"""
Vectorized reflection point calculations using mirror-image method.
"""

import numpy as np
from typing import Tuple, Optional
from app.geometry.intersection import line_intersects_polygons_batch


def calculate_reflection_points_batch(
    tx: np.ndarray, rx: np.ndarray,
    wall_starts: np.ndarray, wall_ends: np.ndarray,
) -> Tuple[np.ndarray, np.ndarray]:
    """Calculate reflection points on N walls via mirror-image method.

    Args:
        tx, rx: shape (2,)
        wall_starts, wall_ends: shape (N, 2)

    Returns:
        reflection_points: (N, 2)
        valid: bool (N,)
    """
    wall_vec = wall_ends - wall_starts
    wall_length = np.linalg.norm(wall_vec, axis=1, keepdims=True)
    wall_unit = wall_vec / np.maximum(wall_length, 1e-10)

    normals = np.stack([-wall_unit[:, 1], wall_unit[:, 0]], axis=1)

    tx_to_wall = tx - wall_starts
    tx_dist_to_wall = np.sum(tx_to_wall * normals, axis=1, keepdims=True)
    tx_mirror = tx - 2 * tx_dist_to_wall * normals

    rx_to_mirror = tx_mirror - rx

    cross_denom = (rx_to_mirror[:, 0] * wall_vec[:, 1] -
                   rx_to_mirror[:, 1] * wall_vec[:, 0])

    valid_denom = np.abs(cross_denom) > 1e-10
    cross_denom_safe = np.where(valid_denom, cross_denom, 1.0)

    rx_to_start = wall_starts - rx
    t = (rx_to_start[:, 0] * rx_to_mirror[:, 1] -
         rx_to_start[:, 1] * rx_to_mirror[:, 0]) / cross_denom_safe

    reflection_points = wall_starts + t[:, np.newaxis] * wall_vec

    valid = valid_denom & (t >= 0) & (t <= 1) & (tx_dist_to_wall[:, 0] > 0)

    return reflection_points, valid


def find_best_reflection_path(
    tx: np.ndarray, rx: np.ndarray,
    building_walls_start: np.ndarray,
    building_walls_end: np.ndarray,
    wall_to_building: np.ndarray,
    obstacle_polygons_x: np.ndarray,
    obstacle_polygons_y: np.ndarray,
    obstacle_lengths: np.ndarray,
    max_candidates: int = 50,
    max_walls: int = 100,
    max_los_checks: int = 10,
) -> Tuple[Optional[np.ndarray], float, float]:
    """Find best single-reflection path using vectorized ops.

    Args:
        max_walls: Only consider closest N walls for reflection candidates.
        max_los_checks: Only verify LOS for top N shortest reflection paths.

    Returns:
        best_reflection_point: (2,) or None
        best_path_length: meters
        best_reflection_loss: dB
    """
    num_walls = len(building_walls_start)
    if num_walls == 0:
        return None, np.inf, 0.0

    # Limit walls by distance to path midpoint
    if num_walls > max_walls:
        midpoint = (tx + rx) / 2
        wall_midpoints = (building_walls_start + building_walls_end) / 2
        wall_distances = np.linalg.norm(wall_midpoints - midpoint, axis=1)
        closest = np.argpartition(wall_distances, max_walls)[:max_walls]
        building_walls_start = building_walls_start[closest]
        building_walls_end = building_walls_end[closest]
        wall_to_building = wall_to_building[closest]

    refl_points, valid = calculate_reflection_points_batch(
        tx, rx, building_walls_start, building_walls_end,
    )

    if not np.any(valid):
        return None, np.inf, 0.0

    valid_indices = np.where(valid)[0]
    valid_refl = refl_points[valid]

    tx_to_refl = np.linalg.norm(valid_refl - tx, axis=1)
    refl_to_rx = np.linalg.norm(rx - valid_refl, axis=1)
    path_lengths = tx_to_refl + refl_to_rx

    # Direct distance filter
    direct_dist = np.linalg.norm(rx - tx)
    within_range = path_lengths <= direct_dist * 2.0
    if not np.any(within_range):
        return None, np.inf, 0.0

    valid_indices = valid_indices[within_range]
    valid_refl = valid_refl[within_range]
    path_lengths = path_lengths[within_range]

    # Keep top candidates by shortest path
    if len(valid_indices) > max_candidates:
        top_idx = np.argpartition(path_lengths, max_candidates)[:max_candidates]
        valid_indices = valid_indices[top_idx]
        valid_refl = valid_refl[top_idx]
        path_lengths = path_lengths[top_idx]

    # Sort by path length for early exit
    sort_order = np.argsort(path_lengths)
    valid_refl = valid_refl[sort_order]
    path_lengths = path_lengths[sort_order]

    # Check LOS only for top N shortest candidates
    check_count = min(len(valid_refl), max_los_checks)
    best_idx = -1
    best_length = np.inf

    for i in range(check_count):
        length = path_lengths[i]
        if length >= best_length:
            continue

        refl_pt = valid_refl[i]

        intersects1, _ = line_intersects_polygons_batch(
            tx, refl_pt, obstacle_polygons_x, obstacle_polygons_y, obstacle_lengths,
        )
        if np.any(intersects1):
            continue

        intersects2, _ = line_intersects_polygons_batch(
            refl_pt, rx, obstacle_polygons_x, obstacle_polygons_y, obstacle_lengths,
        )
        if np.any(intersects2):
            continue

        best_idx = i
        best_length = length
        break  # sorted by length, first valid is best

    if best_idx < 0:
        return None, np.inf, 0.0

    best_point = valid_refl[best_idx]

    # Reflection loss: 3-10 dB depending on path ratio
    path_ratio = best_length / max(direct_dist, 1.0)
    reflection_loss = 3.0 + 7.0 * min(1.0, (path_ratio - 1.0) * 2)

    return best_point, best_length, reflection_loss