// TDD: RED phase - Tests for mesh refinement algorithms

use nalgebra::Vector3;
use rtx_cfd::mesh::Mesh;
use rtx_cfd::mesh::refinement::{AdaptiveRefinement, RefinementCriteria, RefinementStrategy};
use rtx_cfd::mesh::structured::StructuredMesh;
use rtx_cfd::mesh::unstructured::UnstructuredMesh;

#[test]
fn test_adaptive_refinement_criteria_validation() {
    let criteria = RefinementCriteria {
        max_error: 1e-3,
        min_cell_size: 1e-6,
        max_cell_size: 1e6,
        max_levels: 10,
    };

    let refinement = AdaptiveRefinement::new(criteria);

    // Test refinement decision logic
    assert!(refinement.needs_refinement(1e-2, 1e-3, 5)); // High error, reasonable size, low level
    assert!(!refinement.needs_refinement(1e-4, 1e-3, 5)); // Low error
    assert!(!refinement.needs_refinement(1e-2, 1e-7, 5)); // Too small cell
    assert!(!refinement.needs_refinement(1e-2, 1e-3, 15)); // Too many levels
}

#[test]
fn test_error_based_cell_marking() {
    let criteria = RefinementCriteria::default();
    let refinement = AdaptiveRefinement::new(criteria);

    // Test with various error distributions
    let errors = vec![1e-2, 1e-4, 5e-3, 1e-5, 2e-3, 1e-6];
    let cell_sizes = vec![1e-3, 1e-3, 1e-3, 1e-3, 1e-3, 1e-3];
    let levels = vec![2, 2, 2, 2, 2, 2];

    let marked_cells = refinement
        .mark_cells_for_refinement(&errors, &cell_sizes, &levels)
        .unwrap();

    // Should mark cells 0, 2, 4 (indices with errors > 1e-3)
    let expected_marked: Vec<usize> = vec![0, 2, 4];
    assert_eq!(marked_cells, expected_marked);
}

#[test]
fn test_gradient_based_error_indicator() {
    let criteria = RefinementCriteria::default();
    let refinement = AdaptiveRefinement::new(criteria);

    // Create a simple 2D velocity field with gradients
    let velocity_field = vec![
        Vector3::new(0.0, 0.0, 0.0), // Cell 0: no gradient
        Vector3::new(1.0, 0.0, 0.0), // Cell 1: moderate gradient
        Vector3::new(2.0, 1.0, 0.0), // Cell 2: high gradient
        Vector3::new(0.1, 0.1, 0.0), // Cell 3: low gradient
    ];

    let errors = refinement
        .compute_gradient_error_indicator(&velocity_field)
        .unwrap();

    // Cell 2 should have highest error (highest velocity magnitude)
    assert!(errors[2] > errors[1]);
    assert!(errors[1] > errors[0]);
    assert!(errors[1] > errors[3]);
}

#[test]
fn test_residual_based_error_indicator() {
    let criteria = RefinementCriteria::default();
    let refinement = AdaptiveRefinement::new(criteria);

    // Mock residuals for momentum and continuity equations
    let momentum_residuals = vec![1e-3, 1e-2, 5e-3, 1e-4];
    let continuity_residuals = vec![1e-4, 1e-3, 2e-3, 1e-5];

    let errors = refinement
        .compute_residual_error_indicator(&momentum_residuals, &continuity_residuals)
        .unwrap();

    // Cell 1 should have highest combined residual
    assert!(errors[1] > errors[2]);
    assert!(errors[2] > errors[0]);
    assert!(errors[0] > errors[3]);
}

#[test]
fn test_structured_mesh_refinement() {
    let mut mesh = StructuredMesh::new(3, 3, 1.0, 1.0).unwrap();
    let initial_cell_count = mesh.cell_count();

    // Test uniform refinement
    mesh.refine().unwrap();

    // Should quadruple the number of cells in 2D
    assert_eq!(mesh.cell_count(), initial_cell_count * 4);

    // Grid spacing should be halved
    assert!((mesh.dx() - 0.25).abs() < 1e-10);
    assert!((mesh.dy() - 0.25).abs() < 1e-10);
}

#[test]
fn test_unstructured_mesh_cell_subdivision() {
    let mut mesh = UnstructuredMesh::new();

    // Create a simple triangle
    let n1 = mesh.add_node(Vector3::new(0.0, 0.0, 0.0)).unwrap();
    let n2 = mesh.add_node(Vector3::new(1.0, 0.0, 0.0)).unwrap();
    let n3 = mesh.add_node(Vector3::new(0.5, 1.0, 0.0)).unwrap();
    let cell_id = mesh.add_triangle_cell(n1, n2, n3).unwrap();

    let initial_cell_count = mesh.cell_count();

    // Mark this cell for refinement and subdivide
    let cells_to_refine = vec![cell_id];
    mesh.refine_cells(&cells_to_refine).unwrap();

    // Triangle subdivision should create 4 triangles
    assert_eq!(mesh.cell_count(), initial_cell_count + 3); // 1 original -> 4 total, so +3
}

#[test]
fn test_hanging_node_consistency() {
    let mut mesh = UnstructuredMesh::new();

    // Create two adjacent triangles
    let n1 = mesh.add_node(Vector3::new(0.0, 0.0, 0.0)).unwrap();
    let n2 = mesh.add_node(Vector3::new(1.0, 0.0, 0.0)).unwrap();
    let n3 = mesh.add_node(Vector3::new(0.5, 1.0, 0.0)).unwrap();
    let n4 = mesh.add_node(Vector3::new(1.5, 1.0, 0.0)).unwrap();

    let cell1 = mesh.add_triangle_cell(n1, n2, n3).unwrap();
    let cell2 = mesh.add_triangle_cell(n2, n4, n3).unwrap();

    // Refine only the first cell
    mesh.refine_cells(&vec![cell1]).unwrap();

    // Should handle hanging nodes correctly
    assert!(mesh.validate().is_ok());
}

#[test]
fn test_adaptive_refinement_quality_metrics() {
    let mut mesh = StructuredMesh::new(4, 4, 2.0, 2.0).unwrap();

    // Get initial quality metrics
    let initial_stats = mesh.statistics();
    let initial_aspect_ratio = initial_stats.aspect_ratio;

    // Refine mesh
    mesh.refine().unwrap();

    // Quality should be maintained or improved
    let refined_stats = mesh.statistics();
    assert!(refined_stats.aspect_ratio <= initial_aspect_ratio * 1.1); // Allow small degradation
}

#[test]
fn test_refinement_level_tracking() {
    let criteria = RefinementCriteria {
        max_levels: 3,
        ..Default::default()
    };
    let refinement = AdaptiveRefinement::new(criteria);

    // Test level enforcement
    let errors = vec![1e-2; 10]; // All high error
    let cell_sizes = vec![1e-3; 10]; // All reasonable size
    let levels = vec![0, 1, 2, 3, 4, 0, 1, 2, 3, 4]; // Mixed levels

    let marked_cells = refinement
        .mark_cells_for_refinement(&errors, &cell_sizes, &levels)
        .unwrap();

    // Should not mark cells with level >= max_levels (indices 3, 4, 8, 9)
    assert!(!marked_cells.contains(&3));
    assert!(!marked_cells.contains(&4));
    assert!(!marked_cells.contains(&8));
    assert!(!marked_cells.contains(&9));
}