using System.IO;
using System.Text;
using BinaryObjectScanner.Models.PAK;
using BinaryObjectScanner.Utilities;
using static BinaryObjectScanner.Models.PAK.Constants;

namespace BinaryObjectScanner.Builders
{
    public static class PAK
    {
        #region Byte Data

        /// <summary>
        /// Parse a byte array into a Half-Life Package
        /// </summary>
        /// <param name="data">Byte array to parse</param>
        /// <param name="offset">Offset into the byte array</param>
        /// <returns>Filled Half-Life Package on success, null on error</returns>
        public static Models.PAK.File ParseFile(byte[] data, int offset)
        {
            // If the data is invalid
            if (data == null)
                return null;

            // If the offset is out of bounds
            if (offset < 0 || offset >= data.Length)
                return null;

            // Create a memory stream and parse that
            MemoryStream dataStream = new MemoryStream(data, offset, data.Length - offset);
            return ParseFile(dataStream);
        }

        #endregion

        #region Stream Data

        /// <summary>
        /// Parse a Stream into a Half-Life Package
        /// </summary>
        /// <param name="data">Stream to parse</param>
        /// <returns>Filled Half-Life Package on success, null on error</returns>
        public static Models.PAK.File ParseFile(Stream data)
        {
            // If the data is invalid
            if (data == null || data.Length == 0 || !data.CanSeek || !data.CanRead)
                return null;

            // If the offset is out of bounds
            if (data.Position < 0 || data.Position >= data.Length)
                return null;

            // Cache the current offset
            long initialOffset = data.Position;

            // Create a new Half-Life Package to fill
            var file = new Models.PAK.File();

            #region Header

            // Try to parse the header
            var header = ParseHeader(data);
            if (header == null)
                return null;

            // Set the package header
            file.Header = header;

            #endregion

            #region Directory Items

            // Get the directory items offset
            uint directoryItemsOffset = header.DirectoryOffset;
            if (directoryItemsOffset < 0 || directoryItemsOffset >= data.Length)
                return null;

            // Seek to the directory items
            data.Seek(directoryItemsOffset, SeekOrigin.Begin);

            // Create the directory item array
            file.DirectoryItems = new DirectoryItem[header.DirectoryLength / 64];

            // Try to parse the directory items
            for (int i = 0; i < file.DirectoryItems.Length; i++)
            {
                var directoryItem = ParseDirectoryItem(data);
                file.DirectoryItems[i] = directoryItem;
            }

            #endregion

            return file;
        }

        /// <summary>
        /// Parse a Stream into a Half-Life Package header
        /// </summary>
        /// <param name="data">Stream to parse</param>
        /// <returns>Filled Half-Life Package header on success, null on error</returns>
        private static Header ParseHeader(Stream data)
        {
            // TODO: Use marshalling here instead of building
            Header header = new Header();

            byte[] signature = data.ReadBytes(4);
            header.Signature = Encoding.ASCII.GetString(signature);
            if (header.Signature != SignatureString)
                return null;

            header.DirectoryOffset = data.ReadUInt32();
            header.DirectoryLength = data.ReadUInt32();

            return header;
        }

        /// <summary>
        /// Parse a Stream into a Half-Life Package directory item
        /// </summary>
        /// <param name="data">Stream to parse</param>
        /// <returns>Filled Half-Life Package directory item on success, null on error</returns>
        private static DirectoryItem ParseDirectoryItem(Stream data)
        {
            // TODO: Use marshalling here instead of building
            DirectoryItem directoryItem = new DirectoryItem();

            byte[] itemName = data.ReadBytes(56);
            directoryItem.ItemName = Encoding.ASCII.GetString(itemName).TrimEnd('\0');
            directoryItem.ItemOffset = data.ReadUInt32();
            directoryItem.ItemLength = data.ReadUInt32();

            return directoryItem;
        }

        #endregion
    }
}