using Foreign Function Call (libffi) library.

    See the file COPYING.FPC, included in this distribution,
    for details about the copyright.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 **********************************************************************}
unit ffi.manager;

{$mode objfpc}{$H+}

interface

implementation

uses
  TypInfo, Rtti, ffi;

type
  Tpffi_typeArray = array of pffi_type;

procedure FreeFFIType(t: pffi_type);
var
  elements: Tpffi_typeArray;
  i: LongInt;
begin
  if t^._type <> _FFI_TYPE_STRUCT then
    Exit;
  elements := Tpffi_typeArray(t^.elements);
  for i := Low(elements) to High(elements) do
    FreeFFIType(elements[i]);
  { with this the array will be freed }
  elements := Nil;
  Dispose(t);
end;

function TypeInfoToFFIType(aTypeInfo: PTypeInfo; aFlags: TParamFlags): pffi_type; forward;

function RecordOrObjectToFFIType(aTypeInfo: PTypeInfo): pffi_type;
var
  curindex: SizeInt;
  elements: Tpffi_typeArray;

  procedure AddElement(t: pffi_type);
  begin
    if curindex = Length(elements) then begin
      SetLength(elements, Length(elements) * 2);
    end;
    elements[curindex] := t;
    Inc(curindex);
  end;

var
  td, fieldtd: PTypeData;
  i, j, curoffset, remoffset: SizeInt;
  field: PManagedField;
  ffitype: pffi_type;
begin
  td := GetTypeData(aTypeInfo);
  if td^.TotalFieldCount = 0 then
    { uhm... }
    Exit(Nil);
  New(Result);
  FillChar(Result^, SizeOf(Result), 0);
  Result^._type := _FFI_TYPE_STRUCT;
  Result^.elements := Nil;
  curoffset := 0;
  curindex := 0;
  field := PManagedField(PByte(@td^.TotalFieldCount) + SizeOf(td^.TotalFieldCount));
  { assume first that there are no paddings }
  SetLength(elements, td^.TotalFieldCount);
  for i := 0 to td^.TotalFieldCount - 1 do begin
    { ToDo: what about fields that are larger that what we have currently? }
    if field^.FldOffset < curoffset then begin
      Inc(field);
      Continue;
    end;
    remoffset := field^.FldOffset - curoffset;
    { insert padding elements }
    while remoffset >= SizeOf(QWord) do begin
      AddElement(@ffi_type_uint64);
      Dec(remoffset, SizeOf(QWord));
    end;
    while remoffset >= SizeOf(LongWord) do begin
      AddElement(@ffi_type_uint32);
      Dec(remoffset, SizeOf(LongWord));
    end;
    while remoffset >= SizeOf(Word) do begin
      AddElement(@ffi_type_uint16);
      Dec(remoffset, SizeOf(Word));
    end;
    while remoffset >= SizeOf(Byte) do begin
      AddElement(@ffi_type_uint8);
      Dec(remoffset, SizeOf(Byte))
    end;
    { now add the real field type (Note: some are handled differently from
      being passed as arguments, so we handle those here) }
    if field^.TypeRef^.Kind = tkObject then
      AddElement(RecordOrObjectToFFIType(field^.TypeRef))
    else if field^.TypeRef^.Kind = tkSString then begin
      fieldtd := GetTypeData(field^.TypeRef);
      for j := 0 to fieldtd^.MaxLength + 1 do
        AddElement(@ffi_type_uint8);
    end else if field^.TypeRef^.Kind = tkArray then begin
      fieldtd := GetTypeData(field^.TypeRef);
      ffitype := TypeInfoToFFIType(fieldtd^.ArrayData.ElType, []);
      for j := 0 to fieldtd^.ArrayData.ElCount - 1 do
        AddElement(ffitype);
    end else
      AddElement(TypeInfoToFFIType(field^.TypeRef, []));
    Inc(field);
    curoffset := field^.FldOffset;
  end;
  { add a final Nil element }
  AddElement(Nil);
  { reduce array to final size }
  SetLength(elements, curindex);
  { this is a bit cheeky, but it works }
  Tpffi_typeArray(Result^.elements) := elements;
end;

