#!/usr/bin/env python3
"""Run a PostgreSQL source->dest sync on a cron schedule."""

from __future__ import annotations

import os
import subprocess
import sys
import time
from datetime import datetime
from zoneinfo import ZoneInfo

from croniter import croniter

CRON_MACROS = {
    "@yearly": "0 0 1 1 *",
    "@annually": "0 0 1 1 *",
    "@monthly": "0 0 1 * *",
    "@weekly": "0 0 * * 0",
    "@daily": "0 0 * * *",
    "@midnight": "0 0 * * *",
    "@hourly": "0 * * * *",
}

SYNC_SCRIPT = os.environ.get("SYNC_SCRIPT", "/usr/local/bin/sync.sh")


def log(msg: str) -> None:
    print(f"[{datetime.now().astimezone().isoformat(timespec='seconds')}] {msg}", file=sys.stderr)


def zone() -> ZoneInfo:
    name = os.environ.get("TZ") or "UTC"
    try:
        return ZoneInfo(name)
    except Exception as exc:
        raise SystemExit(f"Invalid TZ '{name}': {exc}") from exc


def resolve_cron_expr() -> str:
    cron = os.environ.get("CRON", "").strip()
    if not cron:
        raise SystemExit("CRON must be set (e.g. '0 3 * * *')")

    expr = CRON_MACROS.get(cron.lower(), cron)
    if not croniter.is_valid(expr):
        raise SystemExit(f"Invalid CRON '{expr}' (expected a 5-field cron expression)")
    return expr


def require_env(name: str) -> str:
    value = os.environ.get(name, "").strip()
    if not value:
        raise SystemExit(f"{name} must be set")
    return value


def run_on_startup() -> bool:
    return os.environ.get("ON_STARTUP", "true").lower() in ("1", "true", "yes", "on")


def next_run(expr: str, after: datetime) -> datetime:
    return croniter(expr, after).get_next(datetime)


def redacted(url: str) -> str:
    """Hide password in postgresql://user:pass@host/db style URLs."""
    if "://" not in url:
        return url
    scheme, rest = url.split("://", 1)
    if "@" not in rest or ":" not in rest.split("@", 1)[0]:
        return url
    creds, hostpart = rest.split("@", 1)
    user = creds.split(":", 1)[0]
    return f"{scheme}://{user}:***@{hostpart}"


def do_sync() -> None:
    log("Running sync...")
    result = subprocess.run([SYNC_SCRIPT], check=False)
    if result.returncode != 0:
        log(f"Sync failed with exit code {result.returncode}")
    else:
        log("Sync finished OK")


def sleep_until(target: datetime, tz: ZoneInfo) -> None:
    while True:
        remaining = (target - datetime.now(tz)).total_seconds()
        if remaining <= 0:
            return
        time.sleep(min(remaining, 60.0))


def main() -> None:
    source = require_env("SOURCE_DB_URL")
    dest = require_env("DEST_DB_URL")
    expr = resolve_cron_expr()
    tz = zone()
    on_startup = run_on_startup()

    log(
        "Starting database-syncer "
        f"(TZ={tz.key}, CRON='{expr}', "
        f"SOURCE='{redacted(source)}', DEST='{redacted(dest)}')"
    )

    if on_startup:
        do_sync()

    now = datetime.now(tz)
    nxt = next_run(expr, now)
    log(f"Next scheduled sync at {nxt.isoformat(timespec='seconds')}")

    while True:
        sleep_until(nxt, tz)
        do_sync()
        nxt = next_run(expr, datetime.now(tz))
        log(f"Next scheduled sync at {nxt.isoformat(timespec='seconds')}")


if __name__ == "__main__":
    main()