bristol-eurostar/trip_planner.py

"""
Combine GWR Bristol→Paddington trains with Eurostar St Pancras→destination trains.
"""
from datetime import datetime, timedelta, time as _time

MIN_CONNECTION_MINUTES = 50
MAX_CONNECTION_MINUTES = 110
MAX_GWR_MINUTES = 110
DATE_FMT = '%Y-%m-%d'
TIME_FMT = '%H:%M'


# Bristol Temple Meads → London Paddington walk-on single fares.
# Weekday restrictions (Mon–Fri only):
#   Super Off-Peak (£45.00, SSS): not valid if 05:05 ≤ dep ≤ 09:57
#   Off-Peak (£63.60, SVS):       not valid if dep < 08:26, except 02:00–05:10
#   Anytime (£138.70, SDS):       no restrictions
_TICKET_SUPER_OFF_PEAK = {'ticket': 'Super Off-Peak', 'price': 45.00,   'code': 'SSS'}
_TICKET_OFF_PEAK       = {'ticket': 'Off-Peak',       'price': 63.60,   'code': 'SVS'}
_TICKET_ANYTIME        = {'ticket': 'Anytime',        'price': 138.70,  'code': 'SDS'}


def cheapest_gwr_ticket(depart_time: str, travel_date: str) -> dict:
    """
    Return the cheapest walk-on single for Bristol Temple Meads → Paddington.

    Weekday (Mon–Fri) restrictions derived from the SSS/SVS ticket conditions:
      Super Off-Peak valid: dep ≤ 05:04  or  dep ≥ 09:58
      Off-Peak valid:       02:00 ≤ dep ≤ 05:10  or  dep ≥ 08:26
    Weekends: no restrictions — always Super Off-Peak.
    """
    dt = datetime.strptime(f"{travel_date} {depart_time}", f"{DATE_FMT} {TIME_FMT}")
    if dt.weekday() >= 5:  # Saturday or Sunday
        return _TICKET_SUPER_OFF_PEAK

    dep = dt.time()
    if dep <= _time(5, 4) or dep >= _time(9, 58):
        return _TICKET_SUPER_OFF_PEAK
    if dep >= _time(8, 26):
        return _TICKET_OFF_PEAK
    return _TICKET_ANYTIME


def _parse_dt(date: str, time: str) -> datetime:
    return datetime.strptime(f"{date} {time}", f"{DATE_FMT} {TIME_FMT}")


def _fmt_duration(minutes: int) -> str:
    h, m = divmod(minutes, 60)
    if h and m:
        return f"{h}h {m}m"
    if h:
        return f"{h}h"
    return f"{m}m"


def _is_viable_connection(
    gwr: dict,
    eurostar: dict,
    travel_date: str,
    min_connection_minutes: int,
    max_connection_minutes: int,
) -> tuple[datetime, datetime, datetime, datetime] | None:
    try:
        arr_pad = _parse_dt(travel_date, gwr['arrive_paddington'])
        dep_bri = _parse_dt(travel_date, gwr['depart_bristol'])
        dep_stp = _parse_dt(travel_date, eurostar['depart_st_pancras'])
        arr_dest = _parse_dt(travel_date, eurostar['arrive_destination'])
    except (ValueError, KeyError):
        return None

    if int((arr_pad - dep_bri).total_seconds() / 60) > MAX_GWR_MINUTES:
        return None

    if arr_dest < dep_stp:
        arr_dest += timedelta(days=1)

    connection_minutes = (dep_stp - arr_pad).total_seconds() / 60
    if connection_minutes < min_connection_minutes:
        return None
    if connection_minutes > max_connection_minutes:
        return None

    return dep_bri, arr_pad, dep_stp, arr_dest


def combine_trips(
    gwr_trains: list[dict],
    eurostar_trains: list[dict],
    travel_date: str,
    min_connection_minutes: int = MIN_CONNECTION_MINUTES,
    max_connection_minutes: int = MAX_CONNECTION_MINUTES,
) -> list[dict]:
    """
    Return a list of valid combined trips, sorted by Bristol departure time.

    Each trip dict:
      depart_bristol        HH:MM
      arrive_paddington     HH:MM
      gwr_duration          str   (e.g. "1h 45m")
      connection_duration   str
      depart_st_pancras     HH:MM
      arrive_destination    HH:MM
      total_duration        str   (e.g. "5h 30m")
      destination           str
    """
    trips = []

    for gwr in gwr_trains:
        # Find only the earliest viable Eurostar for this GWR departure
        for es in eurostar_trains:
            connection = _is_viable_connection(
                gwr,
                es,
                travel_date,
                min_connection_minutes,
                max_connection_minutes,
            )
            if not connection:
                continue
            dep_bri, arr_pad, dep_stp, arr_dest = connection

            total_mins = int((arr_dest - dep_bri).total_seconds() / 60)
            ticket = cheapest_gwr_ticket(gwr['depart_bristol'], travel_date)
            trips.append({
                'depart_bristol': gwr['depart_bristol'],
                'arrive_paddington': gwr['arrive_paddington'],
                'headcode': gwr.get('headcode', ''),
                'gwr_duration': _fmt_duration(int((arr_pad - dep_bri).total_seconds() / 60)),
                'connection_duration': _fmt_duration(int((dep_stp - arr_pad).total_seconds() / 60)),
                'depart_st_pancras': es['depart_st_pancras'],
                'arrive_destination': es['arrive_destination'],
                'train_number': es.get('train_number', ''),
                'total_duration': _fmt_duration(total_mins),
                'total_minutes': total_mins,
                'destination': es['destination'],
                'ticket_name': ticket['ticket'],
                'ticket_price': ticket['price'],
                'ticket_code': ticket['code'],
            })
            break  # Only the earliest valid Eurostar per GWR departure

    trips.sort(key=lambda t: (t['depart_bristol'], t['depart_st_pancras']))
    return trips


def find_unreachable_morning_eurostars(
    gwr_trains: list[dict],
    eurostar_trains: list[dict],
    travel_date: str,
    min_connection_minutes: int = MIN_CONNECTION_MINUTES,
    max_connection_minutes: int = MAX_CONNECTION_MINUTES,
) -> list[dict]:
    unreachable = []

    for es in eurostar_trains:
        if any(
            _is_viable_connection(
                gwr,
                es,
                travel_date,
                min_connection_minutes,
                max_connection_minutes,
            )
            for gwr in gwr_trains
        ):
            continue

        unreachable.append(es)

    return sorted(unreachable, key=lambda s: s['depart_st_pancras'])