using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using CommunityToolkit.Mvvm.Messaging;
using MailKit;
using MailKit.Net.Imap;
using MoreLinq;
using Serilog;
using Wino.Core.Domain;
using Wino.Core.Domain.Entities.Mail;
using Wino.Core.Domain.Entities.Shared;
using Wino.Core.Domain.Enums;
using Wino.Core.Domain.Interfaces;
using Wino.Core.Domain.Models.Accounts;
using Wino.Core.Domain.Models.MailItem;
using Wino.Core.Domain.Models.Synchronization;
using Wino.Core.Requests.Bundles;
using Wino.Core.Requests.Folder;
using Wino.Core.Requests.Mail;
using Wino.Messaging.UI;

namespace Wino.Core.Synchronizers
{
    public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEventType> : BaseSynchronizer<TBaseRequest>, IWinoSynchronizerBase
    {
        protected bool IsDisposing { get; private set; }

        protected Dictionary<MailSynchronizationOptions, CancellationTokenSource> PendingSynchronizationRequest = new();

        protected ILogger Logger = Log.ForContext<WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEventType>>();

        protected WinoSynchronizer(MailAccount account) : base(account) { }

        /// <summary>
        /// How many items per single HTTP call can be modified.
        /// </summary>
        public abstract uint BatchModificationSize { get; }

        /// <summary>
        /// How many items must be downloaded per folder when the folder is first synchronized.
        /// </summary>
        public abstract uint InitialMessageDownloadCountPerFolder { get; }

        /// <summary>
        /// Creates a new Wino Mail Item package out of native message type with full Mime.
        /// </summary>
        /// <param name="message">Native message type for the synchronizer.</param>
        /// <param name="cancellationToken">Cancellation token</param>
        /// <returns>Package that encapsulates downloaded Mime and additional information for adding new mail.</returns>
        public abstract Task<List<NewMailItemPackage>> CreateNewMailPackagesAsync(TMessageType message, MailItemFolder assignedFolder, CancellationToken cancellationToken = default);

        /// <summary>
        /// Refreshes the aliases of the account.
        /// Only available for Gmail right now.
        /// </summary>
        protected virtual Task SynchronizeAliasesAsync() => Task.CompletedTask;

        /// <summary>
        /// Internally synchronizes the account's mails with the given options.
        /// Not exposed and overriden for each synchronizer.
        /// </summary>
        /// <param name="options">Synchronization options.</param>
        /// <param name="cancellationToken">Cancellation token.</param>
        /// <returns>Synchronization result that contains summary of the sync.</returns>
        protected abstract Task<MailSynchronizationResult> SynchronizeMailsInternalAsync(MailSynchronizationOptions options, CancellationToken cancellationToken = default);

        /// <summary>
        /// Internally synchronizes the events of the account with given options.
        /// Not exposed and overriden for each synchronizer.
        /// </summary>
        /// <param name="options">Synchronization options.</param>
        /// <param name="cancellationToken">Cancellation token.</param>
        /// <returns>Synchronization result that contains summary of the sync.</returns>
        protected abstract Task<CalendarSynchronizationResult> SynchronizeCalendarEventsInternalAsync(CalendarSynchronizationOptions options, CancellationToken cancellationToken = default);

        /// <summary>
        /// Batches network requests, executes them, and does the needed synchronization after the batch request execution.
        /// </summary>
        /// <param name="options">Synchronization options.</param>
        /// <param name="cancellationToken">Cancellation token.</param>
        /// <returns>Synchronization result that contains summary of the sync.</returns>
        public async Task<MailSynchronizationResult> SynchronizeMailsAsync(MailSynchronizationOptions options, CancellationToken cancellationToken = default)
        {
            try
            {
                if (!ShouldQueueMailSynchronization(options))
                {
                    Log.Debug($"{options.Type} synchronization is ignored.");
                    return MailSynchronizationResult.Canceled;
                }

                var newCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);

                PendingSynchronizationRequest.Add(options, newCancellationTokenSource);
                activeSynchronizationCancellationToken = newCancellationTokenSource.Token;

                await synchronizationSemaphore.WaitAsync(activeSynchronizationCancellationToken);

                PublishSynchronizationProgress(1);

