"""Sync configurations from the Notion 'Recurring Events' database into the
'Gemeinsamer Kalender' database by expanding each configuration into its
individual occurrences.

Uses only the Python standard library (urllib, json, datetime).
"""

import json
import urllib.request
import urllib.error
from datetime import date, timedelta, datetime
from calendar import monthrange

NOTION_SECRET = "secret_b7PiPL2FqC9QEikqkAEWOht7LmzPMIJMWTzUPWwbw4H"
RECURRING_DB_ID = "34010a5f51bd804091dafc91d094bf8b"
CALENDAR_DB_ID = "34010a5f51bd8093ad67d3d3cd3908a4"
NOTION_VERSION = "2022-06-28"
API_BASE = "https://api.notion.com/v1"

# If a configuration has no End Date, we cap occurrence generation at this
# many years from today so the calendar does not balloon.
DEFAULT_HORIZON_YEARS = 2

WEEKDAY_INDEX = {
    "Monday": 0,
    "Tuesday": 1,
    "Wednesday": 2,
    "Thursday": 3,
    "Friday": 4,
    "Saturday": 5,
    "Sunday": 6,
}


# ---------------------------------------------------------------------------
# Notion HTTP helpers
# ---------------------------------------------------------------------------


def _request(method, path, payload=None):
    url = f"{API_BASE}{path}"
    data = None
    if payload is not None:
        data = json.dumps(payload).encode("utf-8")
    req = urllib.request.Request(url, data=data, method=method)
    req.add_header("Authorization", f"Bearer {NOTION_SECRET}")
    req.add_header("Notion-Version", NOTION_VERSION)
    req.add_header("Content-Type", "application/json")
    try:
        with urllib.request.urlopen(req) as resp:
            return json.loads(resp.read().decode("utf-8"))
    except urllib.error.HTTPError as e:
        body = e.read().decode("utf-8", errors="replace")
        raise RuntimeError(f"Notion API {method} {path} -> {e.code}: {body}") from e


def query_database(database_id, filter_=None):
    results = []
    payload = {}
    if filter_ is not None:
        payload["filter"] = filter_
    while True:
        data = _request("POST", f"/databases/{database_id}/query", payload)
        results.extend(data.get("results", []))
        if not data.get("has_more"):
            break
        payload["start_cursor"] = data["next_cursor"]
    return results


def create_page(properties, icon=None):
    body = {"parent": {"database_id": CALENDAR_DB_ID}, "properties": properties}
    if icon is not None:
        body["icon"] = icon
    return _request("POST", "/pages", body)


def update_page(page_id, properties, icon=None):
    body = {"properties": properties}
    if icon is not None:
        body["icon"] = icon
    return _request("PATCH", f"/pages/{page_id}", body)


def archive_page(page_id):
    return _request("PATCH", f"/pages/{page_id}", {"archived": True})


# ---------------------------------------------------------------------------
# Property extraction
# ---------------------------------------------------------------------------


def _title_text(prop):
    return "".join(t.get("plain_text", "") for t in prop.get("title", []))


def _rich_text(prop):
    return "".join(t.get("plain_text", "") for t in prop.get("rich_text", []))


def _select_name(prop):
    sel = prop.get("select")
    return sel["name"] if sel else None


def _multi_select_names(prop):
    return [o["name"] for o in prop.get("multi_select", [])]


def _date_start(prop):
    d = prop.get("date")
    if not d or not d.get("start"):
        return None
    return date.fromisoformat(d["start"][:10])


def parse_recurring_event(page):
    props = page["properties"]
    return {
        "page_id": page["id"],
        "icon": page.get("icon"),
        "name": _title_text(props["Event Name"]),
        "description": _rich_text(props["Description"]),
        "location": _rich_text(props["Location"]),
        "start_date": _date_start(props["Start Date"]),
        "end_date": _date_start(props["End Date"]),
        "interval": int(props["Interval"].get("number") or 1),
        "frequency": _select_name(props["Frequency"]),
        "days_of_week": _multi_select_names(props["Days of Week"]),
        "days_of_month": [int(x) for x in _multi_select_names(props["Days of Month"])],
        "betroffen": _multi_select_names(props.get("Betroffen", {"multi_select": []})),
        "bereich": _multi_select_names(props.get("Bereich", {"multi_select": []})),
    }


# ---------------------------------------------------------------------------
# Occurrence calculation
# ---------------------------------------------------------------------------


def _add_months(d, months):
    """Return a date `months` months after d, clamped to last day of month."""
    total = d.month - 1 + months
    year = d.year + total // 12
    month = total % 12 + 1
    day = min(d.day, monthrange(year, month)[1])
    return date(year, month, day)


def _effective_end(cfg, today):
    horizon = date(today.year + DEFAULT_HORIZON_YEARS, today.month, today.day)
    if cfg["end_date"] is None:
        return horizon
    return min(cfg["end_date"], horizon)


def compute_occurrences(cfg, today=None):
    today = today or date.today()
    if cfg["start_date"] is None or not cfg["frequency"]:
        return []
    start = cfg["start_date"]
    end = _effective_end(cfg, today)
    if end < start:
        return []
    interval = max(1, cfg["interval"])
    freq = cfg["frequency"]

    if freq == "Daily":
        return _daily(start, end, interval)
    if freq == "Weekly":
        return _weekly(start, end, interval, cfg["days_of_week"])
    if freq == "Monthly":
        return _monthly(start, end, interval, cfg["days_of_month"])
    if freq == "Yearly":
        return _yearly(start, end, interval)
    return []


