"""Offline generator for backend/cities.json — the finite set of cities that get
crawlable climate pages (/climate/<slug>). Run occasionally to refresh the list:

    python gen_cities.py [N]        # default N=500 top metros by population

It reuses the GeoNames index that places.py already downloads/parses (calling
places._load() synchronously fills places._data), takes the top-N places by
population, and assigns each a stable, unique, URL-safe slug. Committing the output
keeps the routable city set explicit and reviewable, and decouples page-serving
from the async place-name loader.
"""
import json
import os
import re
import sys
import unicodedata

import places

OUT_PATH = os.path.join(os.path.dirname(__file__), "cities.json")

# GeoNames entry tuple layout (see places._load): the fields we keep.
_NAME, _ADMIN1, _COUNTRY, _CC, _LAT, _LON, _POP = 1, 2, 3, 4, 5, 6, 7


def slugify(*parts: str) -> str:
    """ASCII, lowercase, hyphenated slug from name/admin/country parts."""
    text = " ".join(p for p in parts if p)
    text = unicodedata.normalize("NFKD", text).encode("ascii", "ignore").decode()
    text = re.sub(r"[^a-zA-Z0-9]+", "-", text).strip("-").lower()
    return re.sub(r"-{2,}", "-", text)


def build(n: int = 500) -> list[dict]:
    places._load()  # synchronous parse; fills places._data (entries are pop-desc)
    if not places._data:
        raise SystemExit("GeoNames index failed to load (see logs); cannot generate cities.")
    entries = places._data[0]

    out: list[dict] = []
    seen_slugs: set[str] = set()
    for e in entries:
        if len(out) >= n:
            break
        name, admin1, country, cc = e[_NAME], e[_ADMIN1], e[_COUNTRY], e[_CC]
        # Drop admin1 from the slug when it just repeats the city name
        # (e.g. Tokyo/Tokyo, Singapore/Singapore) to avoid "tokyo-tokyo-jp".
        admin_part = admin1 if admin1 and slugify(admin1) != slugify(name) else ""
        base = slugify(name, admin_part, cc or "")
        if not base:
            continue
        slug = base
        i = 2
        while slug in seen_slugs:      # disambiguate the rare collision
            slug = f"{base}-{i}"
            i += 1
        seen_slugs.add(slug)
        out.append({
            "slug": slug,
            "name": name,
            "admin1": admin1,
            "country": country,
            "country_code": cc,
            "lat": round(e[_LAT], 5),
            "lon": round(e[_LON], 5),
            "population": e[_POP],
        })
    return out


def main() -> None:
    n = int(sys.argv[1]) if len(sys.argv) > 1 else 500
    cities = build(n)
    with open(OUT_PATH, "w", encoding="utf-8") as f:
        json.dump(cities, f, ensure_ascii=False, indent=0, separators=(",", ":"))
        f.write("\n")
    print(f"wrote {len(cities)} cities -> {OUT_PATH}")
    print("sample:", ", ".join(c["slug"] for c in cities[:8]))


if __name__ == "__main__":
    main()