"""
Scrape GWR trains from Bristol Temple Meads to London Paddington using Realtime Trains.

Uses httpx (not Playwright) with browser-like headers.

Two fetches run concurrently:
  BRI/to/PAD  → departure times from Bristol (div.time.plan.d)
  PAD/from/BRI → arrival times at Paddington (div.time.plan.a)
Matched by train ID (div.tid).
"""
import asyncio
import re
import httpx
import lxml.html

BRI_TO_PAD = (
    "https://www.realtimetrains.co.uk/search/detailed/"
    "gb-nr:BRI/to/gb-nr:PAD/{date}/0000-2359"
    "?stp=WVS&show=pax-calls&order=wtt"
)
PAD_FROM_BRI = (
    "https://www.realtimetrains.co.uk/search/detailed/"
    "gb-nr:PAD/from/gb-nr:BRI/{date}/0000-2359"
    "?stp=WVS&show=pax-calls&order=wtt"
)

DEFAULT_UA = (
    "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 "
    "(KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36"
)


def _browser_headers(user_agent: str) -> dict:
    return {
        "User-Agent": user_agent,
        "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8",
        "Accept-Language": "en-GB,en;q=0.9",
        "Accept-Encoding": "gzip, deflate, br",
        "Connection": "keep-alive",
        "Upgrade-Insecure-Requests": "1",
        "Sec-Fetch-Dest": "document",
        "Sec-Fetch-Mode": "navigate",
        "Sec-Fetch-Site": "none",
        "Sec-Fetch-User": "?1",
    }


def _fmt(hhmm: str) -> str:
    """Convert '0830' → '08:30'."""
    hhmm = re.sub(r'[^0-9]', '', hhmm)
    if len(hhmm) == 4:
        return f"{hhmm[:2]}:{hhmm[2:]}"
    return hhmm


def _parse_services(html: str, time_selector: str) -> dict[str, str]:
    """Return {train_id: time_string} from a servicelist page."""
    root = lxml.html.fromstring(html)
    sl = root.cssselect('div.servicelist')
    if not sl:
        return {}
    result = {}
    for svc in sl[0].cssselect('a.service'):
        tid_els  = svc.cssselect('div.tid')
        time_els = svc.cssselect(time_selector)
        if tid_els and time_els:
            tid = tid_els[0].text_content().strip()
            time_text = time_els[0].text_content().strip()
            if time_text:
                result[tid] = _fmt(time_text)
    return result


async def fetch(date: str, user_agent: str = DEFAULT_UA) -> list[dict]:
    """Fetch GWR trains concurrently; returns [{'depart_bristol', 'arrive_paddington'}]."""
    headers = _browser_headers(user_agent)
    async with httpx.AsyncClient(headers=headers, follow_redirects=True, timeout=30) as client:
        r_bri, r_pad = await asyncio.gather(
            client.get(BRI_TO_PAD.format(date=date)),
            client.get(PAD_FROM_BRI.format(date=date)),
        )

    departures = _parse_services(r_bri.text, 'div.time.plan.d')
    arrivals   = _parse_services(r_pad.text, 'div.time.plan.a')

    trains = [
        {'depart_bristol': dep, 'arrive_paddington': arr}
        for tid, dep in departures.items()
        if (arr := arrivals.get(tid))
    ]
    return sorted(trains, key=lambda t: t['depart_bristol'])


def get_gwr_trains(date: str, user_agent: str = DEFAULT_UA) -> list[dict]:
    """Synchronous wrapper around fetch() for CLI/testing use."""
    return asyncio.run(fetch(date, user_agent))