LocalDocumentDBRepository.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Threading.Tasks;
using Newtonsoft.Json;
using TailSpin.SpaceGame.Web.Models;

namespace TailSpin.SpaceGame.Web
{
    public class LocalDocumentDBRepository<T> : IDocumentDBRepository<T> where T : Model
    {
        // An in-memory list of all items in the collection.
        private readonly List<T> _items;

        public LocalDocumentDBRepository(string fileName)
        {
            // Serialize the items from the provided JSON document.
            _items = JsonConvert.DeserializeObject<List<T>>(File.ReadAllText(fileName));
        }

        /// <summary>
        /// Retrieves the item from the store with the given identifier.
        /// </summary>
        /// <returns>
        /// A task that represents the asynchronous operation.
        /// The task result contains the retrieved item.
        /// </returns>
        /// <param name="id">The identifier of the item to retrieve.</param>
        public Task<T> GetItemAsync(string id)
        {
            return Task<T>.FromResult(_items.Single(item => item.Id == id));
        }

        /// <summary>
        /// Retrieves items from the store that match the given query predicate.
        /// Results are given in descending order by the given ordering predicate.
        /// </summary>
        /// <returns>
        /// A task that represents the asynchronous operation.
        /// The task result contains the collection of retrieved items.
        /// </returns>
        /// <param name="queryPredicate">Predicate that specifies which items to select.</param>
        /// <param name="orderDescendingPredicate">Predicate that specifies how to sort the results in descending order.</param>
        /// <param name="page">The 1-based page of results to return.</param>
        /// <param name="pageSize">The number of items on a page.</param>
        public Task<IEnumerable<T>> GetItemsAsync(
            Expression<Func<T, bool>> queryPredicate,
            Expression<Func<T, int>> orderDescendingPredicate,
            int page = 1, int pageSize = 10
        )
        {
            var result = _items.AsQueryable()
                .Where(queryPredicate) // filter
                .OrderByDescending(orderDescendingPredicate) // sort
                .Skip(page * pageSize) // find page
                .Take(pageSize) // take items
                .AsEnumerable(); // make enumeratable

            return Task<IEnumerable<T>>.FromResult(result);
        }

        /// <summary>
        /// Retrieves the number of items that match the given query predicate.
        /// </summary>
        /// <returns>
        /// A task that represents the asynchronous operation.
        /// The task result contains the number of items that match the query predicate.
        /// </returns>
        /// <param name="queryPredicate">Predicate that specifies which items to select.</param>
        public Task<int> CountItemsAsync(Expression<Func<T, bool>> queryPredicate)
        {
            var count = _items.AsQueryable()
                .Where(queryPredicate) // filter
                .Count(); // count

            return Task<int>.FromResult(count);
        }
    }
}