"""Unified Schedule service — ADP v0.1."""

from __future__ import annotations

from datetime import date, datetime, time, timedelta, timezone
from typing import Any, Literal, Optional

from psycopg2.extras import RealDictCursor

from db import get_connection

ScheduleKind = Literal["interval", "weekdays"]

_SCHEDULE_COLUMNS = """
    id, tenant_id, schedule_kind, interval_days, weekday_mask, pause_until,
    created_at, updated_at
"""

WEEKDAY_LABELS = ("Mo", "Di", "Mi", "Do", "Fr", "Sa", "So")


def weekday_bit(weekday: int) -> int:
    """ISO weekday: Monday=0 … Sunday=6."""
    return 1 << weekday


def _serialize_row(row: dict[str, Any]) -> dict[str, Any]:
    result = dict(row)
    for key in ("id", "tenant_id"):
        if result.get(key):
            result[key] = str(result[key])
    for ts_key in ("created_at", "updated_at"):
        if result.get(ts_key):
            result[ts_key] = result[ts_key].isoformat()
    if result.get("pause_until"):
        result["pause_until"] = result["pause_until"].isoformat()
    return result


def validate_schedule_payload(
    *,
    schedule_kind: str,
    interval_days: Optional[int],
    weekday_mask: int,
) -> None:
    if schedule_kind not in ("interval", "weekdays"):
        raise ValueError("Ungültiger schedule_kind")
    if schedule_kind == "interval":
        days = int(interval_days or 1)
        if days <= 0:
            raise ValueError("interval_days muss positiv sein")
    elif weekday_mask <= 0 or weekday_mask > 127:
        raise ValueError("Mindestens ein Wochentag auswählen")


def format_schedule_label(schedule: dict[str, Any]) -> str:
    kind = schedule.get("schedule_kind") or "interval"
    if kind == "weekdays":
        mask = int(schedule.get("weekday_mask") or 0)
        days = [WEEKDAY_LABELS[i] for i in range(7) if mask & weekday_bit(i)]
        label = ", ".join(days) if days else "Wochentage"
    else:
        days = max(int(schedule.get("interval_days") or 1), 1)
        if days == 1:
            label = "Täglich"
        elif days == 7:
            label = "Wöchentlich"
        else:
            label = f"Alle {days} Tage"
    pause = schedule.get("pause_until")
    if pause:
        label = f"{label} (Pause bis {pause})"
    return label


def _parse_pause_until(value: Any) -> Optional[date]:
    if value is None:
        return None
    if isinstance(value, date) and not isinstance(value, datetime):
        return value
    if isinstance(value, datetime):
        return value.date()
    text = str(value).strip()
    if not text:
        return None
    return date.fromisoformat(text[:10])


def is_paused_on(schedule: dict[str, Any], on_date: date) -> bool:
    pause = _parse_pause_until(schedule.get("pause_until"))
    return pause is not None and on_date <= pause


def _weekday_matches(schedule: dict[str, Any], on_date: date) -> bool:
    mask = int(schedule.get("weekday_mask") or 0)
    return bool(mask & weekday_bit(on_date.weekday()))


def _as_utc_midnight(d: date) -> datetime:
    return datetime.combine(d, time.min, tzinfo=timezone.utc)


def _next_weekday_on_or_after(
    start: date, *, weekday_mask: int, pause_until: Optional[date]
) -> date:
    for offset in range(366):
        candidate = start + timedelta(days=offset)
        if pause_until is not None and candidate <= pause_until:
            continue
        if weekday_mask & weekday_bit(candidate.weekday()):
            return candidate
    return start + timedelta(days=7)


def initial_due_at(*, schedule: dict[str, Any], now: Optional[datetime] = None) -> datetime:
    now = now or datetime.now(timezone.utc)
    today = now.date()
    if is_paused_on(schedule, today):
        pause = _parse_pause_until(schedule.get("pause_until"))
        assert pause is not None
        start = pause + timedelta(days=1)
    else:
        start = today

    kind = schedule.get("schedule_kind") or "interval"
    if kind == "weekdays":
        mask = int(schedule.get("weekday_mask") or 0)
        pause = _parse_pause_until(schedule.get("pause_until"))
        due_date = _next_weekday_on_or_after(start, weekday_mask=mask, pause_until=pause)
        return _as_utc_midnight(due_date)

    return _as_utc_midnight(start)


def next_due_after_completion(
    *, schedule: dict[str, Any], completed_at: Optional[datetime] = None
) -> datetime:
    now = completed_at or datetime.now(timezone.utc)
    today = now.date()
    kind = schedule.get("schedule_kind") or "interval"

    if kind == "weekdays":
        mask = int(schedule.get("weekday_mask") or 0)
        pause = _parse_pause_until(schedule.get("pause_until"))
        start = today + timedelta(days=1)
        due_date = _next_weekday_on_or_after(start, weekday_mask=mask, pause_until=pause)
        return _as_utc_midnight(due_date)

    days = max(int(schedule.get("interval_days") or 1), 1)
    next_date = today + timedelta(days=days)
    pause = _parse_pause_until(schedule.get("pause_until"))
    if pause is not None and next_date <= pause:
        next_date = pause + timedelta(days=1)
    return _as_utc_midnight(next_date)


