#include <gtest/gtest.h>
#include "vde/mesh/mesh_lod.h"
#include "vde/mesh/halfedge_mesh.h"
#include <cmath>

using namespace vde::mesh;

/// Create a simple box mesh (12 triangles, 8 vertices)
static HalfedgeMesh make_box_mesh() {
    // Unit cube vertices
    std::vector<Point3D> verts = {
        {0, 0, 0}, {1, 0, 0}, {1, 1, 0}, {0, 1, 0},  // bottom
        {0, 0, 1}, {1, 0, 1}, {1, 1, 1}, {0, 1, 1},  // top
    };
    // 12 triangles (2 per face)
    std::vector<std::array<int, 3>> tris = {
        {0, 2, 1}, {0, 3, 2},   // front
        {1, 2, 6}, {1, 6, 5},   // right
        {5, 6, 7}, {5, 7, 4},   // back
        {4, 7, 3}, {4, 3, 0},   // left
        {3, 7, 6}, {3, 6, 2},   // top
        {4, 0, 1}, {4, 1, 5},   // bottom
    };

    HalfedgeMesh mesh;
    mesh.build_from_triangles(verts, tris);
    return mesh;
}

// ──────────────────────────────────────────────────────
//  LOD generation
// ──────────────────────────────────────────────────────

TEST(LODMeshTest, GenerateLOD_DefaultLevels) {
    auto box = make_box_mesh();
    auto lod = generate_lod(box, 3, 0.5);

    // Default: 3 levels (base + 2 simplified)
    EXPECT_EQ(lod.levels.size(), 3u);
    EXPECT_EQ(lod.thresholds.size(), 3u);

    // Level 0 is the original mesh (12 faces)
    EXPECT_GE(lod.levels[0].num_faces(), 8u);
    // Each level should have ≤ faces than previous
    EXPECT_LE(lod.levels[1].num_faces(), lod.levels[0].num_faces());
    EXPECT_LE(lod.levels[2].num_faces(), lod.levels[1].num_faces());
}

TEST(LODMeshTest, GenerateLOD_SingleLevel) {
    auto box = make_box_mesh();
    auto lod = generate_lod(box, 1, 0.5);

    // Only 1 level = base (no simplification)
    EXPECT_EQ(lod.levels.size(), 1u);
    EXPECT_EQ(lod.levels[0].num_faces(), 12u);
}

TEST(LODMeshTest, GenerateLOD_AggressiveReduction) {
    auto box = make_box_mesh();
    auto lod = generate_lod(box, 5, 0.1);  // keep only 10% each level

    // Should stop early when < 4 faces remain
    EXPECT_GE(lod.levels.size(), 1u);
    EXPECT_LE(lod.levels.size(), 5u);
}

TEST(LODMeshTest, GenerateLOD_EmptyMesh) {
    HalfedgeMesh empty;
    auto lod = generate_lod(empty, 3, 0.5);

    EXPECT_EQ(lod.levels.size(), 1u);  // only base
    EXPECT_EQ(lod.levels[0].num_faces(), 0u);
}

// ──────────────────────────────────────────────────────
//  level_for_error
// ──────────────────────────────────────────────────────

TEST(LODMeshTest, LevelForError_ZeroError) {
    auto box = make_box_mesh();
    auto lod = generate_lod(box, 3, 0.5);

    // error 0 → base level (threshold 0.0)
    EXPECT_EQ(lod.level_for_error(0.0), 0);
}

TEST(LODMeshTest, LevelForError_ThresholdBoundary) {
    auto box = make_box_mesh();
    auto lod = generate_lod(box, 3, 0.5);

    // thresholds: [0.0, 100.0, 200.0]
    EXPECT_EQ(lod.level_for_error(50.0), 0);
    EXPECT_EQ(lod.level_for_error(100.0), 1);   // ≥ 100 → level 1
    EXPECT_EQ(lod.level_for_error(150.0), 1);
    EXPECT_EQ(lod.level_for_error(200.0), 2);   // ≥ 200 → level 2
    EXPECT_EQ(lod.level_for_error(999.0), 2);
}

TEST(LODMeshTest, LevelForError_NegativeError) {
    auto box = make_box_mesh();
    auto lod = generate_lod(box, 3, 0.5);

    // Negative error → level 0 (base)
    EXPECT_EQ(lod.level_for_error(-1.0), 0);
}

// ──────────────────────────────────────────────────────
//  mesh_at
// ──────────────────────────────────────────────────────

TEST(LODMeshTest, MeshAt_ValidLevels) {
    auto box = make_box_mesh();
    auto lod = generate_lod(box, 3, 0.5);

    EXPECT_EQ(lod.mesh_at(0).num_faces(), 12u);
    EXPECT_LE(lod.mesh_at(1).num_faces(), 12u);
    EXPECT_LE(lod.mesh_at(2).num_faces(), lod.mesh_at(1).num_faces());
}

TEST(LODMeshTest, MeshAt_ClampNegative) {
    auto box = make_box_mesh();
    auto lod = generate_lod(box, 3, 0.5);

    // Negative level → clamped to 0
    EXPECT_EQ(lod.mesh_at(-1).num_faces(), lod.mesh_at(0).num_faces());
    EXPECT_EQ(lod.mesh_at(-100).num_faces(), lod.mesh_at(0).num_faces());
}

TEST(LODMeshTest, MeshAt_ClampTooHigh) {
    auto box = make_box_mesh();
    auto lod = generate_lod(box, 3, 0.5);

    int last = static_cast<int>(lod.levels.size()) - 1;
    EXPECT_EQ(lod.mesh_at(999).num_faces(), lod.mesh_at(last).num_faces());
}

TEST(LODMeshTest, MeshAt_EmptyLOD) {
    LODMesh empty_lod;
    // mesh_at returns a static empty mesh for empty LOD
    EXPECT_EQ(empty_lod.mesh_at(0).num_faces(), 0u);
    EXPECT_EQ(empty_lod.mesh_at(5).num_faces(), 0u);
}

// ──────────────────────────────────────────────────────
//  generate_brep_lod (integration)
// ──────────────────────────────────────────────────────

// Forward-declare for linking only (no brep::make_box in this TU's link deps)
// This test is compile-time only; runtime needs brep linked.
// We test through the LOD API directly above; brep path is tested
// in the brep test suite.