JsonCache (File System)

public interface IJsonCache : ICache
{
    // Properties
    string Extension { get; }
    string Path { get; }

    // Methods
    string GetFileName(string key);
    void EnsureDirectory();
}

public class JsonCache : ICache
{
    public JsonCache(string path,
        string extension)
    {
        Path = path;
        Extension = extension;
        EnsureDirectory();
    }

    /*** Properties ***/

    public string Extension { get; }
    public string Path { get; }

    /*** Helpers ***/

    public string GetFileName(string key)
    {
        var fileName = $"{Regex.Replace(key, "[^a-zA-Z0-9 -]", "_")}.{Extension}";
        return System.IO.Path.Combine(Path, fileName);
    }

    public void EnsureDirectory()
    {
        if (Directory.Exists(Path) == false)
        {
            Directory.CreateDirectory(Path);
        }
    }

    /*** Methods ***/

    public void Add<T>(string key,
        T value,
        int expiration = 180,
        bool throwException = true)
    {
        var fileName = GetFileName(key);
        var contains = Contains(key);
        if (contains)
        {
            if (throwException)
            {
                throw new Exception($"File '{fileName}' already exists.");
            }
        }
        File.WriteAllText(fileName, JsonConvert.SerializeObject(value));
    }

    public void Add<T>(CacheItem<T> item,
        bool throwException = true)
    {
        Add<T>(item.Key, item.Value, item.CacheItemExpiration, throwException);
    }

    public void Clear()
    {
        Directory.Delete(Path, true);
        EnsureDirectory();
    }

    public bool Contains(string key)
    {
        var fileName = GetFileName(key);
        return File.Exists(fileName);
    }

    public CacheItem<T> Get<T>(string key,
        bool throwException = true)
    {
        var fileName = GetFileName(key);
        if (File.Exists(fileName))
        {
            var value = JsonConvert.DeserializeObject<T>(File.ReadAllText(fileName));
            return new CacheItem<T>(key, value);
        }
        if (throwException)
        {
            throw new FileNotFoundException($"File '{fileName}' is not found.");
        }
        return null;
    }

    public void Remove(string key,
        bool throwException = true)
    {
        var fileName = GetFileName(key);
        if (File.Exists(fileName))
        {
            File.Delete(fileName);
        }
        if (throwException)
        {
            throw new FileNotFoundException($"File '{fileName}' is not found.");
        }
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        foreach (var fileName in Directory.GetFiles(Path))
        {
            yield return JsonConvert.DeserializeObject<object>(File.ReadAllText(fileName));
        }
    }
}

public static class CacheFactory
{
    private static object _syncLock = new object();
    private static ICache _cache = null;
    
    public static ICache CreateCacher()
    {
        if (_cache == null)
        {
            lock (_syncLock)
            {
                if (_cache == null)
                {
                    _cache = new JsonCache();
                }
            }
        }
        return _cache;
    }
}

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();

    // Registration
    services.AddSingleton<IJsonCache, JsonCache>();
}