                // ImapSynchronizer will send this type when an Idle client receives a notification of changes.
                // We should not execute requests in this case.
                bool shouldExecuteRequests = options.Type != MailSynchronizationType.IMAPIdle;

                bool shouldDelayExecution = false;
                int maxExecutionDelay = 0;

                if (shouldExecuteRequests && changeRequestQueue.Any())
                {
                    State = AccountSynchronizerState.ExecutingRequests;

                    List<IRequestBundle<TBaseRequest>> nativeRequests = new();

                    List<IRequestBase> requestCopies = new(changeRequestQueue);

                    var keys = changeRequestQueue.GroupBy(a => a.GroupingKey());

                    foreach (var group in keys)
                    {
                        var key = group.Key;

                        if (key is MailSynchronizerOperation mailSynchronizerOperation)
                        {
                            switch (mailSynchronizerOperation)
                            {
                                case MailSynchronizerOperation.MarkRead:
                                    nativeRequests.AddRange(MarkRead(new BatchMarkReadRequest(group.Cast<MarkReadRequest>())));
                                    break;
                                case MailSynchronizerOperation.Move:
                                    nativeRequests.AddRange(Move(new BatchMoveRequest(group.Cast<MoveRequest>())));
                                    break;
                                case MailSynchronizerOperation.Delete:
                                    nativeRequests.AddRange(Delete(new BatchDeleteRequest(group.Cast<DeleteRequest>())));
                                    break;
                                case MailSynchronizerOperation.CreateDraft:
                                    nativeRequests.AddRange(CreateDraft(group.ElementAt(0) as CreateDraftRequest));
                                    break;
                                case MailSynchronizerOperation.Send:
                                    nativeRequests.AddRange(SendDraft(group.ElementAt(0) as SendDraftRequest));
                                    break;
                                case MailSynchronizerOperation.ChangeFlag:
                                    nativeRequests.AddRange(ChangeFlag(new BatchChangeFlagRequest(group.Cast<ChangeFlagRequest>())));
                                    break;
                                case MailSynchronizerOperation.AlwaysMoveTo:
                                    nativeRequests.AddRange(AlwaysMoveTo(new BatchAlwaysMoveToRequest(group.Cast<AlwaysMoveToRequest>())));
                                    break;
                                case MailSynchronizerOperation.MoveToFocused:
                                    nativeRequests.AddRange(MoveToFocused(new BatchMoveToFocusedRequest(group.Cast<MoveToFocusedRequest>())));
                                    break;
                                case MailSynchronizerOperation.Archive:
                                    nativeRequests.AddRange(Archive(new BatchArchiveRequest(group.Cast<ArchiveRequest>())));
                                    break;
                                default:
                                    break;
                            }
                        }
                        else if (key is FolderSynchronizerOperation folderSynchronizerOperation)
                        {
                            switch (folderSynchronizerOperation)
                            {
                                case FolderSynchronizerOperation.RenameFolder:
                                    nativeRequests.AddRange(RenameFolder(group.ElementAt(0) as RenameFolderRequest));
                                    break;
                                case FolderSynchronizerOperation.EmptyFolder:
                                    nativeRequests.AddRange(EmptyFolder(group.ElementAt(0) as EmptyFolderRequest));
                                    break;
                                case FolderSynchronizerOperation.MarkFolderRead:
                                    nativeRequests.AddRange(MarkFolderAsRead(group.ElementAt(0) as MarkFolderAsReadRequest));
                                    break;
                                default:
                                    break;
                            }
                        }
                    }

                    changeRequestQueue.Clear();

                    Console.WriteLine($"Prepared {nativeRequests.Count()} native requests");

                    await ExecuteNativeRequestsAsync(nativeRequests, activeSynchronizationCancellationToken).ConfigureAwait(false);

                    PublishUnreadItemChanges();

                    // Execute request sync options should be re-calculated after execution.
                    // This is the part we decide which individual folders must be synchronized
                    // after the batch request execution.
                    if (options.Type == MailSynchronizationType.ExecuteRequests)
                        options = GetSynchronizationOptionsAfterRequestExecution(requestCopies, options.Id);

                    // Let servers to finish their job. Sometimes the servers doesn't respond immediately.
                    // Bug: if Outlook can't create the message in Sent Items folder before this delay,
                    // message will not appear in user's inbox since it's not in the Sent Items folder.

                    shouldDelayExecution =
                        (Account.ProviderType == MailProviderType.Outlook)
                        && requestCopies.Any(a => a.ResynchronizationDelay > 0);

                    if (shouldDelayExecution)
                    {
                        maxExecutionDelay = requestCopies.Aggregate(0, (max, next) => Math.Max(max, next.ResynchronizationDelay));
                    }

                    // In terms of flag/read changes, there is no point of synchronizing must have folders.
                    options.ExcludeMustHaveFolders = requestCopies.All(a => a is ICustomFolderSynchronizationRequest request && request.ExcludeMustHaveFolders);
                }

                State = AccountSynchronizerState.Synchronizing;

                // Handle special synchronization types.

