"""Run inside Unreal (Python console / Execute Python Script).

Reads terrain_config.json (next to this script) and:
  1. builds a heightfield mesh with GeometryScript (fractal value noise),
     bakes it to a StaticMesh, and drops it into the level;
  2. scatters tree/rock StaticMeshActors across it per "scatter_layers",
     using the same noise field so foliage height always matches the
     ground beneath it (no raycasting needed).

Run import_environment_assets.py first so the mesh paths referenced in
terrain_config.json actually exist.

Set the TERRAIN_CONFIG env var to point at a different config file, e.g. to
run terrain_config_variants_demo.json without touching the default config.

See generate_terrain_from_heightmap.py for the same pipeline driven by a real
heightmap image instead of procedural noise - both share terrain_common.py.
"""
import os, json, math, random, unreal
import terrain_common as tc

CONFIG_PATH = os.environ.get(
    "TERRAIN_CONFIG",
    os.path.join(os.path.dirname(os.path.abspath(__file__)), "terrain_config_variants_demo.json"),
)


# ---------------------------------------------------------------------------
# Fractal value noise (pure Python, no engine dependency) -------------------
# ---------------------------------------------------------------------------
class ValueNoise2D:
    """Seeded, smooth, tileable-enough value noise for terrain-style height fields."""

    def __init__(self, seed):
        rng = random.Random(seed)
        table = list(range(256))
        rng.shuffle(table)
        self._perm = table + table  # avoid overflow when indexing i+1

    @staticmethod
    def _fade(t):
        return t * t * t * (t * (t * 6 - 15) + 10)

    @staticmethod
    def _lerp(a, b, t):
        return a + t * (b - a)

    def _gradient(self, ix, iy):
        h = self._perm[(self._perm[ix & 255] + iy) & 255]
        angle = (h / 255.0) * 2.0 * math.pi
        return math.cos(angle), math.sin(angle)

    def sample(self, x, y):
        x0, y0 = math.floor(x), math.floor(y)
        x1, y1 = x0 + 1, y0 + 1
        sx, sy = x - x0, y - y0

        def dot_grid(ix, iy, px, py):
            gx, gy = self._gradient(ix, iy)
            return gx * (px - ix) + gy * (py - iy)

        n00 = dot_grid(x0, y0, x, y)
        n10 = dot_grid(x1, y0, x, y)
        n01 = dot_grid(x0, y1, x, y)
        n11 = dot_grid(x1, y1, x, y)

        u, v = self._fade(sx), self._fade(sy)
        return self._lerp(self._lerp(n00, n10, u), self._lerp(n01, n11, u), v)


class FractalHeightField:
    def __init__(self, noise_cfg, height_scale):
        self.height_scale = height_scale
        self.frequency = noise_cfg["frequency"]
        self.octaves = noise_cfg["octaves"]
        self.lacunarity = noise_cfg["lacunarity"]
        self.gain = noise_cfg["gain"]
        self.noise = ValueNoise2D(noise_cfg["seed"])

    def height(self, x, y):
        amplitude, frequency, total, max_amp = 1.0, self.frequency, 0.0, 0.0
        for _ in range(self.octaves):
            total += amplitude * self.noise.sample(x * frequency, y * frequency)
            max_amp += amplitude
            amplitude *= self.gain
            frequency *= self.lacunarity
        return (total / max_amp) * self.height_scale

    def normal(self, x, y, step=200.0):
        return tc.finite_difference_normal(self.height, x, y, step)


# ---------------------------------------------------------------------------
def generate_tile(config, terrain_cfg, tile_label):
    """Builds one terrain + its scatter layers + its explicit placements, all
    under a dedicated Outliner folder so multiple tiles can coexist in one level.
    """
    field = FractalHeightField(terrain_cfg["noise"], terrain_cfg["height_scale"])
    base_folder = f"ProceduralTerrain/{tile_label}"

    print(f"[{tile_label}] building terrain mesh (seed={terrain_cfg['noise']['seed']})...")
    static_mesh, bounds = tc.build_terrain_mesh(terrain_cfg, field)

    loc = terrain_cfg["location"]
    origin = unreal.Vector(loc[0], loc[1], loc[2])
    tc.spawn_terrain_actor(static_mesh, origin, base_folder, f"Terrain_{tile_label}")

    for layer_cfg in config.get("scatter_layers", []):
        tc.scatter_layer(layer_cfg, field, bounds, origin, base_folder)

    explicit_entries = config.get("explicit_placements", [])
    if explicit_entries:
        tc.place_explicit(explicit_entries, field, origin, base_folder)


def main():
    with open(CONFIG_PATH, "r") as f:
        config = json.load(f)

    base_terrain_cfg = config["terrain"]
    variants = config.get("variants")

    if not variants:
        # Single-tile mode: unchanged behavior for existing configs.
        generate_tile(config, base_terrain_cfg, "Main")
        print("Done.")
        return

    # Variant mode: one JSON list of seeds becomes N independent, deterministic
    # tiles laid out side by side in a single run - each a full reproducible
    # world driven by nothing but that seed. There's no "batch-produce N baked,
    # comparable layouts from one data file" workflow in the Foliage tool or a
    # PCG graph; you'd re-author or re-seed each one by hand, one at a time.
    gap = base_terrain_cfg["size_x"] * 1.2
    base_seed = base_terrain_cfg["noise"]["seed"]
    base_layer_seeds = {layer["name"]: layer.get("seed", 0) for layer in config.get("scatter_layers", [])}

    for i, seed_offset in enumerate(variants):
        tile_label = f"Variant_{seed_offset}"
        terrain_cfg = json.loads(json.dumps(base_terrain_cfg))  # cheap deep copy
        terrain_cfg["noise"]["seed"] = base_seed + seed_offset
        terrain_cfg["asset_name"] = f"{base_terrain_cfg['asset_name']}_{tile_label}"
        terrain_cfg["location"] = [
            base_terrain_cfg["location"][0] + i * gap,
            base_terrain_cfg["location"][1],
            base_terrain_cfg["location"][2],
        ]

        tile_config = json.loads(json.dumps(config))
        tile_config["terrain"] = terrain_cfg
        for layer_cfg in tile_config.get("scatter_layers", []):
            layer_cfg["seed"] = base_layer_seeds.get(layer_cfg["name"], 0) + seed_offset

        generate_tile(tile_config, terrain_cfg, tile_label)

    print(f"Done: {len(variants)} variant(s) generated side by side.")


main()