#!/usr/bin/env python3

import json
from subprocess import check_output
from datetime import datetime, timedelta


now = datetime.now()
two_days_ago = now - timedelta(days=2)

with open('/etc/backup-freshness-check.json', 'r') as file:
    config = json.load(file)

local_datasets = check_output(['zfs', 'list', '-H', '-o', 'name']).decode().splitlines()
errors = set()

for dataset in config['datasets']:
    if f'tank/{dataset}' not in local_datasets:
        errors.add(f'dataset "{dataset}" not present at all')
        continue

    snapshots = [
        snapshot
            for snapshot in check_output(['zfs', 'list', '-H', '-o', 'name', '-t', 'snapshot', f'tank/{dataset}', '-s', 'creation']).decode().splitlines()
            if f"@{config['prefix']}" in snapshot
    ]

    if not snapshots:
        errors.add(f'dataset "{dataset}" has no backup snapshots')
        continue

    newest_backup_snapshot = snapshots[-1]
    snapshot_datetime = datetime.utcfromtimestamp(
        int(check_output(['zfs', 'list', '-p', '-H', '-o', 'creation', '-t', 'snapshot', newest_backup_snapshot]).decode())
    )

    if snapshot_datetime < two_days_ago:
        days_ago = (now - snapshot_datetime).days
        errors.add(f'dataset "{dataset}" has not been backed up for {days_ago} days')
        continue

if errors:
    for error in errors:
        print(error)
    exit(2)
else:
    print(f"all {len(config['datasets'])} datasets have fresh backups.")