"""Pre-bake per-handle GPS tracks for the Explore page.

Reads all activity GeoJSON files for a handle, applies RDP simplification,
and writes per-year tracks_YYYY.json shards plus a tracks_index.json manifest
for progressive client-side loading.
"""
from __future__ import annotations

import json
import time
from pathlib import Path

from bincio.extract.simplify import _rdp_mask

_VERSION     = 2
_RDP_EPSILON = 0.0001   # ~10 m on the ground


_SPORT_MAP: dict[str, str] = {
    "cycling": "cycling", "road_cycling": "cycling", "gravel_cycling": "cycling",
    "mountain_biking": "cycling", "e_biking": "cycling", "indoor_cycling": "cycling",
    "biking": "cycling", "bike": "cycling", "ride": "cycling",
    "running": "running", "trail_running": "running", "treadmill_running": "running",
    "jogging": "running",
    "hiking": "hiking", "walking": "hiking", "trekking": "hiking",
    "mountaineering": "hiking",
    "skiing": "skiing", "cross_country_skiing": "skiing", "alpine_skiing": "skiing",
    "snowboarding": "skiing",
}


def _sport_to_type(sport: str | None) -> str:
    if not sport:
        return "other"
    return _SPORT_MAP.get(sport.lower(), "other")


def bake_tracks(handle: str, data_dir: Path) -> int:
    """Build tracks.json for handle. Returns number of tracks included."""
    acts_dir = data_dir / handle / "activities"
    if not acts_dir.exists():
        return 0

    tracks = []
    for gj_path in sorted(acts_dir.glob("*.geojson")):
        act_id = gj_path.stem

        meta: dict = {}
        meta_path = acts_dir / f"{act_id}.json"
        if meta_path.exists():
            try:
                meta = json.loads(meta_path.read_text(encoding="utf-8"))
            except (OSError, json.JSONDecodeError):
                pass
        else:
            # bare-timestamp geojson with no metadata — superseded by a slug version
            if list(acts_dir.glob(f"{act_id}-*.geojson")):
                continue

        if meta.get("virtual") or meta.get("sub_sport") == "indoor":
            continue

        try:
            gj = json.loads(gj_path.read_text(encoding="utf-8"))
        except (OSError, json.JSONDecodeError):
            continue

        raw_coords = gj.get("geometry", {}).get("coordinates") or []
        if len(raw_coords) < 2:
            continue

        lng_lat = [[float(c[0]), float(c[1])] for c in raw_coords if len(c) >= 2]
        if len(lng_lat) < 2:
            continue

        mask = _rdp_mask(lng_lat, epsilon=_RDP_EPSILON)
        simplified = [pt for pt, keep in zip(lng_lat, mask) if keep]
        if len(simplified) < 2:
            continue

        tracks.append({
            "id":     act_id,
            "date":   (meta.get("started_at") or "")[:10],
            "type":   _sport_to_type(meta.get("sport")),
            "name":   meta.get("title") or act_id,
            "dist":   int(meta.get("distance_m") or 0),
            "coords": simplified,
        })

    tracks.sort(key=lambda t: t["date"], reverse=True)

    user_dir = data_dir / handle
    now = int(time.time())

    # Group into per-year buckets
    by_year: dict[str, list] = {}
    for t in tracks:
        year = t["date"][:4] or "0000"
        by_year.setdefault(year, []).append(t)

    # Remove stale year shards that no longer have data
    for old in user_dir.glob("tracks_*.json"):
        stem = old.stem  # e.g. "tracks_2024" or "tracks_index"
        if stem == "tracks_index":
            continue
        year_part = stem[len("tracks_"):]
        if year_part not in by_year:
            old.unlink(missing_ok=True)

    # Write per-year shards
    for year, year_tracks in by_year.items():
        shard_path = user_dir / f"tracks_{year}.json"
        shard_path.write_text(
            json.dumps({
                "v":            _VERSION,
                "handle":       handle,
                "year":         year,
                "generated_at": now,
                "tracks":       year_tracks,
            }),
            encoding="utf-8",
        )

    # Write manifest
    years_sorted = sorted(by_year.keys(), reverse=True)
    index_path = user_dir / "tracks_index.json"
    index_path.write_text(
        json.dumps({
            "v":            _VERSION,
            "handle":       handle,
            "generated_at": now,
            "total":        len(tracks),
            "years":        years_sorted,
        }),
        encoding="utf-8",
    )

    # Remove legacy monolithic file if present
    legacy = user_dir / "tracks.json"
    legacy.unlink(missing_ok=True)

    return len(tracks)