// 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("SWMA: Symmetric Weighted Moving Average", shorttitle="SWMA", overlay=true)

// @function Calculates the Symmetric Weighted Moving Average.
//   Uses triangular/symmetric weights that peak at the center of the window.
//   For period N, weight at position i (0-based from newest) is:
//     w(i) = (N/2 + 1) - |i - N/2|  (triangular shape)
//   This is equivalent to convolving two rectangular windows (SMA of SMA)
//   and produces a smooth, low-lag FIR filter with zero phase distortion
//   at the center of the window.
//   For period=4 (Pine's built-in ta.swma): weights are [1, 2, 2, 1] / 6.
// @param src Series to smooth.
// @param period Window length. Must be >= 2.
// @returns The symmetric weighted moving average value.
swma(series float src, simple int period) =>
    float sumWV = 0.0
    float sumW  = 0.0
    float half  = (period - 1) / 2.0
    for i = 0 to period - 1
        float w = half + 1.0 - math.abs(i - half)
        sumWV += src[i] * w
        sumW  += w
    sumWV / sumW

// ── Inputs ──────────────────────────────────────────────
p = input.int(4, "Period", minval=2)

// ── Calculation ─────────────────────────────────────────
result = swma(close, p)

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