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 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;
                }
        }
        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;
        }

        public bool isOk() { return _ok; }
        public void askForRefresh() { _needUpd = true; }
        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;
            }
        }
    }
}