using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using UnityEngine;

public class AliasModel
{
    private static readonly Regex AnimationRegex = new Regex(@"^[a-zA-Z]+");

    private readonly string name;
    private readonly QAliasFrameType frameType;
    private readonly List<(int, Mesh)> animationMeshes = new List<(int, Mesh)>();

    public string Name => name;

    public AliasModel(string name, QAliasFrameType frameType)
    {
        this.name = name;
        this.frameType = frameType;
    }
    
    public int GetAnimationFrameCount(float frameNum)
    {
        if (!FindAnimation((int)frameNum, out Mesh mesh, out int startFrame))
            return 0;

        if (mesh.blendShapeCount == 0)
            return 1;

        return mesh.GetBlendShapeFrameCount(0);
    }

    public void Animate(float frameNum, out Mesh mesh, out float blendWeight)
    {
        blendWeight = 0;
        
        int frameIndex = (int)frameNum;
        if (!FindAnimation(frameIndex, out mesh, out int startFrame))
            return;

        if (mesh.blendShapeCount == 0)
            return;

        int numFrames = mesh.GetBlendShapeFrameCount(0);
        blendWeight = ((frameNum - startFrame) / numFrames) % 1;
    }

    private bool FindAnimation(int frameIndex, out Mesh mesh, out int startFrame)
    {
        mesh = null;
        startFrame = 0;
        
        for (int i = 0; i < animationMeshes.Count; ++i)
        {
            startFrame = animationMeshes[i].Item1;
            if (frameIndex >= startFrame)
            {
                mesh = animationMeshes[i].Item2;
                return true;
            }
        }

        return false;   // Shouldn't happen
    }

    public void Dispose()
    {
        foreach (var mesh in animationMeshes)
        {
            UnityEngine.Object.Destroy(mesh.Item2);
        }
        
        animationMeshes.Clear();
    }

    public void ImportMeshData(QAliasHeader header, QTriVertex[][] poseVertices, QTriangle[] triangles, QSTVert[] stVertices)
    {
        // Massage the input data for easier conversion
        PreprocessMeshData(header, triangles, ref poseVertices, ref stVertices);
        
        // Triangle indices and UVs are the same for all animation frames
        ConvertTriangles(triangles, out var indices);
        ConvertUVs(stVertices, header.skinWidth, header.skinHeight, out var uvs);

        // Identify animation sequences and turn each one into a separate Mesh with a single blend shape animation
        if (frameType == QAliasFrameType.Single)
            ImportSingleFrameAnimations(header, poseVertices, indices, uvs);
        else
            ImportGroupFrameAnimations(header, poseVertices, indices, uvs);
    }

    private void ImportSingleFrameAnimations(QAliasHeader header, QTriVertex[][] poseVertices, ushort[] indices, Vector2[] uvs)
    {
        Mesh mesh;
        string animName = null;
        int startFrame = 0;
        for (int frameIdx = 0; frameIdx < header.numFrames; ++frameIdx)
        {
            // Individual sequences are identified by their prefix
            string frameName = AnimationRegex.Match(header.frames[frameIdx].name).Value;
            if (animName == null)
            {
                animName = frameName;
                continue;
            }

            if (frameName != animName)
            {
                // New animation sequence; convert the previous sequence into a blend shape animation
                mesh = CreateAnimatedMesh(header, poseVertices, indices, uvs, $"{name}_{animName}", startFrame, frameIdx);
                animationMeshes.Add((startFrame, mesh));
                
                animName = frameName;
                startFrame = frameIdx;
            }
        }
        
        // Convert the final (or only) sequence into a blend shape animation
        mesh = CreateAnimatedMesh(header, poseVertices, indices, uvs, $"{name}_{animName}", startFrame, header.numFrames);
        animationMeshes.Add((startFrame, mesh));
    }

    private void ImportGroupFrameAnimations(QAliasHeader header, QTriVertex[][] poseVertices, ushort[] indices, Vector2[] uvs)
    {
        for (int frameIdx = 0; frameIdx < header.numFrames; ++frameIdx)
        {
            var frame = header.frames[frameIdx];
            Mesh mesh = CreateAnimatedMesh(header, poseVertices, indices, uvs, $"{name}_{frameIdx}", 
                frame.firstPose, frame.firstPose + frame.numPoses);
            
            animationMeshes.Add((frame.firstPose, mesh));
        }
    }
    
    /// <summary>
    /// Quake has a bit of a weird outdated mesh setup where skin textures are split into a front side and a back side.
    /// Vertices on the seam between the front and back are used by triangles on both sides, but require a correction
    /// to their UVs when rendering the backside. To handle this properly, we duplicate these vertices and correct the
    /// UVs ahead of time. We do this as a separate pre-process step to keep things simple. 
    /// </summary>
    private static void PreprocessMeshData(QAliasHeader header, QTriangle[] triangles, 
        ref QTriVertex[][] poseVertices, ref QSTVert[] stVerts)
    {
        HashSet<int> seamVertices = new HashSet<int>();
        
        // First count how many new vertices we need to make, so we can preallocate the required arrays
        for (int triIdx = 0; triIdx < header.numTriangles; ++triIdx)
        {
            if (triangles[triIdx].facesFront != 0)
                continue;

            for (int indIdx = 0; indIdx < 3; ++indIdx)
            {
                int vertIndex = triangles[triIdx].vertIndex[indIdx];
                if (stVerts[vertIndex].onSeam == 0)
                    continue;
                
                // Back-side vertex on seam, needs to be duplicated and corrected
                seamVertices.Add(vertIndex);
            }
        }
        
        if (seamVertices.Count == 0)
            return;
        
