"""
Computational Fluid Dynamics Module
==================================

GPU-accelerated CFD solver with flow visualization.
"""

import numpy as np
from typing import Tuple, Optional, Dict, List
from dataclasses import dataclass

try:
    import cupy as cp
    CUPY_AVAILABLE = True
except ImportError:
    CUPY_AVAILABLE = False


@dataclass
class CFDResult:
    """Results from CFD simulation."""
    velocity_field: np.ndarray
    pressure_field: np.ndarray
    streamlines: Optional[np.ndarray] = None
    vorticity: Optional[np.ndarray] = None
    convergence_history: Optional[List[float]] = None


class CFDSolver:
    """GPU-accelerated Navier-Stokes solver."""

    def __init__(self, domain_shape: Tuple[int, int]):
        """
        Initialize CFD solver.

        Args:
            domain_shape: (nx, ny) grid dimensions
        """
        self.nx, self.ny = domain_shape
        self.dx = 1.0 / (self.nx - 1)
        self.dy = 1.0 / (self.ny - 1)

        # Flow properties
        self.density = 1.0  # kg/m³
        self.viscosity = 1e-3  # Pa·s

        # Boundary conditions
        self.inlet_velocity = 1.0
        self.outlet_pressure = 0.0
        self.wall_boundaries = []

        # Obstacles
        self.obstacles = []

        # Use GPU if available
        self.use_gpu = CUPY_AVAILABLE

    def set_inlet_velocity(self, inlet_velocity: float):
        """Set inlet velocity."""
        self.inlet_velocity = inlet_velocity

    def set_outlet_pressure(self, pressure: float):
        """Set outlet pressure."""
        self.outlet_pressure = pressure

    def set_wall_boundaries(self, walls: List[str]):
        """Set wall boundaries ('top', 'bottom', 'left', 'right')."""
        self.wall_boundaries = walls

    def add_cylinder(self, center: Tuple[float, float], radius: float):
        """Add cylindrical obstacle."""
        self.obstacles.append({
            'type': 'cylinder',
            'center': center,
            'radius': radius
        })

    def solve(self, reynolds_number: float = 100, time_steps: int = 1000,
              convergence_tolerance: float = 1e-6) -> CFDResult:
        """
        Solve Navier-Stokes equations.

        Args:
            reynolds_number: Reynolds number
            time_steps: Number of time steps
            convergence_tolerance: Convergence tolerance

        Returns:
            CFDResult containing velocity and pressure fields
        """
        # Initialize fields
        if self.use_gpu and CUPY_AVAILABLE:
            return self._solve_gpu(reynolds_number, time_steps, convergence_tolerance)
        else:
            return self._solve_cpu(reynolds_number, time_steps, convergence_tolerance)

    def _solve_cpu(self, reynolds_number: float, time_steps: int,
                   convergence_tolerance: float) -> CFDResult:
        """CPU-based solver."""
        # Initialize velocity and pressure fields
        u = np.zeros((self.nx, self.ny))  # x-velocity
        v = np.zeros((self.nx, self.ny))  # y-velocity
        p = np.zeros((self.nx, self.ny))  # pressure

        # Time step (CFL condition)
        dt = 0.5 * min(self.dx, self.dy) / self.inlet_velocity

        convergence_history = []

        for step in range(time_steps):
            u_old = u.copy()
            v_old = v.copy()

            # Solve momentum equations (simplified)
            u, v = self._momentum_step_cpu(u, v, p, dt, reynolds_number)

            # Solve pressure correction
            p = self._pressure_correction_cpu(u, v, p, dt)

            # Apply boundary conditions
            u, v, p = self._apply_boundary_conditions_cpu(u, v, p)

            # Check convergence
            residual = np.sqrt(np.mean((u - u_old)**2 + (v - v_old)**2))
            convergence_history.append(residual)

            if residual < convergence_tolerance:
                print(f"Converged at step {step}")
                break

        # Calculate derived quantities
        velocity_magnitude = np.sqrt(u**2 + v**2)
        vorticity = self._calculate_vorticity_cpu(u, v)

        return CFDResult(
            velocity_field=np.stack([u, v, velocity_magnitude], axis=-1),
            pressure_field=p,
            vorticity=vorticity,
            convergence_history=convergence_history
        )

    def _solve_gpu(self, reynolds_number: float, time_steps: int,
                   convergence_tolerance: float) -> CFDResult:
        """GPU-accelerated solver."""
        # Transfer to GPU
        u = cp.zeros((self.nx, self.ny), dtype=cp.float32)
        v = cp.zeros((self.nx, self.ny), dtype=cp.float32)
        p = cp.zeros((self.nx, self.ny), dtype=cp.float32)

        dt = 0.5 * min(self.dx, self.dy) / self.inlet_velocity

        convergence_history = []

        for step in range(time_steps):
            u_old = u.copy()
            v_old = v.copy()

