using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using Lumina.Data.Parsing;

namespace Penumbra.GameData.Files;

public partial class MdlFile
{
    private static uint Write( BinaryWriter w, string s, long basePos )
    {
        var currentPos = w.BaseStream.Position;
        w.Write( Encoding.UTF8.GetBytes( s ) );
        w.Write( ( byte )0 );
        return ( uint )( currentPos - basePos );
    }

    private List< uint > WriteStrings( BinaryWriter w )
    {
        var startPos = ( int )w.BaseStream.Position;
        var basePos  = startPos + 8;
        var count    = ( ushort )( Attributes.Length + Bones.Length + Materials.Length + Shapes.Length );

        w.Write( count );
        w.Seek( basePos, SeekOrigin.Begin );
        var ret = Attributes.Concat( Bones )
           .Concat( Materials )
           .Concat( Shapes.Select( s => s.ShapeName ) )
           .Select( attribute => Write( w, attribute, basePos ) ).ToList();

        w.Write( ( ushort )0 ); // Seems to always have two additional null-bytes, not padding.
        var size = ( int )w.BaseStream.Position - basePos;
        w.Seek( startPos                        + 4, SeekOrigin.Begin );
        w.Write( ( uint )size );
        w.Seek( basePos + size, SeekOrigin.Begin );
        return ret;
    }

    private void WriteModelFileHeader( BinaryWriter w, uint runtimeSize )
    {
        w.Write( Version );
        w.Write( StackSize );
        w.Write( runtimeSize );
        w.Write( ( ushort )VertexDeclarations.Length );
        w.Write( ( ushort )Materials.Length );
        w.Write( VertexOffset[ 0 ] > 0 ? VertexOffset[ 0 ] + runtimeSize : 0u );
        w.Write( VertexOffset[ 1 ] > 0 ? VertexOffset[ 1 ] + runtimeSize : 0u );
        w.Write( VertexOffset[ 2 ] > 0 ? VertexOffset[ 2 ] + runtimeSize : 0u );
        w.Write( IndexOffset[ 0 ]  > 0 ? IndexOffset[ 0 ]  + runtimeSize : 0u );
        w.Write( IndexOffset[ 1 ]  > 0 ? IndexOffset[ 1 ]  + runtimeSize : 0u );
        w.Write( IndexOffset[ 2 ]  > 0 ? IndexOffset[ 2 ]  + runtimeSize : 0u );
        w.Write( VertexBufferSize[ 0 ] );
        w.Write( VertexBufferSize[ 1 ] );
        w.Write( VertexBufferSize[ 2 ] );
        w.Write( IndexBufferSize[ 0 ] );
        w.Write( IndexBufferSize[ 1 ] );
        w.Write( IndexBufferSize[ 2 ] );
        w.Write( LodCount );
        w.Write( EnableIndexBufferStreaming );
        w.Write( EnableEdgeGeometry );
        w.Write( ( byte )0 ); // Padding
    }

    private void WriteModelHeader( BinaryWriter w )
    {
        w.Write( Radius );
        w.Write( ( ushort )Meshes.Length );
        w.Write( ( ushort )Attributes.Length );
        w.Write( ( ushort )SubMeshes.Length );
        w.Write( ( ushort )Materials.Length );
        w.Write( ( ushort )Bones.Length );
        w.Write( ( ushort )BoneTables.Length );
        w.Write( ( ushort )Shapes.Length );
        w.Write( ( ushort )ShapeMeshes.Length );
        w.Write( ( ushort )ShapeValues.Length );
        w.Write( LodCount );
        w.Write( ( byte )Flags1 );
        w.Write( ( ushort )ElementIds.Length );
        w.Write( ( byte )TerrainShadowMeshes.Length );
        w.Write( ( byte )Flags2 );
        w.Write( ModelClipOutDistance );
        w.Write( ShadowClipOutDistance );
        w.Write( Unknown4 );
        w.Write( ( ushort )TerrainShadowSubMeshes.Length );
        w.Write( Unknown5 );
        w.Write( BgChangeMaterialIndex );
        w.Write( BgCrestChangeMaterialIndex );
        w.Write( Unknown6 );
        w.Write( Unknown7 );
        w.Write( Unknown8 );
        w.Write( Unknown9 );
        w.Write( ( uint )0 ); // 6 byte padding
        w.Write( ( ushort )0 );
    }


    private static void Write( BinaryWriter w, in MdlStructs.VertexElement vertex )
    {
        w.Write( vertex.Stream );
        w.Write( vertex.Offset );
        w.Write( vertex.Type );
        w.Write( vertex.Usage );
        w.Write( vertex.UsageIndex );
        w.Write( ( ushort )0 ); // 3 byte padding
        w.Write( ( byte )0 );
    }

    private static void Write( BinaryWriter w, in MdlStructs.VertexDeclarationStruct vertexDecl )
    {
        foreach( var vertex in vertexDecl.VertexElements )
        {
            Write( w, vertex );
        }

