Help with EA opening a buy at a fixed price.

 
Would anyone be able to help me out with this?

I'm trying to make an EA that will open up a buy on a symbol at a fixed price if there is not already a trade open at that price.

As example say I want the expert to buy on EUR/USD everytime the price hits 1.700 unless there is a trade currently open at that price.
I have been trying to without much luck to get it to open on a symbol at a fixed price. I keep going throgh the manual but its just not clicking for me!
Is this something that can actually be done?
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