def _daily(start, end, interval):
    out = []
    d = start
    while d <= end:
        out.append(d)
        d += timedelta(days=interval)
    return out


def _weekly(start, end, interval, days_of_week):
    # Fall back to start date's weekday if nothing is selected.
    if days_of_week:
        target_weekdays = {WEEKDAY_INDEX[name] for name in days_of_week if name in WEEKDAY_INDEX}
    else:
        target_weekdays = {start.weekday()}
    if not target_weekdays:
        return []
    # Anchor at the start of the week containing `start` (Monday).
    week_anchor = start - timedelta(days=start.weekday())
    out = []
    w = week_anchor
    while w <= end:
        for wd in sorted(target_weekdays):
            d = w + timedelta(days=wd)
            if start <= d <= end:
                out.append(d)
        w += timedelta(weeks=interval)
    return sorted(out)


def _monthly(start, end, interval, days_of_month):
    if days_of_month:
        target_days = sorted(set(days_of_month))
    else:
        target_days = [start.day]
    out = []
    cursor = date(start.year, start.month, 1)
    months_step = interval
    # Walk month-by-month in steps of `interval`, starting from start's month.
    m = date(start.year, start.month, 1)
    while m <= end:
        last_day = monthrange(m.year, m.month)[1]
        for d_num in target_days:
            if 1 <= d_num <= last_day:
                d = date(m.year, m.month, d_num)
                if start <= d <= end:
                    out.append(d)
        m = _add_months(m, months_step)
    return sorted(out)


def _yearly(start, end, interval):
    out = []
    y = start.year
    while True:
        try:
            d = date(y, start.month, start.day)
        except ValueError:
            # Feb 29 on non-leap year: skip.
            d = None
        if d is not None:
            if d > end:
                break
            if d >= start:
                out.append(d)
        y += interval
        # Safety: if start.month/day can never exist (shouldn't happen), break.
        if y > end.year + interval:
            break
    return out


# ---------------------------------------------------------------------------
# Calendar upsert
# ---------------------------------------------------------------------------


def _build_calendar_properties(cfg, occurrence_date, today):
    props = {
        "Event Name": {"title": [{"text": {"content": cfg["name"]}}]},
        "Date": {"date": {"start": occurrence_date.isoformat()}},
        "Is Recurring": {"checkbox": True},
        "Sync Date": {"date": {"start": today.isoformat()}},
        "Description": {
            "rich_text": [{"text": {"content": cfg["description"]}}] if cfg["description"] else []
        },
        "Location": {
            "rich_text": [{"text": {"content": cfg["location"]}}] if cfg["location"] else []
        },
        "Betroffen": {"multi_select": [{"name": n} for n in cfg["betroffen"]]},
        "Bereich": {"multi_select": [{"name": n} for n in cfg["bereich"]]},
    }
    return props


def _existing_index(calendar_pages):
    """Map (event_name, date_iso) -> page_id for existing entries."""
    index = {}
    for page in calendar_pages:
        props = page["properties"]
        name = _title_text(props["Event Name"])
        d = _date_start(props["Date"])
        if name and d:
            index[(name, d.isoformat())] = page["id"]
    return index


def sync():
    today = date.today()
    print(f"Sync started at {today.isoformat()}")

    recurring_pages = query_database(RECURRING_DB_ID)
    print(f"Fetched {len(recurring_pages)} recurring event configuration(s).")

    calendar_pages = query_database(CALENDAR_DB_ID)
    existing = _existing_index(calendar_pages)
    print(f"Found {len(existing)} existing calendar entrie(s).")

    created = 0
    updated = 0
    skipped = 0
    desired_keys = set()

    for page in recurring_pages:
        cfg = parse_recurring_event(page)
        if not cfg["name"]:
            print("  Skipping row without Event Name.")
            skipped += 1
            continue
        occurrences = compute_occurrences(cfg, today=today)
        print(f"  '{cfg['name']}' ({cfg['frequency']}, interval {cfg['interval']}): "
              f"{len(occurrences)} occurrence(s) computed.")
        for occ in occurrences:
            key = (cfg["name"], occ.isoformat())
            desired_keys.add(key)
            props = _build_calendar_properties(cfg, occ, today)
            icon = cfg["icon"]
            if key in existing:
                update_page(existing[key], props, icon=icon)
                updated += 1
            else:
                create_page(props, icon=icon)
                created += 1

    # Purge stale recurring entries: any calendar page marked as recurring
    # that no longer corresponds to a desired (name, date) occurrence.
    archived = _purge_stale(calendar_pages, desired_keys)

    print(f"Done. Created {created}, updated {updated}, archived {archived}, "
          f"skipped {skipped}.")


def _purge_stale(calendar_pages, desired_keys):
    archived = 0
    for page in calendar_pages:
        # Skip pages that are already archived / in trash.
        if page.get("archived") or page.get("in_trash"):
            continue
        props = page["properties"]
        # Only consider entries flagged as recurring — manual entries are
        # always left untouched.
        is_recurring = props.get("Is Recurring", {}).get("checkbox", False)
        if not is_recurring:
            continue
        name = _title_text(props["Event Name"])
        d = _date_start(props["Date"])
        if not name or not d:
            continue
        key = (name, d.isoformat())
        if key not in desired_keys:
            archive_page(page["id"])
            archived += 1
            print(f"  Archived stale occurrence: {name} @ {d.isoformat()}")
    return archived


if __name__ == "__main__":
    sync()