        Write( w, new MdlStructs.VertexElement() { Stream = 255 } );
        w.Seek( ( int )( NumVertices - 1 - vertexDecl.VertexElements.Length ) * 8, SeekOrigin.Current );
    }

    private static void Write( BinaryWriter w, in MdlStructs.ElementIdStruct elementId )
    {
        w.Write( elementId.ElementId );
        w.Write( elementId.ParentBoneName );
        w.Write( elementId.Translate[ 0 ] );
        w.Write( elementId.Translate[ 1 ] );
        w.Write( elementId.Translate[ 2 ] );
        w.Write( elementId.Rotate[ 0 ] );
        w.Write( elementId.Rotate[ 1 ] );
        w.Write( elementId.Rotate[ 2 ] );
    }

    private static unsafe void Write< T >( BinaryWriter w, in T data ) where T : unmanaged
    {
        fixed( T* ptr = &data )
        {
            var bytePtr = ( byte* )ptr;
            var size    = sizeof( T );
            var span    = new ReadOnlySpan< byte >( bytePtr, size );
            w.Write( span );
        }
    }

    private static void Write( BinaryWriter w, MdlStructs.MeshStruct mesh )
    {
        w.Write( mesh.VertexCount );
        w.Write( ( ushort )0 ); // padding
        w.Write( mesh.IndexCount );
        w.Write( mesh.MaterialIndex );
        w.Write( mesh.SubMeshIndex );
        w.Write( mesh.SubMeshCount );
        w.Write( mesh.BoneTableIndex );
        w.Write( mesh.StartIndex );
        w.Write( mesh.VertexBufferOffset[ 0 ] );
        w.Write( mesh.VertexBufferOffset[ 1 ] );
        w.Write( mesh.VertexBufferOffset[ 2 ] );
        w.Write( mesh.VertexBufferStride[ 0 ] );
        w.Write( mesh.VertexBufferStride[ 1 ] );
        w.Write( mesh.VertexBufferStride[ 2 ] );
        w.Write( mesh.VertexStreamCount );
    }

    private static void Write( BinaryWriter w, MdlStructs.BoneTableStruct bone )
    {
        foreach( var index in bone.BoneIndex )
        {
            w.Write( index );
        }

        w.Write( bone.BoneCount );
        w.Write( ( ushort )0 ); // 3 bytes padding
        w.Write( ( byte )0 );
    }

    private void Write( BinaryWriter w, int shapeIdx, IReadOnlyList< uint > offsets )
    {
        var shape  = Shapes[ shapeIdx ];
        var offset = offsets[ Attributes.Length + Bones.Length + Materials.Length + shapeIdx ];
        w.Write( offset );
        w.Write( shape.ShapeMeshStartIndex[ 0 ] );
        w.Write( shape.ShapeMeshStartIndex[ 1 ] );
        w.Write( shape.ShapeMeshStartIndex[ 2 ] );
        w.Write( shape.ShapeMeshCount[ 0 ] );
        w.Write( shape.ShapeMeshCount[ 1 ] );
        w.Write( shape.ShapeMeshCount[ 2 ] );
    }

    private static void Write( BinaryWriter w, MdlStructs.BoundingBoxStruct box )
    {
        w.Write( box.Min[ 0 ] );
        w.Write( box.Min[ 1 ] );
        w.Write( box.Min[ 2 ] );
        w.Write( box.Min[ 3 ] );
        w.Write( box.Max[ 0 ] );
        w.Write( box.Max[ 1 ] );
        w.Write( box.Max[ 2 ] );
        w.Write( box.Max[ 3 ] );
    }

    public byte[] Write()
    {
        using var stream = new MemoryStream();
        using( var w = new BinaryWriter( stream ) )
        {
            // Skip and write this later when we actually know it.
            w.Seek( ( int )FileHeaderSize, SeekOrigin.Begin );

            foreach( var vertexDecl in VertexDeclarations )
            {
                Write( w, vertexDecl );
            }

            var offsets = WriteStrings( w );
            WriteModelHeader( w );

            foreach( var elementId in ElementIds )
            {
                Write( w, elementId );
            }

            foreach( var lod in Lods )
            {
                Write( w, lod );
            }

            if( Flags2.HasFlag( MdlStructs.ModelFlags2.ExtraLodEnabled ) )
            {
                foreach( var extraLod in ExtraLods )
                {
                    Write( w, extraLod );
                }
            }

            foreach( var mesh in Meshes )
            {
                Write( w, mesh );
            }

            for( var i = 0; i < Attributes.Length; ++i )
            {
                w.Write( offsets[ i ] );
            }

            foreach( var terrainShadowMesh in TerrainShadowMeshes )
            {
                Write( w, terrainShadowMesh );
            }

            foreach( var subMesh in SubMeshes )
            {
                Write( w, subMesh );
            }

            foreach( var terrainShadowSubMesh in TerrainShadowSubMeshes )
            {
                Write( w, terrainShadowSubMesh );
            }

            for( var i = 0; i < Materials.Length; ++i )
            {
                w.Write( offsets[ Attributes.Length + Bones.Length + i ] );
            }

            for( var i = 0; i < Bones.Length; ++i )
            {
                w.Write( offsets[ Attributes.Length + i ] );
            }

            foreach( var boneTable in BoneTables )
            {
                Write( w, boneTable );
            }

            for( var i = 0; i < Shapes.Length; ++i )
            {
                Write( w, i, offsets );
            }

            foreach( var shapeMesh in ShapeMeshes )
            {
                Write( w, shapeMesh );
            }

            foreach( var shapeValue in ShapeValues )
            {
                Write( w, shapeValue );
            }

            w.Write( SubMeshBoneMap.Length * 2 );
            foreach( var bone in SubMeshBoneMap )
            {
                w.Write( bone );
            }

            w.Write( ( byte )0 ); // number of padding bytes, which is 0 for us.

            Write( w, BoundingBoxes );
            Write( w, ModelBoundingBoxes );
            Write( w, WaterBoundingBoxes );
            Write( w, VerticalFogBoundingBoxes );
            foreach( var box in BoneBoundingBoxes )
            {
                Write( w, box );
            }

            var totalSize   = w.BaseStream.Position;
            var runtimeSize = ( uint )( totalSize - StackSize - FileHeaderSize );
            w.Write( RemainingData );

            // Write header data.
            w.Seek( 0, SeekOrigin.Begin );
            WriteModelFileHeader( w, runtimeSize );
        }

        return stream.ToArray();
    }
}