"""
Mercury (GJ0b) terrain builder.

Data source:
  - Elevation: MESSENGER DEM from USGS Astrogeology
    665m/px global DEM, GeoTIFF.

Mercury properties:
  - Min elevation: ~-5380 m
  - Max elevation: ~4480 m
  - No atmosphere, no water
  - Extreme temperature range: ~100K (night) to ~700K (day)
  - body_type: "planet", planet_class: "barren", atmosphere: "none"
"""

import numpy as np
from pathlib import Path

from sol_data.download import ensure_cached
from sol_data.shared import (
    GRID_W, GRID_H,
    load_tiff_as_array, load_raw_binary,
    resample_to_grid, normalize_01,
    compute_hillshade, assemble_terrain,
    temperature_grid_analytical,
)

# MESSENGER DEM — try PDS binary first (compact), fall back to USGS GeoTIFF
MESSENGER_PDS_URL = "https://pds-geosciences.wustl.edu/messenger/mess-h-mdis_mla-6-dem-elevation-v1/messdmdem_1001/data/global_dem_16ppd.img"
MESSENGER_PDS_FILE = "messenger_dem_16ppd.img"
MESSENGER_PDS_W = 5760
MESSENGER_PDS_H = 2880

# USGS GeoTIFF fallback (~506 MB, but PIL-loadable)
MESSENGER_TIFF_URL = "https://planetarymaps.usgs.gov/mosaic/Mercury_Messenger_USGS_DEM_Global_665m_v2.tif"
MESSENGER_TIFF_FILE = "Mercury_Messenger_USGS_DEM_Global_665m_v2.tif"

MERCURY_MIN_ELEV_M = -5380.0
MERCURY_MAX_ELEV_M = 4480.0
MERCURY_EQUATORIAL_TEMP_K = 440.0  # mean dayside
MERCURY_POLAR_TEMP_K = 200.0


def _load_messenger() -> np.ndarray:
    """Load MESSENGER DEM, return elevation in metres."""
    # Try PDS binary first (compact ~33 MB)
    try:
        path = ensure_cached(MESSENGER_PDS_URL, MESSENGER_PDS_FILE)
        print(f"    loading MESSENGER PDS: {path}")
        arr = load_raw_binary(str(path), MESSENGER_PDS_W, MESSENGER_PDS_H,
                              dtype=">i2", offset=0)
        arr[arr > 20000] = 0.0
        arr[arr < -20000] = 0.0
        print(f"    MESSENGER range: [{arr.min():.0f}, {arr.max():.0f}] m")
        return arr
    except Exception as e:
        print(f"    PDS load failed ({e}), trying USGS GeoTIFF...")

    # Fallback: USGS GeoTIFF (~506 MB)
    try:
        path = ensure_cached(MESSENGER_TIFF_URL, MESSENGER_TIFF_FILE)
        print(f"    loading MESSENGER GeoTIFF: {path}")
        arr = load_tiff_as_array(str(path))
        arr[arr < -20000] = 0.0
        print(f"    MESSENGER shape: {arr.shape}, range: [{arr.min():.0f}, {arr.max():.0f}] m")
        return arr
    except Exception as e2:
        print(f"    GeoTIFF also failed ({e2}), using procedural")
        return None


def build_terrain(body_def: dict) -> dict:
    """Build Mercury terrain dict from MESSENGER data."""
    import sys
    sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
    from planet_simulation import compute_biome

    print("  Mercury: loading MESSENGER data...")

    # ── 1. Elevation ────────────────────────────────────────────────────
    raw = _load_messenger()
    if raw is None:
        import sys
        sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
        from planet_simulation import simulate
        return simulate(body_def)

    from sol_data.shared import greenwich_to_dateline
    shifted = greenwich_to_dateline(raw)
    elevation_m = resample_to_grid(shifted, GRID_H, GRID_W, order=1)
    elevation = normalize_01(elevation_m, MERCURY_MIN_ELEV_M, MERCURY_MAX_ELEV_M)

    sea_level = 0.0
    surface_water = np.zeros((GRID_H, GRID_W), dtype=bool)

    # ── 2. Temperature ──────────────────────────────────────────────────
    temperature_K = temperature_grid_analytical(
        base_T_K=MERCURY_EQUATORIAL_TEMP_K,
        elevation=elevation,
        lapse_rate_K_per_unit=20.0,
        lat_gradient_K=240.0,
    )
    temperature_K = np.maximum(temperature_K, 100.0)

    # ── 3. Moisture ─────────────────────────────────────────────────────
    moisture = np.zeros((GRID_H, GRID_W), dtype=np.float32)

    # ── 4. Biome ────────────────────────────────────────────────────────
    biome = compute_biome(body_def, elevation, sea_level, surface_water,
                          temperature_K, moisture)

    # ── 5. Hillshade ────────────────────────────────────────────────────
    hillshade = compute_hillshade(elevation)

    return assemble_terrain(
        elevation=elevation, temperature_K=temperature_K,
        moisture=moisture, biome=biome,
        surface_water=surface_water, hillshade=hillshade,
        rivers=[], sea_level=sea_level,
    )