"""GPS track simplification using the Ramer-Douglas-Peucker algorithm."""

from typing import Optional

from rdp import rdp

from bincio.extract.models import DataPoint


def simplify_track(
    points: list[DataPoint],
    epsilon: float = 0.0001,
) -> list[DataPoint]:
    """Return a simplified subset of points using RDP.

    epsilon is in degrees (~11m at equator for 0.0001).
    Points without GPS coordinates are dropped.
    """
    gps_pts = [(p, p.lat, p.lon) for p in points if p.lat is not None and p.lon is not None]
    if len(gps_pts) < 2:
        return [p for p, _, _ in gps_pts]

    coords = [[lon, lat] for _, lat, lon in gps_pts]
    mask = rdp(coords, epsilon=epsilon, return_mask=True)
    return [p for (p, _, _), keep in zip(gps_pts, mask) if keep]


def preview_coords(
    points: list[DataPoint],
    max_points: int = 20,
) -> list[list[float]] | None:
    """Return a small list of [lat, lon] pairs for card thumbnail rendering.

    Uses a coarser RDP pass, then subsamples to at most max_points.
    Returns None if there is no GPS data.
    """
    gps = [(p.lat, p.lon) for p in points if p.lat is not None and p.lon is not None]
    if len(gps) < 2:
        return None

    # Coarse RDP (larger epsilon = fewer points)
    coords = [[lon, lat] for lat, lon in gps]
    mask = rdp(coords, epsilon=0.001, return_mask=True)
    reduced = [gps[i] for i, keep in enumerate(mask) if keep]

    # Subsample if still too many
    if len(reduced) > max_points:
        step = len(reduced) / max_points
        reduced = [reduced[int(i * step)] for i in range(max_points)]
        reduced.append(gps[-1])  # always include the last point

    return [[round(lat, 5), round(lon, 5)] for lat, lon in reduced]


def build_geojson(
    points: list[DataPoint],
    activity_id: str,
    epsilon: float = 0.0001,
    original_count: Optional[int] = None,
) -> dict:
    """Build a GeoJSON Feature for the simplified track."""
    simplified = simplify_track(points, epsilon=epsilon)

    coordinates = [
        [p.lon, p.lat, p.elevation_m] if p.elevation_m is not None else [p.lon, p.lat]
        for p in simplified
        if p.lon is not None and p.lat is not None
    ]

    # Parallel speed array for gradient coloring
    speeds = [round(p.speed_kmh, 2) if p.speed_kmh is not None else None for p in simplified]

    return {
        "type": "Feature",
        "geometry": {
            "type": "LineString",
            "coordinates": coordinates,
        },
        "properties": {
            "id": activity_id,
            "speeds": speeds,
            "simplification": "rdp",
            "rdp_epsilon": epsilon,
            "point_count_original": original_count or len(points),
            "point_count_simplified": len(coordinates),
        },
    }