we now ask the user if he/she want to remove a previously installed version under windows

gajim.iss

@@ -13,6 +13,7 @@ Name: "main"; Description: "Main Files"; Types: full compact custom; Flags: fixe
 
 [Tasks]
 Name: desktopicon; Description: "Create a &desktop icon"; GroupDescription: "Additional icons:"; Components: main
+Name: removeprevious; Description: "Remouve previously installed version"; GroupDescription: "Previous install:"; Components: main; Check: IsAlreadyInstalled('Gajim');
 
 [Files]
 Source: "dist\*.pyd"; DestDir: "{app}\src"
@@ -31,3 +32,51 @@ Name: "{userdesktop}\Gajim"; Filename: "{app}\src\gajim.exe"; WorkingDir: "{app}
 
 [Run]
 Filename: "{app}\src\gajim.exe"; Description: "Launch application"; Flags: postinstall nowait skipifsilent
+
+[Code]
+
+function GetUninstallPath( AppID: String ): String;
+var
+   sPrevPath: String;
+begin
+  sPrevPath := '';
+  if not RegQueryStringValue( HKLM,
+    'Software\Microsoft\Windows\CurrentVersion\Uninstall\'+AppID+'_is1',
+    'UninstallString', sPrevpath) then
+    RegQueryStringValue( HKCU, 'Software\Microsoft\Windows\CurrentVersion\Uninstall\'+AppID+'_is1' ,
+      'UninstallString', sPrevpath);
+
+  Result := sPrevPath;
+end;
+
+function IsAlreadyInstalled( AppID: String ): Boolean;
+var
+	sPrevPath: String;
+begin
+  sPrevPath := GetUninstallPath( AppID );
+
+
+  if ( Length(sPrevPath) > 0 ) then
+    Result:=true
+  else
+    Result:=false;
+ end;
+
+procedure CurStepChanged(CurStep: TSetupStep);
+var
+	sUninstPath: String;
+	sPrevID: String;
+	ResultCode: Integer;
+begin
+  if CurStep = ssInstall then
+  begin
+    sPrevID := 'Gajim';
+    sUninstPath := GetUninstallPath( sprevID );
+
+    if ( Length(sUninstPath) > 0 ) then
+    begin
+      sUninstPath := RemoveQuotes(sUninstPath);
+      Exec( RemoveQuotes(sUninstPath), '/silent', '', SW_SHOW, ewWaitUntilTerminated, ResultCode);
+    end;
+  end;
+end;