"""Shared helpers."""
import re
from datetime import date, datetime, timedelta

DAY_NAMES = ["Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag", "Sonntag"]
MONTHS = ["Jan", "Feb", "Mär", "Apr", "Mai", "Jun", "Jul", "Aug", "Sep", "Okt", "Nov", "Dez"]


def week_start(d: date) -> date:
    return d - timedelta(days=d.weekday())


def week_label(d: date) -> str:
    iso = d.isocalendar()
    return f"KW {iso[1]}"


def fmt_day(d: date) -> str:
    return f"{d.day:02d}.{MONTHS[d.month - 1]}"


def fmt_range(d1: date, d2: date) -> str:
    return f"{fmt_day(d1)} - {fmt_day(d2)} {d2.year}"


def current_semester(semesters: list[dict], now: datetime | None = None) -> str:
    now = now or datetime.now()
    ts = now.replace(tzinfo=None).timestamp()
    for s in semesters:
        if s["begin"] <= ts <= s["ende"]:
            return s["label"]
    # fallback: most recent past semester
    past = [s for s in semesters if s["ende"] >= ts]
    if past:
        return past[0]["label"]
    return semesters[0]["label"] if semesters else ""


def decode_matrikel(m: str, stgs: list[dict]) -> dict | None:
    """Decode FH-Burgenland matrikel: YY + startcode + StG(3) + nr(3)."""
    m = m.strip()
    if not re.fullmatch(r"\d{9,10}", m):
        return None
    stg_code = m[-6:-3]
    nr = m[-3:]
    year = m[:2]
    startcode = m[2:4] if len(m) == 10 else ""
    start = None
    if startcode == "10":
        start = f"WS 20{year}"
    elif startcode == "20":
        start = f"SS 20{year}"
    stg = next((s for s in stgs if s["kz"] == stg_code), None)
    return {
        "matrikel": m,
        "start": start or f"20{year}",
        "stg_kz": stg_code,
        "stg_code": stg["code"] if stg else None,
        "stg_name": stg["name"] if stg else None,
        "nr": int(nr),
    }


def lv_color(lv: str) -> str:
    """Stable hue for an LV code."""
    h = sum(ord(c) for c in lv) * 47
    hue = h % 360
    return f"hsl({hue}, 55%, 45%)"


def events_to_json(events) -> list[dict]:
    return [{
        "lv": e.lv, "lektor": e.lektor, "gruppe": e.gruppe, "ort": e.ort,
        "start": e.start.isoformat(), "end": e.end.isoformat(),
        "uid": e.uid,
    } for e in events]