#!/usr/bin/env python3
"""Read-only S3 admission and bounded evidence evaluation. Never fetch Secrets."""
from __future__ import annotations

import argparse
from datetime import datetime, timezone
import hashlib
import importlib.util
import json
import math
from pathlib import Path
import sys

import yaml

ROOT = Path(__file__).resolve().parents[1]


def load_module(name, path):
    spec = importlib.util.spec_from_file_location(name, path)
    module = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(module)
    return module


def timestamp(value):
    if not isinstance(value, str):
        raise ValueError('invalid timestamp')
    result = datetime.fromisoformat(value.replace('Z', '+00:00'))
    if result.tzinfo is None:
        raise ValueError('timezone required')
    return result.astimezone(timezone.utc)


def digest(path):
    return hashlib.sha256(path.read_bytes()).hexdigest()


def admission(root=ROOT, package=None):
    package = package or root.parent / 'rapp-postgres'
    local = load_module('apps_capacity', root / 'tools/verify_apps_pg_capacity.py')
    native = load_module('postgres_consumers', package / 'scripts/render_consumers.py')
    manifests = [root / 'helm' / (name + '-cluster.yaml') for name in local.REVIEWED_CELLS]
    local.verify(manifests)
    paths = sorted((package / 'consumers').glob('*.yaml'))
    if not paths:
        raise ValueError('package consumers missing')
    consumers = [native.load(path) for path in paths]
    native.validate_cluster_capacity(consumers)
    registry = json.loads((root / 'assurance/placement-owners.json').read_text())
    cells = {}
    source_files = manifests + paths + [root / 'tools/verify_apps_pg_capacity.py',
        root / 'assurance/placement-owners.json', package / 'scripts/render_consumers.py']
    for manifest in manifests:
        doc = yaml.safe_load(manifest.read_text())
        name, spec = doc['metadata']['name'], doc['spec']
        roles = spec.get('managed', {}).get('roles', [])
        names = sorted(r['name'] for r in roles)
        cells[name] = {'consumers': names, 'ceiling': local.MAX_CONSUMERS,
            'retention_days': int(spec['backup']['retentionPolicy'].removesuffix('d')),
            'instances': spec['instances'], 'memory_limit': spec['resources']['limits']['memory'],
            'max_connections': int(spec['postgresql']['parameters']['max_connections']),
            'service_classes': {n: registry[n]['service_class'] for n in names},
            'connection_limits': {r['name']: r['connectionLimit'] for r in roles}}
        if cells[name]['retention_days'] != 30:
            raise ValueError('apps-pg retention differs from disclosed 30-day contract')
    for name in sorted(native.ALLOWED_CLUSTERS):
        manifest = package / 'helm' / (name + '-cluster.yaml')
        spec = yaml.safe_load(manifest.read_text())['spec']
        source_files.append(manifest)
        selected = [d for d in consumers if native.cluster_name(d) == name]
        horizon = native.erasure_horizon(selected)
        retention = int(spec['backup']['retentionPolicy'].removesuffix('d'))
        if retention != horizon['instanceRetentionDays']:
            raise ValueError('package retention differs from effective consumer horizon')
        if any(not d['honoured'] for d in horizon['consumers'].values()):
            raise ValueError('consumer retention request cannot be honoured on shared cell')
        cells[name] = {'consumers': sorted(horizon['consumers']),
            'ceiling': native.MAX_CONSUMERS_PER_CLUSTER, 'retention_days': retention,
            'instances': spec['instances'], 'memory_limit': spec['resources']['limits']['memory'],
            'max_connections': int(spec['postgresql']['parameters']['max_connections']),
            'service_classes': horizon['serviceClasses']}
    names = {n for c in cells.values() for n in c['consumers']}
    if names != set(registry) or any(not r.get('owner') or not r.get('evidence') for r in registry.values()):
        raise ValueError('missing or stale placement owner')
    for name, cell in cells.items():
        for consumer in cell['consumers']:
            if registry[consumer]['cell'] != name:
                raise ValueError('placement owner cell mismatch')
        cell['owners'] = {n: registry[n]['owner'] for n in cell['consumers']}
    return {'schema': 'railiance-platform.admission.v1', 'basis': 'source-declarations',
        'cells': cells, 'sources': {str(p.relative_to(root.parent)): digest(p) for p in source_files}}


