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using System;
using System.Collections.Generic;
using System.Linq;
using System.Security;
using Microsoft.Win32;

namespace Cyotek.AzureContainerEcho
{
  internal static class MimeHelpers
  {
    #region Constants

    private static readonly IDictionary<string, string> _mimeTypeExtensionCache;

    private static readonly object _lock = new object();

    #endregion

    #region Static Constructors

    static MimeHelpers()
    {
      _mimeTypeExtensionCache = new Dictionary<string, string>(StringComparer.InvariantCultureIgnoreCase);
    }

    #endregion

    #region Class Members

    public static string GetDefaultExtension(string mimeType)
    {
      string result;

      if (!_mimeTypeExtensionCache.TryGetValue(mimeType, out result))
      {
        try
        {
          RegistryKey key;
          object value;

          key = Registry.ClassesRoot.OpenSubKey(@"MIME\Database\Content Type\" + mimeType, false);
          if (key != null)
          {
            value = key.GetValue("Extension", null);
            result = value != null ? value.ToString() : null;
          }
          else
          {
            // HACK: Nasty
            foreach (string name in Registry.ClassesRoot.GetSubKeyNames().Where(name => name[0] == '.'))
            {
              try
              {
                key = Registry.ClassesRoot.OpenSubKey(name, false);
              }
              catch (SecurityException)
              {
                key = null;
              }

              if (key != null)
              {
                value = key.GetValue("Content Type", null);
                if (value != null && value.ToString() == mimeType)
                {
                  result = name;
                  break;
                }
              }
            }
          }
        }
        catch (SecurityException)
        {
          result = null;
        }

        lock (_lock)
        {
          if (!_mimeTypeExtensionCache.ContainsKey(mimeType))
            _mimeTypeExtensionCache.Add(mimeType, result);
        }
      }

      return result;
    }

    public static string GetMimeType(string contentType)
    {
      string result;

      if (contentType == null)
        contentType = string.Empty;

      if (contentType.Contains(";"))
      {
        // TODO: Assume first or check all?
        result = contentType.Split(new[]
        {
          ";"
        }, StringSplitOptions.RemoveEmptyEntries)[0];
      }
      else
        result = contentType;

      return result.ToLowerInvariant().Trim();
    }

    public static string GetMimeTypeFromExtension(string extension)
    {
      string result;
      RegistryKey key;
      object value;

      if (!extension.StartsWith("."))
        extension = "." + extension;

      key = Registry.ClassesRoot.OpenSubKey(extension, false);
      value = key != null ? key.GetValue("Content Type", null) : null;
      result = value != null ? value.ToString() : null;

      return result;
    }

    public static string GetPerceivedType(string mimeType)
    {
      string result;
      string extension;

      extension = GetDefaultExtension(mimeType);
      if (!string.IsNullOrEmpty(extension))
      {
        RegistryKey key;
        object value;

        key = Registry.ClassesRoot.OpenSubKey(extension, false);
        value = key != null ? key.GetValue("PerceivedType", null) : null;
        result = value != null ? value.ToString() : null;
      }
      else
        result = null;

      return result;
    }

    #endregion
  }
}