Convert custom indicator to EA

I have a custom indicator that gives sell and buy alerts. I want to convert it to EA that convert these alerts into orders as follows " when a buy signals comes, it closes the sell order and opens a buy order. when a sell signal comes , it closes the buy order and open a sell order. Depending on these two rules above : the maximum opened orders at the same time is always only one trade. there is always a trade opened. I have to be able to set a default lot size to the orders. note : when the ea is launched it must check if there is order opened or not, to make sure not to open more the one order at the same direction. what I need is to convert the code itself from an indicator code to EA code ( the use of icustom function is not allowed ) This has to be work on any pair with 4-digit metatrader, and 5-digit [login to view URL] must open trades even on renko offline charts when the signal comes buy or sell.