def create_schedule(
    *,
    tenant_id: str,
    schedule_kind: ScheduleKind = "interval",
    interval_days: Optional[int] = 1,
    weekday_mask: int = 0,
    pause_until: Optional[date] = None,
) -> dict[str, Any]:
    validate_schedule_payload(
        schedule_kind=schedule_kind,
        interval_days=interval_days,
        weekday_mask=weekday_mask,
    )
    conn = get_connection()
    try:
        with conn.cursor(cursor_factory=RealDictCursor) as cur:
            cur.execute(
                f"""
                INSERT INTO schedules (
                    tenant_id, schedule_kind, interval_days, weekday_mask, pause_until
                )
                VALUES (%s, %s, %s, %s, %s)
                RETURNING {_SCHEDULE_COLUMNS}
                """,
                (
                    tenant_id,
                    schedule_kind,
                    interval_days if schedule_kind == "interval" else None,
                    weekday_mask,
                    pause_until,
                ),
            )
            row = _serialize_row(dict(cur.fetchone()))
        conn.commit()
    finally:
        conn.close()
    row["label"] = format_schedule_label(row)
    return row


def get_schedule(*, tenant_id: str, schedule_id: str) -> Optional[dict[str, Any]]:
    conn = get_connection()
    try:
        with conn.cursor(cursor_factory=RealDictCursor) as cur:
            cur.execute(
                f"""
                SELECT {_SCHEDULE_COLUMNS}
                FROM schedules
                WHERE id = %s AND tenant_id = %s
                """,
                (schedule_id, tenant_id),
            )
            row = cur.fetchone()
            if not row:
                return None
            result = _serialize_row(dict(row))
            result["label"] = format_schedule_label(result)
            return result
    finally:
        conn.close()


def update_schedule(
    *,
    tenant_id: str,
    schedule_id: str,
    schedule_kind: Optional[ScheduleKind] = None,
    interval_days: Optional[int] = None,
    weekday_mask: Optional[int] = None,
    pause_until: Optional[date] = None,
    clear_pause_until: bool = False,
) -> Optional[dict[str, Any]]:
    existing = get_schedule(tenant_id=tenant_id, schedule_id=schedule_id)
    if not existing:
        return None

    kind = schedule_kind or existing["schedule_kind"]
    interval = interval_days if interval_days is not None else existing.get("interval_days")
    mask = weekday_mask if weekday_mask is not None else int(existing.get("weekday_mask") or 0)
    validate_schedule_payload(
        schedule_kind=kind, interval_days=interval, weekday_mask=mask
    )

    updates: list[str] = []
    params: list[Any] = []
    if schedule_kind is not None:
        updates.append("schedule_kind = %s")
        params.append(schedule_kind)
    if interval_days is not None or schedule_kind == "weekdays":
        updates.append("interval_days = %s")
        params.append(None if kind == "weekdays" else interval)
    if weekday_mask is not None:
        updates.append("weekday_mask = %s")
        params.append(mask)
    if clear_pause_until:
        updates.append("pause_until = NULL")
    elif pause_until is not None:
        updates.append("pause_until = %s")
        params.append(pause_until)

    if not updates:
        return existing

    updates.append("updated_at = NOW()")
    params.extend([schedule_id, tenant_id])

    conn = get_connection()
    try:
        with conn.cursor(cursor_factory=RealDictCursor) as cur:
            cur.execute(
                f"""
                UPDATE schedules
                SET {", ".join(updates)}
                WHERE id = %s AND tenant_id = %s
                RETURNING {_SCHEDULE_COLUMNS}
                """,
                params,
            )
            row = cur.fetchone()
            if not row:
                return None
            result = _serialize_row(dict(row))
        conn.commit()
    finally:
        conn.close()
    result["label"] = format_schedule_label(result)
    return result


def attach_schedules_to_items(
    items: list[dict[str, Any]], *, tenant_id: str, schedule_id_key: str = "schedule_id"
) -> list[dict[str, Any]]:
    ids = [
        str(item[schedule_id_key])
        for item in items
        if item.get(schedule_id_key)
    ]
    if not ids:
        return [dict(item, schedule=None) for item in items]

    conn = get_connection()
    try:
        with conn.cursor(cursor_factory=RealDictCursor) as cur:
            cur.execute(
                f"""
                SELECT {_SCHEDULE_COLUMNS}
                FROM schedules
                WHERE tenant_id = %s AND id = ANY(%s::uuid[])
                """,
                (tenant_id, ids),
            )
            by_id = {}
            for row in cur.fetchall():
                sched = _serialize_row(dict(row))
                sched["label"] = format_schedule_label(sched)
                by_id[str(row["id"])] = sched
    finally:
        conn.close()

    enriched = []
    for item in items:
        copy = dict(item)
        sid = copy.get(schedule_id_key)
        copy["schedule"] = by_id.get(str(sid)) if sid else None
        enriched.append(copy)
    return enriched


def resolve_schedule_for_recurring(
    recurring: dict[str, Any], *, tenant_id: str
) -> Optional[dict[str, Any]]:
    sid = recurring.get("schedule_id")
    if sid:
        return get_schedule(tenant_id=tenant_id, schedule_id=str(sid))
    interval = recurring.get("interval_days")
    if interval is None:
        return None
    return {
        "schedule_kind": "interval",
        "interval_days": max(int(interval), 1),
        "weekday_mask": 0,
        "pause_until": None,
        "label": format_schedule_label(
            {"schedule_kind": "interval", "interval_days": interval, "weekday_mask": 0}
        ),
    }