using System;
using System.Buffers.Binary;
using System.Collections.Generic;
using System.IO;
using Wabbajack.Common;

namespace Compression.BSA
{
    public class FolderRecord : IFolder
    {
        internal readonly BSAReader BSA;
        private readonly ReadOnlyMemorySlice<byte> _data;
        internal Lazy<FileRecord[]> _files = null!;
        private int _prevFileCount;
        internal FileNameBlock FileNameBlock = null!;
        internal int Index { get; }
        public string? Name { get; private set; }

        public IEnumerable<IFile> Files => _files.Value;

        internal FolderRecord(BSAReader bsa, ReadOnlyMemorySlice<byte> data, int index)
        {
            BSA = bsa;
            _data = data;
            Index = index;
        }

        private bool IsLongform => BSA.HeaderType == VersionType.SSE;

        public ulong Hash => BinaryPrimitives.ReadUInt64LittleEndian(_data);

        public int FileCount => checked((int)BinaryPrimitives.ReadUInt32LittleEndian(_data.Slice(0x8)));

        public uint Unknown => IsLongform ?
            BinaryPrimitives.ReadUInt32LittleEndian(_data.Slice(0xC)) : 
            0;

        public ulong Offset => IsLongform ?
            BinaryPrimitives.ReadUInt64LittleEndian(_data.Slice(0x10)) : 
            BinaryPrimitives.ReadUInt32LittleEndian(_data.Slice(0xC));

        public static int HeaderLength(VersionType version)
        {
            return version switch
            {
                VersionType.SSE => 0x18,
                _ => 0x10,
            };
        }

        internal void ProcessFileRecordHeadersBlock(BinaryReader rdr, int fileCountTally)
        {
            _prevFileCount = fileCountTally;
            var totalFileLen = checked((int)(FileCount * FileRecord.HeaderLength));

            ReadOnlyMemorySlice<byte> data;
            if (BSA.HasFolderNames)
            {
                var len = rdr.ReadByte();
                data = rdr.ReadBytes(len + totalFileLen);
                Name = data.Slice(0, len).ReadStringTerm(BSA.HeaderType);
                data = data.Slice(len);
            }
            else
            {
                data = rdr.ReadBytes(totalFileLen);
            }

            _files = new Lazy<FileRecord[]>(
                isThreadSafe: true,
                valueFactory: () => ParseFileRecords(data));
        }

        private FileRecord[] ParseFileRecords(ReadOnlyMemorySlice<byte> data)
        {
            var fileCount = FileCount;
            var ret = new FileRecord[fileCount];
            for (var idx = 0; idx < fileCount; idx += 1)
            {
                var fileData = data.Slice(idx * FileRecord.HeaderLength, FileRecord.HeaderLength);
                ret[idx] = new FileRecord(this, fileData, idx, idx + _prevFileCount, FileNameBlock);
            }
            return ret;
        }
    }
}