// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("TD Sequential (TD_SEQ)", "TD_SEQ", overlay=false)

//@function Calculates TD Sequential — Tom DeMark's exhaustion counting system
//@param comparePeriod Lookback for setup comparison (close vs close[comparePeriod])
//@returns [setupCount, countdownCount] signed setup (1-9) and countdown (1-13) values
//@description TD Sequential identifies trend exhaustion via two phases:
//  Phase 1 — Setup (1 to 9):
//    Buy Setup: consecutive bars where close < close[comparePeriod] (count negative)
//    Sell Setup: consecutive bars where close > close[comparePeriod] (count positive)
//    A completed setup reaches ±9. The count resets when the condition breaks.
//  Phase 2 — Countdown (1 to 13):
//    After a completed 9-count setup, countdown begins:
//    Buy Countdown: close < low[2] (counts negative, toward −13)
//    Sell Countdown: close > high[2] (counts positive, toward +13)
//    Countdown is non-consecutive — only qualifying bars increment.
//    Countdown resets if an opposite setup completes (±9 in other direction).
//    A completed ±13 signals potential exhaustion reversal.
//  Setup values: −9 to −1 (buy) or +1 to +9 (sell), 0 = no active setup bar
//  Countdown values: −13 to −1 (buy) or +1 to +13 (sell), 0 = no active countdown
//  The oscillator output combines both: setup during phase 1, countdown during phase 2.
//  All state is O(1) via var scalars — no buffers needed.
td_seq(simple int comparePeriod) =>
    if comparePeriod <= 0
        runtime.error("Compare period must be greater than 0")

    var int setupCount     = 0
    var int countdownCount = 0
    var int countdownDir   = 0
    var bool setupComplete = false

    float curClose  = nz(close)
    float prevClose = nz(close[comparePeriod])

    // --- Phase 1: Setup counting ---
    int newSetup = 0
    if curClose < prevClose
        newSetup := setupCount < 0 ? setupCount - 1 : -1
    else if curClose > prevClose
        newSetup := setupCount > 0 ? setupCount + 1 : 1
    else
        newSetup := 0

    if newSetup > 9
        newSetup := 9
    if newSetup < -9
        newSetup := -9

    // --- Check for completed setup (reached ±9) ---
    bool justCompleted = false
    if math.abs(newSetup) == 9 and not setupComplete
        setupComplete := true
        justCompleted := true
        countdownCount := 0
        countdownDir := newSetup > 0 ? 1 : -1

    if math.abs(newSetup) < math.abs(setupCount) or (newSetup > 0 and setupCount < 0) or (newSetup < 0 and setupCount > 0)
        setupComplete := false

    setupCount := newSetup

    // --- Phase 2: Countdown (non-consecutive) ---
    if countdownDir != 0
        float low2  = nz(low[2])
        float high2 = nz(high[2])

        if countdownDir == -1 and curClose < low2
            countdownCount -= 1
        else if countdownDir == 1 and curClose > high2
            countdownCount += 1

        if math.abs(countdownCount) >= 13
            countdownCount := countdownDir == 1 ? 13 : -13
            countdownDir := 0

        if (countdownDir == 1 and newSetup == -9) or (countdownDir == -1 and newSetup == 9)
            countdownCount := 0
            countdownDir := newSetup > 0 ? 1 : -1

    // --- Output: show countdown if active, else setup ---
    int result = countdownDir != 0 ? countdownCount : setupCount
    [setupCount, countdownCount]

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

// Inputs
i_comparePeriod = input.int(4, "Compare Period", minval=1)

// Calculation
[setup, countdown] = td_seq(i_comparePeriod)

// Plot
plot(setup, "Setup", color=color.yellow, linewidth=2, style=plot.style_histogram)
plot(countdown, "Countdown", color=color.aqua, linewidth=1)
hline(0, "Zero", color=color.gray, linestyle=hline.style_dotted)
hline(9, "Sell Setup Complete", color=color.red, linestyle=hline.style_dashed)
hline(-9, "Buy Setup Complete", color=color.green, linestyle=hline.style_dashed)
hline(13, "Sell Countdown", color=color.red, linestyle=hline.style_dotted)
hline(-13, "Buy Countdown", color=color.green, linestyle=hline.style_dotted)