// This Pine Script™ code is subject to the terms of the Mozilla Public License 2.0
// https://mozilla.org/MPL/2.0/
// © QuanTAlib

//@version=6
indicator("TUKEY_W: Tukey (Tapered Cosine) Window MA", shorttitle="TUKEY_W", overlay=true)

// @function Calculates the Tukey (Tapered Cosine) Window Moving Average.
//   The Tukey window has cosine-tapered edges and a flat-top center.
//   Parameter alpha controls the taper fraction:
//     alpha=0 → rectangular window (SMA)
//     alpha=1 → Hann window (full cosine taper)
//     alpha=0.5 → half tapered, half flat (typical default)
//   For sample n in [0, N-1]:
//     if n < alpha*(N-1)/2: w(n) = 0.5*(1 - cos(2π*n / (alpha*(N-1))))
//     if n > (N-1)*(1 - alpha/2): w(n) = 0.5*(1 - cos(2π*(N-1-n) / (alpha*(N-1))))
//     else: w(n) = 1.0  (flat-top center)
// @param src Series to smooth.
// @param period Window length. Must be >= 2.
// @param alpha Taper fraction (0 = rectangular, 1 = Hann). Default 0.5.
// @returns The Tukey window weighted average.
tukey_w(series float src, simple int period, simple float alpha) =>
    float sumWV = 0.0
    float sumW  = 0.0
    int N = period - 1
    float aN = alpha * N
    for i = 0 to N
        float w = 1.0
        if aN > 0.0
            if i < aN / 2.0
                w := 0.5 * (1.0 - math.cos(2.0 * math.pi * i / aN))
            else if i > N - aN / 2.0
                w := 0.5 * (1.0 - math.cos(2.0 * math.pi * (N - i) / aN))
        sumWV += src[i] * w
        sumW  += w
    sumWV / sumW

// ── Inputs ──────────────────────────────────────────────
p = input.int(20, "Period", minval=2)
a = input.float(0.5, "Alpha (taper fraction)", minval=0.0, maxval=1.0, step=0.05, tooltip="0=SMA, 1=Hann, 0.5=half taper")

// ── Calculation ─────────────────────────────────────────
result = tukey_w(close, p, a)

// ── Plot ────────────────────────────────────────────────
plot(result, "TUKEY_W", color=color.yellow, linewidth=2)