bristol-eurostar/circle_line.py

"""
Circle Line timetable: Paddington (H&C Line) → King's Cross St Pancras.

Parses the TransXChange XML file on first use and caches the result in memory.
"""
import os
import re
import xml.etree.ElementTree as ET
from datetime import datetime, timedelta

_PAD_STOP = '9400ZZLUPAH1'   # Paddington (H&C Line)
_KXP_STOP = '9400ZZLUKSX3'   # King's Cross St Pancras

from config.default import CIRCLE_LINE_XML as _TXC_XML  # overridden by app config after import
_NS = {'t': 'http://www.transxchange.org.uk/'}

# Populated on first call to next_service(); maps day-type -> sorted list of
# (pad_depart_seconds, kxp_arrive_seconds) measured from midnight.
_timetable: dict[str, list[tuple[int, int]]] | None = None


def _parse_duration(s: str | None) -> int:
    if not s:
        return 0
    m = re.match(r'PT(?:(\d+)H)?(?:(\d+)M)?(?:(\d+)S)?', s)
    return int(m.group(1) or 0) * 3600 + int(m.group(2) or 0) * 60 + int(m.group(3) or 0)


def _load_timetable() -> dict[str, list[tuple[int, int]]]:
    tree = ET.parse(_TXC_XML)
    root = tree.getroot()

    # Build JPS id -> [(from_stop, to_stop, runtime_secs, wait_secs)]
    jps_map: dict[str, list[tuple]] = {}
    for jps_el in root.find('t:JourneyPatternSections', _NS):
        links = []
        for link in jps_el.findall('t:JourneyPatternTimingLink', _NS):
            fr   = link.find('t:From/t:StopPointRef', _NS)
            to   = link.find('t:To/t:StopPointRef',   _NS)
            rt   = link.find('t:RunTime',              _NS)
            wait = link.find('t:From/t:WaitTime',      _NS)
            links.append((
                fr.text   if fr   is not None else None,
                to.text   if to   is not None else None,
                _parse_duration(rt.text   if rt   is not None else None),
                _parse_duration(wait.text if wait is not None else None),
            ))
        jps_map[jps_el.get('id')] = links

    def _seconds_to_depart(links, stop):
        """Seconds from journey start until departure from *stop*."""
        elapsed = 0
        for fr, to, rt, wait in links:
            elapsed += wait
            if fr == stop:
                return elapsed
            elapsed += rt
        return None

    def _seconds_to_arrive(links, stop):
        """Seconds from journey start until arrival at *stop*."""
        elapsed = 0
        for fr, to, rt, wait in links:
            elapsed += wait + rt
            if to == stop:
                return elapsed
        return None

    # Map JP id -> (pad_offset_secs, kxp_arrive_offset_secs)
    jp_offsets: dict[str, tuple[int, int]] = {}
    for svc in root.find('t:Services', _NS):
        for jp in svc.findall('.//t:JourneyPattern', _NS):
            jps_ref = jp.find('t:JourneyPatternSectionRefs', _NS)
            if jps_ref is None:
                continue
            links = jps_map.get(jps_ref.text, [])
            stops = [l[0] for l in links] + ([links[-1][1]] if links else [])
            if (
                _PAD_STOP in stops
                and _KXP_STOP in stops
                and stops.index(_PAD_STOP) < stops.index(_KXP_STOP)
            ):
                pad_off = _seconds_to_depart(links, _PAD_STOP)
                kxp_off = _seconds_to_arrive(links, _KXP_STOP)
                if pad_off is not None and kxp_off is not None:
                    jp_offsets[jp.get('id')] = (pad_off, kxp_off)

    result: dict[str, list[tuple[int, int]]] = {
        'MondayToFriday': [],
        'Saturday':       [],
        'Sunday':         [],
    }

    for vj in root.find('t:VehicleJourneys', _NS):
        jp_ref   = vj.find('t:JourneyPatternRef', _NS)
        dep_time = vj.find('t:DepartureTime',      _NS)
        op       = vj.find('t:OperatingProfile',   _NS)
        if jp_ref is None or dep_time is None or jp_ref.text not in jp_offsets:
            continue
        pad_off, kxp_off = jp_offsets[jp_ref.text]
        h, m, s = map(int, dep_time.text.split(':'))
        dep_secs = h * 3600 + m * 60 + s
        rdt = op.find('.//t:DaysOfWeek', _NS) if op is not None else None
        if rdt is None:
            continue
        for day_el in rdt:
            day_type = day_el.tag.split('}')[-1]
            if day_type in result:
                result[day_type].append((dep_secs + pad_off, dep_secs + kxp_off))

    for key in result:
        result[key].sort()
    return result


def _get_timetable() -> dict[str, list[tuple[int, int]]]:
    global _timetable
    if _timetable is None:
        _timetable = _load_timetable()
    return _timetable


def _day_type(weekday: int) -> str:
    if weekday < 5:
        return 'MondayToFriday'
    return 'Saturday' if weekday == 5 else 'Sunday'


def next_service(earliest_board: datetime) -> tuple[datetime, datetime] | None:
    """
    Given the earliest time a passenger can board at Paddington (H&C Line),
    return (circle_line_depart, arrive_kings_cross) as datetimes, or None if
    no service is found before midnight.

    The caller is responsible for adding any walk time from the GWR platform
    before passing *earliest_board*.
    """
    timetable = _get_timetable()[_day_type(earliest_board.weekday())]
    board_secs = (
        earliest_board.hour * 3600
        + earliest_board.minute * 60
        + earliest_board.second
    )
    midnight = earliest_board.replace(hour=0, minute=0, second=0, microsecond=0)
    for pad_secs, kxp_secs in timetable:
        if pad_secs >= board_secs:
            return midnight + timedelta(seconds=pad_secs), midnight + timedelta(seconds=kxp_secs)
    return None