"""
Vectorized line-segment and line-polygon intersection checks.

All operations use NumPy for batch processing.
"""

import numpy as np
from typing import Tuple


def line_segments_intersect_batch(
    p1: np.ndarray, p2: np.ndarray,
    segments_start: np.ndarray, segments_end: np.ndarray,
) -> Tuple[np.ndarray, np.ndarray]:
    """Check if line p1->p2 intersects with N segments.

    Args:
        p1, p2: shape (2,)
        segments_start, segments_end: shape (N, 2)

    Returns:
        intersects: bool array (N,)
        t_values: parameter along p1->p2 (N,)
    """
    d = p2 - p1
    seg_d = segments_end - segments_start

    cross = d[0] * seg_d[:, 1] - d[1] * seg_d[:, 0]
    parallel_mask = np.abs(cross) < 1e-10
    cross_safe = np.where(parallel_mask, 1.0, cross)

    dp = p1 - segments_start
    t = (dp[:, 0] * seg_d[:, 1] - dp[:, 1] * seg_d[:, 0]) / cross_safe
    u = (dp[:, 0] * d[1] - dp[:, 1] * d[0]) / cross_safe

    intersects = ~parallel_mask & (t >= 0) & (t <= 1) & (u >= 0) & (u <= 1)
    return intersects, t


def line_intersects_polygons_batch(
    p1: np.ndarray, p2: np.ndarray,
    polygons_x: np.ndarray, polygons_y: np.ndarray,
    polygon_lengths: np.ndarray,
    max_polygons: int = 30,
) -> Tuple[np.ndarray, np.ndarray]:
    """Check if line p1->p2 intersects multiple polygons.

    Uses bounding-box pre-filter to limit work when polygon count is large.

    Args:
        p1, p2: shape (2,)
        polygons_x, polygons_y: flattened vertex arrays
        polygon_lengths: vertices per polygon (num_polygons,)
        max_polygons: only check nearest N polygons

    Returns:
        intersects: bool (num_polygons,)
        min_distances: distance to first hit (num_polygons,)
    """
    num_polygons = len(polygon_lengths)

    if num_polygons == 0:
        return np.array([], dtype=bool), np.array([])

    intersects = np.zeros(num_polygons, dtype=bool)
    min_t = np.full(num_polygons, np.inf)

    # Pre-filter: bounding box check
    if num_polygons > max_polygons:
        buf = 50.0
        line_min_x = min(p1[0], p2[0]) - buf
        line_max_x = max(p1[0], p2[0]) + buf
        line_min_y = min(p1[1], p2[1]) - buf
        line_max_y = max(p1[1], p2[1]) + buf

        nearby_mask = np.zeros(num_polygons, dtype=bool)
        vi = 0
        for i, length in enumerate(polygon_lengths):
            if length >= 3:
                cx = polygons_x[vi]
                cy = polygons_y[vi]
                if line_min_x <= cx <= line_max_x and line_min_y <= cy <= line_max_y:
                    nearby_mask[i] = True
            vi += length

        nearby_indices = np.where(nearby_mask)[0]
        if len(nearby_indices) > max_polygons:
            nearby_mask = np.zeros(num_polygons, dtype=bool)
            nearby_mask[nearby_indices[:max_polygons]] = True
    else:
        nearby_mask = np.ones(num_polygons, dtype=bool)

    idx = 0
    for i, length in enumerate(polygon_lengths):
        if length < 3 or not nearby_mask[i]:
            idx += length
            continue

        px = polygons_x[idx:idx + length]
        py = polygons_y[idx:idx + length]

        starts = np.stack([px, py], axis=1)
        ends = np.stack([np.roll(px, -1), np.roll(py, -1)], axis=1)

        edge_intersects, t_vals = line_segments_intersect_batch(p1, p2, starts, ends)

        if np.any(edge_intersects):
            intersects[i] = True
            min_t[i] = np.min(t_vals[edge_intersects])

        idx += length

    line_length = np.linalg.norm(p2 - p1)
    min_distances = min_t * line_length

    return intersects, min_distances