"""
Generador paramétrico — Buque mercante / Supply full (inspirado en Serie 60).

Genera cascos para buques de carga, supply vessels y embarcaciones de trabajo
con coeficientes de bloque altos:
  - Fondo casi plano en la zona central
  - Cuadernas rectangulares con pantoque redondeado
  - Proa de bulbo (simplificada) o proa recta
  - Popa transom o popa de crucero

Parámetros típicos:
  Cb: 0.60 – 0.80
  Froude: 0.12 – 0.22

Autor: Álvaro Romero  |  Sprint 2A — AR-ShipDesign
"""
from __future__ import annotations

import numpy as np

from arshipdesign.core.hull import Hull
from arshipdesign.core.offsets import OffsetsTable


def _standard_sheer_z(
    x_sta: np.ndarray, lpp: float, depth: float,
    fwd_rise_frac: float = 0.04, aft_rise_frac: float = 0.020,
) -> np.ndarray:
    """Línea de cubierta parabólica: mínimo en cuaderna maestra, sube hacia proa/popa."""
    xi = x_sta / lpp   # 0=AP, 1=FP, 0.5=midship
    return np.where(
        xi >= 0.5,
        depth * (1.0 + fwd_rise_frac * ((xi - 0.5) / 0.5) ** 2),
        depth * (1.0 + aft_rise_frac  * ((0.5 - xi) / 0.5) ** 2),
    )


def make_merchant_hull(
    name: str = "Buque Mercante / Supply",
    lpp: float = 20.0,
    beam: float = 6.0,
    draft: float = 2.40,
    depth: float = 3.20,
    cb: float = 0.70,
    lcb_frac: float = 0.50,
    cm: float = 0.96,              # sección maestra casi rectangular
    bilge_radius_frac: float = 0.08,
    flat_bottom_frac: float = 0.90,
    n_stations: int = 21,
    n_waterlines: int = 11,
) -> Hull:
    """Genera un casco tipo Serie 60 / buque mercante.

    Parámetros
    ----------
    cb : float
        Coeficiente de bloque objetivo (0.60–0.80).
    cm : float
        Coeficiente de cuaderna maestra (0.93–0.98).
    bilge_radius_frac : float
        Radio del pantoque / calado (0.06–0.14).
    flat_bottom_frac : float
        Ancho del fondo plano / manga (0.85–0.94).
    """
    x_sta   = np.linspace(0.0, lpp, n_stations)
    sheer_z = _standard_sheer_z(x_sta, lpp, depth, fwd_rise_frac=0.04, aft_rise_frac=0.020)
    z_wl    = np.linspace(0.0, float(sheer_z.max()), n_waterlines)
    xi      = (x_sta / lpp - 0.5) * 2.0

    lcb_shift = 2.0 * (lcb_frac - 0.5)
    f_plan = _merchant_plan_form(xi, cb, lcb_shift)

    r_bilge  = draft * bilge_radius_frac
    y_flat_b = (beam / 2.0) * flat_bottom_frac

    data = np.zeros((n_stations, n_waterlines))

    for i in range(n_stations):
        y_wl = (beam / 2.0) * f_plan[i]
        scale = f_plan[i]

        y_flat_i  = y_flat_b  * scale
        r_bilge_i = r_bilge   * max(scale, 0.25)

        for j, z in enumerate(z_wl):
            if z <= r_bilge_i:
                dz = r_bilge_i - z
                inner = max(0.0, r_bilge_i**2 - dz**2)
                y = y_flat_i - r_bilge_i + np.sqrt(inner)
            else:
                # Costados casi verticales (Cm alto)
                t = (z - r_bilge_i) / max(draft - r_bilge_i, 1e-6)
                # Cm ajusta plenitud de la zona de costados
                flare_side = (1.0 - cm) * 0.15
                y = y_flat_i + (y_wl - y_flat_i) * (t + flare_side * t * (1 - t))
                y = min(y, y_wl)

            data[i, j] = max(0.0, y)

    offsets = OffsetsTable(
        x_stations=x_sta,
        z_waterlines=z_wl,
        data=data,
        station_labels=[f"S{i}" for i in range(n_stations)],
        lpp=lpp, beam=beam, draft=draft,
    )
    return Hull(
        name=name, lpp=lpp, beam=beam, depth=depth, draft=draft,
        offsets=offsets, sheer_z=sheer_z,
    )


def _merchant_plan_form(
    xi: np.ndarray, cb: float, lcb_shift: float
) -> np.ndarray:
    """Plan form mercante: central muy llena, extremos redondeados."""
    n = _merchant_plan_exponent(cb)
    xi_s = np.clip(xi - lcb_shift, -1.0, 1.0)
    return np.maximum(0.0, 1.0 - np.abs(xi_s) ** n)


def _merchant_plan_exponent(cb: float) -> float:
    cb_vals = [0.58, 0.65, 0.70, 0.75, 0.82]
    n_vals  = [3.0,  4.0,  5.0,  6.0,  8.0]
    return float(np.interp(cb, cb_vals, n_vals))