using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using MailKit;
using MailKit.Net.Imap;
using MailKit.Search;
using Wino.Core.Domain.Entities.Mail;
using Wino.Core.Domain.Exceptions;
using Wino.Core.Domain.Interfaces;
using Wino.Core.Integration;
using IMailService = Wino.Core.Domain.Interfaces.IMailService;

namespace Wino.Core.Synchronizers.ImapSync
{
    /// <summary>
    /// RFC 5162 QRESYNC IMAP Synchronization strategy.
    /// </summary>
    internal class QResyncSynchronizer : ImapSynchronizationStrategyBase
    {
        public QResyncSynchronizer(IFolderService folderService, IMailService mailService) : base(folderService, mailService)
        {
        }

        public override async Task<List<string>> HandleSynchronizationAsync(IImapClient client,
                                                                            MailItemFolder folder,
                                                                            IImapSynchronizer synchronizer,
                                                                            CancellationToken cancellationToken = default)
        {
            var downloadedMessageIds = new List<string>();

            if (client is not WinoImapClient winoClient)
                throw new ImapSynchronizerStrategyException("Client must be of type WinoImapClient.");

            if (!client.Capabilities.HasFlag(ImapCapabilities.QuickResync))
                throw new ImapSynchronizerStrategyException("Server does not support QRESYNC.");

            if (!winoClient.IsQResyncEnabled)
                throw new ImapSynchronizerStrategyException("QRESYNC is not enabled for WinoImapClient.");

            // Ready to implement QRESYNC synchronization.

            IMailFolder remoteFolder = null;

            Folder = folder;

            try
            {
                remoteFolder = await client.GetFolderAsync(folder.RemoteFolderId, cancellationToken).ConfigureAwait(false);

                // Check the Uid validity first.
                // If they don't match, clear all the local data and perform full-resync.

                bool isCacheValid = remoteFolder.UidValidity == folder.UidValidity;

                if (!isCacheValid)
                {
                    // TODO: Remove all local data.
                }

                // Perform QRESYNC synchronization.
                var localHighestModSeq = (ulong)folder.HighestModeSeq;

                remoteFolder.MessagesVanished += OnMessagesVanished;
                remoteFolder.MessageFlagsChanged += OnMessageFlagsChanged;

                var allUids = await FolderService.GetKnownUidsForFolderAsync(folder.Id);
                var allUniqueIds = allUids.Select(a => new UniqueId(a)).ToList();

                await remoteFolder.OpenAsync(FolderAccess.ReadOnly, folder.UidValidity, localHighestModSeq, allUniqueIds).ConfigureAwait(false);

                var changedUids = await GetChangedUidsAsync(client, remoteFolder, synchronizer, cancellationToken).ConfigureAwait(false);

                downloadedMessageIds = await HandleChangedUIdsAsync(synchronizer, remoteFolder, changedUids, cancellationToken).ConfigureAwait(false);

                // Update the local folder with the new highest mod-seq and validity.
                folder.HighestModeSeq = unchecked((long)remoteFolder.HighestModSeq);
                folder.UidValidity = remoteFolder.UidValidity;

                await ManageUUIdBasedDeletedMessagesAsync(folder, remoteFolder, cancellationToken).ConfigureAwait(false);

                await FolderService.UpdateFolderAsync(folder).ConfigureAwait(false);
            }
            catch (FolderNotFoundException)
            {
                await FolderService.DeleteFolderAsync(folder.MailAccountId, folder.RemoteFolderId).ConfigureAwait(false);

                return default;
            }
            catch (Exception)
            {
                throw;
            }
            finally
            {
                if (!cancellationToken.IsCancellationRequested)
                {
                    if (remoteFolder != null)
                    {
                        remoteFolder.MessagesVanished -= OnMessagesVanished;
                        remoteFolder.MessageFlagsChanged -= OnMessageFlagsChanged;

                        if (remoteFolder.IsOpen)
                        {
                            await remoteFolder.CloseAsync();
                        }
                    }
                }
            }

            return downloadedMessageIds;
        }

        internal override async Task<IList<UniqueId>> GetChangedUidsAsync(IImapClient client, IMailFolder remoteFolder, IImapSynchronizer synchronizer, CancellationToken cancellationToken = default)
        {
            var localHighestModSeq = (ulong)Folder.HighestModeSeq;
            return await remoteFolder.SearchAsync(SearchQuery.ChangedSince(localHighestModSeq), cancellationToken).ConfigureAwait(false);
        }
    }
}