"""Multibeam echosounder (МЛЭ) simulator helpers: seafloor mesh + OBJ export."""

from __future__ import annotations

import json
import math
import random
from datetime import datetime, timezone
from pathlib import Path
from typing import Any


def resolve_mle_dir(output_dir: str | Path = "mle_runs") -> Path:
    out = Path(output_dir)
    if not out.is_absolute():
        project_root = Path(__file__).resolve().parent.parent
        out = project_root / out
    return out


LAST_SETTINGS_FILENAME = "_last_settings.json"


def save_last_settings(
    settings: dict[str, Any],
    *,
    output_dir: str | Path = "mle_runs",
) -> dict[str, Any]:
    """Persist UI preset so it survives app restarts."""
    base = resolve_mle_dir(output_dir)
    base.mkdir(parents=True, exist_ok=True)
    payload = {
        "savedAt": datetime.now(timezone.utc).isoformat(),
        "settings": settings or {},
    }
    path = base / LAST_SETTINGS_FILENAME
    path.write_text(json.dumps(payload, ensure_ascii=False, indent=2), encoding="utf-8")
    return {"ok": True, "path": str(path), "savedAt": payload["savedAt"]}


def load_last_settings(*, output_dir: str | Path = "mle_runs") -> dict[str, Any]:
    """Load last UI preset from mle_runs/_last_settings.json."""
    path = resolve_mle_dir(output_dir) / LAST_SETTINGS_FILENAME
    if not path.is_file():
        return {"settings": None, "savedAt": None, "path": str(path)}
    try:
        data = json.loads(path.read_text(encoding="utf-8"))
    except (OSError, json.JSONDecodeError):
        return {"settings": None, "savedAt": None, "path": str(path)}
    settings = data.get("settings") if isinstance(data, dict) else None
    if not isinstance(settings, dict):
        settings = data if isinstance(data, dict) else None
    saved_at = data.get("savedAt") if isinstance(data, dict) else None
    return {"settings": settings, "savedAt": saved_at, "path": str(path)}


def _height_at(
    x: float,
    y: float,
    *,
    base_z: float,
    amplitude: float,
    frequency: float,
    hills: list[tuple[float, float, float, float]],
    valleys: list[tuple[float, float, float, float]],
    bumps: list[tuple[float, float, float, float]],
) -> float:
    z = base_z + amplitude * math.sin(frequency * x) * math.cos(frequency * 0.7 * y)
    for hx, hy, hamp, hrad in hills:
        d2 = (x - hx) ** 2 + (y - hy) ** 2
        z += hamp * math.exp(-d2 / max(hrad * hrad, 1e-6))
    for vx, vy, vamp, vrad in valleys:
        d2 = (x - vx) ** 2 + (y - vy) ** 2
        z -= vamp * math.exp(-d2 / max(vrad * vrad, 1e-6))
    for bx, by, bamp, brad in bumps:
        d2 = (x - bx) ** 2 + (y - by) ** 2
        z += bamp * math.exp(-d2 / max(brad * brad, 1e-6))
    return z


def build_seafloor_params(
    seed: int = 42,
    *,
    size_x: float = 40.0,
    size_y: float = 60.0,
) -> dict[str, Any]:
    rng = random.Random(int(seed))
    size_x = max(4.0, float(size_x))
    size_y = max(4.0, float(size_y))
    base_z = rng.uniform(-8.0, -3.0)
    amplitude = rng.uniform(0.15, 0.6)
    frequency = rng.uniform(0.15, 0.55)
    hills = [
        (
            rng.uniform(-size_x * 0.4, size_x * 0.4),
            rng.uniform(-size_y * 0.4, size_y * 0.4),
            rng.uniform(0.3, 1.4),
            rng.uniform(2.0, 8.0),
        )
        for _ in range(rng.randint(2, 5))
    ]
    valleys = [
        (
            rng.uniform(-size_x * 0.4, size_x * 0.4),
            rng.uniform(-size_y * 0.4, size_y * 0.4),
            rng.uniform(0.2, 0.9),
            rng.uniform(2.0, 7.0),
        )
        for _ in range(rng.randint(1, 4))
    ]
    bumps = [
        (
            rng.uniform(-size_x * 0.45, size_x * 0.45),
            rng.uniform(-size_y * 0.45, size_y * 0.45),
            rng.uniform(0.05, 0.4),
            rng.uniform(0.4, 2.0),
        )
        for _ in range(rng.randint(8, 20))
    ]
    return {
        "seed": int(seed),
        "sizeX": size_x,
        "sizeY": size_y,
        "baseZ": base_z,
        "amplitude": amplitude,
        "frequency": frequency,
        "hills": hills,
        "valleys": valleys,
        "bumps": bumps,
    }


def sample_seafloor_grid(
    params: dict[str, Any],
    *,
    res_x: int = 80,
    res_y: int = 120,
) -> dict[str, Any]:
    """Build a triangulated seafloor mesh over [-sizeX/2, sizeX/2] × [-sizeY/2, sizeY/2]."""
    res_x = max(4, int(res_x))
    res_y = max(4, int(res_y))
    size_x = float(params["sizeX"])
    size_y = float(params["sizeY"])
    half_x = size_x * 0.5
    half_y = size_y * 0.5

