// TDD: GREEN phase - Implement mesh module to pass tests

//! Mesh generation and management for CFD simulations
//!
//! This module provides structured and unstructured mesh implementations
//! with support for adaptive refinement and GPU-accelerated operations.

/// Mesh entities (nodes, faces, cells)
pub mod entities;
/// Generators for structured curvilinear patches
pub mod patch_gen;
/// Structured curvilinear 2-D patch with face metrics (the overset patch)
pub mod patch_mesh;
/// Adaptive mesh refinement algorithms
pub mod refinement;
/// Mesh quality and statistics calculations
pub mod statistics;
/// Structured mesh implementation for rectangular domains
pub mod structured;
/// Unstructured mesh implementation for complex geometries
pub mod unstructured;

use crate::error::{CfdError, CfdResult};
use nalgebra::Vector3;

// Re-export main types
pub use entities::{Cell, Face, Node};
pub use patch_mesh::{Face as PatchFace, PatchMesh, Side as PatchSide};
pub use structured::StructuredMesh;
pub use unstructured::UnstructuredMesh;

/// Mesh bounds information
#[derive(Debug, Clone)]
pub struct MeshBounds {
    /// Minimum coordinates
    pub min: Vector3<f64>,
    /// Maximum coordinates
    pub max: Vector3<f64>,
}

impl MeshBounds {
    /// Create new mesh bounds
    #[must_use]
    pub fn new(min: Vector3<f64>, max: Vector3<f64>) -> Self {
        Self { min, max }
    }

    /// Get mesh dimensions
    #[must_use]
    pub fn dimensions(&self) -> Vector3<f64> {
        self.max - self.min
    }

    /// Get mesh center
    #[must_use]
    pub fn center(&self) -> Vector3<f64> {
        (self.min + self.max) * 0.5
    }

    /// Check if point is inside bounds
    #[must_use]
    pub fn contains(&self, point: Vector3<f64>) -> bool {
        point.x >= self.min.x
            && point.x <= self.max.x
            && point.y >= self.min.y
            && point.y <= self.max.y
            && point.z >= self.min.z
            && point.z <= self.max.z
    }
}

/// Mesh quality metrics
#[derive(Debug, Clone)]
pub struct MeshStatistics {
    /// Total number of cells
    pub total_cells: usize,
    /// Total number of nodes
    pub total_nodes: usize,
    /// Total number of faces
    pub total_faces: usize,
    /// Number of boundary faces
    pub boundary_faces: usize,
    /// Minimum cell volume
    pub min_cell_volume: f64,
    /// Maximum cell volume
    pub max_cell_volume: f64,
    /// Average cell volume
    pub average_cell_volume: f64,
    /// Mesh aspect ratio (max/min dimensions)
    pub aspect_ratio: f64,
    /// Skewness measure (0 = perfect, 1 = degenerate)
    pub max_skewness: f64,
    /// Orthogonality measure (1 = perfect, 0 = non-orthogonal)
    pub orthogonality: f64,
    /// Non-orthogonality measure (0 = perfect, 1 = non-orthogonal)
    pub non_orthogonality: f64,
}

impl MeshStatistics {
    /// Create default statistics
    #[must_use]
    pub fn new() -> Self {
        Self {
            total_cells: 0,
            total_nodes: 0,
            total_faces: 0,
            boundary_faces: 0,
            min_cell_volume: 0.0,
            max_cell_volume: 0.0,
            average_cell_volume: 0.0,
            aspect_ratio: 1.0,
            max_skewness: 0.0,
            orthogonality: 1.0,
            non_orthogonality: 0.0,
        }
    }
}

impl Default for MeshStatistics {
    fn default() -> Self {
        Self::new()
    }
}

/// Common trait for all mesh types
pub trait Mesh: Send + Sync {
    /// Get total number of cells
    fn cell_count(&self) -> usize;

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

    /// Get mesh bounds
    fn bounds(&self) -> MeshBounds;