        Array.Resize(ref stVerts, header.numVerts + seamVertices.Count);
        for (int frameIdx = 0; frameIdx < header.numPoses; ++frameIdx)
        {
            Array.Resize(ref poseVertices[frameIdx], header.numVerts + seamVertices.Count);
        }

        Dictionary<int, int> vertexCopies = new Dictionary<int, int>();
        int newVertIndex = header.numVerts;

        // Now we go over all the triangles again and duplicate the vertices that are on a seam
        for (int triIdx = 0; triIdx < header.numTriangles; ++triIdx)
        {
            if (triangles[triIdx].facesFront != 0)
                continue;

            for (int indIdx = 0; indIdx < 3; ++indIdx)
            {
                int vertIndex = triangles[triIdx].vertIndex[indIdx];
                if (stVerts[vertIndex].onSeam == 0)
                    continue;

                if (vertexCopies.ContainsKey(vertIndex))
                {
                    // We've already duplicated this vertex before
                    triangles[triIdx].vertIndex[indIdx] = vertexCopies[vertIndex];
                    continue;
                }

                // Clone the ST value and correct it to map onto the backside of the skin
                QSTVert stVertCopy = stVerts[vertIndex];
                stVertCopy.s += header.skinWidth / 2;
                stVerts[newVertIndex] = stVertCopy;

                // Clone the vertex position data for all frames
                for (int frameIdx = 0; frameIdx < header.numPoses; ++frameIdx)
                {
                    QTriVertex triVertCopy = poseVertices[frameIdx][vertIndex];
                    poseVertices[frameIdx][newVertIndex] = triVertCopy;
                }

                triangles[triIdx].vertIndex[indIdx] = newVertIndex;
                vertexCopies.Add(vertIndex, newVertIndex++);
            }
        }

        header.numVerts = newVertIndex;
    }
    
    private static void ConvertVertices(QAliasHeader header, QTriVertex[] triVerts, out Vector3[] vertices, out Vector3[] normals)
    {
        int numVerts = triVerts.Length;
        vertices = new Vector3[numVerts];
        normals = new Vector3[numVerts];

        Vector3 scale = header.scale.ToVector3();
        Vector3 origin = header.scaleOrigin.ToVector3();
        
        for (int i = 0; i < numVerts; ++i)
        {
            vertices[i] = (Vector3.Scale(triVerts[i].ToVector3(), scale) + origin).ToUnity();
            normals[i] = QLightNormals.Get(triVerts[i].lightNormalIndex).ToUnity();
        }
    }

    private static void ConvertTriangles(QTriangle[] triangles, out ushort[] indices)
    {
        int numTris = triangles.Length;
        indices = new ushort[numTris * 3];
        
        for (int i = 0; i < numTris; ++i)
        {
            indices[i * 3 + 0] = (ushort)triangles[i].vertIndex[0];
            indices[i * 3 + 1] = (ushort)triangles[i].vertIndex[1];
            indices[i * 3 + 2] = (ushort)triangles[i].vertIndex[2];
        }
    }

    private static void ConvertUVs(QSTVert[] stVerts, int skinWidth, int skinHeight, out Vector2[] uvs)
    {
        int numVerts = stVerts.Length;
        uvs = new Vector2[numVerts];

        Vector2 scale = new Vector2(1.0f / skinWidth, 1.0f / skinHeight);
        
        for (int i = 0; i < numVerts; ++i)
        {
            uvs[i] = Vector2.Scale(new Vector2(stVerts[i].s, stVerts[i].t), scale);
        }
    }

    private static Mesh CreateAnimatedMesh(
        QAliasHeader header, QTriVertex[][] poseVertices, ushort[] indices, Vector2[] uvs,
        string animationName, int startPose, int endPose)
    {
        ConvertVertices(header, poseVertices[startPose], out var baseVertices, out var baseNormals);
        
        var mesh = new Mesh { name = animationName };
        mesh.SetVertices(baseVertices);
        mesh.SetNormals(baseNormals);

        if (endPose - startPose > 1)
        {
            CreateBlendShapes(mesh, animationName, baseVertices, baseNormals, header, poseVertices, startPose, endPose);
        }

        mesh.SetIndices(indices, MeshTopology.Triangles, 0, false);
        mesh.SetUVs(0, uvs);
        mesh.Optimize();
        mesh.RecalculateBounds();
        mesh.UploadMeshData(true);
        return mesh;
    }

    private static void CreateBlendShapes(
        Mesh mesh, string animName, Vector3[] baseVertices, Vector3[] baseNormals,
        QAliasHeader header, QTriVertex[][] poseVertices, int startPose, int endPose)
    {
        var deltaVertices = new Vector3[header.numVerts];
        var deltaNormals = new Vector3[header.numVerts];
        
        Vector3 scale = header.scale.ToVector3();
        Vector3 origin = header.scaleOrigin.ToVector3();
        
        int numPoses = endPose - startPose;
        
        // Repeat the first pose at the end, so we can smoothly animate the entire cycle and loop the animation without any breaks.
        for (int index = 1; index <= numPoses; ++index)
        {
            int poseIdx = startPose + index % numPoses;
            var poseVerts = poseVertices[poseIdx];
            
            for (int vertIdx = 0; vertIdx < header.numVerts; ++vertIdx)
            {
                Vector3 vert = (Vector3.Scale(poseVerts[vertIdx].ToVector3(), scale) + origin).ToUnity();
                deltaVertices[vertIdx] = vert - baseVertices[vertIdx];
                deltaNormals[vertIdx] = QLightNormals.Get(poseVerts[vertIdx].lightNormalIndex).ToUnity() - baseNormals[vertIdx];
            }
            
            mesh.AddBlendShapeFrame(animName, (float)index / numPoses, deltaVertices, deltaNormals, null);
        }
    }
}