using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

namespace Kruzya.TelegramBot.Core.Cache
{
    public class MemoryCache<TKey, TValue> : ICacheStorage<TKey, TValue>
    {
        /// <summary>
        /// Represents a cache entry in internal dictionary.
        /// </summary>
        /// <typeparam name="TVal"></typeparam>
        internal struct CacheEntry<TVal>
        {
            public TVal Value;
            public DateTime Created;
            public int ExpiresAt;

            public bool IsExpired()
            {
                if (ExpiresAt == Timeout.Infinite)
                {
                    return false;
                }

                return (Created.AddSeconds(ExpiresAt)) < DateTime.Now;
            }
        }
        
        /// <summary>
        /// 
        /// </summary>
        private Dictionary<TKey, CacheEntry<TValue>> dict = new Dictionary<TKey, CacheEntry<TValue>>();
        
        /// <summary>
        /// The TTL for all entries if not set.
        /// </summary>
        private int _defaultTtl;

        public MemoryCache() : this(Timeout.Infinite)
        {
        }

        public MemoryCache(int defaultTtl)
        {
            _defaultTtl = defaultTtl;
        }
        
        public bool TryGetValue(TKey key, ref TValue value)
        {
            if (dict.ContainsKey(key))
            {
                return false;
            }

            CacheEntry<TValue> temp;
            if (!dict.TryGetValue(key, out temp))
            {
                return false;
            }

            if (temp.IsExpired())
            {
                dict.Remove(key);
                return false;
            }

            value = temp.Value;
            return true;
        }

        public void SetValue(TKey key, TValue value)
        {
            SetValue(key, value, _defaultTtl);
        }
        
        public void SetValue(TKey key, TValue value, int timeToLive)
        {
            if (dict.ContainsKey(key))
            {
                dict.Remove(key);
            }

            dict.Add(key, new CacheEntry<TValue>()
            {
                Created = DateTime.Now,
                ExpiresAt = timeToLive,
                Value = value
            });
        }
    }
}