using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using MailKit;
using MailKit.Net.Imap;
using MailKit.Search;
using MoreLinq;
using Serilog;
using Wino.Core.Domain.Entities.Mail;
using Wino.Core.Domain.Interfaces;
using Wino.Core.Domain.Models.MailItem;
using Wino.Services.Extensions;
using IMailService = Wino.Core.Domain.Interfaces.IMailService;

namespace Wino.Core.Synchronizers.ImapSync
{
    public abstract class ImapSynchronizationStrategyBase : IImapSynchronizerStrategy
    {
        // Minimum summary items to Fetch for mail synchronization from IMAP.
        protected readonly MessageSummaryItems MailSynchronizationFlags =
            MessageSummaryItems.Flags |
            MessageSummaryItems.UniqueId |
            MessageSummaryItems.ThreadId |
            MessageSummaryItems.EmailId |
            MessageSummaryItems.Headers |
            MessageSummaryItems.PreviewText |
            MessageSummaryItems.GMailThreadId |
            MessageSummaryItems.References |
            MessageSummaryItems.ModSeq;

        protected IFolderService FolderService { get; }
        protected IMailService MailService { get; }
        protected MailItemFolder Folder { get; set; }

        protected ImapSynchronizationStrategyBase(IFolderService folderService, IMailService mailService)
        {
            FolderService = folderService;
            MailService = mailService;
        }

        public abstract Task<List<string>> HandleSynchronizationAsync(IImapClient client, MailItemFolder folder, IImapSynchronizer synchronizer, CancellationToken cancellationToken = default);
        internal abstract Task<IList<UniqueId>> GetChangedUidsAsync(IImapClient client, IMailFolder remoteFolder, IImapSynchronizer synchronizer, CancellationToken cancellationToken = default);

        protected async Task<List<string>> HandleChangedUIdsAsync(IImapSynchronizer synchronizer, IMailFolder remoteFolder, IList<UniqueId> changedUids, CancellationToken cancellationToken)
        {
            List<string> downloadedMessageIds = new();

            var existingMails = await MailService.GetExistingMailsAsync(Folder.Id, changedUids).ConfigureAwait(false);
            var existingMailUids = existingMails.Select(m => MailkitClientExtensions.ResolveUidStruct(m.Id)).ToArray();

            // These are the non-existing mails. They will be downloaded + processed.
            var newMessageIds = changedUids.Except(existingMailUids).ToList();
            var deletedMessageIds = existingMailUids.Except(changedUids).ToList();

            // Fetch minimum data for the existing mails in one query.
            var existingFlagData = await remoteFolder.FetchAsync(existingMailUids, MessageSummaryItems.Flags | MessageSummaryItems.UniqueId).ConfigureAwait(false);

            foreach (var update in existingFlagData)
            {
                if (update.UniqueId == null)
                {
                    Log.Warning($"Couldn't fetch UniqueId for the mail. FetchAsync failed.");
                    continue;
                }

                if (update.Flags == null)
                {
                    Log.Warning($"Couldn't fetch flags for the mail with UID {update.UniqueId.Id}. FetchAsync failed.");
                    continue;
                }

                var existingMail = existingMails.FirstOrDefault(m => MailkitClientExtensions.ResolveUidStruct(m.Id).Id == update.UniqueId.Id);

                if (existingMail == null)
                {
                    Log.Warning($"Couldn't find the mail with UID {update.UniqueId.Id} in the local database. Flag update is ignored.");
                    continue;
                }

                await HandleMessageFlagsChangeAsync(existingMail, update.Flags.Value).ConfigureAwait(false);
            }

            // Fetch the new mails in batch.

