// Copyright 2009-2022 Josh Close
// This file is a part of CsvHelper and is dual licensed under MS-PL and Apache 2.0.
// See LICENSE.txt for details or visit http://www.opensource.org/licenses/ms-pl.html for MS-PL and http://opensource.org/licenses/Apache-2.0 for Apache 2.0.
// https://github.com/JoshClose/CsvHelper
using System;
using System.Text;
using CsvHelper.Configuration;

namespace CsvHelper.TypeConversion
{
	/// <summary>
	/// Converts a <see cref="T:Byte[]"/> to and from a <see cref="string"/>.
	/// </summary>
	public class ByteArrayConverter : DefaultTypeConverter
	{
		private readonly ByteArrayConverterOptions options;
		private readonly string HexStringPrefix;
		private readonly byte ByteLength;

		/// <summary>
		/// Creates a new ByteArrayConverter using the given <see cref="ByteArrayConverterOptions"/>.
		/// </summary>
		/// <param name="options">The options.</param>
		public ByteArrayConverter(ByteArrayConverterOptions options = ByteArrayConverterOptions.Hexadecimal | ByteArrayConverterOptions.HexInclude0x)
		{
			// Defaults to the literal format used by C# for whole numbers, and SQL Server for binary data.
			this.options = options;
			ValidateOptions();

			HexStringPrefix = (options & ByteArrayConverterOptions.HexDashes) == ByteArrayConverterOptions.HexDashes ? "-" : string.Empty;
			ByteLength = (options & ByteArrayConverterOptions.HexDashes) == ByteArrayConverterOptions.HexDashes ? (byte)3 : (byte)2;
		}

		/// <summary>
		/// Converts the object to a string.
		/// </summary>
		/// <param name="value">The object to convert to a string.</param>
		/// <param name="row">The <see cref="IWriterRow"/> for the current record.</param>
		/// <param name="memberMapData">The <see cref="MemberMapData"/> for the member being written.</param>
		/// <returns>The string representation of the object.</returns>
		public override string? ConvertToString(object? value, IWriterRow row, MemberMapData memberMapData)
		{
			if (value is byte[] byteArray)
			{
				return (options & ByteArrayConverterOptions.Base64) == ByteArrayConverterOptions.Base64
					? Convert.ToBase64String(byteArray)
					: ByteArrayToHexString(byteArray);
			}

			return base.ConvertToString(value, row, memberMapData);
		}

		/// <summary>
		/// Converts the string to an object.
		/// </summary>
		/// <param name="text">The string to convert to an object.</param>
		/// <param name="row">The <see cref="IReaderRow"/> for the current record.</param>
		/// <param name="memberMapData">The <see cref="MemberMapData"/> for the member being created.</param>
		/// <returns>The object created from the string.</returns>
		public override object? ConvertFromString(string? text, IReaderRow row, MemberMapData memberMapData)
		{
			if (text != null)
			{
				return (options & ByteArrayConverterOptions.Base64) == ByteArrayConverterOptions.Base64
					? Convert.FromBase64String(text)
					: HexStringToByteArray(text);
			}

			return base.ConvertFromString(text, row, memberMapData);
		}

		private string ByteArrayToHexString(byte[] byteArray)
		{
			var hexString = new StringBuilder();

			if ((options & ByteArrayConverterOptions.HexInclude0x) == ByteArrayConverterOptions.HexInclude0x)
			{
				hexString.Append("0x");
			}

			if (byteArray.Length >= 1)
			{
				hexString.Append(byteArray[0].ToString("X2"));
			}

			for (var i = 1; i < byteArray.Length; i++)
			{
				hexString.Append(HexStringPrefix + byteArray[i].ToString("X2"));
			}

			return hexString.ToString();
		}

		private byte[] HexStringToByteArray(string hex)
		{
			var has0x = hex.StartsWith("0x");

			var length = has0x
				? (hex.Length - 1) / ByteLength
				: hex.Length + 1 / ByteLength;
			var byteArray = new byte[length];
			var has0xOffset = has0x ? 1 : 0;

			for (var stringIndex = has0xOffset * 2; stringIndex < hex.Length; stringIndex += ByteLength)
			{
				byteArray[(stringIndex - has0xOffset) / ByteLength] = Convert.ToByte(hex.Substring(stringIndex, 2), 16);
			}

			return byteArray;
		}

		private void ValidateOptions()
		{
			if ((options & ByteArrayConverterOptions.Base64) == ByteArrayConverterOptions.Base64)
			{
				if ((options & (ByteArrayConverterOptions.HexInclude0x | ByteArrayConverterOptions.HexDashes | ByteArrayConverterOptions.Hexadecimal)) != ByteArrayConverterOptions.None)
				{
					throw new ConfigurationException($"{nameof(ByteArrayConverter)} must be configured exclusively with HexDecimal options, or exclusively with Base64 options.  Was {options.ToString()}")
					{
						Data = { { "options", options } }
					};
				}
			}
		}
	}
}