// The MIT License (MIT)
// © mihakralj
//@version=6
indicator("Detrended Price Oscillator (DPO)", "DPO", overlay=false)

//@function Calculates Detrended Price Oscillator (DPO) by removing trend component from price
//@doc https://github.com/mihakralj/pinescript/blob/main/indicators/oscillators/dpo.md
//@param source Series to calculate DPO from
//@param period Period for SMA calculation and displacement
//@returns DPO value (current price - displaced SMA)
dpo(series float source, simple int period) =>
    if period <= 0
        runtime.error("Period must be greater than 0")
    int displacement = math.floor(period / 2) + 1
    float sum = 0.0
    for i = 0 to period - 1
        sum += nz(source[i], source)
    float sma = sum / period
    float currentPrice = source
    float displacedSMA = sma[displacement]
    float result = na
    if not na(displacedSMA)
        result := currentPrice - displacedSMA
    
    result

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

// Inputs
i_source = input.source(close, "Source")
i_period = input.int(20, "Period", minval=1)

// Calculation
dpo_value = dpo(i_source, i_period)

// Plot
plot(dpo_value, "DPO", color=color.yellow, linewidth=2)
hline(0, "Zero Line", color.gray, hline.style_dotted)