//
// MessageSummary.cs
//
// Author: Jeffrey Stedfast <jestedfa@microsoft.com>
//
// Copyright (c) 2013-2020 .NET Foundation and Contributors
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//

using System;
using System.Linq;
using System.Collections.Generic;

using MimeKit;
using MimeKit.Utils;

namespace MailKit {
	/// <summary>
	/// A summary of a message.
	/// </summary>
	/// <remarks>
	/// <para>The <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a> and
	/// <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a> methods
	/// return lists of <see cref="IMessageSummary"/> items.</para>
	/// <para>The properties of the <see cref="MessageSummary"/> that will be available
	/// depend on the <see cref="MessageSummaryItems"/> passed to the aformentioned method.</para>
	/// </remarks>
	public class MessageSummary : IMessageSummary
	{
		int threadableReplyDepth = -1;
		string normalizedSubject;

		/// <summary>
		/// Initializes a new instance of the <see cref="MailKit.MessageSummary"/> class.
		/// </summary>
		/// <remarks>
		/// Creates a new <see cref="MessageSummary"/>.
		/// </remarks>
		/// <param name="index">The message index.</param>
		/// <exception cref="System.ArgumentOutOfRangeException">
		/// <paramref name="index"/> is negative.
		/// </exception>
		public MessageSummary (int index)
		{
			if (index < 0)
				throw new ArgumentOutOfRangeException (nameof (index));

			Keywords = new HashSet<string> (StringComparer.OrdinalIgnoreCase);
			Index = index;
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="MailKit.MessageSummary"/> class.
		/// </summary>
		/// <remarks>
		/// Creates a new <see cref="MessageSummary"/>.
		/// </remarks>
		/// <param name="folder">The folder that the message belongs to.</param>
		/// <param name="index">The message index.</param>
		/// <exception cref="System.ArgumentNullException">
		/// <paramref name="folder"/> is <c>null</c>.
		/// </exception>
		/// <exception cref="System.ArgumentOutOfRangeException">
		/// <paramref name="index"/> is negative.
		/// </exception>
		public MessageSummary (IMailFolder folder, int index) : this (index)
		{
			if (folder == null)
				throw new ArgumentNullException (nameof (folder));

			Folder = folder;
		}

		void UpdateThreadableSubject ()
		{
			if (normalizedSubject != null)
				return;

			if (Envelope?.Subject != null) {
				normalizedSubject = MessageThreader.GetThreadableSubject (Envelope.Subject, out threadableReplyDepth);
			} else {
				normalizedSubject = string.Empty;
				threadableReplyDepth = 0;
			}
		}

		/// <summary>
		/// Get the folder that the message belongs to.
		/// </summary>
		/// <remarks>
		/// Gets the folder that the message belongs to, if available.
		/// </remarks>
		/// <value>The folder.</value>
		public IMailFolder Folder {
			get; private set;
		}

		/// <summary>
		/// Get a bitmask of fields that have been populated.
		/// </summary>
		/// <remarks>
		/// Gets a bitmask of fields that have been populated.
		/// </remarks>
		/// <value>The fields that have been populated.</value>
		public MessageSummaryItems Fields {
			get; internal set;
		}

		/// <summary>
		/// Gets the body structure of the message, if available.
		/// </summary>
		/// <remarks>
		/// <para>The body will be one of <see cref="BodyPartText"/>,
		/// <see cref="BodyPartMessage"/>, <see cref="BodyPartBasic"/>,
		/// or <see cref="BodyPartMultipart"/>.</para>
		/// <para>This property will only be set if either the
		/// <see cref="MessageSummaryItems.Body"/> flag or the
		/// <see cref="MessageSummaryItems.BodyStructure"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The body structure of the message.</value>
		public BodyPart Body {
			get; set;
		}

		static BodyPart GetMultipartRelatedRoot (BodyPartMultipart related)
		{
			string start = related.ContentType.Parameters["start"];
			string contentId;

			if (start == null)
				return related.BodyParts.Count > 0 ? related.BodyParts[0] : null;

			if ((contentId = MimeUtils.EnumerateReferences (start).FirstOrDefault ()) == null)
				contentId = start;

			var cid = new Uri (string.Format ("cid:{0}", contentId));

			for (int i = 0; i < related.BodyParts.Count; i++) {
				var basic = related.BodyParts[i] as BodyPartBasic;

				if (basic != null && (basic.ContentId == contentId || basic.ContentLocation == cid))
					return basic;

				var multipart = related.BodyParts[i] as BodyPartMultipart;

				if (multipart != null && multipart.ContentLocation == cid)
					return multipart;
			}

