using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Options;

namespace StellaOps.DependencyInjection.Validation;

/// <summary>
/// A hosted service that validates options at application startup.
/// This ensures configuration errors are detected early rather than at first use.
/// </summary>
/// <typeparam name="TOptions">The options type to validate.</typeparam>
internal sealed class OptionsValidationHostedService<TOptions> : IHostedService
    where TOptions : class
{
    private readonly IOptions<TOptions> _options;

    public OptionsValidationHostedService(IOptions<TOptions> options)
    {
        _options = options;
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        // Accessing .Value triggers validation if IValidateOptions<TOptions> is registered
        _ = _options.Value;
        return Task.CompletedTask;
    }

    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
}