"""Offline comparison of complete HTTP-200 UTF-8 snapshots; no network/actions.
Hashes validate internal consistency, not provenance. HTML projection is not a
browser rendering. Unknown reads never replace a valid comparison baseline.
"""
import json,hashlib,datetime,difflib,re,sys
from html.parser import HTMLParser
from urllib.parse import urlsplit
MAX=131072
class Projection(HTMLParser):
 def __init__(self):super().__init__(convert_charrefs=True);self.skip=[];self.parts=[]
 def handle_starttag(self,t,a):
  if t in ('script','style','template'):self.skip.append(t)
  if not self.skip and t in ('p','div','li','br','h1','h2','h3','tr','section'):self.parts.append('\n')
 def handle_endtag(self,t):
  if self.skip and self.skip[-1]==t:self.skip.pop()
  if not self.skip and t in ('p','div','li','h1','h2','h3','tr','section'):self.parts.append('\n')
 def handle_data(self,s):
  if not self.skip:self.parts.append(s)

def validate(s):
 if not isinstance(s,dict):raise ValueError('snapshot must be an object')
 u=urlsplit(s.get('url',''))
 if u.scheme!='https' or not u.hostname or u.username or u.password or u.query or u.fragment or u.port not in (None,443):raise ValueError('unsupported URL profile')
 when=datetime.datetime.fromisoformat(s['captured_at'])
 if when.tzinfo is None or when.utcoffset()!=datetime.timedelta(0):raise ValueError('UTC timestamp required')
 if s.get('status')!=200 or type(s.get('status')) is not int:raise ValueError('complete HTTP200 required; 304 needs separately validated cache baseline')
 if s.get('complete') is not True:raise ValueError('incomplete capture')
 mime=s.get('content_type','').split(';',1)[0].strip().lower()
 if mime not in ('text/html','text/plain'):raise ValueError('unsupported content type')
 body=s.get('body');
 if not isinstance(body,str) or not body.strip() or len(body.encode('utf-8'))>MAX:raise ValueError('empty/oversize/nontext body')
 digest=hashlib.sha256(body.encode('utf-8')).hexdigest()
 if s.get('body_sha256')!=digest:raise ValueError('body/hash mismatch')
 if mime=='text/html':
  parser=Projection();parser.feed(body);text='\n'.join(' '.join(line.split()) for line in ''.join(parser.parts).splitlines() if line.strip())
 else:text='\n'.join(' '.join(line.split()) for line in body.splitlines() if line.strip())
 if not text:raise ValueError('no comparable static text')
 return when,mime,text

def compare(before,after):
 result={'state':'unknown','baseline_replacement_allowed':False,'limitations':['Internal hashes do not prove capture origin or authenticity.','Static HTML text projection is not browser rendering or semantic importance.','Two observations cannot establish changes between them or continuous uptime.']}
 try:
  bt,bm,btext=validate(before)
 except Exception as e:return dict(result,reason='invalid baseline: '+str(e))
 result.update({'baseline_url':before['url'],'baseline_captured_at':before['captured_at'],'baseline_sha256':before['body_sha256']})
 try:at,am,atext=validate(after)
 except Exception as e:return dict(result,reason='invalid observation: '+str(e))
 if before['url']!=after['url']:return dict(result,reason='different exact URL')
 if bm!=am:return dict(result,reason='content-type profile changed')
 if at<=bt:return dict(result,reason='observation not later than baseline')
 raw_equal=before['body_sha256']==after['body_sha256'];text_equal=btext==atext
 state='raw_equal' if raw_equal else 'raw_changed_static_text_equal' if text_equal else 'static_text_changed'
 diff=list(difflib.unified_diff(btext.splitlines(),atext.splitlines(),fromfile='before-static-text',tofile='after-static-text',lineterm=''))
 return dict(result,state=state,baseline_replacement_allowed=True,observation_captured_at=after['captured_at'],observation_sha256=after['body_sha256'],seconds_between=(at-bt).total_seconds(),static_text_equal=text_equal,raw_equal=raw_equal,diff=diff[:100],diff_truncated=len(diff)>100)
if __name__=='__main__':
 if len(sys.argv)!=3:raise SystemExit('Usage: python snapshot-compare.py before.json after.json')
 print(json.dumps(compare(json.load(open(sys.argv[1])),json.load(open(sys.argv[2]))),indent=2))