// TDD: GREEN phase - Implement core traits to pass tests

use crate::error::CfdResult;
use nalgebra::{Scalar, Vector3};
use std::fmt::Debug;

/// Trait for fluid field data structures that hold velocity, pressure, and other flow variables
pub trait FluidField: Send + Sync + Debug {
    /// Scalar type for field values (typically f32 or f64)
    type Scalar: Scalar + Copy + Send + Sync + Debug;

    /// Vector type for velocity fields
    type Vector: Copy + Send + Sync + Debug;

    /// Get velocity at a specific node/cell index
    fn get_velocity(&self, index: usize) -> CfdResult<Self::Vector>;

    /// Set velocity at a specific node/cell index
    fn set_velocity(&mut self, index: usize, velocity: Self::Vector) -> CfdResult<()>;

    /// Get pressure at a specific node/cell index
    fn get_pressure(&self, index: usize) -> CfdResult<Self::Scalar>;

    /// Set pressure at a specific node/cell index
    fn set_pressure(&mut self, index: usize, pressure: Self::Scalar) -> CfdResult<()>;

    /// Get total number of nodes/cells in the field
    fn node_count(&self) -> usize;

    /// Get temperature at a specific index (optional for thermal problems)
    fn get_temperature(&self, _index: usize) -> CfdResult<Self::Scalar> {
        // Default implementation for non-thermal problems - return zero (not implemented)
        Err(crate::error::CfdError::InvalidParameter(
            "Temperature not implemented for this field".to_string(),
        ))
    }

    /// Set temperature at a specific index (optional for thermal problems)
    fn set_temperature(&mut self, _index: usize, _temperature: Self::Scalar) -> CfdResult<()> {
        // Default implementation - do nothing for non-thermal problems
        Ok(())
    }

    /// Get density at a specific index (for compressible flows)
    fn get_density(&self, _index: usize) -> CfdResult<Self::Scalar> {
        // Default implementation for incompressible flows - return error (not implemented)
        Err(crate::error::CfdError::InvalidParameter(
            "Density not implemented for this field".to_string(),
        ))
    }

    /// Set density at a specific index (for compressible flows)
    fn set_density(&mut self, _index: usize, _density: Self::Scalar) -> CfdResult<()> {
        // Default implementation - do nothing for incompressible flows
        Ok(())
    }

    /// Check if all field values are finite and valid
    fn validate(&self) -> CfdResult<()> {
        for i in 0..self.node_count() {
            let _velocity = self.get_velocity(i)?;
            let _pressure = self.get_pressure(i)?;
            // Add validation logic here if needed
        }
        Ok(())
    }
}

/// Trait for CFD solvers (SIMPLE, PISO, LBM, etc.)
pub trait CfdSolver: Send + Sync + Debug {
    /// Type of fluid field this solver operates on
    type Field: FluidField;

    /// Perform one solution step/iteration
    /// Returns the residual (convergence measure)
    fn solve_step(&mut self, field: &mut Self::Field, dt: f64) -> CfdResult<f64>;

    /// Check if the solution has converged
    fn is_converged(&self, residual: f64, tolerance: f64) -> bool;

    /// Get current iteration count
    fn get_iteration_count(&self) -> usize;

    /// Reset solver state for a new simulation
    fn reset(&mut self) -> CfdResult<()>;

    /// Get solver name/type for diagnostics
    fn solver_name(&self) -> &'static str {
        "Generic CFD Solver"
    }

    /// Solve until convergence or maximum iterations
    fn solve_to_convergence(
        &mut self,
        field: &mut Self::Field,
        dt: f64,
        tolerance: f64,
        max_iterations: usize,
    ) -> CfdResult<(f64, usize)> {
        self.reset()?;

        for iteration in 0..max_iterations {
            let residual = self.solve_step(field, dt)?;

            if self.is_converged(residual, tolerance) {
                return Ok((residual, iteration + 1));
            }
        }

        Err(crate::error::CfdError::convergence(
            max_iterations,
            0.0, // We don't have the final residual here
            tolerance,
        ))
    }

    /// Set solver parameters (optional)
    fn set_parameters(&mut self, _params: &SolverParameters) -> CfdResult<()> {
        Ok(())
    }
}

/// Common solver parameters
#[derive(Debug, Clone)]
pub struct SolverParameters {
    /// Convergence tolerance for residuals
    pub tolerance: f64,
    /// Maximum number of iterations allowed
    pub max_iterations: usize,
    /// Under-relaxation factor for stability
    pub relaxation_factor: f64,
    /// Time step size for transient simulations
    pub time_step: f64,
}

impl Default for SolverParameters {
    fn default() -> Self {
        Self {
            tolerance: 1e-6,
            max_iterations: 1000,
            relaxation_factor: 0.7,
            time_step: 0.001,
        }
    }
}

/// Trait for mesh entities (cells, faces, nodes)
pub trait MeshEntity: Send + Sync + Debug {
    /// Unique identifier for this entity
    fn id(&self) -> usize;

    /// Number of vertices/nodes that define this entity
    fn vertex_count(&self) -> usize;

    /// Indices of vertices that define this entity
    fn vertex_indices(&self) -> &[usize];

