"""
Route matching: identifies when multiple activities were on the same route.
Uses a bounding-box pre-filter + dynamic time warping (DTW) for GPS track similarity.
"""
import math
from typing import Optional
import polyline as polyline_lib
import numpy as np


def decode_polyline_to_coords(encoded: str) -> list[tuple[float, float]]:
    return polyline_lib.decode(encoded)


def bounding_boxes_overlap(bb1: dict, bb2: dict, tolerance_deg: float = 0.005) -> bool:
    """Quick check: do two bounding boxes overlap (with a tolerance margin)?"""
    return (
        bb1["min_lat"] - tolerance_deg <= bb2["max_lat"] + tolerance_deg and
        bb1["max_lat"] + tolerance_deg >= bb2["min_lat"] - tolerance_deg and
        bb1["min_lon"] - tolerance_deg <= bb2["max_lon"] + tolerance_deg and
        bb1["max_lon"] + tolerance_deg >= bb2["min_lon"] - tolerance_deg
    )


def sample_coords(coords: list[tuple], n: int = 100) -> list[tuple]:
    """Downsample a track to n evenly-spaced points for DTW efficiency."""
    if len(coords) <= n:
        return coords
    indices = [int(i * (len(coords) - 1) / (n - 1)) for i in range(n)]
    return [coords[i] for i in indices]


def dtw_distance(track1: list[tuple], track2: list[tuple]) -> float:
    """
    Compute DTW distance between two GPS tracks.
    Each point is (lat, lon). Returns average distance in metres per matched pair.
    """
    n, m = len(track1), len(track2)
    dtw = np.full((n + 1, m + 1), np.inf)
    dtw[0][0] = 0.0

    for i in range(1, n + 1):
        for j in range(1, m + 1):
            cost = haversine_m(track1[i-1], track2[j-1])
            dtw[i][j] = cost + min(dtw[i-1][j], dtw[i][j-1], dtw[i-1][j-1])

    return dtw[n][m] / max(n, m)


def haversine_m(p1: tuple, p2: tuple) -> float:
    R = 6371000
    lat1, lon1 = math.radians(p1[0]), math.radians(p1[1])
    lat2, lon2 = math.radians(p2[0]), math.radians(p2[1])
    dlat = lat2 - lat1
    dlon = lon2 - lon1
    a = math.sin(dlat/2)**2 + math.cos(lat1)*math.cos(lat2)*math.sin(dlon/2)**2
    return 2 * R * math.asin(math.sqrt(a))


def routes_are_similar(
    poly1: str,
    poly2: str,
    bb1: Optional[dict],
    bb2: Optional[dict],
    dtw_threshold_m: float = 80.0,
    dist1: Optional[float] = None,
    dist2: Optional[float] = None,
) -> bool:
    """
    Returns True if two activities are on sufficiently similar routes.
    First does a cheap bounding box check, then DTW on downsampled tracks.
    When dist1/dist2 are provided:
    - Rejects if distance differs by more than 2.5%
    - Uses 3% of route distance as the DTW threshold (capped at 300m)
    """
    if dist1 and dist2 and dist1 > 0 and dist2 > 0:
        if abs(dist1 - dist2) / max(dist1, dist2) > 0.025:
            return False
        dtw_threshold_m = min(max(dist1, dist2) * 0.03, 300.0)

    if bb1 and bb2:
        if not bounding_boxes_overlap(bb1, bb2):
            return False

    try:
        coords1 = sample_coords(decode_polyline_to_coords(poly1), 60)
        coords2 = sample_coords(decode_polyline_to_coords(poly2), 60)
    except Exception:
        return False

    if not coords1 or not coords2:
        return False

    dist = dtw_distance(coords1, coords2)
    return dist < dtw_threshold_m


def find_segment_times(
    data_points: list[dict],
    start_dist_m: float,
    end_dist_m: float,
) -> Optional[float]:
    """
    Given activity data points (with cumulative distance_m),
    find the time to traverse from start_dist_m to end_dist_m.
    Returns duration in seconds, or None if not found.
    """
    start_time = None
    end_time = None

