//@version=6
strategy("MACD Lab: does signal-lag scaling explain buffer activity", overlay=false, initial_capital=10000, default_qty_type=strategy.percent_of_equity, default_qty_value=99, process_orders_on_close=false)

fast_length = input.int(12, "Fast length", minval=1)
slow_length = input.int(26, "Slow length", minval=2)
signal_length = input.int(9, "Signal length", minval=2)
buffer_bps = input.float(5.0, "Histogram buffer (price basis points)", minval=0.0)
buffer_mode = input.int(0, "Buffer mode: 0 original, 1 scale by signal lag", minval=0, maxval=1)

[macd_line, signal_line, histogram] = ta.macd(close, fast_length, slow_length, signal_length)
lag_scale = buffer_mode == 0 ? 1.0 : (signal_length - 1.0) / 8.0
threshold = close * buffer_bps / 10000.0 * lag_scale
valid = fast_length < slow_length and bar_index >= 500
enter_long = valid and histogram > threshold
exit_long = valid and histogram < -threshold

plot(macd_line, "MACD", color=color.blue)
plot(signal_line, "Signal", color=color.orange)
plot(histogram, "MACD minus signal", color=color.green, style=plot.style_histogram)
plot(threshold, "Positive buffer", color=color.gray)
plot(-threshold, "Negative buffer", color=color.gray)
hline(0, "Zero", color=color.gray)

if strategy.position_size > 0 and exit_long
    strategy.close("Long")
if strategy.position_size == 0 and enter_long
    strategy.entry("Long", strategy.long)