    /// Volume (for cells) or area (for faces) or 1.0 (for nodes)
    fn volume(&self) -> f64;

    /// Geometric centroid of the entity
    fn centroid(&self) -> Vector3<f64>;

    /// Entity type (cell, face, edge, node)
    fn entity_type(&self) -> MeshEntityType {
        match self.vertex_count() {
            1 => MeshEntityType::Node,
            2 => MeshEntityType::Edge,
            3 => MeshEntityType::Triangle,
            4 => MeshEntityType::Tetrahedron,
            _ => MeshEntityType::Unknown,
        }
    }

    /// Check if this entity is on the boundary
    fn is_boundary(&self) -> bool {
        false // Default implementation
    }
}

/// Types of mesh entities
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MeshEntityType {
    /// Point entity (0D)
    Node,
    /// Line entity (1D)
    Edge,
    /// Triangular face (2D)
    Triangle,
    /// Quadrilateral face (2D)
    Quadrilateral,
    /// Tetrahedral cell (3D)
    Tetrahedron,
    /// Hexahedral cell (3D)
    Hexahedron,
    /// Unknown or unsupported entity type
    Unknown,
}

/// Trait for boundary conditions
pub trait BoundaryCondition: Send + Sync + Debug {
    /// Type of field this boundary condition applies to
    type Field: FluidField;

    /// Apply the boundary condition to the field
    fn apply(&self, field: &mut Self::Field, time: f64) -> CfdResult<()>;

    /// Get the boundary condition type
    fn bc_type(&self) -> BoundaryConditionType;

    /// Get the boundary patch/region this applies to
    fn boundary_patch(&self) -> &str;

    /// Validate the boundary condition
    fn validate(&self) -> CfdResult<()> {
        Ok(())
    }
}

/// Types of boundary conditions
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum BoundaryConditionType {
    /// Fixed velocity (Dirichlet)
    FixedVelocity,
    /// Fixed pressure (Dirichlet)
    FixedPressure,
    /// No-slip wall
    NoSlipWall,
    /// Slip wall
    SlipWall,
    /// Inlet with specified velocity
    Inlet,
    /// Outlet with specified pressure
    Outlet,
    /// Periodic boundary
    Periodic,
    /// Symmetry plane
    Symmetry,
}

/// Trait for time integration schemes
pub trait TimeIntegrator: Send + Sync + Debug {
    /// Type of field this integrator works with
    type Field: FluidField;

    /// Advance the field by one time step
    fn advance(&mut self, field: &mut Self::Field, dt: f64) -> CfdResult<()>;

    /// Get the integration scheme name
    fn scheme_name(&self) -> &'static str;

    /// Get the order of accuracy
    fn order(&self) -> usize;

    /// Check if the scheme is stable for the given time step
    fn is_stable(&self, dt: f64, cfl_number: f64) -> bool;
}

/// Trait for turbulence models
pub trait TurbulenceModel: Send + Sync + Debug {
    /// Type of field this model works with
    type Field: FluidField;

    /// Compute turbulent viscosity
    fn compute_turbulent_viscosity(&self, field: &Self::Field) -> CfdResult<Vec<f64>>;

    /// Update turbulence variables
    fn update(&mut self, field: &mut Self::Field, dt: f64) -> CfdResult<()>;

    /// Get the turbulence model name
    fn model_name(&self) -> &'static str;

    /// Get turbulence parameters
    fn get_parameters(&self) -> TurbulenceParameters;
}

/// Turbulence model parameters
#[derive(Debug, Clone)]
pub struct TurbulenceParameters {
    /// `C_μ` constant for k-ε model
    pub c_mu: f64,
    /// `C_ε1` constant for k-ε model
    pub c_eps1: f64,
    /// `C_ε2` constant for k-ε model
    pub c_eps2: f64,
    /// Schmidt number for turbulent kinetic energy
    pub sigma_k: f64,
    /// Schmidt number for turbulent dissipation rate
    pub sigma_eps: f64,
}

impl Default for TurbulenceParameters {
    fn default() -> Self {
        // Standard k-epsilon model constants
        Self {
            c_mu: 0.09,
            c_eps1: 1.44,
            c_eps2: 1.92,
            sigma_k: 1.0,
            sigma_eps: 1.3,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_solver_parameters_default() {
        let params = SolverParameters::default();
        assert_eq!(params.tolerance, 1e-6);
        assert_eq!(params.max_iterations, 1000);
        assert_eq!(params.relaxation_factor, 0.7);
        assert_eq!(params.time_step, 0.001);
    }

    #[test]
    fn test_mesh_entity_type() {
        assert_eq!(MeshEntityType::Node as u8, 0);
        assert_ne!(MeshEntityType::Node, MeshEntityType::Edge);
    }

    #[test]
    fn test_boundary_condition_type() {
        assert_ne!(
            BoundaryConditionType::FixedVelocity,
            BoundaryConditionType::FixedPressure
        );
    }

    #[test]
    fn test_turbulence_parameters_default() {
        let params = TurbulenceParameters::default();
        assert_eq!(params.c_mu, 0.09);
        assert_eq!(params.c_eps1, 1.44);
    }
}