using System.Collections.Generic;
using System.IO;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

namespace Smuggler
{
    public static class Importer
    {
        public static Model ImportGLB(GraphicsDevice graphicsDevice, Stream stream)
        {
            var sharpModel = SharpGLTF.Schema2.ModelRoot.ReadGLB(stream);
            var vertexType = InferVertexType(sharpModel);

            if (vertexType == null) { return null; }

            var meshes = new List<Mesh>();

            foreach (var mesh in sharpModel.LogicalMeshes)
            {
                var meshParts = new List<MeshPart>();

                foreach (var primitive in mesh.Primitives)
                {
                    meshParts.Add(
                        ImportMeshPart(graphicsDevice, vertexType, primitive)
                    );
                }

                meshes.Add(new Mesh(meshParts.ToArray()));
            }

            return new Model(meshes.ToArray());
        }

        private static System.Type InferVertexType(SharpGLTF.Schema2.ModelRoot model)
        {
            bool hasColor = false;
            bool hasNormal = false;
            bool hasTexture = false;

            if (model.LogicalMeshes.Count == 0) { return null; }
            if (model.LogicalMeshes[0].Primitives.Count == 0) { return null; }

            var samplePrimitive = model.LogicalMeshes[0].Primitives[0];

            if (samplePrimitive.GetVertexAccessor("POSITION") == null)
            {
                System.Console.WriteLine("There is no Position attribute on this model's vertices. That seems weird!");
                return null;
            }

            if (samplePrimitive.GetVertexAccessor("COLOR") != null)
            {
                hasColor = true;
            }

            if (samplePrimitive.GetVertexAccessor("NORMAL") != null)
            {
                hasNormal = true;
            }

            if (samplePrimitive.GetVertexAccessor("TEXCOORD_0") != null)
            {
                hasTexture = true;
            }

            if (hasColor && hasNormal && hasTexture)
            {
                // FIXME: Implement VertexPositionColorNormalTexture
                return null;
            }

            if (hasColor && hasTexture)
            {
                return typeof(VertexPositionColorTexture);
            }

            if (hasNormal && hasTexture)
            {
                return typeof(VertexPositionNormalTexture);
            }

            if (hasColor)
            {
                return typeof(VertexPositionColor);
            }

            if (hasTexture)
            {
                return typeof(VertexPositionTexture);
            }

            System.Console.WriteLine("Could not infer vertex type");

            return null;
        }

        private static MeshPart ImportMeshPart(GraphicsDevice graphicsDevice, System.Type vertexType, SharpGLTF.Schema2.MeshPrimitive primitive)
        {
            var indices = Indices(primitive);
            var positions = Positions(primitive);
            var triangles = Triangles(primitive);

            var vertexBuffer = new VertexBuffer(
                graphicsDevice,
                vertexType,
                positions.Length,
                BufferUsage.None
            );

            var indexBuffer = new IndexBuffer(
                graphicsDevice,
                IndexElementSize.ThirtyTwoBits,
                indices.Length,
                BufferUsage.None
            );

            indexBuffer.SetData(indices);

            if (vertexType == typeof(VertexPositionColor))
            {
                ImportVertexPositionColor(primitive, vertexBuffer, indices, positions);
            }
            else if (vertexType == typeof(VertexPositionColorTexture))
            {
                ImportVertexPositionColorTexture(primitive, vertexBuffer, indices, positions);
            }
            else if (vertexType == typeof(VertexPositionNormalTexture))
            {
                ImportVertexPositionNormalTexture(primitive, vertexBuffer, indices, positions);
            }
            else if (vertexType == typeof(VertexPositionTexture))
            {
                ImportVertexPositionTexture(primitive, vertexBuffer, indices, positions);
            }

            return new MeshPart(
                vertexBuffer,
                indexBuffer,
                positions,
                triangles,
                new BasicEffect(graphicsDevice)
            );
        }