function SetToFFIType(aSize: SizeInt): pffi_type;
var
  elements: Tpffi_typeArray;
  curindex: SizeInt;

  procedure AddElement(t: pffi_type);
  begin
    if curindex = Length(elements) then begin
      SetLength(elements, Length(elements) * 2);
    end;
    elements[curindex] := t;
    Inc(curindex);
  end;

begin
  if aSize = 0 then
    Exit(Nil);
  New(Result);
  Result^._type := _FFI_TYPE_STRUCT;
  Result^.elements := Nil;
  curindex := 0;
  SetLength(elements, aSize);
  while aSize >= SizeOf(QWord) do begin
    AddElement(@ffi_type_uint64);
    Dec(aSize, SizeOf(QWord));
  end;
  while aSize >= SizeOf(LongWord) do begin
    AddElement(@ffi_type_uint32);
    Dec(aSize, SizeOf(LongWord));
  end;
  while aSize >= SizeOf(Word) do begin
    AddElement(@ffi_type_uint16);
    Dec(aSize, SizeOf(Word));
  end;
  while aSize >= SizeOf(Byte) do begin
    AddElement(@ffi_type_uint8);
    Dec(aSize, SizeOf(Byte));
  end;
  AddElement(Nil);
  SetLength(elements, curindex);
  Tpffi_typeArray(Result^.elements) := elements;
end;

function TypeInfoToFFIType(aTypeInfo: PTypeInfo; aFlags: TParamFlags): pffi_type;

  function TypeKindName: String;
  begin
    Result := '';
    WriteStr(Result, aTypeInfo^.Kind);
  end;

var
  td: PTypeData;
begin
  Result := @ffi_type_void;
  if Assigned(aTypeInfo) then begin
    td := GetTypeData(aTypeInfo);
    if aFlags * [pfArray, pfOut, pfVar, pfConstRef] <> [] then
      Result := @ffi_type_pointer
    else
      case aTypeInfo^.Kind of
        tkInteger,
        tkEnumeration,
        tkBool,
        tkInt64,
        tkQWord:
          case td^.OrdType of
            otSByte:
              Result := @ffi_type_sint8;
            otUByte:
              Result := @ffi_type_uint8;
            otSWord:
              Result := @ffi_type_sint16;
            otUWord:
              Result := @ffi_type_uint16;
            otSLong:
              Result := @ffi_type_sint32;
            otULong:
              Result := @ffi_type_uint32;
            otSQWord:
              Result := @ffi_type_sint64;
            otUQWord:
              Result := @ffi_type_uint64;
          end;
        tkChar:
          Result := @ffi_type_uint8;
        tkFloat:
          case td^.FloatType of
            ftSingle:
              Result := @ffi_type_float;
            ftDouble:
              Result := @ffi_type_double;
            ftExtended:
              Result := @ffi_type_longdouble;
            { Comp and Currency are passed as Int64 (ToDo: on all platforms?) }
            ftComp:
              Result := @ffi_type_sint64;
            ftCurr:
              Result := @ffi_type_sint64;
          end;
        tkSet:
          case td^.OrdType of
            otUByte: begin
              if td^.SetSize = 1 then
                Result := @ffi_type_uint8
              else begin
                { ugh... build a of suitable record }
                Result := SetToFFIType(td^.SetSize);
              end;
            end;
            otUWord:
              Result := @ffi_type_uint16;
            otULong:
              Result := @ffi_type_uint32;
          end;
        tkWChar,
        tkUChar:
          Result := @ffi_type_uint16;
        tkInterface,
        tkAString,
        tkUString,
        tkWString,
        tkInterfaceRaw,
        tkProcVar,
        tkDynArray,
        tkClass,
        tkClassRef,
        tkPointer:
          Result := @ffi_type_pointer;
        tkMethod:
          Result := RecordOrObjectToFFIType(TypeInfo(TMethod));
        tkSString:
          { since shortstrings are rather large they're passed as references }
          Result := @ffi_type_pointer;
        tkObject:
          { passed around as pointer as well }
          Result := @ffi_type_pointer;
        tkArray:
          { arrays are passed as pointers to be compatible to C }
          Result := @ffi_type_pointer;
        tkRecord:
          Result := RecordOrObjectToFFIType(aTypeInfo);
        tkVariant:
          Result := RecordOrObjectToFFIType(TypeInfo(tvardata));
        //tkLString: ;
        //tkHelper: ;
        //tkFile: ;
        else
          raise EInvocationError.CreateFmt(SErrTypeKindNotSupported, [TypeKindName]);
      end;
  end else if aFlags * [pfOut, pfVar, pfConst, pfConstRef] <> [] then
    Result := @ffi_type_pointer;
end;

