using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Net;
using System.Net.Mail;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using AMWD.Common.Extensions;

namespace System
{
	/// <summary>
	/// String extensions.
	/// </summary>
	public static class StringExtensions
	{
		/// <summary>
		/// Converts a hex string into a byte array.
		/// </summary>
		/// <param name="hexString">The hex encoded string.</param>
		/// <param name="delimiter">A delimiter between the bytes (e.g. for MAC address).</param>
		/// <returns>The bytes.</returns>
		public static IEnumerable<byte> HexToBytes(this string hexString, string delimiter = "")
		{
			if (string.IsNullOrWhiteSpace(hexString))
				yield break;

			string str = string.IsNullOrEmpty(delimiter) ? hexString : hexString.Replace(delimiter, "");
			if (str.Length % 2 == 1)
				yield break;

			if (Regex.IsMatch(str, "[^0-9a-fA-F]"))
				yield break;

			for (int i = 0; i < str.Length; i += 2)
				yield return Convert.ToByte(str.Substring(i, 2), 16);
		}

		/// <summary>
		/// Converts a byte collection into a hex string.
		/// </summary>
		/// <param name="bytes">The bytes.</param>
		/// <param name="delimiter">A delimiter to set between the bytes (e.g. for MAC address).</param>
		/// <returns>The hex encoded string.</returns>
		public static string BytesToHex(this IEnumerable<byte> bytes, string delimiter = "")
		{
			if (bytes?.Any() != true)
				return null;

			return string.Join(delimiter, bytes.Select(b => b.ToString("x2")));
		}

		/// <summary>
		/// Encodes a string to the hexadecimal system (base 16).
		/// </summary>
		/// <param name="str">The string to encode hexadecimal.</param>
		/// <param name="encoding">The text encoding to use (default: <see cref="Encoding.Default"/>)</param>
		/// <returns></returns>
		public static string HexEncode(this string str, Encoding encoding = null)
		{
			if (string.IsNullOrEmpty(str))
				return str;

			return (encoding ?? Encoding.Default).GetBytes(str).BytesToHex();
		}

		/// <summary>
		/// Decodes a string from the hexadecimal system (base 16).
		/// </summary>
		/// <param name="str">The hexadecimal encoded string to decode.</param>
		/// <param name="encoding">The text encoding to use (default: <see cref="Encoding.Default"/>)</param>
		/// <returns></returns>
		public static string HexDecode(this string str, Encoding encoding = null)
		{
			if (string.IsNullOrEmpty(str))
				return str;

			return (encoding ?? Encoding.Default).GetString(str.HexToBytes().ToArray());
		}

		/// <summary>
		/// Encodes a string to base64.
		/// </summary>
		/// <param name="str">The string to encode with base64.</param>
		/// <param name="encoding">The text encoding to use (default: <see cref="Encoding.Default"/>)</param>
		/// <returns></returns>
		public static string Base64Encode(this string str, Encoding encoding = null)
			=> Convert.ToBase64String((encoding ?? Encoding.Default).GetBytes(str));

		/// <summary>
		/// Decodes a string from base64.
		/// </summary>
		/// <param name="str">The base64 encoded string to decode.</param>
		/// <param name="encoding">The text encoding to use (default: <see cref="Encoding.Default"/>)</param>
		/// <returns></returns>
		public static string Base64Decode(this string str, Encoding encoding = null)
			=> (encoding ?? Encoding.Default).GetString(Convert.FromBase64String(str));

		/// <summary>
		/// Replaces the search substring with the replacement when it was found at the beginning of the string.
		/// </summary>
		/// <param name="str">The string.</param>
		/// <param name="search">The searched substring.</param>
		/// <param name="replacement">The replacement.</param>
		/// <returns></returns>
		public static string ReplaceStart(this string str, string search, string replacement)
		{
			if (str.StartsWith(search))
				return replacement + str.Substring(search.Length);

			return str;
		}

		/// <summary>
		/// Replaces the search substring with the replacement when it was found at the end of the string.
		/// </summary>
		/// <param name="str">The string.</param>
		/// <param name="search">The searched substring.</param>
		/// <param name="replacement">The replacement.</param>
		/// <returns></returns>
		public static string ReplaceEnd(this string str, string search, string replacement)
		{
			if (str.EndsWith(search))
				return str.Substring(0, str.Length - search.Length) + replacement;

