"""Air VPD and interval-mean DLI; Python 3.10+, standard library only."""
import csv,json,math,sys
from datetime import datetime,timedelta
from pathlib import Path

def number(v,name,lo,hi):
    try:v=float(v)
    except (ValueError,TypeError):raise ValueError(name+': missing or nonnumeric') from None
    if not math.isfinite(v) or not lo<=v<=hi:raise ValueError(f'{name}: expected [{lo}, {hi}]')
    return v

def air_vpd(t,rh):
    t=number(t,'temp_c',0,50);rh=number(rh,'rh_pct',0,100)
    return .6108*math.exp(17.27*t/(t+237.3))*(1-rh/100)

def stamp(v):
    t=datetime.fromisoformat(v)
    if t.utcoffset() is None:raise ValueError('UTC offset required')
    return t

def analyze(rows):
    if not rows:raise ValueError('empty data')
    first=stamp(rows[0]['start']);previous=first;dose=0;out=[]
    if (first.hour,first.minute,first.second,first.microsecond)!=(0,0,0,0):raise ValueError('start at midnight')
    finish=first+timedelta(days=1)
    for r in rows:
        a,b=stamp(r['start']),stamp(r['end'])
        if a.utcoffset()!=first.utcoffset() or b.utcoffset()!=first.utcoffset():raise ValueError('one fixed offset required')
        if a!=previous or b<=a or b>finish:raise ValueError('gap, overlap, order or day boundary error')
        p=number(r['ppfd_umol_m2_s'],'PPFD',0,3000)
        v=air_vpd(r['temp_c'],r['rh_pct']);seconds=(b-a).total_seconds();dose+=p*seconds/1e6
        out.append(dict(start=r['start'],end=r['end'],seconds=seconds,air_vpd_kpa=v,cumulative_mol_m2=dose));previous=b
    if previous!=finish:raise ValueError('incomplete day')
    return dict(integration='interval-mean PPFD; fixed-offset 24-hour day',dli_mol_m2_day=dose,intervals=out)

if __name__=='__main__':
    try:
        with open(sys.argv[1] if len(sys.argv)>1 else Path(__file__).with_name('synthetic.csv'),newline='',encoding='utf-8') as f:result=analyze(list(csv.DictReader(f)))
        print(json.dumps(result,indent=2,allow_nan=False))
    except (ValueError,KeyError,OSError) as e:sys.exit('Invalid input: '+str(e))