function ArgIsIndirect(aKind: TTypeKind; aFlags: TParamFlags; aIsResult: Boolean): Boolean;
const
  ResultTypeNeedsIndirection = [
   tkAString,
   tkWString,
   tkUString,
   tkInterface,
   tkDynArray
  ];
begin
  Result := False;
  if (aKind = tkSString) or
      (aIsResult and (aKind in ResultTypeNeedsIndirection)) or
      (aFlags * [pfArray, pfOut, pfVar, pfConstRef] <> []) or
      ((aKind = tkUnknown) and (pfConst in aFlags)) then
    Result := True;
end;

procedure FFIValueToValue(Source, Dest: Pointer; TypeInfo: PTypeInfo);
var
  size: SizeInt;
  td: PTypeData;
begin
  td := GetTypeData(TypeInfo);
  size := 0;
  case TypeInfo^.Kind of
    tkChar,
    tkWChar,
    tkUChar,
    tkEnumeration,
    tkBool,
    tkInteger,
    tkInt64,
    tkQWord:
      case td^.OrdType of
        otSByte,
        otUByte:
          size := 1;
        otSWord,
        otUWord:
          size := 2;
        otSLong,
        otULong:
          size := 4;
        otSQWord,
        otUQWord:
          size := 8;
      end;
    tkSet:
      size := td^.SetSize;
    tkFloat:
      case td^.FloatType of
        ftSingle:
          size := SizeOf(Single);
        ftDouble:
          size := SizeOf(Double);
        ftExtended:
          size := SizeOf(Extended);
        ftComp:
          size := SizeOf(Comp);
        ftCurr:
          size := SizeOf(Currency);
      end;
    tkMethod:
      size := SizeOf(TMethod);
    tkSString:
      size := td^.MaxLength + 1;
    tkDynArray,
    tkLString,
    tkAString,
    tkUString,
    tkWString,
    tkClass,
    tkPointer,
    tkClassRef,
    tkInterfaceRaw:
      size := SizeOf(Pointer);
    tkVariant:
      size := SizeOf(tvardata);
    tkArray:
      size := td^.ArrayData.Size;
    tkRecord:
      size := td^.RecSize;
    tkProcVar:
      size := SizeOf(CodePointer);
    tkObject: ;
    tkHelper: ;
    tkFile: ;
  end;

  if size > 0 then
    Move(Source^, Dest^, size);
end;

{ move this to type info? }
function RetInParam(aCallConv: TCallConv; aTypeInfo: PTypeInfo): Boolean;
begin
  Result := False;
  if not Assigned(aTypeInfo) then
    Exit;
  case aTypeInfo^.Kind of
    tkSString,
    tkAString,
    tkWString,
    tkUString,
    tkInterface,
    tkDynArray:
      Result := True;
  end;
end;

{ on X86 platforms Currency and Comp results are passed by the X87 if the
  Extended type is available }
{$if (defined(CPUI8086) or defined(CPUI386) or defined(CPUX86_64)) and defined(FPC_HAS_TYPE_EXTENDED) and (not defined(FPC_COMP_IS_INT64) or not defined(FPC_CURRENCY_IS_INT64))}
{$define USE_EXTENDED_AS_COMP_CURRENCY_RES}
{$endif}

type
  TFFIData = record
    Types: array of pffi_type;
    Values: array of Pointer;
    Indirect: array of Boolean;
    ResultType: pffi_type;
    ResultValue: Pointer;
    ResultIndex: SizeInt;
{$ifdef USE_EXTENDED_AS_COMP_CURRENCY_RES}
    ResultTypeData: PTypeData;
    ResultExtended: Extended;
{$endif}
    { put this at the end just in case we messed up the size }
    CIF: ffi_cif;
  end;

