Session Open Line

// This Pine Script® code is subject to the terms of the Mozilla Public License 2.0 at https://mozilla.org/MPL/2.0/
// © Piotr Kowalski "piecioshka"
// Docs (EN): https://github.com/piecioshka/tradingview-pine-scripts/blob/main/indicators/overlays/session-open-line/session-open-line.md
// Docs (PL): https://github.com/piecioshka/tradingview-pine-scripts/blob/main/indicators/overlays/session-open-line/session-open-line.pl.md

//@version=6
// Draws a horizontal line at the session's reference level - from the first
// to the last bar of the session. By default the reference is the previous
// session's close, so the change matches the day change quoted against the
// prior close and opening gaps become visible; the 'Reference level' input
// switches it to the session open, measuring only what happened inside the
// session. A label shows the price change during the session (close vs the
// reference level) as a percent, as a difference in the instrument currency,
// or both - each part has its own checkbox. The 'Percent
// position' input decides where the label sits - above or below the line, or
// behind its end - and the choice applies consistently to completed sessions
// and to the ongoing one. During the ongoing session the value updates on
// every bar. Line and label colors depend on the sign of the change - up,
// down, or unchanged when the close sits exactly at the reference level - and
// the whole session is shaded with the same color (can be turned off). Alerts
// fire when the price crosses the line in either direction, and the
// reference level plus the session change (%) are exposed as hidden series -
// other scripts can use them as external sources. Works on intraday
// timeframes - on D and above every bar is its own session, so the indicator
// only shows a hint.
indicator('Session Open Line', overlay = true, max_lines_count = 500, max_labels_count = 500, max_boxes_count = 500)

refLevelName = input.string('Previous session close', 'Reference level', options = ['Previous session close', 'Session open'], group = 'General', tooltip = 'The level the line sits at and the change is measured from. Previous session close (default): the close of the last bar of the previous session - the change matches the day change quoted against the prior close, and an opening gap shows up as the distance between the line and the first candle. Session open: the open of the first bar of the session - the change measures only what happened inside the session. The first session in the loaded history has no previous close, so in the default mode it gets no line.')
showPct = input.bool(true, 'Show percent change', group = 'General', tooltip = 'Shows the session change as a percent of the reference level, e.g. +0.84%.')
showAbs = input.bool(false, 'Show change in instrument currency', group = 'General', tooltip = 'Shows the session change as a price difference (close minus the reference level) in the currency of the instrument, e.g. +12.50 USD. With both checkboxes on the label reads +0.84% (+12.50 USD).')
GRP = 'Appearance'
upColor = input.color(#26A69A, 'Up color', group = GRP)
downColor = input.color(#EF5350, 'Down color', group = GRP)
flatColor = input.color(#787B86, 'Unchanged color', group = GRP, tooltip = 'Used when the close sits exactly at the reference level - neither a rise nor a fall. Happens on the first bar of a session opening at the previous close, and on illiquid instruments.')
lineStyleName = input.string('Solid', 'Line style', options = ['Solid', 'Dashed', 'Dotted'], group = GRP)
lineWidth = input.int(1, 'Line width', minval = 1, maxval = 4, group = GRP)
textSizeName = input.string('Small', 'Text size', options = ['Auto', 'Tiny', 'Small', 'Normal', 'Large'], group = GRP)
pctPositionName = input.string('Behind the line', 'Percent position', options = ['Above the line', 'Below the line', 'Behind the line'], group = GRP, tooltip = 'Above the line: the value sits over the end of the line. Below the line: the value hangs under the end of the line. Behind the line: the value sits at the reference level, right of the line end, as if continuing it. The choice applies to both completed and ongoing sessions.')
GRP_BG = 'Session highlight'
showBg = input.bool(true, 'Highlight the whole session', group = GRP_BG, tooltip = 'Fills the entire session with a single color, decided by where the price stands against the reference level.')
bgUpColor = input.color(color.new(#26A69A, 90), 'Highlight up color', group = GRP_BG)
bgDownColor = input.color(color.new(#EF5350, 90), 'Highlight down color', group = GRP_BG)
bgFlatColor = input.color(color.new(#787B86, 90), 'Highlight unchanged color', group = GRP_BG)

usePrevClose = refLevelName == 'Previous session close'

lineStyle = switch lineStyleName
    'Dashed' => line.style_dashed
    'Dotted' => line.style_dotted
    => line.style_solid

textSize = switch textSizeName
    'Auto' => size.auto
    'Tiny' => size.tiny
    'Normal' => size.normal
    'Large' => size.large
    => size.small

// One position for every label the indicator draws — completed sessions and
// the ongoing one alike.
pctStyle = switch pctPositionName
    'Above the line' => label.style_label_lower_right
    'Below the line' => label.style_label_upper_right
    => label.style_label_left

// Both checkboxes off means no label at all.
showLabel = showPct or showAbs

// syminfo.currency is empty for some symbols (e.g. indices without a quote
// currency) - then the difference is shown as a bare number.
currencySuffix = not na(syminfo.currency) and syminfo.currency != '' ? ' ' + syminfo.currency : ''

fmtPct(float pct) =>
    (pct >= 0 ? '+' : '') + str.tostring(pct, '0.00') + '%'

fmtAbs(float delta) =>
    (delta >= 0 ? '+' : '') + str.tostring(delta, format.mintick) + currencySuffix

// Percent first, the currency difference in parentheses - or either one
// alone. An undefined percent (reference level at or below zero) falls back
// to the price difference, which stays meaningful at any price.
fmtChange(float delta, float pct) =>
    showPct and showAbs and not na(pct) ? fmtPct(pct) + ' (' + fmtAbs(delta) + ')' : showPct and not na(pct) ? fmtPct(pct) : fmtAbs(delta)

