Add Function for MetaTrader 4 EA

I would like to add a stop and reverse trade function to my EA. This would be based on the Williams % R (WPR) indicator. Basically if I have a Buy Trade in place, should its price move below the -20 level of the WPR. I would like the trade closed and a reverse positon opened or sell trade. I would like this to only happen once. Finally I would like the exact opposite to happen when a sell trade is in place. When it reaches the -80 level I would like for the trade to close and a buy trade opened up. The -20 and -80 level I would like to be changeable.