procedure CreateCIF(constref aArgInfos: array of TFunctionCallParameterInfo; constref aArgValues: array of Pointer; aCallConv: TCallConv; aResultType: PTypeInfo; aResultValue: Pointer; aFlags: TFunctionCallFlags; out aData: TFFIData);

  function CallConvName: String; inline;
  begin
    WriteStr(Result, aCallConv);
  end;

var
  abi: ffi_abi;
  i, arglen, argoffset, argstart: LongInt;
  usevalues, retparam: Boolean;
  kind: TTypeKind;
  types: ppffi_type;
begin
  if not (fcfStatic in aFlags) and (Length(aArgInfos) = 0) then
    raise EInvocationError.Create(SErrMissingSelfParam);

  Assert((Length(aArgInfos) = Length(aArgValues)) or (Length(aArgValues) = 0), 'Amount of arguments does not match needed arguments');

  case aCallConv of
{$if defined(CPUI386)}
    ccReg:
      abi := FFI_REGISTER;
    ccCdecl:
{$ifdef WIN32}
      abi := FFI_MS_CDECL;
{$else}
      abi := FFI_STDCALL;
{$endif}
    ccPascal:
      abi := FFI_PASCAL;
    ccStdCall:
      abi := FFI_STDCALL;
    ccCppdecl:
      abi := FFI_THISCALL;
{$else}
{$ifndef CPUM68K}
    { M68k has a custom register calling convention implementation }
    ccReg,
{$endif}
    ccCdecl,
    ccPascal,
    ccStdCall,
    ccCppdecl:
      abi := FFI_DEFAULT_ABI;
{$endif}
    else
      raise EInvocationError.CreateFmt(SErrCallConvNotSupported, [CallConvName]);
  end;

  { if no values are provided we are called to prepare a callback, otherwise
    we are asked to prepare a invokation }
  usevalues := (Length(aArgInfos) > 0) and (Length(aArgValues) > 0);

  retparam := RetInParam(aCallConv, aResultType);

  arglen := Length(aArgInfos);
  if retparam then begin
    Inc(arglen);
    usevalues := True;
    argoffset := 1;
    aData.ResultIndex := 0;
  end else begin
    argoffset := 0;
    aData.ResultIndex := -1;
  end;

  SetLength(aData.Types, arglen);
  SetLength(aData.Indirect, arglen);
  if usevalues then
    SetLength(aData.Values, arglen);

  { the order is Self/Vmt (if any), Result param (if any), other params }

  if not (fcfStatic in aFlags) and retparam then begin
    aData.Types[0] := TypeInfoToFFIType(aArgInfos[0].ParamType, aArgInfos[0].ParamFlags);
    if Assigned(aArgInfos[0].ParamType) then
      kind := aArgInfos[0].ParamType^.Kind
    else
      kind := tkUnknown;
    aData.Indirect[0] := ArgIsIndirect(kind, aArgInfos[0].ParamFlags, False);
    if usevalues then
      if aData.Indirect[0] then
        aData.Values[0] := @aArgValues[0]
      else
        aData.Values[0] := aArgValues[0];
    if retparam then
      Inc(aData.ResultIndex);
    argstart := 1;
  end else
    argstart := 0;

  for i := argstart to High(aArgInfos) do begin
    aData.Types[i + argoffset] := TypeInfoToFFIType(aArgInfos[i].ParamType, aArgInfos[i].ParamFlags);
    if (pfResult in aArgInfos[i].ParamFlags) and not retparam then
      aData.ResultIndex := i + argoffset;
    if Assigned(aArgInfos[i].ParamType) then
      kind := aArgInfos[i].ParamType^.Kind
    else
      kind := tkUnknown;
    aData.Indirect[i + argoffset] := ArgIsIndirect(kind, aArgInfos[i].ParamFlags, False);
    if usevalues then
      if aData.Indirect[i + argoffset] then
        aData.Values[i + argoffset] := @aArgValues[i]
      else
        aData.Values[i + argoffset] := aArgValues[i];
  end;

