GGMM/GrossesMitaines/GrossesMitainesAPI/Services/DatabaseCacheService.cs

using GrossesMitainesAPI.Data;
using GrossesMitainesAPI.Models;
using Microsoft.EntityFrameworkCore;

namespace GrossesMitainesAPI.Services {
    public class DatabaseCacheService {
        private readonly IServiceScopeFactory _contextFactory; // https://entityframeworkcore.com/knowledge-base/51939451/how-to-use-a-database-context-in-a-singleton-service-
        private readonly ILogger<DatabaseCacheService> _logger;

        private Product[] _cache = new Product[1];
        private Dictionary<uint, uint> _hits = new();
        private bool _ok = false, _needUpd = true;
        private PeriodicTimer _timer = new PeriodicTimer(TimeSpan.FromSeconds(10));

        public DatabaseCacheService(ILogger<DatabaseCacheService> logger, IServiceScopeFactory scopeFactory) {
            _contextFactory = scopeFactory;
            _logger = logger;
            _ok = UpdateCache();
            _needUpd = !_ok;
            UpdateJob();
        }

        private async void UpdateJob() {
            while (await _timer.WaitForNextTickAsync()) { 
                if (_needUpd) {
                    _ok = UpdateCache();
                    _needUpd = !_ok;
                } 
                if (_hits.Count > 0 && _ok) 
                    UpdateMetrics();
            }
        }
        private bool UpdateCache() {
            try {
                Product[] prods;
                using (var scope = _contextFactory.CreateScope()) {
                    var db = scope.ServiceProvider.GetRequiredService<InventoryContext>();
                    prods = db.Products.ToArray();
                }
                lock (_cache) {
                    _cache = prods;
                }
            } catch (Exception e) {
                _logger.LogError(e, "Erreur de mise à jour de cache.");
                return false;
            }
            return true;
        }

        private bool UpdateMetrics() {
            try {
                Dictionary<uint, uint> hits;
                lock (_hits) { 
                    hits = new(_hits);
                    _hits.Clear();
                }
                List<uint> ids = hits.Keys.ToList();
                using (var scope = _contextFactory.CreateScope()) {
                    var db = scope.ServiceProvider.GetRequiredService<InventoryContext>();
                    List<Product> lst = db.Products.Where(x => ids.Contains((uint)x.Id)).ToList();
                    foreach (var x in hits) {
                        //Product prod = lst.First(x => x.Id == x.Id);
                        lst.First(x => x.Id == x.Id).Hits += x.Value;
                       // prod.Hits = prod.Hits + x.Value;
                       // db.Products.Update(prod);
                    }
                    db.UpdateRange(lst);
                    db.SaveChanges();
                }
            } catch (Exception e) {
                _logger.LogError(e, "Erreur de mise à jour de cache.");
                return false;
            }
            return true;
        }

        public bool isOk() { return _ok; }
        public void askForRefresh() { _needUpd = true; }
        public void addHit(uint id) {
            lock (_hits) { 
                if (_hits.ContainsKey(id))
                    _hits[id] = _hits[id] + 1;
                else _hits[id] = 1;
            }
        }
         
        public Product[]? GetCacheCopy() {
            if (!_ok) 
                return null;

            Product[] copy;
            try {
                lock (_cache) {
                    copy = new Product[_cache.Length];
                    _cache.CopyTo(copy, 0);
                }
            } catch (Exception e) {
                _logger.LogError(e, "Erreur de copie de cache.");
                return null;
            }
            return copy;
        }

        public IQueryable<Product> queryCache() {
            if (!_ok) 
                return null;
            try {
                return _cache.AsQueryable();
            } catch (Exception e) {
                _logger.LogError(e, "Erreur de cache.");
                return null;
            }
        }
    }
}