namespace TheLabs;
using System;
using System.Collections.Generic;
using System.IO;
using Assimp; // The library we just installed
using OpenTK.Mathematics;

public static class ModelLoader
{
    public static Mesh LoadMesh(string path)
    {
        var importer = new AssimpContext();
        
        var scene = importer.ImportFile(path, PostProcessSteps.Triangulate | PostProcessSteps.JoinIdenticalVertices);

        if (scene == null || scene.SceneFlags.HasFlag(SceneFlags.Incomplete) || scene.RootNode == null)
        {   
            throw new Exception("Error loading model: " + path);
        }
        
        // --- NEW LOGIC: Combine all meshes into one ---
        List<float> allVertices = new List<float>();
        List<uint> allIndices = new List<uint>();
        
        // We need to track how many vertices we've added so far
        // so the indices point to the correct new location
        uint indexOffset = 0;

        // Loop through EVERY mesh found in the file (Legs, Torso, Head, etc.)
        foreach (var mesh in scene.Meshes)
        {
            // 1. Process Vertices for this specific part
            for (int i = 0; i < mesh.VertexCount; i++)
            {
                // Position (x, y, z)
                var pos = mesh.Vertices[i];
                allVertices.Add(pos.X);
                allVertices.Add(pos.Y);
                allVertices.Add(pos.Z);
                // 2. Normals (NEW)
                if (mesh.HasNormals)
                {
                    var n = mesh.Normals[i];
                    allVertices.Add(n.X); allVertices.Add(n.Y); allVertices.Add(n.Z);
                }
                else
                {
                    allVertices.Add(0); allVertices.Add(1); allVertices.Add(0); // Default up
                }
                // Texture Coordinates (u, v)
                if (mesh.HasTextureCoords(0))
                {
                    var uv = mesh.TextureCoordinateChannels[0][i];
                    allVertices.Add(uv.X);
                    allVertices.Add(uv.Y);
                }
                else
                {
                    allVertices.Add(0.0f);
                    allVertices.Add(0.0f);
                }
            }

            // 2. Process Indices for this specific part
            for (int i = 0; i < mesh.FaceCount; i++)
            {
                var face = mesh.Faces[i];
                for (int j = 0; j < face.IndexCount; j++)
                {
                    // CRITICAL: We add the offset to the index!
                    // If the leg had 100 vertices, the first vertex of the torso
                    // needs to be index 100, not 0.
                    allIndices.Add((uint)(face.Indices[j] + indexOffset));
                }
            }

            // Increase the offset by the number of vertices we just added
            indexOffset += (uint)mesh.VertexCount;
        }

        // Return one giant Mesh containing the whole character
        return new Mesh(allVertices.ToArray(), allIndices.ToArray(), Mesh.VertexLayout.PosTex);
    }

    
}