"""analyze_geo_extent — geographic extent of a cloud of coordinates (EDA `geospatial`).

Pure function: no I/O, no network, deterministic. Given two parallel lists of
latitudes and longitudes it derives the bounding box, centroid, diagonal span
(haversine), per-region counts and hemisphere split of the points, and assigns
each point to a country/region via an OFFLINE lookup against a table of
rectangular bounding boxes embedded as a constant (`_REGION_BBOXES`).

It never reads files, never hits the network and depends only on `math`. The
country boxes are deliberately coarse rectangles (a KISS approximation, NOT a
reverse-geocoder). Reading is defensive throughout and the function NEVER
raises: invalid pairs (None / NaN / out of range) are silently discarded and an
empty cloud yields a zeroed result the caller can skip.
"""

import math

# Earth mean radius in km used by the haversine formula.
_EARTH_RADIUS_KM = 6371.0

# How many distinct regions to surface in `by_region` before collapsing the
# remainder into a single "Otros" bucket.
_TOP_REGIONS = 8

# Offline region lookup: (name, lat_min, lat_max, lon_min, lon_max).
#
# Specific countries are listed FIRST and continental fallbacks LAST: each point
# is assigned to the FIRST box that contains it, so the more specific country box
# wins over the broad continent box. Boxes are coarse rectangles approximating
# the mainland extent of each region; overlapping neighbours are ordered so the
# narrower/more-western country claims its coastal points (e.g. Portugal before
# Spain, Chile before Argentina, the contiguous US before Canada).
_REGION_BBOXES = (
    # --- countries (specific) ---
    ("Portugal", 36.9, 42.2, -9.6, -6.2),
    ("España", 36.0, 43.8, -9.4, 3.4),
    ("Francia", 41.3, 51.1, -5.2, 9.6),
    ("Reino Unido", 49.9, 58.7, -8.6, 1.8),
    ("Irlanda", 51.4, 55.4, -10.6, -5.9),
    ("Países Bajos", 50.7, 53.6, 3.3, 7.2),
    ("Bélgica", 49.5, 51.5, 2.5, 6.4),
    ("Suiza", 45.8, 47.8, 5.9, 10.5),
    ("Alemania", 47.3, 55.1, 5.9, 15.0),
    ("Italia", 36.6, 47.1, 6.6, 18.5),
    ("Marruecos", 27.7, 35.9, -13.2, -1.0),
    ("Egipto", 22.0, 31.7, 25.0, 35.0),
    ("Sudáfrica", -34.8, -22.1, 16.5, 32.9),
    ("China", 18.0, 53.6, 73.5, 135.1),
    ("Japón", 24.0, 45.6, 122.9, 145.9),
    ("India", 6.7, 35.5, 68.1, 97.4),
    ("Australia", -43.7, -10.0, 112.9, 153.7),
    ("México", 14.5, 32.7, -118.4, -86.7),
    ("Estados Unidos", 24.4, 49.4, -125.0, -66.9),
    ("Canadá", 41.7, 83.1, -141.0, -52.6),
    ("Chile", -55.9, -17.5, -75.6, -66.4),
    ("Argentina", -55.1, -21.8, -73.6, -53.6),
    ("Brasil", -33.8, 5.3, -74.0, -34.8),
    ("Rusia", 41.2, 77.0, 19.6, 180.0),
    # --- continental fallbacks (broad) ---
    ("Europa", 34.0, 72.0, -25.0, 45.0),
    ("África", -35.0, 37.5, -18.0, 52.0),
    ("Asia", 5.0, 78.0, 26.0, 180.0),
    ("América del Norte", 7.0, 84.0, -168.0, -52.0),
    ("América del Sur", -56.0, 13.0, -82.0, -34.0),
    ("Oceanía", -50.0, 0.0, 110.0, 180.0),
)


def _coord(value, limit):
    """Coerce a coordinate to a valid float in [-limit, limit] or None.

    bool is a subclass of int but never a real coordinate, so True/False are
    treated as missing. NaN and out-of-range values are rejected.
    """
    if value is None or isinstance(value, bool):
        return None
    try:
        f = float(value)
    except (TypeError, ValueError):
        return None
    # NaN is the only value that is not equal to itself.
    if f != f or f < -limit or f > limit:
        return None
    return f


def _haversine_km(lat1, lon1, lat2, lon2):
    """Great-circle distance in km between two (lat, lon) points in degrees."""
    rlat1, rlat2 = math.radians(lat1), math.radians(lat2)
    dlat = math.radians(lat2 - lat1)
    dlon = math.radians(lon2 - lon1)
    a = math.sin(dlat / 2.0) ** 2 + math.cos(rlat1) * math.cos(rlat2) * math.sin(dlon / 2.0) ** 2
    return 2.0 * _EARTH_RADIUS_KM * math.asin(min(1.0, math.sqrt(a)))


