// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("Money Flow Index (MFI)", "MFI", overlay=false)

//@function Calculates Money Flow Index, a volume-weighted RSI that measures buying/selling pressure
//@param len Period for MFI calculation
//@param src_high High price series
//@param src_low Low price series
//@param src_close Close price series
//@param src_vol Volume series
//@returns float The MFI value (0-100)
//@optimized Uses circular buffers for O(1) performance with proper NA handling
mfi(simple int len, series float src_high=high, series float src_low=low, series float src_close=close, series float src_vol=volume) =>
    float typical_price = (src_high + src_low + src_close) / 3.0
    float raw_money_flow = typical_price * nz(src_vol, 0.0)
    float prev_typical_price = nz(typical_price[1], typical_price)
    bool is_positive = typical_price > prev_typical_price
    bool is_negative = typical_price < prev_typical_price
    float positive_money_flow = is_positive ? raw_money_flow : 0.0
    float negative_money_flow = is_negative ? raw_money_flow : 0.0
    var array<float> pos_buffer = array.new_float(len, na)
    var array<float> neg_buffer = array.new_float(len, na)
    var int head = 0
    var float sum_positive_mf = 0.0
    var float sum_negative_mf = 0.0
    var int count = 0
    float pos_oldest = array.get(pos_buffer, head)
    float neg_oldest = array.get(neg_buffer, head)
    if not na(pos_oldest)
        sum_positive_mf -= pos_oldest
        sum_negative_mf -= neg_oldest
    else
        count += 1
    sum_positive_mf += positive_money_flow
    sum_negative_mf += negative_money_flow
    array.set(pos_buffer, head, positive_money_flow)
    array.set(neg_buffer, head, negative_money_flow)
    head := (head + 1) % len
    float money_flow_ratio = sum_negative_mf != 0 ? sum_positive_mf / sum_negative_mf : 0.0
    float mfi_value = 100.0 - (100.0 / (1.0 + money_flow_ratio))
    mfi_value

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

// Parameters
len = input.int(14, "MFI Period", minval=1, maxval=100)

// Calculation
mfi_line = mfi(len)

// ---------- Plots ----------

plot(mfi_line, "MFI", color=color.yellow, linewidth=2)