"""Belegungsplan: a rooms × days occupancy timeline built from the guest register (the house's
who-is-present record; the ledger is billing and stays out of this).

Date semantics are half-open [arrival, departure): the departure day itself is free — it is the
'Von' of the follow-up row when a weekly renter is carried forward, so the bars tile without
overlapping. An open departure means "still here" only while the arrival is recent; an open stay
older than a year is a forgotten departure (same 365-day rule as the TVB Meldung) and is left to
the Datenprüfung instead of blocking a room forever.
"""
import datetime

from app import db, i18n

FAR = "9999-12-31"
STALE_AFTER_DAYS = 365   # keep in sync with tvb.STALE_AFTER_DAYS
MONTHS = i18n.t("months")
MONTHS_SHORT = i18n.t("months_short")
WEEKDAYS = i18n.t("weekdays_short")


def default_start(today=None):
    """Monday of last week — a little context behind, most of the window ahead."""
    today = today or datetime.date.today()
    return today - datetime.timedelta(days=today.weekday() + 7)


def _pack_lanes(stays):
    """Greedy interval packing: each stay goes into the first lane free at its arrival, so
    concurrent occupants of a room stack while back-to-back ones share a line."""
    lane_ends, out = [], []
    for st in stays:
        dep = st["departure"] or FAR
        for i, end in enumerate(lane_ends):
            if end <= st["arrival"]:
                lane_ends[i] = dep
                out.append((st, i))
                break
        else:
            lane_ends.append(dep)
            out.append((st, len(lane_ends) - 1))
    return out, max(len(lane_ends), 1)


def build(conn, start, days, today=None):
    today = today or datetime.date.today()
    end = start + datetime.timedelta(days=days)
    s_iso, e_iso, t_iso = start.isoformat(), end.isoformat(), today.isoformat()
    fresh = (today - datetime.timedelta(days=STALE_AFTER_DAYS)).isoformat()

    stays = db.rows(conn, """
        SELECT s.id, s.room_id, s.arrival, s.departure, s.sheet_number,
               COALESCE(TRIM(g.last_name || ' ' || COALESCE(g.first_name,'')), s.label) AS name,
               cl.name AS employer
        FROM stay s LEFT JOIN guest g ON g.id=s.guest_id
        LEFT JOIN client cl ON cl.id=s.employer_client_id
        WHERE s.source_sheet='guestsheet' AND s.arrival IS NOT NULL
          AND s.arrival < ? AND COALESCE(s.departure, ?) > ?
          AND (s.departure IS NOT NULL OR s.arrival >= ?)
        ORDER BY s.arrival NULLS FIRST, COALESCE(s.departure, ?), s.id""",
        (e_iso, FAR, s_iso, fresh, FAR))

    per_room, unplaced = {}, []
    for st in stays:
        if st["room_id"] is None:
            unplaced.append(dict(st))
        else:
            per_room.setdefault(st["room_id"], []).append(st)

    # today's occupants per room, independent of the visible window
    counts = {r[0]: r[1] for r in db.rows(conn, """
        SELECT room_id, COUNT(*) FROM stay
        WHERE source_sheet='guestsheet' AND room_id IS NOT NULL AND arrival IS NOT NULL
          AND arrival <= ? AND COALESCE(departure, ?) > ?
          AND (departure IS NOT NULL OR arrival >= ?)
        GROUP BY room_id""", (t_iso, FAR, t_iso, fresh))}

    rooms = []
    for r in db.rows(conn, """SELECT r.id, r.number, r.category, r.capacity, r.long_term,
                                     u.code AS unit FROM room r
                              LEFT JOIN unit u ON u.id=r.unit_id ORDER BY r.number"""):
        packed, lanes = _pack_lanes(per_room.get(r["id"], []))
        bars = []
        for st, lane in packed:
            dep = st["departure"] or FAR
            a, b = max(st["arrival"], s_iso), min(dep, e_iso)
            c1 = (datetime.date.fromisoformat(a) - start).days + 1
            c2 = max((datetime.date.fromisoformat(b) - start).days + 1, c1 + 1)
            state = ("past" if st["departure"] and st["departure"] <= t_iso
                     else "future" if st["arrival"] > t_iso else "current")
            bars.append({
                "stay_id": st["id"], "name": st["name"] or "?", "employer": st["employer"],
                "sheet_number": st["sheet_number"], "arrival": st["arrival"],
                "departure": st["departure"], "col": c1, "col_end": c2, "lane": lane + 1,
                "state": state, "clip_start": st["arrival"] < s_iso, "clip_end": dep > e_iso,
                "open_end": st["departure"] is None,
            })
        rooms.append({**dict(r), "bars": bars, "lanes": lanes,
                      "today_count": counts.get(r["id"], 0), "floor": str(r["number"])[:1]})

    day_list, months = [], []
    for i in range(days):
        d = start + datetime.timedelta(days=i)
        day_list.append({"iso": d.isoformat(), "dom": d.day, "wd": WEEKDAYS[d.weekday()],
                         "weekend": d.weekday() >= 5, "today": d == today,
                         "monday": d.weekday() == 0, "month_start": d.day == 1,
                         "label": f"{d.day:02d}.{d.month:02d}."})
        m = f"{MONTHS[d.month - 1]} {d.year}"
        if months and months[-1]["label"] == m:
            months[-1]["span"] += 1
        else:
            months.append({"label": m, "short": MONTHS_SHORT[d.month - 1], "span": 1})
    for m in months:
        # pick a label that fits the span so it can't run into the next month's divider —
        # 810px is the grid width at 200% display scaling, the narrowest supported case
        est = m["span"] * 810 / days
        m["text"] = m["label"] if est >= 95 else (m["short"] if est >= 40 else "")

    live = [r for r in rooms if not r["long_term"]]
    return {
        "rooms": rooms, "days": day_list, "months": months, "n_days": days,
        "start": start, "end": end, "today": today,
        "last": (end - datetime.timedelta(days=1)).isoformat(),
        "prev_start": (start - datetime.timedelta(days=7)).isoformat(),
        "next_start": (start + datetime.timedelta(days=7)).isoformat(),
        "guests_today": sum(r["today_count"] for r in rooms),
        "free_beds": sum(max(0, (r["capacity"] or 0) - r["today_count"]) for r in live),
        "unplaced": unplaced,
    }