                // Profile information sync.
                if (options.Type == MailSynchronizationType.UpdateProfile)
                {
                    if (!Account.IsProfileInfoSyncSupported) return MailSynchronizationResult.Empty;

                    ProfileInformation newProfileInformation = null;

                    try
                    {
                        newProfileInformation = await SynchronizeProfileInformationInternalAsync();
                    }
                    catch (Exception ex)
                    {
                        Log.Error(ex, "Failed to update profile information for {Name}", Account.Name);

                        return MailSynchronizationResult.Failed;
                    }

                    return MailSynchronizationResult.Completed(newProfileInformation);
                }

                // Alias sync.
                if (options.Type == MailSynchronizationType.Alias)
                {
                    if (!Account.IsAliasSyncSupported) return MailSynchronizationResult.Empty;

                    try
                    {
                        await SynchronizeAliasesAsync();

                        return MailSynchronizationResult.Empty;
                    }
                    catch (Exception ex)
                    {
                        Log.Error(ex, "Failed to update aliases for {Name}", Account.Name);

                        return MailSynchronizationResult.Failed;
                    }
                }

                if (shouldDelayExecution)
                {
                    await Task.Delay(maxExecutionDelay);
                }

                // Start the internal synchronization.
                var synchronizationResult = await SynchronizeMailsInternalAsync(options, activeSynchronizationCancellationToken).ConfigureAwait(false);

                PublishUnreadItemChanges();

                return synchronizationResult;
            }
            catch (OperationCanceledException)
            {
                Logger.Warning("Synchronization canceled.");

                return MailSynchronizationResult.Canceled;
            }
            catch (Exception ex)
            {
                Logger.Error(ex, "Synchronization failed for {Name}", Account.Name);

                throw;
            }
            finally
            {
                // Find the request and remove it from the pending list.

                var pendingRequest = PendingSynchronizationRequest.FirstOrDefault(a => a.Key.Id == options.Id);

                if (pendingRequest.Key != null)
                {
                    PendingSynchronizationRequest.Remove(pendingRequest.Key);
                }

                // Reset account progress to hide the progress.
                PublishSynchronizationProgress(0);

                State = AccountSynchronizerState.Idle;
                synchronizationSemaphore.Release();
            }
        }

        /// <summary>
        /// Batches network requests, executes them, and does the needed synchronization after the batch request execution.
        /// </summary>
        /// <param name="options">Synchronization options.</param>
        /// <param name="cancellationToken">Cancellation token.</param>
        /// <returns>Synchronization result that contains summary of the sync.</returns>
        public Task<CalendarSynchronizationResult> SynchronizeCalendarEventsAsync(CalendarSynchronizationOptions options, CancellationToken cancellationToken = default)
        {
            // TODO: Execute requests for calendar events.
            return SynchronizeCalendarEventsInternalAsync(options, cancellationToken);
        }

        /// <summary>
        /// Updates unread item counts for some folders and account.
        /// Sends a message that shell can pick up and update the UI.
        /// </summary>
        private void PublishUnreadItemChanges()
            => WeakReferenceMessenger.Default.Send(new RefreshUnreadCountsMessage(Account.Id));

        /// <summary>
        /// Sends a message to the shell to update the synchronization progress.
        /// </summary>
        /// <param name="progress">Percentage of the progress.</param>
        public void PublishSynchronizationProgress(double progress)
            => WeakReferenceMessenger.Default.Send(new AccountSynchronizationProgressUpdatedMessage(Account.Id, progress));

