BandExpand.pine

//@version=6
// =============================================================================
//  Band Expand.  Created by TraderOracle 9/20/2026
//
//  - 20-period, 2-SD Bollinger Bands, NO middle (basis) line.
//  - Each band is colored independently by its own slope (rising vs falling).
//  - Wait for the bands to contract into a small space (a squeeze), then fire
//    when they begin expanding again (upper rising AND lower falling).
//  - On that trigger, draw a rectangle over the squeeze "small space" and
//    extend it 7 bars to the right.

// Idea from this video: https://www.youtube.com/watch?v=EZ_L7zovyrw

// =============================================================================
indicator("Band Expand", shorttitle="Band Expand", overlay=true, max_boxes_count=500)

// ─────────────────────────────────────────────────────────────
// Inputs
// ─────────────────────────────────────────────────────────────
bbLen  = input.int(20, "BB Length", minval=1)
bbMult = input.float(2.0, "BB StdDev", minval=0.1, step=0.1)
src    = input.source(close, "Source")

grpSqz = "Squeeze detection"
sqzLook = input.int(120, "Squeeze rank lookback", minval=20, group=grpSqz, tooltip="Bars used to rank how tight the bands are (0 = tightest, 1 = widest).")
sqzThr  = input.float(0.25, "Squeeze threshold", minval=0.01, maxval=1.0, step=0.05, group=grpSqz, tooltip="Bandwidth rank below this counts as 'contracted into a small space'.")

grpBox = "Box"
boxExtend = input.int(7, "Extend box (bars)", minval=1, group=grpBox)
boxMode   = input.string("Squeeze band range", "Box height from", options=["Squeeze band range", "Bands at trigger"], group=grpBox, tooltip="What sets the top/bottom of the rectangle.")
minGap    = input.int(7, "Min bars between boxes", minval=1, group=grpBox, tooltip="If triggers cluster in a row, only the first draws; later ones within this many bars are skipped.")

grpCol = "Colors"
colUp     = input.color(#26a69a, "Rising color", group=grpCol)
colDown   = input.color(#ef5350, "Falling color", group=grpCol)
boxCol    = input.color(color.new(color.purple, 62), "Box fill", group=grpCol)
boxBorder = input.color(color.new(color.purple, 45), "Box border", group=grpCol)

// ─────────────────────────────────────────────────────────────
// Bollinger Bands (basis computed but NOT plotted)
// ─────────────────────────────────────────────────────────────
basis = ta.sma(src, bbLen)
dev   = bbMult * ta.stdev(src, bbLen)
upper = basis + dev
lower = basis - dev

// ─────────────────────────────────────────────────────────────
// Bandwidth + squeeze rank
// ─────────────────────────────────────────────────────────────
bbw  = upper - lower
loW  = ta.lowest(bbw, sqzLook)
hiW  = ta.highest(bbw, sqzLook)
rank = (bbw - loW) / math.max(hiW - loW, 1e-10)     // 0 = tightest, 1 = widest
isSqueeze = rank < sqzThr

// ─────────────────────────────────────────────────────────────
// Track the tightest band range in the current squeeze episode,
// then fire when the bands begin to separate (expansion).
// ─────────────────────────────────────────────────────────────
var bool  sawSqueeze = false
var float sqzTop = na
var float sqzBot = na
var float minW   = na

if isSqueeze
    if not sawSqueeze
        minW   := bbw
        sqzTop := upper
        sqzBot := lower
    else if bbw < minW
        minW   := bbw
        sqzTop := upper
        sqzBot := lower
    sawSqueeze := true

bothExpanding = upper > upper[1] and lower < lower[1]   // both sides going separate ways
trigger = sawSqueeze and bothExpanding

// Only the first of a run draws: skip triggers that land within minGap bars of the last box.
var int lastBoxBar = na
firstOfRun = na(lastBoxBar) or (bar_index - lastBoxBar) >= minGap
drewBox = trigger and firstOfRun

if trigger
    sawSqueeze := false                                  // one box per squeeze episode
if drewBox
    float top = boxMode == "Bands at trigger" ? upper : sqzTop
    float bot = boxMode == "Bands at trigger" ? lower : sqzBot
    box.new(left=bar_index, top=top, right=bar_index + boxExtend, bottom=bot, bgcolor=boxCol, border_color=boxBorder, border_width=1)
    lastBoxBar := bar_index

// ─────────────────────────────────────────────────────────────
// Bands — colored independently by each line's own slope
// ─────────────────────────────────────────────────────────────
upCol = upper >= upper[1] ? colUp : colDown
loCol = lower >= lower[1] ? colUp : colDown
plot(upper, "BB Upper", color=upCol, linewidth=2)
plot(lower, "BB Lower", color=loCol, linewidth=2)

// Marker + alert on the trigger bar
plotshape(drewBox, "Expansion start", style=shape.triangleup, location=location.belowbar, color=color.new(color.purple, 0), size=size.tiny)
alertcondition(drewBox, "Squeeze -> Expansion", "Bands contracted then began expanding.")