using System;
using System.Collections;
using System.Collections.Generic;
using System.Numerics;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Text;

namespace StgSharp.Data
{

    [StructLayout(LayoutKind.Explicit, Size = 16)]
    public struct SSDSegmentHead
    {
        [FieldOffset(0)] internal M128 data;

        [FieldOffset(0)] public int globalID;
        [FieldOffset(4)] public int nextID;


        [FieldOffset(8)] public int previousHash;
        [FieldOffset(12)] internal byte size;
        [FieldOffset(13)] public byte selfDefine_1;
        [FieldOffset(14)] public byte selfDefine_2;
        [FieldOffset(15)] public byte selfDefine_3;

        public int Size
        {
            get { return ((int)size) + 1; }
            set 
            {
                if (value > 256 || value < 0)
                {
                    throw new ArgumentOutOfRangeException();
                }
                size = (byte)(value - 1);
            }
        }

        public unsafe byte[] GetBytes()
        {
            byte[] ret = new byte[16];
            fixed (Vector4* vptr = &data.vec)
            {
                byte* bptr = (byte*)vptr;
                for (int i = 0; i < 15; i++)
                {
                    ret[i] = *bptr;
                }
            }
            return ret;
        }
    }


    public unsafe class SSDrawHead:IEnumerable<int>
    {
        internal SSDSegmentHead _head;

        private List<(int, int)> segmentRange;
        private List<int> freeSegments;
        private string name;

        public SSDrawHead()
        {
            segmentRange = new List<(int, int)>();
            freeSegments = new List<int>();
        }

        internal SSDrawHead(string name)
        {
            int hash;
            this.name = name;
            using (SHA256 sha256Hash = SHA256.Create())
            {
                byte[] bytes = sha256Hash.ComputeHash(Encoding.UTF8.GetBytes(name));

                hash = BitConverter.ToInt32(bytes, 0);
            }
            _head.previousHash = hash;
            segmentRange = new List<(int, int)>();
            freeSegments = new List<int>();
        }

        public void WriteRange(int begin, int end)
        {
            segmentRange.Add((begin, end));
        }

        public void AddSingleSegment(int id)
        {
            freeSegments.Add(id);
        }

        internal void MarkSegment(int id)
        {
            freeSegments.Add(id);
        }

        public unsafe byte[] GetBytes(out int size)
        {
            byte[] namecode = Encoding.UTF8.GetBytes(name);
            size = 16 + 4 +
                segmentRange.Count * 8 +
                freeSegments.Count * 4 +
                namecode.Length;
            byte[] ret = new byte[size];
            fixed (byte* bptr = ret)
            {
                *(SSDSegmentHead*)bptr = _head;
                *(bptr + 16) = (byte)segmentRange.Count;
                *(bptr + 17) = (byte)namecode.Length;
                *(bptr + 18) = (byte)freeSegments.Count;
                int t = 20;
                for (int i = 0; i < segmentRange.Count; i++, t += 8)
                {
                    *(int*)(bptr + t) = segmentRange[i].Item1;
                    *(int*)(bptr + t + 4) = segmentRange[i].Item2;
                }
                for (int i = 0; i < freeSegments.Count; i++, t += 4)
                {
                    *(int*)(bptr + t) = freeSegments[i];
                }
                for (int i = 0; i < namecode.Length; i++, t++)
                {
                    *(bptr + t) = namecode[i];
                }
            }
            return ret;
        }

        IEnumerator<int> IEnumerable<int>.GetEnumerator()
        {
            foreach (var tuple in segmentRange)
            {
                for (int i = tuple.Item1; i <= tuple.Item2; i++)
                {
                    yield return i;
                }
            }

            foreach (var item in freeSegments)
            {
                yield return item;
            }
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            foreach (var tuple in segmentRange)
            {
                for (int i = tuple.Item1; i <= tuple.Item2; i++)
                {
                    yield return i;
                }
            }

            foreach (var item in freeSegments)
            {
                yield return item;
            }
        }
    }

}