using System;
using System.Collections.Generic;
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 readonly Dictionary<TKey, CacheEntry<TValue>> _dict = new();
        
    /// <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, out TValue value)
    {
        value = default;
        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 TValue GetOr(TKey key, TValue defValue = default)
    {
        var doesExist = TryGetValue(key, out var value);
        if (!doesExist)
        {
            value = defValue;
        }

        return value;
    }

    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
        });
    }
}