//@version=6
indicator("Workshop 12 Session VWAP", overlay=true)
session = input.session("0930-1600", "Day session")
zone = input.string("America/New_York", "Time zone")
if not timeframe.isintraday
    runtime.error("Use an intraday time chart")
inside = not na(time(timeframe.period, session, zone))
dayKey = time("1D", "0000-0000", zone)
newDay = ta.change(dayKey) != 0
restart = inside and (not inside[1] or newDay)
var float pv = 0.0
var float total = 0.0
var bool bad = false
if restart
    pv := 0.0
    total := 0.0
    bad := false
if inside
    bad := bad or na(volume)
    if not na(volume) and volume > 0
        pv += hlc3 * volume
        total += volume
value = (inside and not bad and total > 0 ?
    pv / total : na)
plot(value, "Session estimate", color=color.blue,
    style=plot.style_linebr)