			return str;
		}

		/// <summary>
		/// Parses a <see cref="string"/> to a <see cref="decimal"/> using culture "de" or invariant.
		/// </summary>
		/// <param name="decString">The string to parse.</param>
		/// <returns></returns>
		public static decimal ParseDecimal(this string decString)
		{
			int dotIndex = decString.LastIndexOf('.');
			int commaIndex = decString.LastIndexOf(',');

			var culture = dotIndex < commaIndex ? new CultureInfo("de-DE") : CultureInfo.InvariantCulture;

			return decimal.Parse(decString, culture);
		}

		/// <summary>
		/// Checks whether the given <see cref="string"/> is a valid <see cref="MailAddress"/>.
		/// </summary>
		/// <remarks>
		/// You can enhance the check by requesting the MX record of the domain.
		/// </remarks>
		/// <param name="email">The email address as string to validate.</param>
		/// <param name="checkForDnsRecord">A value indicating whether to resolve a MX record (Google DNS is used).</param>
		/// <returns><c>true</c> when the email address is valid, other wise <c>false</c>.</returns>
		public static bool IsValidEmailAddress(this string email, bool checkForDnsRecord = false)
			=> email.IsValidEmailAddress(checkForDnsRecord ? new[] { new IPEndPoint(IPAddress.Parse("8.8.8.8"), 53) } : null);

		/// <summary>
		/// Checks whether the given <see cref="string"/> is a valid <see cref="MailAddress"/>.
		/// </summary>
		/// <remarks>
		/// The check is enhanced by a request for MX records on the defined <paramref name="nameservers"/>.
		/// <br/>
		/// The DNS resolution is only used when the DNS NuGet package is available.
		/// See: https://www.nuget.org/packages/DNS/7.0.0
		/// </remarks>
		/// <param name="emailAddress">The email address as string to validate.</param>
		/// <param name="nameservers">A list of <see cref="IPEndPoint"/>s of nameservers.</param>
		/// <returns><c>true</c> when the email address is valid, other wise <c>false</c>.</returns>
		public static bool IsValidEmailAddress(this string emailAddress, IEnumerable<IPEndPoint> nameservers)
		{
			try
			{
				var mailAddress = new MailAddress(emailAddress);
				bool isValid = mailAddress.Address == emailAddress;

				if (isValid && nameservers?.Any() == true)
				{
					var dnsClientType = Type.GetType("DNS.Client.DnsClient, DNS");
					if (dnsClientType == null)
						throw new DllNotFoundException("The DNS NuGet package is required: https://www.nuget.org/packages/DNS/7.0.0");

					var recordTypeType = Type.GetType("DNS.Protocol.RecordType, DNS");
					var resolveMethodInfo = dnsClientType.GetMethod("Resolve", new[] { typeof(string), recordTypeType, typeof(CancellationToken) });

					bool exists = false;
					foreach (var nameserver in nameservers)
					{
						object dnsClient = Activator.CreateInstance(dnsClientType, new object[] { nameserver });

						var waitTask = Task.Run(async () => await resolveMethodInfo.InvokeAsync<object>(dnsClient, new object[] { mailAddress.Host, 15, CancellationToken.None })); // 15 = MX Record
						waitTask.Wait();

						object response = waitTask.Result;
						waitTask.Dispose();

						int responseCode = (int)response.GetType().GetProperty("ResponseCode").GetValue(response);
						if (responseCode != 0)
							continue;

						object list = response.GetType().GetProperty("AnswerRecords").GetValue(response);
						foreach (object item in (list as IEnumerable))
						{
							int type = (int)item.GetType().GetProperty("Type").GetValue(item);
							if (type == 15)
							{
								exists = true;
								break;
							}
						}

						if (exists)
							break;
					}

					isValid &= exists;
				}

				return isValid;
			}
			catch
			{
				return false;
			}
		}

		/// <summary>
		/// Appends a copy of the specified string followed by the specified line terminator
		/// to the end of the current <see cref="StringBuilder"/> object.
		/// </summary>
		/// <param name="sb">The <see cref="StringBuilder"/> object.</param>
		/// <param name="value">The string to append.</param>
		/// <param name="newLine">The line terminator.</param>
		/// <returns></returns>
		public static StringBuilder AppendLine(this StringBuilder sb, string value, string newLine)
			=> sb.Append(value).Append(newLine);
	}
}