using System.Collections.Concurrent;
using ErrorOr;
using Microsoft.Extensions.Caching.Memory;

namespace Musify.Infrastructure.Services;

public sealed class SingleFlightCache(IMemoryCache cache)
{
    private readonly ConcurrentDictionary<string, object> inFlight = new();

    public async Task<ErrorOr<TValue>> GetOrCreateAsync<TValue>(
        string key,
        TimeSpan duration,
        Func<Task<ErrorOr<TValue>>> factory)
    {
        if (duration <= TimeSpan.Zero)
            return await factory();

        if (cache.TryGetValue(key, out TValue? cached) && cached != null)
            return cached;

        var pending = (Lazy<Task<ErrorOr<TValue>>>)inFlight.GetOrAdd(
            key,
            _ => new Lazy<Task<ErrorOr<TValue>>>(factory));

        try
        {
            var result = await pending.Value;

            if (!result.IsError)
                cache.Set(key, result.Value, duration);

            return result;
        }
        finally
        {
            inFlight.TryRemove(key, out _);
        }
    }
}