How to get the previous candles in Pine script

Question

I am trying to get the qty of candles since it bought.

I mean

if ( something_happens ) 
    strategy.entry("buy", strategy.long)

How could I get this?
candles_since_entry = barssince(bought)

Answer 1

//@version=4
study("My Script")

var bool    something_happens = true
var int     bar_entry = na

if (something_happens)
    // strategy.entry("buy", strategy.long)
    bar_entry := bar_index
    
candles_since_entry = bar_index - bar_entry

plot(na)