        /// <summary>
        /// Attempts to find out the best possible synchronization options after the batch request execution.
        /// </summary>
        /// <param name="batches">Batch requests to run in synchronization.</param>
        /// <returns>New synchronization options with minimal HTTP effort.</returns>
        private MailSynchronizationOptions GetSynchronizationOptionsAfterRequestExecution(List<IRequestBase> requests, Guid existingSynchronizationId)
        {
            List<Guid> synchronizationFolderIds = requests
                    .Where(a => a is ICustomFolderSynchronizationRequest)
                    .Cast<ICustomFolderSynchronizationRequest>()
                    .SelectMany(a => a.SynchronizationFolderIds)
                    .ToList();

            var options = new MailSynchronizationOptions()
            {
                AccountId = Account.Id,
            };

            options.Id = existingSynchronizationId;

            if (synchronizationFolderIds.Count > 0)
            {
                // Gather FolderIds to synchronize.

                options.Type = MailSynchronizationType.CustomFolders;
                options.SynchronizationFolderIds = synchronizationFolderIds;
            }
            else
            {
                // At this point it's a mix of everything. Do full sync.
                options.Type = MailSynchronizationType.FullFolders;
            }

            return options;
        }

        /// <summary>
        /// Checks if the mail synchronization should be queued or not.
        /// </summary>
        /// <param name="options">New mail sync request.</param>
        /// <returns>Whether sync should be queued or not.</returns>
        private bool ShouldQueueMailSynchronization(MailSynchronizationOptions options)
        {
            // Multiple IMAPIdle requests are ignored.
            if (options.Type == MailSynchronizationType.IMAPIdle &&
                PendingSynchronizationRequest.Any(a => a.Key.Type == MailSynchronizationType.IMAPIdle))
            {
                return false;
            }

            // Executing requests may trigger idle sync.
            // If there are pending execute requests cancel idle change.

            // TODO: Ideally this check should only work for Inbox execute requests.
            // Check if request folders contains Inbox.

            if (options.Type == MailSynchronizationType.IMAPIdle &&
                PendingSynchronizationRequest.Any(a => a.Key.Type == MailSynchronizationType.ExecuteRequests))
            {
                return false;
            }

            return true;
        }

        #region Mail/Folder Operations

        public virtual bool DelaySendOperationSynchronization() => false;
        public virtual List<IRequestBundle<TBaseRequest>> Move(BatchMoveRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> ChangeFlag(BatchChangeFlagRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> MarkRead(BatchMarkReadRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> Delete(BatchDeleteRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> AlwaysMoveTo(BatchAlwaysMoveToRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> MoveToFocused(BatchMoveToFocusedRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> CreateDraft(CreateDraftRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> SendDraft(SendDraftRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> Archive(BatchArchiveRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> RenameFolder(RenameFolderRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> EmptyFolder(EmptyFolderRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
        public virtual List<IRequestBundle<TBaseRequest>> MarkFolderAsRead(MarkFolderAsReadRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));

        #endregion

        #region Calendar Operations


        #endregion


        /// <summary>
        /// Downloads a single missing message from synchronizer and saves it to given FileId from IMailItem.
        /// </summary>
        /// <param name="mailItem">Mail item that its mime file does not exist on the disk.</param>
        /// <param name="transferProgress">Optional download progress for IMAP synchronizer.</param>
        /// <param name="cancellationToken">Cancellation token.</param>
        public virtual Task DownloadMissingMimeMessageAsync(IMailItem mailItem, ITransferProgress transferProgress = null, CancellationToken cancellationToken = default) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));

        public List<IRequestBundle<ImapRequest>> CreateSingleTaskBundle(Func<IImapClient, IRequestBase, Task> action, IRequestBase request, IUIChangeRequest uIChangeRequest)
        {
            return [new ImapRequestBundle(new ImapRequest(action, request), request, uIChangeRequest)];
        }

        public List<IRequestBundle<ImapRequest>> CreateTaskBundle<TSingeRequestType>(Func<IImapClient, TSingeRequestType, Task> value,
            List<TSingeRequestType> requests)
            where TSingeRequestType : IRequestBase, IUIChangeRequest
        {
            List<IRequestBundle<ImapRequest>> ret = [];

            foreach (var request in requests)
            {
                ret.Add(new ImapRequestBundle(new ImapRequest<TSingeRequestType>(value, request), request, request));
            }

            return ret;
        }

        public virtual Task KillSynchronizerAsync()
        {
            IsDisposing = true;
            CancelAllSynchronizations();

            return Task.CompletedTask;
        }

        protected void CancelAllSynchronizations()
        {
            foreach (var request in PendingSynchronizationRequest)
            {
                request.Value.Cancel();
                request.Value.Dispose();
            }
        }
    }
}