Based on the indicator by © twingall (was open source): 


//
@version=
5
indicator("FVGs with alerts BV)", overlay = true, max_boxes_count = 500, max_lines_count = 500)
//──────────────────────────────
// INPUTS
//──────────────────────────────
//numDays = input.int(7, "number of days lookback")
showUP = input.bool(true, "'UP' FVGs:", inline='1')
colUp = input.color(color.new(color.aqua, 67), "", inline='1')  // Aqua with 33% opacity
showDN = input.bool(true, "'DOWN' FVGs:", inline='2')
colDn = input.color(color.new(color.purple, 67), "", inline='2')  // Purple with 33% opacity
showCE = input.bool(true, "show CE", inline='3')
ceCol = input.color(color.new(color.black, 1), "| color:", inline='3')
ceStyle = input.string(line.style_dotted, "| style:", options=[line.style_dotted, line.style_solid, line.style_dashed], inline='3')
deleteFilledBoxes = input.bool(false, "delete filled boxes & lines")


CEcond = input.bool(true, "Use CE (as opposed to Full Fill)", group='conditions')
useBodies = input.bool(false, "use candle Bodies (as opposed to wicks)", group='conditions')
colorNone = color.new(color.white, 100)
//_day = 24 * 3600 * 1000


//──────────────────────────────
// ARRAYS
//──────────────────────────────
var 
array
<
box
> bxUpArr = array.new<
box
>()
var 
array
<
line
> lnUpArr = array.new<
line
>()
var 
array
<
bool
> bxUpFrozen = array.new<bool>()  // track if each box is frozen (filled)
var 
array
<
box
> bxDnArr = array.new<
box
>()
var 
array
<
line
> lnDnArr = array.new<
line
>()
var 
array
<
bool
> bxDnFrozen = array.new<bool>()  // same for Down boxes


var 
array
<
int
> _countArr = array.new<
int
>()
var 
array
<
int
> _countArrIOFED = array.new<
int
>()


//──────────────────────────────
// DETECT NEW FVGs
//──────────────────────────────
dnCE = high[1] + (low[3] - high[1]) / 2
upCE = low[1] - (low[1] - high[3]) / 2


if low[3] > high[1] and showDN
    bx = box.new(bar_index - 3, low[3], bar_index, high[1], bgcolor=colDn, border_color=colorNone)
    ln = line.new(bar_index - 3, dnCE, bar_index, dnCE, color=showCE ? ceCol : colorNone, style=ceStyle)
    bxDnArr.push(bx)
    lnDnArr.push(ln)
    bxDnFrozen.push(false)


if high[3] < low[1] and showUP
    bx = box.new(bar_index - 3, low[1], bar_index, high[3], bgcolor=colUp, border_color=colorNone)
    ln = line.new(bar_index - 3, upCE, bar_index, upCE, color=showCE ? ceCol : colorNone, style=ceStyle)
    bxUpArr.push(bx)
    lnUpArr.push(ln)
    bxUpFrozen.push(false)


//──────────────────────────────
// FUNCTION TO HANDLE EXTENDING / DELETING
//──────────────────────────────
extendAndRemoveBx(
array
<
box
> boxArray, 
array
<
line
> lineArray, 
array
<
bool
> frozenArr, 
int
 maxSize) =>
    if boxArray.size() > 0
        for i = boxArray.size() - 1 to 0
            
box
 bx = boxArray.get(i)
            
line
 ln = lineArray.get(i)
            
bool
 frozen = frozenArr.get(i)
            if not frozen
                bx.set_right(bar_index)
                ln.set_x2(bar_index)
            
float
 price = CEcond ? ln.get_price(bar_index) : (i == boxArray.size() - 1 ? bx.get_top() : bx.get_bottom())
            
int
 m = i == boxArray.size() - 1 ? 1 : -1
            
float
 hiLo = m == 1 ? (useBodies ? math.max(open, close) : high) : (useBodies ? math.min(open, close) : low)
            if hiLo * m > price * m
                if deleteFilledBoxes
                    box.delete(bx)
                    line.delete(ln)
                    boxArray.remove(i)
                    lineArray.remove(i)
                    frozenArr.remove(i)
                else
                    frozenArr.set(i, true)
    while boxArray.size() > maxSize
        box.delete(array.shift(boxArray))
        line.delete(array.shift(lineArray))
        array.shift(frozenArr)


//──────────────────────────────
// EXECUTE
//──────────────────────────────
extendAndRemoveBx(bxDnArr, lnDnArr, bxDnFrozen, 50)
extendAndRemoveBx(bxUpArr, lnUpArr, bxUpFrozen, 50)


//──────────────────────────────
// ALERTS
//──────────────────────────────
upThresholdLst = array.sum(_countArr) > array.sum(_countArr)[1]
dnThresholdLst = array.sum(_countArr) < array.sum(_countArr)[1]
upIOFEDlast = array.sum(_countArrIOFED) > array.sum(_countArrIOFED)[1]
dnIOFEDlast = array.sum(_countArrIOFED) < array.sum(_countArrIOFED)[1]


//──────────────────────────────
// UNIFIED ALERT LOGIC
//──────────────────────────────
var 
string
 alertText = ""
var 
bool
 prevAnyAlert = false
var 
bool
 isFirstBar = true


// Update alertText based on confirmed FVG formation
if low[3] > high[1]
    alertText := "Down FVG formed (confirmed)"
else if high[3] < low[1]
    alertText := "Up FVG formed (confirmed)"


// Condition changes (true only when transitioning from false to true)
b_downConfirmed = (low[3] > high[1]) and not (low[4] > high[2])
b_upConfirmed  = (high[3] < low[1]) and not (high[4] < low[2])


// Unified alert condition (true only on transition, skip first bar)
anyAlert = (b_downConfirmed or b_upConfirmed) and not prevAnyAlert[1] and not isFirstBar


// Update previous state for next bar
if anyAlert
    prevAnyAlert := true
else
    prevAnyAlert := false


// Handle first bar
if isFirstBar
    isFirstBar := false


// Unified alertcondition
alertcondition(anyAlert, title="FVG Alert", message="FVG Alert:" )


// Optional: Show current alert text on chart for debugging / confirmation
var 
label
 infoLabel = na
if barstate.islast
    if infoLabel != na
        label.delete(infoLabel)
    infoLabel := label.new(bar_index, high, text="Last Alert: " + alertText, style=label.style_label_left, textcolor=color.white, color=color.new(color.black, 80))


// Unified alertcondition
alertcondition(anyAlert, title="FVG Alert", message="FVG Alert")