  if retparam then begin
    aData.Types[aData.ResultIndex] := TypeInfoToFFIType(aResultType, []);
    aData.Indirect[aData.ResultIndex] := ArgIsIndirect(aResultType^.Kind, [], True);
    if usevalues then
      if aData.Indirect[aData.ResultIndex] then
        aData.Values[aData.ResultIndex] := @aResultValue
      else
        aData.Values[aData.ResultIndex] := aResultValue;
    aData.ResultType := @ffi_type_void;
    aData.ResultValue := Nil;
{$ifdef USE_EXTENDED_AS_COMP_CURRENCY_RES}
    aData.ResultTypeData := Nil;
{$endif}
  end else begin
    aData.ResultValue := Nil;
{$ifdef USE_EXTENDED_AS_COMP_CURRENCY_RES}
    { special case for Comp/Currency as such arguments are passed as Int64,
      but the result is handled through the X87 }
    if Assigned(aResultType) and (aResultType^.Kind = tkFloat) then begin
      aData.ResultTypeData := GetTypeData(aResultType);
      case aData.ResultTypeData^.FloatType of
{$ifndef FPC_CURRENCY_IS_INT64}
        ftCurr: begin
          aData.ResultType := @ffi_type_longdouble;
          aData.ResultValue := @aData.ResultExtended;
        end;
{$endif}
{$ifndef FPC_COMP_IS_INT64}
        ftComp: begin
          aData.ResultType := @ffi_type_longdouble;
          aData.ResultValue := @aData.ResultExtended;
        end;
{$endif}
      end;
    end else
      aData.ResultTypeData := Nil;
{$endif}
    if not Assigned(aData.ResultValue) then begin
      aData.ResultType := TypeInfoToFFIType(aResultType, []);
      if Assigned(aResultType) then
        aData.ResultValue := aResultValue
      else
        aData.ResultValue := Nil;
    end;
  end;

  if Assigned(aData.Types) then
    types := @aData.Types[0]
  else
    types := Nil;

  if ffi_prep_cif(@aData.CIF, abi, arglen, aData.ResultType, types) <> FFI_OK then
    raise EInvocationError.Create(SErrInvokeFailed);
end;

procedure FFIInvoke(aCodeAddress: Pointer; const aArgs: TFunctionCallParameterArray; aCallConv: TCallConv;
            aResultType: PTypeInfo; aResultValue: Pointer; aFlags: TFunctionCallFlags);
var
  ffidata: TFFIData;
  i: SizeInt;
  arginfos: array of TFunctionCallParameterInfo;
  argvalues: array of Pointer;
begin
  if Assigned(aResultType) and not Assigned(aResultValue) then
    raise EInvocationError.Create(SErrInvokeResultTypeNoValue);

  SetLength(arginfos, Length(aArgs));
  SetLength(argvalues, Length(aArgs));
  for i := 0 to High(aArgs) do begin
    arginfos[i] := aArgs[i].Info;
    argvalues[i] := aArgs[i].ValueRef;
  end;
  CreateCIF(arginfos, argvalues, aCallConv, aResultType, aResultValue, aFlags, ffidata);

  arginfos := Nil;
  argvalues := Nil;

  ffi_call(@ffidata.CIF, ffi_fn(aCodeAddress), ffidata.ResultValue, @ffidata.Values[0]);

{$ifdef USE_EXTENDED_AS_COMP_CURRENCY_RES}
  if Assigned(ffidata.ResultTypeData) then begin
    case ffidata.ResultTypeData^.FloatType of
{$ifndef FPC_CURRENCY_IS_INT64}
      ftCurr:
        PCurrency(aResultValue)^ := Currency(ffidata.ResultExtended / 10000);
{$endif}
{$ifndef FPC_COMP_IS_INT64}
      ftComp:
        PComp(aResultValue)^ := Comp(ffidata.ResultExtended);
{$endif}
    end;
  end;
{$endif}
end;

type
  TFFIFunctionCallback = class(TFunctionCallCallback)
  private
    fFFIData: TFFIData;
    fData: Pointer;
    fCode: CodePointer;
    fContext: Pointer;
  private
    class procedure ClosureFunc(aCIF: pffi_cif; aRet: Pointer; aArgs: PPointer; aUserData: Pointer); cdecl; static;
    procedure PassToHandler(aRet: Pointer; aArgs: PPointer);
  protected
    function GetCodeAddress: CodePointer; override;
    procedure CallHandler(constref aArgs: specialize TArray<Pointer>; aResult: Pointer; aContext: Pointer); virtual; abstract;
  public
    constructor Create(aContext: Pointer; aCallConv: TCallConv; constref aArgs: array of TFunctionCallParameterInfo; aResultType: PTypeInfo; aFlags: TFunctionCallFlags);
    destructor Destroy; override;
  end;

