Pour the orange juice, lemon juice and sugar into a medium pot and cook over low heat, stirring with a spoon until the sugar dissolves. Let this preparation cool off, and add the red wine. Stir well with a spoon. Add the sangria to an aluminum container (may be disposable), and put it in the freezer for at least an hour. Take it out of the freezer and use a fork to scrape off the frozen sangria. Freeze again for another two hours to make sure the granita is firm. You can scrape off the granita again before serving to form thinner ice crystals. Serve in glasses and garnish with edible flowers.