    vertices: list[list[float]] = []
    heights: list[list[float]] = []
    for j in range(res_y):
        row: list[float] = []
        y = -half_y if res_y == 1 else (-half_y + size_y * j / (res_y - 1))
        for i in range(res_x):
            x = -half_x if res_x == 1 else (-half_x + size_x * i / (res_x - 1))
            z = _height_at(
                x,
                y,
                base_z=float(params["baseZ"]),
                amplitude=float(params["amplitude"]),
                frequency=float(params["frequency"]),
                hills=params["hills"],
                valleys=params["valleys"],
                bumps=params["bumps"],
            )
            vertices.append([x, y, z])
            row.append(z)
        heights.append(row)

    faces: list[list[int]] = []
    for j in range(res_y - 1):
        for i in range(res_x - 1):
            a = j * res_x + i
            b = a + 1
            c = a + res_x
            d = c + 1
            faces.append([a + 1, c + 1, b + 1])  # 1-based OBJ indices
            faces.append([b + 1, c + 1, d + 1])

    return {
        "resX": res_x,
        "resY": res_y,
        "vertices": vertices,
        "faces": faces,
        "heights": heights,
        "vertexCount": len(vertices),
        "faceCount": len(faces),
    }


def export_mesh_obj(
    vertices: list[list[float]],
    faces: list[list[int]],
    *,
    object_name: str = "seafloor",
) -> str:
    safe = "".join(ch if ch.isalnum() or ch in "_-" else "_" for ch in (object_name or "seafloor")) or "seafloor"
    lines = [
        f"# DotsToSurface MLE seafloor ({len(vertices)} vertices, {len(faces)} faces)",
        f"o {safe}",
    ]
    for v in vertices:
        lines.append(f"v {v[0]:.8f} {v[1]:.8f} {v[2]:.8f}")
    for f in faces:
        lines.append(f"f {f[0]} {f[1]} {f[2]}")
    return "\n".join(lines) + "\n"


def write_mesh_obj_file(
    path: Path,
    vertices: list[list[float]],
    faces: list[list[int]],
    *,
    object_name: str = "seafloor",
) -> Path:
    path.parent.mkdir(parents=True, exist_ok=True)
    path.write_text(
        export_mesh_obj(vertices, faces, object_name=object_name),
        encoding="utf-8",
    )
    return path


def save_survey_surface(
    *,
    output_dir: str | Path,
    vertices: list[list[float]],
    faces: list[list[int]],
    filename: str = "seafloor.obj",
) -> dict[str, Any]:
    """Overwrite the survey OBJ inside an existing MLE run folder."""
    run_dir = Path(output_dir)
    if not run_dir.is_absolute():
        run_dir = resolve_mle_dir(run_dir)
    if not run_dir.is_dir():
        raise FileNotFoundError(f"MLE run folder not found: {run_dir}")
    if not vertices:
        raise ValueError("vertices must not be empty")
    obj_path = write_mesh_obj_file(
        run_dir / filename,
        vertices,
        faces,
        object_name="seafloor",
    )
    return {
        "outputDir": str(run_dir),
        "seafloorObj": str(obj_path),
        "vertexCount": len(vertices),
        "faceCount": len(faces),
    }


def prepare_mle_scene(
    *,
    seed: int = 42,
    size_x: float = 40.0,
    size_y: float = 60.0,
    res_x: int = 80,
    res_y: int = 120,
    output_dir: str | Path = "mle_runs",
    settings: dict[str, Any] | None = None,
) -> dict[str, Any]:
    """Generate seafloor for simulation; create run folder with empty survey OBJ."""
    base = resolve_mle_dir(output_dir)
    base.mkdir(parents=True, exist_ok=True)
    stamp = datetime.now().strftime("%Y-%m-%d_%H-%M-%S")
    run_dir = base / stamp
    n = 2
    while run_dir.exists():
        run_dir = base / f"{stamp}_{n}"
        n += 1
    run_dir.mkdir(parents=True, exist_ok=False)

    params = build_seafloor_params(seed, size_x=size_x, size_y=size_y)
    mesh = sample_seafloor_grid(params, res_x=res_x, res_y=res_y)
    # Survey OBJ starts empty and is filled from multibeam hits during motion.
    obj_path = run_dir / "seafloor.obj"
    obj_path.write_text(
        "# DotsToSurface MLE survey surface (populated during AUV motion)\no seafloor\n",
        encoding="utf-8",
    )
    # Keep full terrain for reference / debugging (not the survey panel content).
    write_mesh_obj_file(
        run_dir / "terrain_full.obj",
        mesh["vertices"],
        mesh["faces"],
        object_name="terrain_full",
    )

    manifest = {
        "generatedAt": datetime.now(timezone.utc).isoformat(),
        "runName": run_dir.name,
        "outputDir": str(run_dir),
        "seafloorObj": str(obj_path),
        "params": params,
        "mesh": {
            "resX": mesh["resX"],
            "resY": mesh["resY"],
            "vertexCount": mesh["vertexCount"],
            "faceCount": mesh["faceCount"],
        },
        "settings": settings or {},
    }
    (run_dir / "mle_run.json").write_text(
        json.dumps(manifest, ensure_ascii=False, indent=2),
        encoding="utf-8",
    )

    return {
        "runName": run_dir.name,
        "outputDir": str(run_dir),
        "seafloorObj": str(obj_path),
        "params": params,
        "mesh": {
            "resX": mesh["resX"],
            "resY": mesh["resY"],
            "vertices": mesh["vertices"],
            "faces": mesh["faces"],
            "heights": mesh["heights"],
            "vertexCount": mesh["vertexCount"],
            "faceCount": mesh["faceCount"],
        },
    }