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

namespace SongCore.Arcache
{
    public class Lz4ArchiveReader : Lz4ArchiveBase
    {
        public Dictionary<string, Lz4ArchiveEntry> Entries { get; }
        private readonly byte[] _blob;

        public Lz4ArchiveReader(string pathAndBaseName, bool readBlobToMemory) : base(pathAndBaseName)
        {
            //read entries
            var entries = new List<Lz4ArchiveEntry>();

            var bufLz4 = File.ReadAllBytes(IndexFilePath);
            var bufRaw = DecompressPickle(bufLz4);
            using (var fs = new MemoryStream(bufRaw))
            {
                while (fs.Position < fs.Length)
                {
                    var entry = new Lz4ArchiveEntry();
                    entry.ReadFromStream(fs);
                    entries.Add(entry);
                }
            }

            Entries = entries.ToDictionary(p => p.FileName);
            //open file / or read all into memory
            if (readBlobToMemory)
            {
                _blob = File.ReadAllBytes(BlobFilePath);
            }
        }

        private byte[] FetchData(long offset, long size)
        {
            byte[] buf;
            if (_blob != null)
            {
                buf = new byte[size];
                Buffer.BlockCopy(_blob, (int)offset, buf, 0, (int)size);
            }
            else
            {
                using var fs = File.OpenRead(BlobFilePath);
                fs.Position = offset;
                using var br = new BinaryReader(fs);
                buf = br.ReadBytes((int)size);
            }

            return buf;
        }

        public byte[] ReadData(Lz4ArchiveEntry entry)
        {
            var compressed = FetchData(entry.Offset, entry.CompressedSize);
            var data = Decompress(compressed, (int)entry.OriginalSize);
            return data;
        }

        public string ReadText(Lz4ArchiveEntry entry, Encoding encoding)
        {
            var data = ReadData(entry);
            return encoding.GetString(data);
        }
    }
}