// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Negative Volume Index (NVI)", "NVI", overlay=false)

//@function Calculates Negative Volume Index, tracks price changes on days with lower volume
//@param src Price series to use for calculation
//@param vol Volume series
//@param start_value Starting value for NVI (typically 100 or 1000)
//@returns float The NVI value
nvi(series float src, series float vol = volume, simple float start_value = 100.0) =>
    var float nvi_value = start_value
    if not (na(src) or na(vol) or na(src[1]) or na(vol[1]) or src[1] == 0.0 or vol[1] <= 0.0) and vol < vol[1]
        nvi_value := nvi_value * src / src[1]
    nvi_value

// ---------- Main Calculation ----------

// Parameters
src = input.source(close, "Price Source")

// Calculations
nvi_line = nvi(src, volume)

// Plot
plot(nvi_line, "NVI", color=color.yellow, linewidth=2)