Wino-Mail/Wino.Services/Threading/ImapThreadingStrategy.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using SqlKata;
using Wino.Core.Domain.Entities.Mail;
using Wino.Core.Domain.Enums;
using Wino.Core.Domain.Interfaces;
using Wino.Core.Domain.Models.Folders;
using Wino.Core.Domain.Models.MailItem;
using Wino.Services.Extensions;

namespace Wino.Services.Threading;

public class ImapThreadingStrategy : BaseDatabaseService, IImapThreadingStrategy
{
    private readonly IFolderService _folderService;

    public ImapThreadingStrategy(IDatabaseService databaseService, IFolderService folderService) : base(databaseService)
    {
        _folderService = folderService;
    }

    private Task<MailCopy> GetReplyParentAsync(IMailItem replyItem, Guid accountId, Guid threadingFolderId, Guid sentFolderId, Guid draftFolderId)
    {
        if (string.IsNullOrEmpty(replyItem?.MessageId)) return Task.FromResult<MailCopy>(null);

        var query = new Query("MailCopy")
            .Distinct()
            .Take(1)
            .Join("MailItemFolder", "MailItemFolder.Id", "MailCopy.FolderId")
            .Where("MailItemFolder.MailAccountId", accountId)
            .WhereIn("MailItemFolder.Id", new List<Guid> { threadingFolderId, sentFolderId, draftFolderId })
            .Where("MailCopy.MessageId", replyItem.InReplyTo)
            .WhereNot("MailCopy.Id", replyItem.Id)
            .Select("MailCopy.*");

        return Connection.FindWithQueryAsync<MailCopy>(query.GetRawQuery());
    }

    private Task<MailCopy> GetInReplyToReplyAsync(IMailItem originalItem, Guid accountId, Guid threadingFolderId, Guid sentFolderId, Guid draftFolderId)
    {
        if (string.IsNullOrEmpty(originalItem?.MessageId)) return Task.FromResult<MailCopy>(null);

        var query = new Query("MailCopy")
            .Distinct()
            .Take(1)
            .Join("MailItemFolder", "MailItemFolder.Id", "MailCopy.FolderId")
            .WhereNot("MailCopy.Id", originalItem.Id)
            .Where("MailItemFolder.MailAccountId", accountId)
            .Where("MailCopy.InReplyTo", originalItem.MessageId)
            .WhereIn("MailItemFolder.Id", new List<Guid> { threadingFolderId, sentFolderId, draftFolderId })
            .Select("MailCopy.*");

        var raq = query.GetRawQuery();

        return Connection.FindWithQueryAsync<MailCopy>(query.GetRawQuery());
    }

    public async Task<List<IMailItem>> ThreadItemsAsync(List<MailCopy> items, IMailItemFolder threadingForFolder)
    {
        var threads = new List<ThreadMailItem>();

        var account = items.First().AssignedAccount;
        var accountId = account.Id;

        // Child -> Parent approach.

        var mailLookupTable = new Dictionary<string, bool>();

        // Fill up the mail lookup table to prevent double thread creation.
        foreach (var mail in items)
            if (!mailLookupTable.ContainsKey(mail.Id))
                mailLookupTable.Add(mail.Id, false);

        var sentFolder = await _folderService.GetSpecialFolderByAccountIdAsync(accountId, SpecialFolderType.Sent);
        var draftFolder = await _folderService.GetSpecialFolderByAccountIdAsync(accountId, SpecialFolderType.Draft);

        // Threading is not possible. Return items as it is.

        if (sentFolder == null || draftFolder == null) return new List<IMailItem>(items);

        foreach (var replyItem in items)
        {
            if (mailLookupTable[replyItem.Id])
                continue;

            mailLookupTable[replyItem.Id] = true;

            var threadItem = new ThreadMailItem();

            threadItem.AddThreadItem(replyItem);

            var replyToChild = await GetReplyParentAsync(replyItem, accountId, replyItem.AssignedFolder.Id, sentFolder.Id, draftFolder.Id);

            // Build up 
            while (replyToChild != null)
            {
                replyToChild.AssignedAccount = account;

                if (replyToChild.FolderId == draftFolder.Id)
                    replyToChild.AssignedFolder = draftFolder;

                if (replyToChild.FolderId == sentFolder.Id)
                    replyToChild.AssignedFolder = sentFolder;

                if (replyToChild.FolderId == replyItem.AssignedFolder.Id)
                    replyToChild.AssignedFolder = replyItem.AssignedFolder;

                threadItem.AddThreadItem(replyToChild);

                if (mailLookupTable.ContainsKey(replyToChild.Id))
                    mailLookupTable[replyToChild.Id] = true;

                replyToChild = await GetReplyParentAsync(replyToChild, accountId, replyToChild.AssignedFolder.Id, sentFolder.Id, draftFolder.Id);
            }

            // Build down
            var replyToParent = await GetInReplyToReplyAsync(replyItem, accountId, replyItem.AssignedFolder.Id, sentFolder.Id, draftFolder.Id);

            while (replyToParent != null)
            {
                replyToParent.AssignedAccount = account;

                if (replyToParent.FolderId == draftFolder.Id)
                    replyToParent.AssignedFolder = draftFolder;

                if (replyToParent.FolderId == sentFolder.Id)
                    replyToParent.AssignedFolder = sentFolder;

                if (replyToParent.FolderId == replyItem.AssignedFolder.Id)
                    replyToParent.AssignedFolder = replyItem.AssignedFolder;

                threadItem.AddThreadItem(replyToParent);

                if (mailLookupTable.ContainsKey(replyToParent.Id))
                    mailLookupTable[replyToParent.Id] = true;

                replyToParent = await GetInReplyToReplyAsync(replyToParent, accountId, replyToParent.AssignedFolder.Id, sentFolder.Id, draftFolder.Id);
            }

            // It's a thread item.

            if (threadItem.ThreadItems.Count > 1 && !threads.Exists(a => a.Id == threadItem.Id))
            {
                threads.Add(threadItem);
            }
            else
            {
                // False alert. This is not a thread item.
                mailLookupTable[replyItem.Id] = false;

                // TODO: Here potentially check other algorithms for threading like References.
            }
        }

        // At this points all mails in the list belong to single items.
        // Merge with threads.
        // Last sorting will be done later on in MailService.

        // Remove single mails that are included in thread.
        items.RemoveAll(a => mailLookupTable.ContainsKey(a.Id) && mailLookupTable[a.Id]);

        var finalList = new List<IMailItem>(items);

        finalList.AddRange(threads);

        return finalList;
    }

    public bool ShouldThreadWithItem(IMailItem originalItem, IMailItem targetItem)
    {
        bool isChild = originalItem.InReplyTo != null && originalItem.InReplyTo == targetItem.MessageId;
        bool isParent = originalItem.MessageId != null && originalItem.MessageId == targetItem.InReplyTo;

        return isChild || isParent;
    }
}