import json
import sys
import os

def write_polygon(f, coords):
    """Write a single polygon ring to the poly file."""
    # Close polygon if not already closed
    if coords[0] != coords[-1]:
        coords.append(coords[0])
    for lon, lat in coords:
        f.write(f"  {lon} {lat}\n")
    f.write("END\n")

def geojson_to_poly(geojson_file):
    base_name = os.path.splitext(os.path.basename(geojson_file))[0]
    poly_file = f"{base_name}.poly"

    with open(geojson_file, 'r', encoding='utf-8') as f:
        data = json.load(f)

    with open(poly_file, 'w', encoding='utf-8') as f:
        f.write(f"{base_name}\n")
        feature_index = 1

        for feature in data["features"]:
            geom_type = feature["geometry"]["type"]
            coords = feature["geometry"]["coordinates"]

            if geom_type == "Polygon":
                # Handle flat array: [ [lon, lat], ... ]
                if isinstance(coords[0][0], float):
                    coords = [coords]
                for ring in coords:
                    f.write(f"{feature_index}\n")
                    write_polygon(f, ring)
                    feature_index += 1

            elif geom_type == "MultiPolygon":
                for poly in coords:
                    # Each poly is [ [ [lon, lat], ... ] ]
                    ring = poly[0]  # use outer ring only
                    f.write(f"{feature_index}\n")
                    write_polygon(f, ring)
                    feature_index += 1
            else:
                print(f"Skipping unsupported geometry type: {geom_type}")

        f.write("END\n")

    print(f"Created .poly file: {poly_file}")

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Usage: python geojson_to_poly.py <geojson_file>")
        sys.exit(1)

    geojson_file = sys.argv[1]
    geojson_to_poly(geojson_file)