  TFFIFunctionCallbackMethod = class(TFFIFunctionCallback)
  private
    fHandler: TFunctionCallMethod;
  protected
    procedure CallHandler(constref aArgs: specialize TArray<Pointer>; aResult: Pointer; aContext: Pointer); override;
  public
    constructor Create(aHandler: TFunctionCallMethod; aContext: Pointer; aCallConv: TCallConv; constref aArgs: array of TFunctionCallParameterInfo; aResultType: PTypeInfo; aFlags: TFunctionCallFlags);
  end;

  TFFIFunctionCallbackProc = class(TFFIFunctionCallback)
  private
    fHandler: TFunctionCallProc;
  protected
    procedure CallHandler(constref aArgs: specialize TArray<Pointer>; aResult: Pointer; aContext: Pointer); override;
  public
    constructor Create(aHandler: TFunctionCallProc; aContext: Pointer; aCallConv: TCallConv; constref aArgs: array of TFunctionCallParameterInfo; aResultType: PTypeInfo; aFlags: TFunctionCallFlags);
  end;

class procedure TFFIFunctionCallback.ClosureFunc(aCIF: pffi_cif; aRet: Pointer; aArgs: PPointer; aUserData: Pointer); cdecl;
var
  this: TFFIFunctionCallback absolute aUserData;
begin
  this.PassToHandler(aRet, aArgs);
end;

procedure TFFIFunctionCallback.PassToHandler(aRet: Pointer; aArgs: PPointer);
var
  args: array of Pointer;
  i, arglen, argidx: SizeInt;
  resptr: Pointer;
{$ifdef USE_EXTENDED_AS_COMP_CURRENCY_RES}
{$ifndef FPC_COMP_IS_INT64}
  rescomp: Comp;
{$endif}
{$ifndef FPC_CURR_IS_INT64}
  rescurr: Currency;
{$endif}
{$endif}
begin
  arglen := Length(fFFIData.Types);
  if fFFIData.ResultIndex >= 0 then
    Dec(arglen);
  SetLength(args, arglen);
  argidx := 0;
  for i := 0 to High(fFFIData.Types) do begin
    if i = fFFIData.ResultIndex then
      Continue;
    args[argidx] := aArgs[i];
    if fFFIData.Indirect[i] then
      args[argidx] := PPointer(aArgs[i])^
    else
      args[argidx] := aArgs[i];
    Inc(argidx);
  end;

  if fFFIData.ResultIndex >= 0 then begin
    if fFFIData.Indirect[fFFIData.ResultIndex] then
      resptr := PPointer(aArgs[fFFIData.ResultIndex])^
    else
      resptr := aArgs[fFFIData.ResultIndex];
  end else begin
{$ifdef USE_EXTENDED_AS_COMP_CURRENCY_RES}
    resptr := Nil;
    if Assigned(fFFIData.ResultTypeData) then begin
      case fFFIData.ResultTypeData^.FloatType of
{$ifndef FPC_COMP_IS_INT64}
        ftComp:
          resptr := @rescomp;
{$endif}
{$ifndef FPC_CURR_IS_INT64}
        ftCurr:
          resptr := @rescurr;
{$endif}
      end;
    end;
    if not Assigned(resptr) then
{$endif}
      resptr := aRet;
  end;

  CallHandler(args, resptr, fContext);