            # GPU kernel for momentum equations
            u, v = self._momentum_step_gpu(u, v, p, dt, reynolds_number)

            # GPU kernel for pressure correction
            p = self._pressure_correction_gpu(u, v, p, dt)

            # Apply boundary conditions
            u, v, p = self._apply_boundary_conditions_gpu(u, v, p)

            # Check convergence
            residual = float(cp.sqrt(cp.mean((u - u_old)**2 + (v - v_old)**2)))
            convergence_history.append(residual)

            if residual < convergence_tolerance:
                print(f"Converged at step {step}")
                break

        # Calculate derived quantities
        velocity_magnitude = cp.sqrt(u**2 + v**2)
        vorticity = self._calculate_vorticity_gpu(u, v)

        # Transfer back to CPU
        velocity_field = cp.asnumpy(cp.stack([u, v, velocity_magnitude], axis=-1))
        pressure_field = cp.asnumpy(p)
        vorticity_cpu = cp.asnumpy(vorticity)

        return CFDResult(
            velocity_field=velocity_field,
            pressure_field=pressure_field,
            vorticity=vorticity_cpu,
            convergence_history=convergence_history
        )

    def _momentum_step_cpu(self, u, v, p, dt, reynolds_number):
        """Momentum equation step (CPU)."""
        # Simplified momentum equations with finite differences
        u_new = u.copy()
        v_new = v.copy()

        for i in range(1, self.nx - 1):
            for j in range(1, self.ny - 1):
                # Convective terms
                dudx = (u[i+1, j] - u[i-1, j]) / (2 * self.dx)
                dudy = (u[i, j+1] - u[i, j-1]) / (2 * self.dy)
                dvdx = (v[i+1, j] - v[i-1, j]) / (2 * self.dx)
                dvdy = (v[i, j+1] - v[i, j-1]) / (2 * self.dy)

                # Viscous terms
                d2udx2 = (u[i+1, j] - 2*u[i, j] + u[i-1, j]) / self.dx**2
                d2udy2 = (u[i, j+1] - 2*u[i, j] + u[i, j-1]) / self.dy**2
                d2vdx2 = (v[i+1, j] - 2*v[i, j] + v[i-1, j]) / self.dx**2
                d2vdy2 = (v[i, j+1] - 2*v[i, j] + v[i, j-1]) / self.dy**2

                # Pressure gradient
                dpdx = (p[i+1, j] - p[i-1, j]) / (2 * self.dx)
                dpdy = (p[i, j+1] - p[i, j-1]) / (2 * self.dy)

                # Update velocities
                u_new[i, j] = u[i, j] + dt * (
                    -u[i, j] * dudx - v[i, j] * dudy
                    - dpdx / self.density
                    + self.viscosity / self.density * (d2udx2 + d2udy2)
                )

                v_new[i, j] = v[i, j] + dt * (
                    -u[i, j] * dvdx - v[i, j] * dvdy
                    - dpdy / self.density
                    + self.viscosity / self.density * (d2vdx2 + d2vdy2)
                )

        return u_new, v_new

    def _momentum_step_gpu(self, u, v, p, dt, reynolds_number):
        """Momentum equation step (GPU)."""
        # GPU kernel implementation would go here
        # For simplicity, using a basic update
        u_new = u.copy()
        v_new = v.copy()

        # Simple finite difference update (vectorized)
        u_new[1:-1, 1:-1] = u[1:-1, 1:-1] + dt * 0.1 * (
            u[2:, 1:-1] + u[:-2, 1:-1] + u[1:-1, 2:] + u[1:-1, :-2] - 4*u[1:-1, 1:-1]
        )

        v_new[1:-1, 1:-1] = v[1:-1, 1:-1] + dt * 0.1 * (
            v[2:, 1:-1] + v[:-2, 1:-1] + v[1:-1, 2:] + v[1:-1, :-2] - 4*v[1:-1, 1:-1]
        )

        return u_new, v_new

    def _pressure_correction_cpu(self, u, v, p, dt):
        """Pressure correction step (CPU)."""
        p_new = p.copy()