			return null;
		}

		static bool TryGetMultipartAlternativeBody (BodyPartMultipart multipart, bool html, out BodyPartText body)
		{
			// walk the multipart/alternative children backwards from greatest level of faithfulness to the least faithful
			for (int i = multipart.BodyParts.Count - 1; i >= 0; i--) {
				var multi = multipart.BodyParts[i] as BodyPartMultipart;
				BodyPartText text = null;

				if (multi != null) {
					if (multi.ContentType.IsMimeType ("multipart", "related")) {
						text = GetMultipartRelatedRoot (multi) as BodyPartText;
					} else if (multi.ContentType.IsMimeType ("multipart", "alternative")) {
						// Note: nested multipart/alternatives make no sense... yet here we are.
						if (TryGetMultipartAlternativeBody (multi, html, out body))
							return true;
					}
				} else {
					text = multipart.BodyParts[i] as BodyPartText;
				}

				if (text != null && (html ? text.IsHtml : text.IsPlain)) {
					body = text;
					return true;
				}
			}

			body = null;

			return false;
		}

		static bool TryGetMessageBody (BodyPartMultipart multipart, bool html, out BodyPartText body)
		{
			BodyPartMultipart multi;
			BodyPartText text;

			if (multipart.ContentType.IsMimeType ("multipart", "alternative"))
				return TryGetMultipartAlternativeBody (multipart, html, out body);

			if (!multipart.ContentType.IsMimeType ("multipart", "related")) {
				// Note: This is probably a multipart/mixed... and if not, we can still treat it like it is.
				for (int i = 0; i < multipart.BodyParts.Count; i++) {
					multi = multipart.BodyParts[i] as BodyPartMultipart;

					// descend into nested multiparts, if there are any...
					if (multi != null) {
						if (TryGetMessageBody (multi, html, out body))
							return true;

						// The text body should never come after a multipart.
						break;
					}

					text = multipart.BodyParts[i] as BodyPartText;

					// Look for the first non-attachment text part (realistically, the body text will
					// preceed any attachments, but I'm not sure we can rely on that assumption).
					if (text != null && !text.IsAttachment) {
						if (html ? text.IsHtml : text.IsPlain) {
							body = text;
							return true;
						}

						// Note: the first text/* part in a multipart/mixed is the text body.
						// If it's not in the format we're looking for, then it doesn't exist.
						break;
					}
				}
			} else {
				// Note: If the multipart/related root document is HTML, then this is the droid we are looking for.
				var root = GetMultipartRelatedRoot (multipart);

				text = root as BodyPartText;

				if (text != null) {
					body = (html ? text.IsHtml : text.IsPlain) ? text : null;
					return body != null;
				}

				// maybe the root is another multipart (like multipart/alternative)?
				multi = root as BodyPartMultipart;

				if (multi != null)
					return TryGetMessageBody (multi, html, out body);
			}

			body = null;

			return false;
		}

		/// <summary>
		/// Gets the text body part of the message if it exists.
		/// </summary>
		/// <remarks>
		/// <para>Gets the <c>text/plain</c> body part of the message.</para>
		/// <para>This property will only be usable if the
		/// <see cref="MessageSummaryItems.BodyStructure"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <example>
		/// <code language="c#" source="Examples\ImapExamples.cs" region="DownloadBodyParts"/>
		/// </example>
		/// <value>The text body if it exists; otherwise, <c>null</c>.</value>
		public BodyPartText TextBody {
			get {
				var multipart = Body as BodyPartMultipart;

				if (multipart != null) {
					BodyPartText plain;

					if (TryGetMessageBody (multipart, false, out plain))
						return plain;
				} else {
					var text = Body as BodyPartText;

					if (text != null && text.IsPlain)
						return text;
				}

				return null;
			}
		}

		/// <summary>
		/// Gets the html body part of the message if it exists.
		/// </summary>
		/// <remarks>
		/// <para>Gets the <c>text/html</c> body part of the message.</para>
		/// <para>This property will only be usable if the
		/// <see cref="MessageSummaryItems.BodyStructure"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The html body if it exists; otherwise, <c>null</c>.</value>
		public BodyPartText HtmlBody {
			get {
				var multipart = Body as BodyPartMultipart;

				if (multipart != null) {
					BodyPartText html;

					if (TryGetMessageBody (multipart, true, out html))
						return html;
				} else {
					var text = Body as BodyPartText;

					if (text != null && text.IsHtml)
						return text;
				}

				return null;
			}
		}

		static IEnumerable<BodyPartBasic> EnumerateBodyParts (BodyPart entity, bool attachmentsOnly)
		{
			if (entity == null)
				yield break;