{$ifdef USE_EXTENDED_AS_COMP_CURRENCY_RES}
  if Assigned(fFFIData.ResultTypeData) then begin
    case fFFIData.ResultTypeData^.FloatType of
{$ifndef FPC_COMP_IS_INT64}
      ftComp:
        PExtended(aRet)^ := rescomp;
{$endif}
{$ifndef FPC_CURR_IS_INT64}
      ftCurr:
        PExtended(aRet) ^ := rescurr * 10000;
{$endif}
    end;
  end;
{$endif}
end;

function TFFIFunctionCallback.GetCodeAddress: CodePointer;
begin
  Result := fData;
end;

constructor TFFIFunctionCallback.Create(aContext: Pointer; aCallConv: TCallConv; constref aArgs: array of TFunctionCallParameterInfo; aResultType: PTypeInfo; aFlags: TFunctionCallFlags);
var
  res: ffi_status;
begin
  fContext := aContext;

  CreateCIF(aArgs, [], aCallConv, aResultType, Nil, aFlags, fFFIData);

  fData := ffi_closure_alloc(SizeOf(ffi_closure), @fCode);
  if not Assigned(fData) or not Assigned(fCode) then
    raise ERTTI.Create(SErrMethodImplCreateFailed);

  res := ffi_prep_closure_loc(pffi_closure(fData), @fFFIData.CIF, @ClosureFunc, Self, fCode);
  if res <> FFI_OK then
    raise ERTTI.Create(SErrMethodImplCreateFailed);
end;

destructor TFFIFunctionCallback.Destroy;
begin
  if Assigned(fData) then
    ffi_closure_free(fData);
end;

constructor TFFIFunctionCallbackProc.Create(aHandler: TFunctionCallProc; aContext: Pointer; aCallConv: TCallConv; constref aArgs: array of TFunctionCallParameterInfo; aResultType: PTypeInfo; aFlags: TFunctionCallFlags);
begin
  inherited Create(aContext, aCallConv, aArgs, aResultType, aFlags);
  fHandler := aHandler;
end;

procedure TFFIFunctionCallbackProc.CallHandler(constref aArgs: specialize TArray<Pointer>; aResult: Pointer; aContext: Pointer);
begin
  fHandler(aArgs, aResult, aContext);
end;

constructor TFFIFunctionCallbackMethod.Create(aHandler: TFunctionCallMethod; aContext: Pointer; aCallConv: TCallConv; constref aArgs: array of TFunctionCallParameterInfo; aResultType: PTypeInfo; aFlags: TFunctionCallFlags);
begin
  inherited Create(aContext, aCallConv, aArgs, aResultType, aFlags);
  fHandler := aHandler;
end;

procedure TFFIFunctionCallbackMethod.CallHandler(constref aArgs: specialize TArray<Pointer>; aResult: Pointer; aContext: Pointer);
begin
  fHandler(aArgs, aResult, aContext);
end;

function FFICreateCallbackProc(aHandler: TFunctionCallProc; aCallConv: TCallConv; aArgs: array of TFunctionCallParameterInfo; aResultType: PTypeInfo; aFlags: TFunctionCallFlags; aContext: Pointer): TFunctionCallCallback;
begin
  Result := TFFIFunctionCallbackProc.Create(aHandler, aContext, aCallConv, aArgs, aResultType, aFlags);
end;

function FFICreateCallbackMethod(aHandler: TFunctionCallMethod; aCallConv: TCallConv; aArgs: array of TFunctionCallParameterInfo; aResultType: PTypeInfo; aFlags: TFunctionCallFlags; aContext: Pointer): TFunctionCallCallback;
begin
  Result := TFFIFunctionCallbackMethod.Create(aHandler, aContext, aCallConv, aArgs, aResultType, aFlags);
end;


const
  FFIManager: TFunctionCallManager = (
    Invoke: @FFIInvoke;
    CreateCallbackProc: @FFICreateCallbackProc;
    CreateCallbackMethod: @FFICreateCallbackMethod;
  );

var
  OldManagers: TFunctionCallManagerArray;

const
  SupportedCallConvs = [ccReg, ccCdecl, ccStdCall, {ccCppdecl,} ccPascal];

procedure InitFuncCallManager;
begin
  SetFunctionCallManager(SupportedCallConvs, FFIManager, OldManagers);
end;

procedure DoneFuncCallManager;
begin
  SetFunctionCallManagers(SupportedCallConvs, OldManagers);
end;

initialization
  InitFuncCallManager;
finalization
  DoneFuncCallManager;
end.