#!/usr/bin/env python3
"""Call a URL on a cron schedule."""

from __future__ import annotations

import os
import sys
import time
from datetime import datetime
from typing import Any
from urllib.error import URLError
from urllib.request import Request, urlopen
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 * * * *",
}


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 resolve_url() -> str:
    url = os.environ.get("URL", "").strip()
    if not url:
        raise SystemExit("URL must be set")
    return url


def timeout_seconds() -> int:
    raw = os.environ.get("TIMEOUT", "30").strip()
    try:
        value = int(raw)
    except ValueError as exc:
        raise SystemExit(f"Invalid TIMEOUT '{raw}' (expected integer)") from exc
    if value <= 0:
        raise SystemExit("Invalid TIMEOUT (expected a positive integer)")
    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 do_request(url: str, timeout: int) -> None:
    req = Request(url, method="GET")
    try:
        with urlopen(req, timeout=timeout) as response:
            log(f"GET {url} -> HTTP {response.status}")
    except URLError as exc:
        reason = exc.reason if hasattr(exc, "reason") else str(exc)
        log(f"GET {url} failed: {reason}")


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:
    url = resolve_url()
    expr = resolve_cron_expr()
    tz = zone()
    timeout = timeout_seconds()
    on_startup = run_on_startup()

    log(f"Starting cron-url-caller (TZ={tz.key}, CRON='{expr}', URL='{url}', TIMEOUT={timeout}s)")

    if on_startup:
        do_request(url, timeout)

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

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


if __name__ == "__main__":
    main()