    for p in data_points:
        dist = p.get("distance_m")
        ts = p.get("timestamp")
        if dist is None or ts is None:
            continue

        if start_time is None and dist >= start_dist_m:
            start_time = ts

        if start_time is not None and dist >= end_dist_m:
            end_time = ts
            break

    if start_time and end_time:
        from datetime import datetime
        t1 = datetime.fromisoformat(start_time) if isinstance(start_time, str) else start_time
        t2 = datetime.fromisoformat(end_time) if isinstance(end_time, str) else end_time
        return (t2 - t1).total_seconds()

    return None


def find_best_split_time(
    data_points: list[dict],
    target_distance_m: float,
) -> Optional[float]:
    """
    Find the best (fastest) time over any target_distance_m window within an activity.
    E.g. fastest 1km split in a 10km run.
    Returns duration in seconds.
    """
    points_with_dist = [
        p for p in data_points
        if p.get("distance_m") is not None and p.get("timestamp") is not None
    ]

    if not points_with_dist:
        return None

    best = None
    j = 0

    for i, start_p in enumerate(points_with_dist):
        start_dist = start_p["distance_m"]
        start_ts = start_p["timestamp"]

        # Advance j until distance covered >= target
        while j < len(points_with_dist):
            end_p = points_with_dist[j]
            covered = end_p["distance_m"] - start_dist
            if covered >= target_distance_m:
                from datetime import datetime
                t1 = datetime.fromisoformat(start_ts) if isinstance(start_ts, str) else start_ts
                t2 = datetime.fromisoformat(end_p["timestamp"]) if isinstance(end_p["timestamp"], str) else end_p["timestamp"]
                duration = (t2 - t1).total_seconds()
                if best is None or duration < best:
                    best = duration
                break
            j += 1

        if j >= len(points_with_dist):
            break

    return best


def _bearing(p1: tuple, p2: tuple) -> float:
    """Compass bearing in degrees (0-360) from p1 to p2."""
    lat1, lon1 = math.radians(p1[0]), math.radians(p1[1])
    lat2, lon2 = math.radians(p2[0]), math.radians(p2[1])
    dlon = lon2 - lon1
    x = math.sin(dlon) * math.cos(lat2)
    y = math.cos(lat1) * math.sin(lat2) - math.sin(lat1) * math.cos(lat2) * math.cos(dlon)
    return math.degrees(math.atan2(x, y)) % 360


def generate_1km_segments(encoded_polyline: str, total_dist_m: float) -> list[tuple[str, float, float]]:
    """Generate 1-km splits along a route. Returns list of (name, start_m, end_m)."""
    if not encoded_polyline:
        return []
    km_count = int(total_dist_m / 1000)
    segments = []
    for i in range(km_count):
        segments.append((f"km {i + 1}", float(i * 1000), float((i + 1) * 1000)))
    remainder = total_dist_m - km_count * 1000
    if remainder >= 200:
        segments.append((f"km {km_count + 1}", float(km_count * 1000), total_dist_m))
    return segments


def generate_turn_segments(
    encoded_polyline: str,
    turn_angle_deg: float = 45.0,
) -> list[tuple[str, float, float]]:
    """Detect sharp turns in a route polyline. Returns list of (name, start_m, end_m)."""
    coords = decode_polyline_to_coords(encoded_polyline)
    if len(coords) < 3:
        return []

    cum_dists = [0.0]
    for i in range(1, len(coords)):
        cum_dists.append(cum_dists[-1] + haversine_m(coords[i - 1], coords[i]))
    total = cum_dists[-1]

    HALF_WINDOW = 100.0  # metres either side of candidate turn point

    turn_centers: list[float] = []
    for i in range(1, len(coords) - 1):
        # Find index ~HALF_WINDOW before and after
        start_i = i
        while start_i > 0 and cum_dists[i] - cum_dists[start_i] < HALF_WINDOW:
            start_i -= 1
        end_i = i
        while end_i < len(coords) - 1 and cum_dists[end_i] - cum_dists[i] < HALF_WINDOW:
            end_i += 1
        if start_i == i or end_i == i:
            continue

        b1 = _bearing(coords[start_i], coords[i])
        b2 = _bearing(coords[i], coords[end_i])
        diff = abs(b2 - b1) % 360
        if diff > 180:
            diff = 360 - diff
        if diff >= turn_angle_deg:
            turn_centers.append(cum_dists[i])

    if not turn_centers:
        return []

