unit IdHeaderCoderBase;

interface

{$i IdCompilerDefines.inc}

uses
  Classes, IdGlobal, IdException;

type
  TIdHeaderDecodingNeededEvent = procedure(const ACharSet: String; const AData: TIdBytes; var VResult: String; var VHandled: Boolean) of object;
  TIdHeaderEncodingNeededEvent = procedure(const ACharSet, AData: String; var VResult: TIdBytes; var VHandled: Boolean) of object;

  TIdHeaderCoder = class(TObject)
  public
    class function Decode(const ACharSet: String; const AData: TIdBytes): String; virtual;
    class function Encode(const ACharSet, AData: String): TIdBytes; virtual;
    class function CanHandle(const ACharSet: String): Boolean; virtual;
  end;

  TIdHeaderCoderClass = class of TIdHeaderCoder;

  EIdHeaderEncodeError = class(EIdException);

var
  GHeaderEncodingNeeded: TIdHeaderEncodingNeededEvent = nil;
  GHeaderDecodingNeeded: TIdHeaderDecodingNeededEvent = nil;

function HeaderCoderByCharSet(const ACharSet: String): TIdHeaderCoderClass;
function DecodeHeaderData(const ACharSet: String; const AData: TIdBytes; var VResult: String): Boolean;
function EncodeHeaderData(const ACharSet, AData: String): TIdBytes;
procedure RegisterHeaderCoder(const ACoder: TIdHeaderCoderClass);
procedure UnregisterHeaderCoder(const ACoder: TIdHeaderCoderClass);

implementation

uses
  {$IFDEF VCL_XE3_OR_ABOVE}
  System.Types,
  {$ENDIF}
  {$IFDEF HAS_UNIT_Generics_Collections}
  System.Generics.Collections,
  {$ENDIF}
  SysUtils, IdResourceStringsProtocols;

type
  TIdHeaderCoderList = class(TList{$IFDEF HAS_GENERICS_TList}<TIdHeaderCoderClass>{$ENDIF})
  public
    function ByCharSet(const ACharSet: String): TIdHeaderCoderClass;
  end;

var
  GHeaderCoderList: TIdHeaderCoderList = nil;

{ TIdHeaderCoder }

class function TIdHeaderCoder.Decode(const ACharSet: String; const AData: TIdBytes): String;
begin
  Result := '';
end;

class function TIdHeaderCoder.Encode(const ACharSet, AData: String): TIdBytes;
begin
  Result := nil;
end;

class function TIdHeaderCoder.CanHandle(const ACharSet: String): Boolean;
begin
  Result := False;
end;

{ TIdHeaderCoderList }

function TIdHeaderCoderList.ByCharSet(const ACharSet: string): TIdHeaderCoderClass;
var
  I: Integer;
  LCoder: TIdHeaderCoderClass;
begin
  Result := nil;
  // loop backwards so that user-defined coders can override native coders
  for I := Count-1 downto 0 do begin
    LCoder := TIdHeaderCoderClass(Items[I]);
    if LCoder.CanHandle(ACharSet) then begin
      Result := LCoder;
      Exit;
    end;
  end;
end;

function HeaderCoderByCharSet(const ACharSet: String): TIdHeaderCoderClass;
begin
  if Assigned(GHeaderCoderList) then begin
    Result := GHeaderCoderList.ByCharSet(ACharSet);
  end else begin
    Result := nil;
  end;
end;

function DecodeHeaderData(const ACharSet: String; const AData: TIdBytes; var VResult: String): Boolean;
var
  LCoder: TIdHeaderCoderClass;
begin
  LCoder := HeaderCoderByCharSet(ACharSet);
  if LCoder <> nil then begin
    VResult := LCoder.Decode(ACharSet, AData);
    Result := True;
  end else
  begin
    VResult := '';
    Result := False;
    if Assigned(GHeaderDecodingNeeded) then begin
      GHeaderDecodingNeeded(ACharSet, AData, VResult, Result);
    end;
    { RLebeau: TODO - enable this?
    if not LDecoded then begin
      raise EIdHeaderDecodeError.Create(RSHeaderDecodeError, [ACharSet]);
    end;
    }
  end;
end;

function EncodeHeaderData(const ACharSet, AData: String): TIdBytes;
var
  LCoder: TIdHeaderCoderClass;
  LEncoded: Boolean;
begin
  LCoder := HeaderCoderByCharSet(ACharSet);
  if LCoder <> nil then begin
    Result := LCoder.Encode(ACharSet, AData);
  end else
  begin
    Result := nil;
    LEncoded := False;
    if Assigned(GHeaderEncodingNeeded) then begin
      GHeaderEncodingNeeded(ACharSet, AData, Result, LEncoded);
    end;
    if not LEncoded then begin
      raise EIdHeaderEncodeError.CreateFmt(RSHeaderEncodeError, [ACharSet]);
    end;
  end;
end;

procedure RegisterHeaderCoder(const ACoder: TIdHeaderCoderClass);
begin
  if Assigned(ACoder) and
     Assigned(GHeaderCoderList) and
     (GHeaderCoderList.IndexOf(
        {$IFDEF HAS_GENERICS_TList}ACoder{$ELSE}TObject(ACoder){$ENDIF}
     ) = -1) then
  begin
    GHeaderCoderList.Add(
      {$IFDEF HAS_GENERICS_TList}ACoder{$ELSE}TObject(ACoder){$ENDIF}
    );
  end;
end;

procedure UnregisterHeaderCoder(const ACoder: TIdHeaderCoderClass);
begin
  if Assigned(GHeaderCoderList) then begin
    GHeaderCoderList.Remove(
      {$IFDEF HAS_GENERICS_TList}ACoder{$ELSE}TObject(ACoder){$ENDIF}
    );
  end;
end;

initialization
  GHeaderCoderList := TIdHeaderCoderList.Create;
finalization
  FreeAndNil(GHeaderCoderList);

end.