#!/usr/bin/env python3
"""Clip CityGML LoD2 buildings per terrain tile and export as OBJ meshes.

Inputs
- raw_3dgeb_lod2/LoD2_<utm>_<easting>_<northing>.gml : source building tiles
- export_unity/tile_index.csv : manifest produced by export_heightmaps.py

Outputs
- export_unity/buildings_obj/<tile_id>.obj : clipped building geometries per tile
"""
from __future__ import annotations

import csv
import os
from pathlib import Path

from osgeo import gdal

RAW_GML_DIR = Path("raw_3dgeb_lod2")
TILE_INDEX = Path("export_unity/tile_index.csv")
OUT_DIR = Path("export_unity/buildings_obj")

OUTPUT_FORMAT = "OBJ"  # glTF driver is not always available; OBJ is widely supported.

gdal.UseExceptions()
OUT_DIR.mkdir(parents=True, exist_ok=True)


def gml_path_for_tile(tile_id: str) -> Path:
    """Map a DGM tile id (dgm1_utm_easting_northing) to the corresponding CityGML file."""
    parts = tile_id.split("_")
    if len(parts) != 4 or parts[0] != "dgm1":
        raise ValueError(f"Unexpected tile_id format: {tile_id}")
    utm_zone, easting, northing = parts[1:]
    return RAW_GML_DIR / f"LoD2_{utm_zone}_{easting}_{northing}.gml"


def open_dataset(path: str, purpose: str):
    """Open a dataset and fail fast with context."""
    try:
        ds = gdal.OpenEx(path)
    except RuntimeError as exc:
        raise SystemExit(f"{purpose}: {exc}") from exc
    if ds is None:
        raise SystemExit(f"{purpose}: GDAL returned None for {path}")
    return ds


def main() -> None:
    if not TILE_INDEX.exists():
        raise SystemExit(f"Tile index missing: {TILE_INDEX}. Run export_heightmaps.py first.")

    written = 0
    skipped = 0

    with TILE_INDEX.open(newline="", encoding="utf-8") as f:
        reader = csv.DictReader(f)
        for row in reader:
            try:
                tile_id = row["tile_id"]
                xmin = float(row["xmin"])
                ymin = float(row["ymin"])
                xmax = float(row["xmax"])
                ymax = float(row["ymax"])
            except (KeyError, ValueError) as exc:
                print(f"Skipping malformed row {row}: {exc}")
                skipped += 1
                continue

            gml_path = gml_path_for_tile(tile_id)
            if not gml_path.exists():
                print(f"Missing CityGML for {tile_id}: {gml_path}")
                skipped += 1
                continue

            out_path = OUT_DIR / f"{tile_id}.obj"

            src_ds = open_dataset(str(gml_path), f"Could not open {gml_path}")

            opts = gdal.VectorTranslateOptions(
                format=OUTPUT_FORMAT,
                spatFilter=(xmin, ymin, xmax, ymax),
                layerName="Building",  # matches GML layer name
            )

            try:
                gdal.VectorTranslate(destNameOrDestDS=str(out_path), srcDS=src_ds, options=opts)
            except RuntimeError as exc:
                print(f"VectorTranslate failed for {tile_id}: {exc}")
                skipped += 1
                continue

            written += 1
            print(f"Wrote {out_path}")

    print(f"Summary: wrote {written} building tiles; skipped {skipped}.")
    if skipped:
        raise SystemExit(1)


if __name__ == "__main__":
    main()