    /// Validate mesh topology and quality
    fn validate(&self) -> CfdResult<()>;

    /// Get mesh statistics
    fn statistics(&self) -> MeshStatistics;

    /// Check if a cell is on the boundary
    fn is_boundary_cell(&self, cell_id: usize) -> bool;

    /// Get neighboring cells for a given cell
    fn get_cell_neighbors(&self, cell_id: usize) -> CfdResult<Vec<usize>>;

    /// Refine the mesh (adaptive refinement)
    fn refine(&mut self) -> CfdResult<()>;

    /// Coarsen the mesh
    fn coarsen(&mut self) -> CfdResult<()> {
        // Default implementation - not supported
        Err(CfdError::mesh(
            "Mesh coarsening not implemented for this mesh type",
        ))
    }
}

/// Mesh generation utilities
pub struct MeshGenerator;

impl MeshGenerator {
    /// Generate a structured rectangular mesh
    pub fn rectangle(width: f64, height: f64, nx: usize, ny: usize) -> CfdResult<StructuredMesh> {
        StructuredMesh::new(nx, ny, width, height)
    }

    /// Generate a structured cuboid mesh
    pub fn cuboid(
        width: f64,
        height: f64,
        depth: f64,
        nx: usize,
        ny: usize,
        nz: usize,
    ) -> CfdResult<StructuredMesh> {
        StructuredMesh::new_3d(nx, ny, nz, width, height, depth)
    }

    /// Generate an unstructured triangular mesh for a circle
    pub fn circle(radius: f64, elements: usize) -> CfdResult<UnstructuredMesh> {
        let mut mesh = UnstructuredMesh::new();

        // Add center node
        let center = mesh.add_node(Vector3::new(0.0, 0.0, 0.0))?;

        // Add perimeter nodes
        let mut perimeter_nodes = Vec::new();
        for i in 0..elements {
            let angle = 2.0 * std::f64::consts::PI * i as f64 / elements as f64;
            let x = radius * angle.cos();
            let y = radius * angle.sin();
            let node = mesh.add_node(Vector3::new(x, y, 0.0))?;
            perimeter_nodes.push(node);
        }

        // Create triangular cells connecting center to perimeter
        for i in 0..elements {
            let next_i = (i + 1) % elements;
            mesh.add_triangle_cell(center, perimeter_nodes[i], perimeter_nodes[next_i])?;
        }

        Ok(mesh)
    }
}

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

    #[test]
    fn test_mesh_bounds() {
        let min = Vector3::new(0.0, 0.0, 0.0);
        let max = Vector3::new(1.0, 2.0, 3.0);
        let bounds = MeshBounds::new(min, max);

        assert_eq!(bounds.dimensions(), Vector3::new(1.0, 2.0, 3.0));
        assert_eq!(bounds.center(), Vector3::new(0.5, 1.0, 1.5));
        assert!(bounds.contains(Vector3::new(0.5, 1.0, 1.5)));
        assert!(!bounds.contains(Vector3::new(-1.0, 0.0, 0.0)));
    }

    #[test]
    fn test_mesh_statistics_default() {
        let stats = MeshStatistics::default();
        assert_eq!(stats.total_cells, 0);
        assert_eq!(stats.total_nodes, 0);
        assert_eq!(stats.aspect_ratio, 1.0);
    }

    #[test]
    fn test_mesh_generator_rectangle() {
        let mesh = MeshGenerator::rectangle(2.0, 3.0, 5, 6).unwrap();
        assert_eq!(mesh.nx(), 5);
        assert_eq!(mesh.ny(), 6);
        assert_eq!(mesh.width(), 2.0);
        assert_eq!(mesh.height(), 3.0);
    }

    #[test]
    fn test_mesh_generator_circle() {
        let mesh = MeshGenerator::circle(1.0, 8).unwrap();
        assert_eq!(mesh.node_count(), 9); // 1 center + 8 perimeter
        assert_eq!(mesh.cell_count(), 8); // 8 triangular cells
    }
}