            var batchedMessageIds = newMessageIds.Batch(50);

            foreach (var group in batchedMessageIds)
            {
                var summaries = await remoteFolder.FetchAsync(group, MailSynchronizationFlags, cancellationToken).ConfigureAwait(false);

                foreach (var summary in summaries)
                {
                    var mimeMessage = await remoteFolder.GetMessageAsync(summary.UniqueId, cancellationToken).ConfigureAwait(false);

                    var creationPackage = new ImapMessageCreationPackage(summary, mimeMessage);

                    var mailPackages = await synchronizer.CreateNewMailPackagesAsync(creationPackage, Folder, cancellationToken).ConfigureAwait(false);

                    if (mailPackages != null)
                    {
                        foreach (var package in mailPackages)
                        {
                            // Local draft is mapped. We don't need to create a new mail copy.
                            if (package == null) continue;

                            bool isCreatedNew = await MailService.CreateMailAsync(Folder.MailAccountId, package).ConfigureAwait(false);

                            // This is upsert. We are not interested in updated mails.
                            if (isCreatedNew) downloadedMessageIds.Add(package.Copy.Id);
                        }
                    }
                }
            }


            return downloadedMessageIds;
        }

        protected async Task HandleMessageFlagsChangeAsync(UniqueId? uniqueId, MessageFlags flags)
        {
            if (Folder == null) return;
            if (uniqueId == null) return;

            var localMailCopyId = MailkitClientExtensions.CreateUid(Folder.Id, uniqueId.Value.Id);

            var isFlagged = MailkitClientExtensions.GetIsFlagged(flags);
            var isRead = MailkitClientExtensions.GetIsRead(flags);

            await MailService.ChangeReadStatusAsync(localMailCopyId, isRead).ConfigureAwait(false);
            await MailService.ChangeFlagStatusAsync(localMailCopyId, isFlagged).ConfigureAwait(false);
        }

        protected async Task HandleMessageFlagsChangeAsync(MailCopy mailCopy, MessageFlags flags)
        {
            if (mailCopy == null) return;

            var isFlagged = MailkitClientExtensions.GetIsFlagged(flags);
            var isRead = MailkitClientExtensions.GetIsRead(flags);

            if (isFlagged != mailCopy.IsFlagged)
            {
                await MailService.ChangeFlagStatusAsync(mailCopy.Id, isFlagged).ConfigureAwait(false);
            }

            if (isRead != mailCopy.IsRead)
            {
                await MailService.ChangeReadStatusAsync(mailCopy.Id, isRead).ConfigureAwait(false);
            }
        }

        protected async Task HandleMessageDeletedAsync(IList<UniqueId> uniqueIds)
        {
            if (Folder == null) return;
            if (uniqueIds == null || uniqueIds.Count == 0) return;

            foreach (var uniqueId in uniqueIds)
            {
                if (uniqueId == null) continue;
                var localMailCopyId = MailkitClientExtensions.CreateUid(Folder.Id, uniqueId.Id);

                await MailService.DeleteMailAsync(Folder.MailAccountId, localMailCopyId).ConfigureAwait(false);
            }
        }

        protected void OnMessagesVanished(object sender, MessagesVanishedEventArgs args)
            => HandleMessageDeletedAsync(args.UniqueIds).ConfigureAwait(false);

        protected void OnMessageFlagsChanged(object sender, MessageFlagsChangedEventArgs args)
            => HandleMessageFlagsChangeAsync(args.UniqueId, args.Flags).ConfigureAwait(false);

        protected async Task ManageUUIdBasedDeletedMessagesAsync(MailItemFolder localFolder, IMailFolder remoteFolder, CancellationToken cancellationToken = default)
        {
            var allUids = (await FolderService.GetKnownUidsForFolderAsync(localFolder.Id)).Select(a => new UniqueId(a)).ToList();

            if (allUids.Count > 0)
            {
                var remoteAllUids = await remoteFolder.SearchAsync(SearchQuery.All, cancellationToken);
                var deletedUids = allUids.Except(remoteAllUids).ToList();

                await HandleMessageDeletedAsync(deletedUids).ConfigureAwait(false);
            }
        }
    }
}