    # Cluster turns within 150 m of each other → one segment per cluster
    clusters: list[list[float]] = [[turn_centers[0]]]
    for d in turn_centers[1:]:
        if d - clusters[-1][-1] < 150:
            clusters[-1].append(d)
        else:
            clusters.append([d])

    segments = []
    for cluster in clusters:
        center = sum(cluster) / len(cluster)
        start = max(0.0, center - HALF_WINDOW)
        end = min(total, center + HALF_WINDOW)
        segments.append((f"Turn at {center / 1000:.1f} km", start, end))
    return segments


def generate_hill_segments(
    data_points: list[dict],
    gradient_pct: float = 5.0,
) -> list[tuple[str, float, float]]:
    """
    Detect uphill sections using activity data points (with altitude_m + distance_m).
    Returns list of (name, start_m, end_m).
    """
    pts = [
        (p["distance_m"], p["altitude_m"])
        for p in data_points
        if p.get("distance_m") is not None and p.get("altitude_m") is not None
    ]
    if len(pts) < 10:
        return []
    pts.sort(key=lambda x: x[0])
    dists = [p[0] for p in pts]
    alts = [p[1] for p in pts]

    # Smooth altitude with a sliding window to reduce GPS noise
    SMOOTH = 10
    smooth_alts = []
    for i in range(len(alts)):
        lo, hi = max(0, i - SMOOTH), min(len(alts), i + SMOOTH + 1)
        smooth_alts.append(sum(alts[lo:hi]) / (hi - lo))

    grad_threshold = gradient_pct / 100.0
    MIN_HILL_M = 200.0

    in_hill = False
    hill_start_idx = 0
    segments = []

    for i in range(1, len(dists)):
        d_dist = dists[i] - dists[i - 1]
        if d_dist <= 0:
            continue
        grad = (smooth_alts[i] - smooth_alts[i - 1]) / d_dist

        if grad >= grad_threshold and not in_hill:
            in_hill = True
            hill_start_idx = i - 1
        elif grad < grad_threshold and in_hill:
            length = dists[i - 1] - dists[hill_start_idx]
            if length >= MIN_HILL_M:
                gain = round(smooth_alts[i - 1] - smooth_alts[hill_start_idx])
                start_km = dists[hill_start_idx] / 1000
                segments.append((
                    f"Hill at {start_km:.1f} km (+{gain} m)",
                    dists[hill_start_idx],
                    dists[i - 1],
                ))
            in_hill = False

    if in_hill:
        length = dists[-1] - dists[hill_start_idx]
        if length >= MIN_HILL_M:
            gain = round(smooth_alts[-1] - smooth_alts[hill_start_idx])
            start_km = dists[hill_start_idx] / 1000
            segments.append((
                f"Hill at {start_km:.1f} km (+{gain} m)",
                dists[hill_start_idx],
                dists[-1],
            ))

    return segments


STANDARD_DISTANCES = [
    (400, "400m"),
    (800, "800m"),
    (1000, "1k"),
    (1609.34, "1 mile"),
    (3000, "3k"),
    (5000, "5k"),
    (10000, "10k"),
    (21097.5, "Half marathon"),
    (42195, "Marathon"),
    (50000, "50k"),
    (100000, "100k"),
]


def compute_best_splits(data_points: list[dict], total_distance_m: float) -> dict[str, float]:
    """Compute best split times for all standard distances that fit within the activity."""
    results = {}
    for dist_m, label in STANDARD_DISTANCES:
        if total_distance_m >= dist_m * 0.95:  # allow 5% tolerance
            best = find_best_split_time(data_points, dist_m)
            if best:
                results[label] = best
    return results