// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Bill Williams Market Facilitation Index (BW_MFI)", "BW_MFI", overlay=false)

//@function Bill Williams MFI with 4-zone classification
//@returns [mfi, zone] where zone: 1=Green, 2=Fade, 3=Fake, 4=Squat
//@optimized O(1) per bar — division + two comparisons
bw_mfi() =>
    float mfi = volume != 0 ? (high - low) / volume : 0.0
    float prev_mfi = nz(mfi[1])
    float prev_vol = nz(volume[1])

    int zone = na
    if bar_index < 1
        zone := 0
    else
        bool mfi_up = mfi > prev_mfi
        bool vol_up = volume > prev_vol
        if mfi_up and vol_up
            zone := 1    // Green: trend continuation
        else if not mfi_up and not vol_up
            zone := 2    // Fade: fading momentum
        else if mfi_up and not vol_up
            zone := 3    // Fake: unsupported price move
        else
            zone := 4    // Squat: accumulation/distribution
    [mfi, zone]

// ---------- Main loop ----------

[mfi_val, zone_val] = bw_mfi()

// Zone-based bar coloring
zone_color = switch zone_val
    1 => color.green    // Green zone
    2 => color.new(#8B4513, 0)  // Fade (brown)
    3 => color.blue     // Fake zone
    4 => color.fuchsia  // Squat zone
    => color.gray       // First bar / unknown

plot(mfi_val, title="BW_MFI", color=zone_color, style=plot.style_columns, linewidth=3)
hline(0, "Zero", color=color.gray, linestyle=hline.style_dashed)