        /* Attribute Getters */
        
        private static Vector3[] Positions(SharpGLTF.Schema2.MeshPrimitive primitive)
        {
            var positionAccessor = primitive.GetVertexAccessor("POSITION").AsVector3Array();
            var positions = new Vector3[positionAccessor.Count];

            for (int i = 0; i < positions.Length; i++)
            {
                var position = positionAccessor[i];
                positions[i] = new Vector3(-position.X, -position.Z, position.Y);
            }

            return positions;
        }

        private static Color[] Colors(SharpGLTF.Schema2.MeshPrimitive primitive)
        {
            var colorAccessor = primitive.GetVertexAccessor("COLOR").AsColorArray();
            var colors = new Color[colorAccessor.Count];

            for (int i = 0; i < colors.Length; i++)
            {
                var color = colorAccessor[i];
                colors[i] = new Color(color.X, color.Y, color.Z, color.W);
            }

            return colors;
        }

        private static Vector3[] Normals(SharpGLTF.Schema2.MeshPrimitive primitive)
        {
            var normalAccessor = primitive.GetVertexAccessor("NORMAL").AsVector3Array();
            var normals = new Vector3[normalAccessor.Count];

            for (int i = 0; i < normals.Length; i++)
            {
                var normal = normalAccessor[i];
                normals[i] = -new Vector3(normal.X, normal.Z, normal.Y);
            }

            return normals;
        }

        private static Vector2[] TexCoords(SharpGLTF.Schema2.MeshPrimitive primitive)
        {
            var texcoordAccessor = primitive.GetVertexAccessor("TEXCOORD_0").AsVector2Array();
            var texcoords = new Vector2[texcoordAccessor.Count];

            for (int i = 0; i < texcoords.Length; i++)
            {
                var texcoord = texcoordAccessor[i];
                texcoords[i] = new Vector2(texcoord.X, texcoord.Y);
            }

            return texcoords;
        }

        private static Triangle[] Triangles(SharpGLTF.Schema2.MeshPrimitive primitive)
        {
            var triangles = new List<Triangle>();
            
            foreach (var (a, b, c) in primitive.GetTriangleIndices())
            {
                triangles.Add(new Triangle(a, b, c));
            }

            return triangles.ToArray();
        }

        private static uint[] Indices(SharpGLTF.Schema2.MeshPrimitive primitive)
        {
            var indexAccessor = primitive.GetIndexAccessor().AsIndicesArray();
            var indices = new uint[indexAccessor.Count];

            for (int i = 0; i < indices.Length; i++)
            {
                indices[i] = indexAccessor[i];
            }

            return indices;
        }

        /* Vertex Builders */

        private static void ImportVertexPositionColor(
            SharpGLTF.Schema2.MeshPrimitive primitive,
            VertexBuffer vertexBuffer,
            uint[] indices,
            Vector3[] positions
        ) {
            var colors = Colors(primitive);

            var vertices = new VertexPositionColor[positions.Length];

            foreach (var index in indices)
            {
                var position = positions[index];
                var color = colors[index];

                vertices[index] = new VertexPositionColor(
                    position,
                    color
                );
            }

            vertexBuffer.SetData(vertices);
        }

        private static void ImportVertexPositionColorTexture(
            SharpGLTF.Schema2.MeshPrimitive primitive,
            VertexBuffer vertexBuffer,
            uint[] indices,
            Vector3[] positions
        ) {
            var colors = Colors(primitive);
            var texcoords = TexCoords(primitive);

            var vertices = new VertexPositionColorTexture[positions.Length];

            foreach (var index in indices)
            {
                var position = positions[index];
                var color = colors[index];
                var texcoord = texcoords[index];

                vertices[index] = new VertexPositionColorTexture(
                    position,
                    color,
                    texcoord
                );
            }

            vertexBuffer.SetData(vertices);
        }

        private static void ImportVertexPositionNormalTexture(
            SharpGLTF.Schema2.MeshPrimitive primitive,
            VertexBuffer vertexBuffer,
            uint[] indices,
            Vector3[] positions
        ) {
            var normals = Normals(primitive);
            var texcoords = TexCoords(primitive);

            var vertices = new VertexPositionNormalTexture[positions.Length];

            foreach (var index in indices)
            {
                var position = positions[index];
                var normal = normals[index];
                var texcoord = texcoords[index];

                vertices[index] = new VertexPositionNormalTexture(
                    position,
                    normal,
                    texcoord
                );
            }

            vertexBuffer.SetData(vertices);
        }

        private static void ImportVertexPositionTexture(
            SharpGLTF.Schema2.MeshPrimitive primitive,
            VertexBuffer vertexBuffer,
            uint[] indices,
            Vector3[] positions
        ) {
            var texcoords = TexCoords(primitive);

            var vertices = new VertexPositionTexture[positions.Length];

            foreach (var index in indices)
            {
                var position = positions[index];
                var texcoord = texcoords[index];

                vertices[index] = new VertexPositionTexture(
                    position,
                    texcoord
                );
            }

            vertexBuffer.SetData(vertices);
        }
    }
}