// label_lower_right - anchor at the bottom-right corner, the text sits above
// the line and does not stick out past the session end. label_upper_right -
// anchor at the top-right corner, the text hangs below the line, again inside
// the session. label_left - anchor on the left edge, the text sits at the
// reference level, to the right of the line end, as if continuing the line.
newLabel(int x, float y, float delta, float pct, color col, string sizeName, string labelStyle) =>
    label.new(x, y, fmtChange(delta, pct), xloc = xloc.bar_index, style = labelStyle, textcolor = col, color = color.new(color.black, 100), size = sizeName)

// Vertical bounds of the session highlight. TradingView silently skips boxes
// whose top/bottom lie extremely far from the price scale (measured on an
// instrument near 85: bounds of +-1e8 still draw, +-1e9 do not), so absurd
// constants like 1e17 produce boxes that exist but never render. Instead
// the bounds follow the price range of the loaded data - 100x that range
// above and below covers the full height of the pane at any realistic zoom
// while staying far inside the renderer's limits.
BG_PAD = 100.0
var float dataHigh = na
var float dataLow = na
if not na(high) and not na(low)
    dataHigh := na(dataHigh) ? high : math.max(dataHigh, high)
    dataLow := na(dataLow) ? low : math.min(dataLow, low)
bgPad = math.max(dataHigh - dataLow, syminfo.mintick) * BG_PAD
bgTop = dataHigh + bgPad
bgBottom = dataLow - bgPad

// time('D') changes on the first bar of the trading day, so it also works
// for sessions crossing midnight (e.g. futures).
newSession = timeframe.change('D')

var line ln = na
var label lb = na
var box bg = na
var float sessionRef = na

// The reference level of the session: its own open, or the close of the
// previous session (close[1] on the session's first bar). On the very first
// loaded bar close[1] is na - in 'Previous session close' mode the first
// session has no reference, so it draws nothing.
if timeframe.isintraday and (newSession or barstate.isfirst)
    sessionRef := usePrevClose ? close[1] : open
    lb := na
    if not na(sessionRef)
        ln := line.new(bar_index, sessionRef, bar_index, sessionRef, xloc = xloc.bar_index, color = flatColor, style = lineStyle, width = lineWidth)
        // One box per session instead of bgcolor(), which paints a single bar
        // and cannot be repainted later - a box spans the whole session and
        // keeps one color, corrected on every bar of that session. Box
        // 'extend' works on the time axis only, so the vertical coverage
        // comes from the bgTop/bgBottom bounds.
        bg := showBg ? box.new(bar_index, bgTop, bar_index, bgBottom, xloc = xloc.bar_index, border_color = color.new(color.black, 100), bgcolor = bgFlatColor) : na
    else
        ln := na
        bg := na

// The sign of the change comes from the price difference, not from the
// percent - for a reference level at or below zero (possible on futures
// spreads) the percent flips sign or loses meaning, the difference never
// does.
delta = close - sessionRef
pct = sessionRef > 0 ? delta / sessionRef * 100 : na
// Three states, not two: a close exactly at the reference level is neither a
// rise nor a fall and gets its own neutral color instead of being folded into
// one of them.
col = delta > 0 ? upColor : delta < 0 ? downColor : flatColor

if timeframe.isintraday and not na(ln)
    line.set_x2(ln, bar_index)
    line.set_color(ln, col)
    if not na(bg)
        box.set_right(bg, bar_index)
        box.set_bgcolor(bg, delta > 0 ? bgUpColor : delta < 0 ? bgDownColor : bgFlatColor)
    // The label follows the end of the line and updates on every bar of
    // the session.
    if showLabel
        if na(lb)
            lb := newLabel(bar_index, sessionRef, delta, pct, col, textSize, pctStyle)
        else
            label.set_x(lb, bar_index)
            label.set_text(lb, fmtChange(delta, pct))
            label.set_textcolor(lb, col)

if timeframe.isintraday
    // Boxes of earlier sessions were created while less data was loaded, so
    // their bounds are narrower - on the last bar bring every box to the
    // final bounds. Runs only when the bounds actually change.
    var float sweptTop = na
    if barstate.islast and (na(sweptTop) or bgTop != sweptTop)
        sweptTop := bgTop
        for b in box.all
            box.set_top(b, bgTop)
            box.set_bottom(b, bgBottom)
else
    if barstate.islast
        var table hint = table.new(position.top_right, 1, 1)
        table.cell(hint, 0, 0, 'Session Open Line: the indicator works on intraday timeframes', text_color = color.gray, text_size = size.small)

// A cross is only meaningful against the current session's line, so the
// first bar of a session - where the line jumps to the new reference - is
// excluded.
crossUp = ta.crossover(close, sessionRef)
crossDown = ta.crossunder(close, sessionRef)
alertOk = timeframe.isintraday and not newSession
alertcondition(alertOk and crossUp, 'Cross above the reference level', 'Price crossed above the session reference level (session open or previous session close)')
alertcondition(alertOk and crossDown, 'Cross below the reference level', 'Price crossed below the session reference level (session open or previous session close)')

// Hidden series - rows in the Data Window and external sources for other
// scripts (any input.source field): the reference level and the session
// change as a percent.
plot(timeframe.isintraday ? sessionRef : na, 'Reference level', display = display.data_window, editable = false)
plot(timeframe.isintraday ? pct : na, 'Session change %', display = display.data_window, editable = false)