def evaluate(contract, observation, now):
    """Classify a value-safe observation, not certify its underlying truth."""
    if set(observation) != {'schema', 'cluster_uid', 'captured_at', 'signals'}:
        raise ValueError('invalid observation envelope')
    if observation['schema'] != 'railiance-platform.observation.v1':
        raise ValueError('unsupported observation version')
    if observation['cluster_uid'] != contract['cluster_uid']:
        raise ValueError('wrong cluster')
    capture = timestamp(observation['captured_at'])
    capture_age = (now - capture).total_seconds()
    if capture_age < 0:
        raise ValueError('future capture')
    specs = contract['signals']
    if not isinstance(observation['signals'], dict) or set(observation['signals']) - set(specs):
        raise ValueError('unknown signals')
    results = {}
    for name, spec in specs.items():
        sample = observation['signals'].get(name)
        state = 'missing'
        if sample is not None:
            if not isinstance(sample, dict) or set(sample) != {'observed_at', 'result'}:
                raise ValueError('invalid signal fields')
            if sample['result'] not in ('pass', 'fail', 'unavailable'):
                raise ValueError('invalid result')
            observed = timestamp(sample['observed_at'])
            age = (now - observed).total_seconds()
            if observed > capture:
                raise ValueError('signal newer than capture')
            if sample['result'] == 'unavailable':
                state = 'unavailable'
            elif sample['result'] == 'fail':
                state = 'failed'
            elif capture_age > contract['capture_max_age_seconds']:
                state = 'stale'
            elif age > spec['max_age_seconds']:
                state = 'stale'
            else:
                state = 'healthy'
        results[name] = {'state': state, 'owner': spec['owner']}
    return {'schema': 'railiance-platform.assurance-signal.v1',
        'cluster_uid': contract['cluster_uid'], 'evaluated_at': now.isoformat(),
        'signals': results, 'transport': 'unmonitored',
        'guarantees': 'unsupported', 'threshold_status': 'local-diagnostic-only',
        'healthy': all(r['state'] == 'healthy' for r in results.values())}


def read_contract(path):
    doc = json.loads(path.read_text())
    if doc['schema'] != 'railiance-platform.assurance-contract.v1' or not doc['signals']:
        raise ValueError('invalid contract')
    for budget in [doc['capture_max_age_seconds'], *(s['max_age_seconds'] for s in doc['signals'].values())]:
        if type(budget) not in (int, float) or not math.isfinite(budget) or budget <= 0:
            raise ValueError('invalid freshness budget')
    if any(not s.get('owner') for s in doc['signals'].values()):
        raise ValueError('signal owner missing')
    return doc


def main(argv=None):
    parser = argparse.ArgumentParser(description=__doc__)
    sub = parser.add_subparsers(dest='command', required=True)
    a = sub.add_parser('admission')
    a.add_argument('--package', type=Path, default=ROOT.parent / 'rapp-postgres')
    a.add_argument('--check', type=Path)
    e = sub.add_parser('evaluate')
    e.add_argument('observation', type=Path)
    e.add_argument('--contract', type=Path, default=ROOT / 'assurance/service-contract.json')
    e.add_argument('--now', help='Explicit UTC time for deterministic replay')
    args = parser.parse_args(argv)
    try:
        if args.command == 'admission':
            report = admission(package=args.package)
            if args.check and report != json.loads(args.check.read_text()):
                raise ValueError('admission source or disclosure drift; review before refreshing')
            code = 0
        else:
            now = timestamp(args.now) if args.now else datetime.now(timezone.utc)
            report = evaluate(read_contract(args.contract), json.loads(args.observation.read_text()), now)
            code = 0 if report['healthy'] else 1
    except (OSError, ValueError, KeyError, TypeError, AttributeError, yaml.YAMLError):
        # Do not print parser errors, raw input, values, source paths or subprocess stderr.
        print(json.dumps({'schema': 'railiance-platform.assurance-error.v1', 'error': 'invalid-or-unavailable-input'}))
        return 2
    print(json.dumps(report, indent=2, allow_nan=False))
    return code


if __name__ == '__main__':
    sys.exit(main())