def _region_of(lat, lon):
    """Return the name of the first embedded box containing (lat, lon)."""
    for name, lat_min, lat_max, lon_min, lon_max in _REGION_BBOXES:
        if lat_min <= lat <= lat_max and lon_min <= lon <= lon_max:
            return name
    return "Océano/Otros"


def _empty_result():
    """Result shape when there are no valid coordinate pairs."""
    return {
        "n_points": 0,
        "bbox": None,
        "centroid": None,
        "span_km": 0.0,
        "by_region": [],
        "hemisphere": {"north": 0, "south": 0, "east": 0, "west": 0},
        "note": "sin coordenadas validas",
    }


def analyze_geo_extent(lats: list, lons: list) -> dict:
    """Summarise the geographic extent of a cloud of lat/lon coordinates.

    Pairs `lats[i]` with `lons[i]` by index (over the common length when the two
    lists differ in size), discards any pair where either value is None / NaN or
    outside [-90, 90] (lat) / [-180, 180] (lon), and derives the bounding box,
    centroid, diagonal span, per-region counts and hemisphere split. Each valid
    point is matched to a country/region by an offline lookup against coarse
    rectangular bounding boxes (`_REGION_BBOXES`).

    Args:
        lats: List of latitudes in degrees ([-90, 90]); read defensively.
        lons: List of longitudes in degrees ([-180, 180]); read defensively.
            Paired with `lats` by index; the shorter length wins when they differ.

    Returns:
        Dict with the geographic summary:
        {n_points, bbox={lat_min,lat_max,lon_min,lon_max}, centroid={lat,lon},
         span_km (haversine of the SW->NE bbox diagonal), by_region=[{region,count}]
         (descending, top-8 with the rest folded into "Otros"),
         hemisphere={north,south,east,west}, note (Spanish summary phrase)}.
        With no valid pairs returns the zeroed shape: n_points 0, bbox None,
        centroid None, span_km 0.0, empty by_region, zeroed hemisphere and the
        note "sin coordenadas validas". Never raises.
    """
    if not isinstance(lats, (list, tuple)) or not isinstance(lons, (list, tuple)):
        return _empty_result()

    valid = []
    # zip already stops at the shorter list -> unbalanced lengths are handled.
    for raw_lat, raw_lon in zip(lats, lons):
        lat = _coord(raw_lat, 90.0)
        lon = _coord(raw_lon, 180.0)
        if lat is None or lon is None:
            continue
        valid.append((lat, lon))

    if not valid:
        return _empty_result()

    n = len(valid)
    lat_vals = [p[0] for p in valid]
    lon_vals = [p[1] for p in valid]

    lat_min, lat_max = min(lat_vals), max(lat_vals)
    lon_min, lon_max = min(lon_vals), max(lon_vals)

    centroid_lat = sum(lat_vals) / n
    centroid_lon = sum(lon_vals) / n

    # Diagonal span: SW corner (lat_min, lon_min) to NE corner (lat_max, lon_max).
    span_km = _haversine_km(lat_min, lon_min, lat_max, lon_max)

    # Hemisphere split: the equator/prime-meridian go to north/east respectively.
    north = sum(1 for lat in lat_vals if lat >= 0.0)
    south = n - north
    east = sum(1 for lon in lon_vals if lon >= 0.0)
    west = n - east

    # Count points per region (offline bbox lookup).
    counts = {}
    for lat, lon in valid:
        region = _region_of(lat, lon)
        counts[region] = counts.get(region, 0) + 1

    # Descending by count, then by name for a deterministic tie-break.
    ranked = sorted(counts.items(), key=lambda kv: (-kv[1], kv[0]))
    by_region = [{"region": name, "count": count} for name, count in ranked[:_TOP_REGIONS]]
    rest = sum(count for _, count in ranked[_TOP_REGIONS:])
    if rest > 0:
        by_region.append({"region": "Otros", "count": rest})

    top_region, top_count = ranked[0]
    note = (
        "los puntos se concentran en {region} ({count} de {n})".format(
            region=top_region, count=top_count, n=n
        )
    )

    return {
        "n_points": n,
        "bbox": {
            "lat_min": lat_min,
            "lat_max": lat_max,
            "lon_min": lon_min,
            "lon_max": lon_max,
        },
        "centroid": {"lat": centroid_lat, "lon": centroid_lon},
        "span_km": span_km,
        "by_region": by_region,
        "hemisphere": {"north": north, "south": south, "east": east, "west": west},
        "note": note,
    }