CA/backend/utils/geo.py

"""
Geographic utilities: point-in-polygon testing via ray casting.
"""


def point_in_polygon(lat: float, lon: float, polygon_coords: list) -> bool:
    """Check if a point is inside a polygon (supports Polygon and MultiPolygon)."""
    if not polygon_coords:
        return False

    # MultiPolygon: check each polygon
    if isinstance(polygon_coords[0], list) and polygon_coords[0] and isinstance(polygon_coords[0][0], list):
        for polygon in polygon_coords:
            if polygon and isinstance(polygon[0], list):
                ring = polygon[0] if isinstance(polygon[0][0], list) else polygon
                if point_in_ring(lat, lon, ring):
                    return True
        return False

    # Single Polygon: use first ring (outer boundary)
    ring = polygon_coords[0] if isinstance(polygon_coords[0], list) else polygon_coords
    return point_in_ring(lat, lon, ring)


def point_in_ring(lat: float, lon: float, ring: list) -> bool:
    """Ray casting algorithm for point-in-ring test."""
    n = len(ring)
    if n < 3:
        return False
    inside = False

    x, y = lon, lat
    p1x, p1y = ring[0]

    for i in range(1, n + 1):
        p2x, p2y = ring[i % n]
        if y > min(p1y, p2y):
            if y <= max(p1y, p2y):
                if x <= max(p1x, p2x):
                    xinters = (y - p1y) * (p2x - p1x) / (p2y - p1y) if p1y != p2y else p1x
                    if p1x == p2x or x <= xinters:
                        inside = not inside
        p1x, p1y = p2x, p2y

    return inside