using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using SmartStore.Core.Data;
using SmartStore.Core.Domain.Configuration;

namespace SmartStore.Data.Setup
{
	
	internal class SettingsMigrator
	{
		private readonly SmartObjectContext _ctx;
		private readonly DbSet<Setting> _settings;

		public SettingsMigrator(SmartObjectContext ctx)
		{
			Guard.NotNull(ctx, nameof(ctx));

			_ctx = ctx;
			_settings = _ctx.Set<Setting>();
		}

		public void Migrate(IEnumerable<SettingEntry> entries)
		{
			Guard.NotNull(entries, nameof(entries));

			if (!entries.Any())
				return;

			using (var scope = new DbContextScope(_ctx, autoDetectChanges: false))
			{
				var toDelete = new List<Setting>();
				var toAdd = new List<Setting>();

				// First perform DELETE actions
				foreach (var entry in entries.Where(x => x.Value == null))
				{
					bool isPattern = entry.KeyIsGroup;
					if (!HasSettings(entry.Key, isPattern))
						continue; // nothing to delete

					var db = GetSettings(entry.Key, isPattern);
					_settings.RemoveRange(db);
				}

				_ctx.SaveChanges();

				// Then perform ADD actions
				foreach (var entry in entries.Where(x => x.Value.HasValue()))
				{
					var existing = toAdd.FirstOrDefault(x => x.Name.Equals(entry.Key, StringComparison.InvariantCultureIgnoreCase));
					if (existing != null)
					{
						existing.Value = entry.Value;
						continue;
					}

					if (HasSettings(entry.Key, false))
						continue; // skip existing (we don't perform updates)

					_settings.Add(new Setting { 
						Name = entry.Key,
						Value = entry.Value,
						StoreId = 0
					});
				}

				_ctx.SaveChanges();
			}
		}

		private bool HasSettings(string key, bool isPattern = false)
		{
			var query = BuildQuery(key, isPattern);
			return query.Any();
		}

		private IList<Setting> GetSettings(string key, bool isPattern = false)
		{
			var query = BuildQuery(key, isPattern);
			return query.ToList();
		}

		private IQueryable<Setting> BuildQuery(string key, bool isPattern = false)
		{
			var query = _settings.AsQueryable();
			if (isPattern)
			{
				query = query.Where(x => x.Name.StartsWith(key));
			}
			else
			{
				query = query.Where(x => x.Name.Equals(key));
			}

			return query;
		}
	}

}
