/* PatchInfo.cs
 * License: NCSA Open Source License
 * 
 * Copyright: Merijn Hendriks
 * AUTHORS:
 * Basuro
 */


using System;
using System.Collections.Generic;
using System.IO;
using System.Text;

namespace Aki.ByteBanger
{
    public class PatchInfo
    {
        public const string BYBA = "BYBA";
        public byte[] OriginalChecksum { get; set; }
        public int OriginalLength { get; set; }
        public byte[] PatchedChecksum { get; set; }
        public int PatchedLength { get; set; }
        public PatchItem[] Items { get; set; }

        public static PatchInfo FromBytes(byte[] bytes)
        {
            if (bytes.Length < 82) throw new Exception("Input data too short, cannot be a valid patch");

            PatchInfo pi = new PatchInfo();

            using (MemoryStream ms = new MemoryStream(bytes))
            using (BinaryReader br = new BinaryReader(ms))
            {
                byte[] buf = null;

                buf = br.ReadBytes(4);
                if (Encoding.ASCII.GetString(buf) != BYBA) throw new Exception("Invalid identifier");

                if (br.ReadByte() != 1) throw new Exception("Invalid major file version (1 expected)");
                if (br.ReadByte() != 0) throw new Exception("Invalid minor file version (0 expected)");

                pi.OriginalLength = br.ReadInt32();
                pi.OriginalChecksum = br.ReadBytes(32);
                pi.PatchedLength = br.ReadInt32();
                pi.PatchedChecksum = br.ReadBytes(32);

                int itemCount = br.ReadInt32();

                List<PatchItem> items = new List<PatchItem>();
                for (int i = 0; i < itemCount; i++)
                    items.Add(PatchItem.FromReader(br));
                pi.Items = items.ToArray();
            }

            return pi;
        }

        public byte[] ToBytes()
        {
            byte[] data;

            using (MemoryStream ms = new MemoryStream())
            {
                using (BinaryWriter bw = new BinaryWriter(ms, Encoding.ASCII, true))
                {
                    // identifier "BYBA" // 4B
                    byte[] byba = Encoding.ASCII.GetBytes(BYBA);
                    bw.Write(byba, 0, byba.Length);

                    // version "1.0" // 2B
                    bw.Write((byte)1);
                    bw.Write((byte)0);

                    // original len // 4B
                    bw.Write(OriginalLength);

                    // original chk // 32B
                    bw.Write(OriginalChecksum, 0, OriginalChecksum.Length);

                    // patched len // 4B
                    bw.Write(PatchedLength);

                    // patched chk // 32B
                    bw.Write(PatchedChecksum, 0, PatchedChecksum.Length);

                    // item count // 4B
                    bw.Write(Items.Length);

                    // data
                    foreach (PatchItem pi in Items)
                        pi.ToWriter(bw);
                }

                data = new byte[ms.Length];
                ms.Seek(0, SeekOrigin.Begin);
                ms.Read(data, 0, (int)ms.Length);
            }

            return data;
        }
    }
}