// (c) Copyright Ascensio System SIA 2010-2022
//
// This program is a free software product.
// You can redistribute it and/or modify it under the terms
// of the GNU Affero General Public License (AGPL) version 3 as published by the Free Software
// Foundation. In accordance with Section 7(a) of the GNU AGPL its Section 15 shall be amended
// to the effect that Ascensio System SIA expressly excludes the warranty of non-infringement of
// any third-party rights.
//
// This program is distributed WITHOUT ANY WARRANTY, without even the implied warranty
// of MERCHANTABILITY or FITNESS FOR A PARTICULAR  PURPOSE. For details, see
// the GNU AGPL at: http://www.gnu.org/licenses/agpl-3.0.html
//
// You can contact Ascensio System SIA at Lubanas st. 125a-25, Riga, Latvia, EU, LV-1021.
//
// The  interactive user interfaces in modified source and object code versions of the Program must
// display Appropriate Legal Notices, as required under Section 5 of the GNU AGPL version 3.
//
// Pursuant to Section 7(b) of the License you must retain the original Product logo when
// distributing the program. Pursuant to Section 7(e) we decline to grant you any rights under
// trademark law for use of our trademarks.
//
// All the Product's GUI elements, including illustrations and icon sets, as well as technical writing
// content are licensed under the terms of the Creative Commons Attribution-ShareAlike 4.0
// International. See the License terms at http://creativecommons.org/licenses/by-sa/4.0/legalcode

namespace ASC.Web.Studio.Core.Statistic;

[Scope]
public class StatisticManager
{
    private static DateTime _lastSave = DateTime.UtcNow;
    private static readonly TimeSpan _cacheTime = TimeSpan.FromMinutes(2);
    private static readonly IDictionary<string, UserVisit> _cache = new Dictionary<string, UserVisit>();

    private readonly Lazy<WebstudioDbContext> _lazyWebstudioDbContext;
    private WebstudioDbContext WebstudioDbContext { get => _lazyWebstudioDbContext.Value; }

    public StatisticManager(DbContextManager<WebstudioDbContext> dbContextManager)
    {
        _lazyWebstudioDbContext = new Lazy<WebstudioDbContext>(() => dbContextManager.Value);
    }

    public void SaveUserVisit(int tenantID, Guid userID, Guid productID)
    {
        var now = DateTime.UtcNow;
        var key = string.Format("{0}|{1}|{2}|{3}", tenantID, userID, productID, now.Date);

        lock (_cache)
        {
            var visit = _cache.ContainsKey(key) ?
                            _cache[key] :
                            new UserVisit
                            {
                                TenantID = tenantID,
                                UserID = userID,
                                ProductID = productID,
                                VisitDate = now
                            };

            visit.VisitCount++;
            visit.LastVisitTime = now;
            _cache[key] = visit;
        }

        if (_cacheTime < DateTime.UtcNow - _lastSave)
        {
            FlushCache();
        }
    }

    public List<Guid> GetVisitorsToday(int tenantID, Guid productID)
    {
        var users = WebstudioDbContext.WebstudioUserVisit
            .Where(r => r.VisitDate == DateTime.UtcNow.Date)
            .Where(r => r.TenantId == tenantID)
            .Where(r => r.ProductId == productID)
            .OrderBy(r => r.FirstVisitTime)
            .GroupBy(r => r.UserId)
            .Select(r => r.Key)
            .ToList();

        lock (_cache)
        {
            foreach (var visit in _cache.Values)
            {
                if (!users.Contains(visit.UserID) && visit.VisitDate.Date == DateTime.UtcNow.Date)
                {
                    users.Add(visit.UserID);
                }
            }
        }
        return users;
    }

    public List<UserVisit> GetHitsByPeriod(int tenantID, DateTime startDate, DateTime endPeriod)
    {
        return WebstudioDbContext.WebstudioUserVisit
            .Where(r => r.TenantId == tenantID)
            .Where(r => r.VisitDate >= startDate && r.VisitDate <= endPeriod)
            .OrderBy(r => r.VisitDate)
            .GroupBy(r => r.VisitDate)
            .Select(r => new UserVisit { VisitDate = r.Key, VisitCount = r.Sum(a => a.VisitCount) })
            .ToList();
    }

    public List<UserVisit> GetHostsByPeriod(int tenantID, DateTime startDate, DateTime endPeriod)
    {
        return
            WebstudioDbContext.WebstudioUserVisit
            .Where(r => r.TenantId == tenantID)
            .Where(r => r.VisitDate >= startDate && r.VisitDate <= endPeriod)
            .OrderBy(r => r.VisitDate)
            .GroupBy(r => new { r.UserId, r.VisitDate })
            .Select(r => new UserVisit { VisitDate = r.Key.VisitDate, UserID = r.Key.UserId })
            .ToList();
    }

    private void FlushCache()
    {
        if (_cache.Count == 0)
        {
            return;
        }

        List<UserVisit> visits;
        lock (_cache)
        {
            visits = new List<UserVisit>(_cache.Values);
            _cache.Clear();
            _lastSave = DateTime.UtcNow;
        }

        var strategy = WebstudioDbContext.Database.CreateExecutionStrategy();

        strategy.Execute(() =>
        {
            using var tx = WebstudioDbContext.Database.BeginTransaction(IsolationLevel.ReadUncommitted);

            foreach (var v in visits)
            {
                var w = new DbWebstudioUserVisit
                {
                    TenantId = v.TenantID,
                    ProductId = v.ProductID,
                    UserId = v.UserID,
                    VisitDate = v.VisitDate.Date,
                    FirstVisitTime = v.VisitDate,
                    VisitCount = v.VisitCount
                };

                if (v.LastVisitTime.HasValue)
                {
                    w.LastVisitTime = v.LastVisitTime.Value;
                }

                WebstudioDbContext.WebstudioUserVisit.Add(w);
                WebstudioDbContext.SaveChanges();
            }
            tx.Commit();
        });
    }
}