"""Minimal validity gates, not a claim of forecast accuracy or model ranking."""
from math import isfinite


def assess_family(family, *, minimum_steps=3):
    points=family.get('points',[])
    if len(points)<minimum_steps:
        return {'valid':False,'reason':'Forecast has too few intervals'}
    loads=[]
    for point in points:
        for key in ('loadW','pvW'):
            value=point.get(key)
            if isinstance(value,bool) or not isinstance(value,(int,float)) or not isfinite(value) or value<0:
                return {'valid':False,'reason':'Forecast contains missing or invalid power'}
        loads.append(point['loadW'])
    # A PV-only plant or confirmed shutdown may legitimately forecast zero load.
    # It must be explicit; missing observations filled with zero are not savings.
    if max(loads)==0 and family.get('zeroLoadConfirmed') is not True:
        return {'valid':False,'reason':'Unconfirmed all-zero load forecast; likely missing data, not zero electricity costs'}
    return {'valid':True,'reason':None,'loadMaximumW':max(loads),
        'loadZeroFraction':sum(v==0 for v in loads)/len(loads)}