//@version=4
//Full credit to AlexGrover: https://www.tradingview.com/script/fIvlS64B-G-Channels-Efficient-Calculation-Of-Upper-Lower-Extremities/
study("G-Channel Trend Detection", shorttitle="G-Trend", overlay=true)

length = input(100)
src = input(close)

//----
var a = 0.0
var b = 0.0

a := max(src, nz(a[1])) - nz(a[1] - b[1]) / length
b := min(src, nz(b[1])) + nz(a[1] - b[1]) / length

avg = avg(a, b)

//----
crossup = b[1] < close[1] and b > close
crossdn = a[1] < close[1] and a > close
bullish = barssince(crossdn) <= barssince(crossup)

c = bullish ? color.lime : color.red

//plot(a, "Upper", color=color.blue, linewidth=2, transp=100)
//plot(b, "Lower", color=color.blue, linewidth=2, transp=100)

p1 = plot(avg, "Average", color=c, linewidth=1, transp=90)
p2 = plot(close, "Close price", color=c, linewidth=1, transp=100)
fill(p1, p2, color=c, transp=90)

showcross = input(true)

buy_signal = showcross and bullish and not bullish[1] ? avg : na
sell_signal = showcross and not bullish and bullish[1] ? avg : na

plotshape(buy_signal, location=location.absolute, style=shape.labelup, color=color.lime, size=size.tiny, text="Buy", textcolor=#ffffff, transp=0, offset=-1)
plotshape(sell_signal, location=location.absolute, style=shape.labeldown, color=color.red, size=size.tiny, text="Sell", textcolor=#ffffff, transp=0, offset=-1)