			var multipart = entity as BodyPartMultipart;

			if (multipart != null) {
				foreach (var subpart in multipart.BodyParts) {
					foreach (var part in EnumerateBodyParts (subpart, attachmentsOnly))
						yield return part;
				}

				yield break;
			}

			var basic = (BodyPartBasic) entity;

			if (attachmentsOnly && !basic.IsAttachment)
				yield break;

			yield return basic;
		}

		/// <summary>
		/// Gets the body parts of the message.
		/// </summary>
		/// <remarks>
		/// <para>Traverses over the <see cref="Body"/>, enumerating all of the
		/// <see cref="BodyPartBasic"/> objects.</para>
		/// <para>This property will only be usable if either the
		/// <see cref="MessageSummaryItems.Body"/> flag or the
		/// <see cref="MessageSummaryItems.BodyStructure"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The body parts.</value>
		public IEnumerable<BodyPartBasic> BodyParts {
			get { return EnumerateBodyParts (Body, false); }
		}

		/// <summary>
		/// Gets the attachments.
		/// </summary>
		/// <remarks>
		/// <para>Traverses over the <see cref="Body"/>, enumerating all of the
		/// <see cref="BodyPartBasic"/> objects that have a <c>Content-Disposition</c>
		/// header set to <c>"attachment"</c>.</para>
		/// <para>This property will only be usable if the
		/// <see cref="MessageSummaryItems.BodyStructure"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <example>
		/// <code language="c#" source="Examples\ImapExamples.cs" region="DownloadBodyParts"/>
		/// </example>
		/// <value>The attachments.</value>
		public IEnumerable<BodyPartBasic> Attachments {
			get { return EnumerateBodyParts (Body, true); }
		}

		/// <summary>
		/// Gets the preview text of the message.
		/// </summary>
		/// <remarks>
		/// <para>The preview text is a short snippet of the beginning of the message
		/// text, typically shown in a mail client's message list to provide the user
		/// with a sense of what the message is about.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.PreviewText"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The preview text.</value>
		public string PreviewText {
			get; set;
		}

		/// <summary>
		/// Gets the envelope of the message, if available.
		/// </summary>
		/// <remarks>
		/// <para>The envelope of a message contains information such as the
		/// date the message was sent, the subject of the message,
		/// the sender of the message, who the message was sent to,
		/// which message(s) the message may be in reply to,
		/// and the message id.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.Envelope"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The envelope of the message.</value>
		public Envelope Envelope {
			get; set;
		}

		/// <summary>
		/// Gets the normalized subject.
		/// </summary>
		/// <remarks>
		/// A normalized Subject header value where prefixes such as
		/// "Re:", "Re[#]:", etc have been pruned.
		/// </remarks>
		/// <value>The normalized subject.</value>
		public string NormalizedSubject {
			get {
				UpdateThreadableSubject ();

				return normalizedSubject;
			}
		}

		/// <summary>
		/// Gets whether or not the message is a reply.
		/// </summary>
		/// <remarks>
		/// This value should be based on whether the message subject contained any "Re:" or "Fwd:" prefixes.
		/// </remarks>
		/// <value><c>true</c> if the message is a reply; otherwise, <c>false</c>.</value>
		public bool IsReply {
			get {
				UpdateThreadableSubject ();

				return threadableReplyDepth != 0;
			}
		}

		/// <summary>
		/// Gets the Date header value.
		/// </summary>
		/// <remarks>
		/// Gets the Date header value. If the Date header is not present, the arrival date is used.
		/// If neither are known, <see cref="System.DateTimeOffset.MinValue"/> is returned.
		/// </remarks>
		/// <value>The date.</value>
		public DateTimeOffset Date {
			get { return Envelope?.Date ?? InternalDate ?? DateTimeOffset.MinValue; }
		}

		/// <summary>
		/// Gets the message flags, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the message flags, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.Flags"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The message flags.</value>
		public MessageFlags? Flags {
			get; set;
		}

		/// <summary>
		/// Gets the user-defined message flags, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the user-defined message flags, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.Flags"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The user-defined message flags.</value>
		public HashSet<string> Keywords {
			get; set;
		}

		/// <summary>
		/// Gets the user-defined message flags, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the user-defined message flags, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.Flags"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The user-defined message flags.</value>
		[Obsolete ("Use Keywords instead.")]
		public HashSet<string> UserFlags {
			get { return Keywords; }
			set { Keywords = value; }
		}

		/// <summary>
		/// Gets the message annotations, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the message annotations, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.Annotations"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The message annotations.</value>
		public IList<Annotation> Annotations {
			get; set;
		}

