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

namespace DiskAccessLibrary
{
    public class BddInfo
    {
        public const int BlockIndexEntrySize = 8;

        public string BasedImagePath { get; }
        public string SnapshotImagePath { get; }

        public long Length { get; }

        public int BlockSize { get; }
        public int NumberOfBlocks { get; }

        public long DataOffset { get; }

        public long EntryTableOffset { get; }

        public BlockEntryAllocateFlagIndexer Allocated { get; }

        public BlockEntryOffsetIndexer Offset { get; set; }

        public IReadOnlyList<ulong> Entries { get; }

        public BddInfo(string snapshotImagePath, bool readEntries = true)
        {
            SnapshotImagePath = snapshotImagePath;
            using var fs = new FileStream(snapshotImagePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
            using var reader = new BinaryReader(fs);

            int basedPathLength = reader.ReadUInt16(); //2
            if (basedPathLength != 0) BasedImagePath = Encoding.UTF8.GetString(reader.ReadBytes(basedPathLength)); //N
            BlockSize = reader.ReadInt32(); //4
            NumberOfBlocks = reader.ReadInt32(); //4

            var snapMatchLength = NumberOfBlocks * (long)BlockSize;
            Length = snapMatchLength;

            if (false == readEntries) return;
            if (null != BasedImagePath)
            {
                if (false == File.Exists(BasedImagePath)) throw new FileNotFoundException("based image not found", BasedImagePath);
                using var ms = new FileStream(BasedImagePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                if (snapMatchLength != ms.Length) throw new InvalidDataException("Snapshot size no match to based image");
            }

            EntryTableOffset = fs.Position;

            var arr = new ulong[NumberOfBlocks];
            for (var i = 0; i < NumberOfBlocks; i++)
            {
                arr[i] = reader.ReadUInt64();
            }

            Entries = arr;
            DataOffset = fs.Position;

            Allocated = new BlockEntryAllocateFlagIndexer(arr);
            Offset = new BlockEntryOffsetIndexer(arr);
        }

        public static int CalcHeaderSize(string basedImagePath, int blockSize, out int blocks)
        {
            var baseLength = new FileInfo(basedImagePath).Length;
            blocks = (int)(baseLength / blockSize);

            return 2 + Encoding.UTF8.GetByteCount(basedImagePath) + 8 + blocks * BlockIndexEntrySize;
        }

        public static int CalcHeaderSize(long baseLength, int blockSize, out int blocks)
        {
            blocks = (int)(baseLength / blockSize);

            return 2 + +8 + blocks * BlockIndexEntrySize;
        }
    }
}