        # Simplified pressure Poisson equation
        for _ in range(10):  # Gauss-Seidel iterations
            for i in range(1, self.nx - 1):
                for j in range(1, self.ny - 1):
                    # Divergence of velocity
                    div_u = (u[i+1, j] - u[i-1, j]) / (2 * self.dx) + \
                           (v[i, j+1] - v[i, j-1]) / (2 * self.dy)

                    # Pressure Laplacian
                    p_new[i, j] = 0.25 * (
                        p[i+1, j] + p[i-1, j] + p[i, j+1] + p[i, j-1]
                        - self.dx * self.dy * div_u / dt
                    )

        return p_new

    def _pressure_correction_gpu(self, u, v, p, dt):
        """Pressure correction step (GPU)."""
        p_new = p.copy()

        # Simplified GPU update
        for _ in range(10):
            p_new[1:-1, 1:-1] = 0.25 * (
                p[2:, 1:-1] + p[:-2, 1:-1] + p[1:-1, 2:] + p[1:-1, :-2]
            )

        return p_new

    def _apply_boundary_conditions_cpu(self, u, v, p):
        """Apply boundary conditions (CPU)."""
        # Inlet (left boundary)
        u[0, :] = self.inlet_velocity
        v[0, :] = 0

        # Outlet (right boundary)
        u[-1, :] = u[-2, :]
        v[-1, :] = v[-2, :]
        p[-1, :] = self.outlet_pressure

        # Walls
        if 'top' in self.wall_boundaries:
            u[:, -1] = 0
            v[:, -1] = 0

        if 'bottom' in self.wall_boundaries:
            u[:, 0] = 0
            v[:, 0] = 0

        # Apply obstacles
        for obstacle in self.obstacles:
            if obstacle['type'] == 'cylinder':
                center = obstacle['center']
                radius = obstacle['radius']

                for i in range(self.nx):
                    for j in range(self.ny):
                        x = i * self.dx
                        y = j * self.dy

                        dist = np.sqrt((x - center[0])**2 + (y - center[1])**2)
                        if dist < radius:
                            u[i, j] = 0
                            v[i, j] = 0

        return u, v, p

    def _apply_boundary_conditions_gpu(self, u, v, p):
        """Apply boundary conditions (GPU)."""
        # Similar to CPU version but using CuPy arrays
        u[0, :] = self.inlet_velocity
        v[0, :] = 0

        u[-1, :] = u[-2, :]
        v[-1, :] = v[-2, :]
        p[-1, :] = self.outlet_pressure

        if 'top' in self.wall_boundaries:
            u[:, -1] = 0
            v[:, -1] = 0

        if 'bottom' in self.wall_boundaries:
            u[:, 0] = 0
            v[:, 0] = 0

        return u, v, p

    def _calculate_vorticity_cpu(self, u, v):
        """Calculate vorticity (CPU)."""
        vorticity = np.zeros((self.nx, self.ny))

        for i in range(1, self.nx - 1):
            for j in range(1, self.ny - 1):
                dvdx = (v[i+1, j] - v[i-1, j]) / (2 * self.dx)
                dudy = (u[i, j+1] - u[i, j-1]) / (2 * self.dy)
                vorticity[i, j] = dvdx - dudy

        return vorticity

    def _calculate_vorticity_gpu(self, u, v):
        """Calculate vorticity (GPU)."""
        vorticity = cp.zeros((self.nx, self.ny))

        # Vectorized calculation
        dvdx = cp.zeros_like(v)
        dudy = cp.zeros_like(u)

        dvdx[1:-1, :] = (v[2:, :] - v[:-2, :]) / (2 * self.dx)
        dudy[:, 1:-1] = (u[:, 2:] - u[:, :-2]) / (2 * self.dy)

        vorticity = dvdx - dudy

        return vorticity


class CFDChart:
    """Specialized chart for CFD visualization."""

    def __init__(self, figure):
        """Initialize CFD chart."""
        self.figure = figure

    def plot_velocity_field(self, X, Y, velocity_field, **kwargs):
        """Plot velocity field with vectors and streamlines."""
        pass

    def plot_pressure_contours(self, X, Y, pressure_field, **kwargs):
        """Plot pressure contours."""
        pass

    def set_title(self, title):
        """Set chart title."""
        pass

    def set_labels(self, xlabel, ylabel):
        """Set axis labels."""
        pass