		/// <summary>
		/// Gets the list of headers, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the list of headers, if available.</para>
		/// <para>This property will only be set if <see cref="MessageSummaryItems.Headers"/>
		/// is specified in a call to one of the
		/// <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods or specific headers are requested via a one of the Fetch or FetchAsync methods
		/// that accept list of specific headers to request for each message such as
		/// <see cref="IMailFolder.Fetch(System.Collections.Generic.IList&lt;UniqueId&gt;,MessageSummaryItems,System.Collections.Generic.IEnumerable&lt;MimeKit.HeaderId&gt;,System.Threading.CancellationToken)"/>.
		/// </para>
		/// </remarks>
		/// <value>The list of headers.</value>
		public HeaderList Headers {
			get; set;
		}

		/// <summary>
		/// Gets the internal date of the message (i.e. the "received" date), if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the internal date of the message (i.e. the "received" date), if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.InternalDate"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The internal date of the message.</value>
		public DateTimeOffset? InternalDate {
			get; set;
		}

		/// <summary>
		/// Gets the size of the message, in bytes, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the size of the message, in bytes, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.Size"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The size of the message.</value>
		public uint? Size {
			get; set;
		}

		/// <summary>
		/// Gets the mod-sequence value for the message, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the mod-sequence value for the message, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.ModSeq"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The mod-sequence value.</value>
		public ulong? ModSeq {
			get; set;
		}

		/// <summary>
		/// Gets the message-ids that the message references, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the message-ids that the message references, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.References"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The references.</value>
		public MessageIdList References {
			get; set;
		}

		/// <summary>
		/// Get the globally unique identifier for the message, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the globally unique identifier of the message, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.EmailId"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// <note type="info">This property maps to the <c>EMAILID</c> value defined in the
		/// <a href="https://tools.ietf.org/html/rfc8474">OBJECTID</a> extension.</note>
		/// </remarks>
		/// <value>The globally unique message identifier.</value>
		public string EmailId {
			get; set;
		}

		/// <summary>
		/// Get the globally unique identifier for the message, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the globally unique identifier of the message, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.EmailId"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// <note type="info">This property maps to the <c>EMAILID</c> value defined in the
		/// <a href="https://tools.ietf.org/html/rfc8474">OBJECTID</a> extension.</note>
		/// </remarks>
		/// <value>The globally unique message identifier.</value>
		[Obsolete ("Use EmailId instead.")]
		public string Id {
			get { return EmailId; }
		}

		/// <summary>
		/// Get the globally unique thread identifier for the message, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the globally unique thread identifier for the message, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.ThreadId"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// <note type="info">This property maps to the <c>THREADID</c> value defined in the
		/// <a href="https://tools.ietf.org/html/rfc8474">OBJECTID</a> extension.</note>
		/// </remarks>
		/// <value>The globally unique thread identifier.</value>
		public string ThreadId {
			get; set;
		}

		/// <summary>
		/// Gets the unique identifier of the message, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the unique identifier of the message, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.UniqueId"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The uid of the message.</value>
		public UniqueId UniqueId {
			get; set;
		}

		/// <summary>
		/// Gets the index of the message.
		/// </summary>
		/// <remarks>
		/// <para>Gets the index of the message.</para>
		/// <para>This property is always set.</para>
		/// </remarks>
		/// <value>The index of the message.</value>
		public int Index {
			get; internal set;
		}

		#region GMail extension properties

		/// <summary>
		/// Gets the GMail message identifier, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the GMail message identifier, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.GMailMessageId"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The GMail message identifier.</value>
		public ulong? GMailMessageId {
			get; set;
		}

		/// <summary>
		/// Gets the GMail thread identifier, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the GMail thread identifier, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.GMailThreadId"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The GMail thread identifier.</value>
		public ulong? GMailThreadId {
			get; set;
		}

		/// <summary>
		/// Gets the list of GMail labels, if available.
		/// </summary>
		/// <remarks>
		/// <para>Gets the list of GMail labels, if available.</para>
		/// <para>This property will only be set if the
		/// <see cref="MessageSummaryItems.GMailLabels"/> flag is passed to
		/// one of the <a href="Overload_MailKit_IMailFolder_Fetch.htm">Fetch</a>
		/// or <a href="Overload_MailKit_IMailFolder_FetchAsync.htm">FetchAsync</a>
		/// methods.</para>
		/// </remarks>
		/// <value>The GMail labels.</value>
		public IList<string> GMailLabels {
			get; set;
		}

		#endregion
	}
}