"""궤적 유사도 — DTW(Dynamic Time Warping) 기반."""
import math

_MAX_RESAMPLE_POINTS = 50


def haversine_m(lat1: float, lon1: float, lat2: float, lon2: float) -> float:
    """두 좌표 간 거리 (미터)."""
    R = 6371000
    phi1, phi2 = math.radians(lat1), math.radians(lat2)
    dphi = math.radians(lat2 - lat1)
    dlam = math.radians(lon2 - lon1)
    a = math.sin(dphi / 2) ** 2 + math.cos(phi1) * math.cos(phi2) * math.sin(dlam / 2) ** 2
    return R * 2 * math.atan2(math.sqrt(a), math.sqrt(1 - a))


def _resample(track: list[tuple[float, float]], n: int) -> list[tuple[float, float]]:
    """궤적을 n 포인트로 균등 리샘플링 (선형 보간)."""
    if len(track) == 0:
        return []
    if len(track) == 1:
        return [track[0]] * n
    if len(track) <= n:
        return list(track)

    # 누적 거리 계산
    cumulative = [0.0]
    for i in range(1, len(track)):
        d = haversine_m(track[i - 1][0], track[i - 1][1], track[i][0], track[i][1])
        cumulative.append(cumulative[-1] + d)

    total_dist = cumulative[-1]
    if total_dist == 0.0:
        return [track[0]] * n

    step = total_dist / (n - 1)
    result: list[tuple[float, float]] = []

    seg = 0
    for k in range(n):
        target = step * k
        # 해당 target 거리에 해당하는 선분 찾기
        while seg < len(cumulative) - 2 and cumulative[seg + 1] < target:
            seg += 1
        seg_len = cumulative[seg + 1] - cumulative[seg]
        if seg_len == 0.0:
            result.append(track[seg])
        else:
            t = (target - cumulative[seg]) / seg_len
            lat = track[seg][0] + t * (track[seg + 1][0] - track[seg][0])
            lon = track[seg][1] + t * (track[seg + 1][1] - track[seg][1])
            result.append((lat, lon))

    return result


def _dtw_distance(
    track_a: list[tuple[float, float]],
    track_b: list[tuple[float, float]],
) -> float:
    """두 궤적 간 DTW 거리 (미터 단위 평균 거리)."""
    n, m = len(track_a), len(track_b)
    if n == 0 or m == 0:
        return float('inf')

    INF = float('inf')
    # 1D 롤링 DP (공간 최적화)
    prev = [INF] * (m + 1)
    prev[0] = 0.0
    # 첫 행 초기화
    row = [INF] * (m + 1)
    row[0] = INF

    dp_prev = [INF] * (m + 1)
    dp_curr = [INF] * (m + 1)
    dp_prev[0] = 0.0
    for j in range(1, m + 1):
        dp_prev[j] = INF

    for i in range(1, n + 1):
        dp_curr[0] = INF
        for j in range(1, m + 1):
            cost = haversine_m(track_a[i - 1][0], track_a[i - 1][1],
                               track_b[j - 1][0], track_b[j - 1][1])
            min_prev = min(dp_curr[j - 1], dp_prev[j], dp_prev[j - 1])
            dp_curr[j] = cost + min_prev
        dp_prev, dp_curr = dp_curr, [INF] * (m + 1)

    # dp_prev는 마지막으로 계산된 행
    total = dp_prev[m]
    if total == INF:
        return INF
    return total / (n + m)


def compute_track_similarity(
    track_a: list[tuple[float, float]],
    track_b: list[tuple[float, float]],
    max_dist_m: float = 10000.0,
) -> float:
    """두 궤적의 DTW 거리 기반 유사도 (0~1).

    track이 비어있으면 0.0 반환.
    유사할수록 1.0에 가까움.
    """
    if not track_a or not track_b:
        return 0.0

    a = _resample(track_a, _MAX_RESAMPLE_POINTS)
    b = _resample(track_b, _MAX_RESAMPLE_POINTS)

    avg_dist = _dtw_distance(a, b)
    if avg_dist == float('inf') or max_dist_m <= 0.0:
        return 0.0

    similarity = 1.0 - (avg_dist / max_dist_m)
    return max(0.0, min(1.0, similarity))


def match_gear_by_track(
    gear_tracks: dict[str, list[tuple[float, float]]],
    vessel_tracks: dict[str, list[tuple[float, float]]],
    threshold: float = 0.6,
) -> list[dict]:
    """어구 궤적을 선단 선박 궤적과 비교하여 매칭.

    Args:
        gear_tracks: mmsi → [(lat, lon), ...] — 어구 궤적
        vessel_tracks: mmsi → [(lat, lon), ...] — 선박 궤적
        threshold: 유사도 하한 (이상이면 매칭)

    Returns:
        [{gear_mmsi, vessel_mmsi, similarity, match_method: 'TRACK_SIMILAR'}]
    """
    results: list[dict] = []

    for gear_mmsi, g_track in gear_tracks.items():
        if not g_track:
            continue

        best_mmsi: str | None = None
        best_sim = -1.0

        for vessel_mmsi, v_track in vessel_tracks.items():
            if not v_track:
                continue
            sim = compute_track_similarity(g_track, v_track)
            if sim > best_sim:
                best_sim = sim
                best_mmsi = vessel_mmsi

        if best_mmsi is not None and best_sim >= threshold:
            results.append({
                'gear_mmsi': gear_mmsi,
                'vessel_mmsi': best_mmsi,
                'similarity': best_sim,
                'match_method': 'TRACK_SIMILAR',
            })

    return results