#!/usr/bin/env python3
"""Offline endpoint error analysis. Does not authenticate inputs or qualify a profile.

Inputs are preserved independent-observer receipts, not recovery grants. Review
their NTS reports, process restrictions and exact platform provenance separately.
"""
import argparse
from decimal import Decimal
import hashlib
import json
from pathlib import Path
import re


def analyze(before, after):
    a, b = before['observation'], after['observation']
    if not re.fullmatch('[0-9a-f]{32}', a['boot_id']) or a['boot_id'] == '0' * 32 or a['boot_id'] != b['boot_id']:
        raise ValueError('different or missing boot identity')
    for receipt, observation in ((before, a), (after, b)):
        for field in ('boottime_ns', 'utc_ns', 'sampling_bracket_ns', 'observation_error_ns', 'collected_at_ns'):
            if type(observation[field]) is not int or observation[field] < 0:
                raise ValueError('invalid endpoint time/error')
        if observation['collected_at_ns'] != observation['boottime_ns'] + observation['sampling_bracket_ns']:
            raise ValueError('incoherent endpoint bracket')
        if observation['observation_error_ns'] < observation['sampling_bracket_ns']:
            raise ValueError('endpoint uncertainty excludes its bracket')
        reference = Decimal(observation['assessment']['reference_time'])
        started = receipt['observer_started_wall_ns']
        if not reference.is_finite() or type(started) is not int or reference * 10**9 <= started:
            raise ValueError('no new reference after observer start')
    if a['collected_at_ns'] >= b['boottime_ns']:
        raise ValueError('overlapping or reordered endpoints')
    elapsed = b['boottime_ns'] - a['boottime_ns']
    residual = elapsed - (b['utc_ns'] - a['utc_ns'])
    endpoint_error = a['observation_error_ns'] + b['observation_error_ns']
    envelope = abs(residual) + endpoint_error
    return dict(boot_id=a['boot_id'], boottime_elapsed_ns=elapsed,
                elapsed_error_interval_ns=[residual-endpoint_error, residual+endpoint_error],
                endpoint_error_envelope_ns=envelope,
                observed_interval_envelope_ppb=(envelope*10**9+elapsed-1)//elapsed,
                qualified=False, max_elapsed_error_ppb=None,
                limitation='Endpoint interval only; no future or intermediate-time guarantee; input authenticity is external.')


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('before', type=Path)
    parser.add_argument('after', type=Path)
    args = parser.parse_args()
    raw = [p.read_bytes() for p in (args.before, args.after)]
    result = analyze(*(json.loads(data) for data in raw))
    result['receipt_sha256'] = [hashlib.sha256(data).hexdigest() for data in raw]
    print(json.dumps(result, indent=2))


if __name__ == '__main__':
    main()