/// <summary>
///     Collects diagnostic messages during the build pipeline.
/// </summary>
public sealed class DiagnosticBag
{
    private readonly List<Diagnostic> _diagnostics = [];
    /// <summary>All collected diagnostics.</summary>
    public IReadOnlyList<Diagnostic> All => _diagnostics;
    /// <summary>Whether there are any error-level diagnostics.</summary>
    public bool HasErrors => _diagnostics.Exists(d => d.Severity == DiagnosticSeverity.Error);
    /// <summary>Whether there are any warning-level diagnostics.</summary>
    public bool HasWarnings => _diagnostics.Exists(d => d.Severity == DiagnosticSeverity.Warning);
    /// <summary>Number of diagnostics.</summary>
    public int Count => _diagnostics.Count;

    /// <summary>Add an error diagnostic.</summary>
    public void Error(string message, string? source = null)
    {
        _diagnostics.Add(new Diagnostic { Severity = DiagnosticSeverity.Error, Message = message, Source = source });
    }

    /// <summary>Add a warning diagnostic.</summary>
    public void Warning(string message, string? source = null)
    {
        _diagnostics.Add(new Diagnostic { Severity = DiagnosticSeverity.Warning, Message = message, Source = source });
    }

    /// <summary>Add an info diagnostic.</summary>
    public void Info(string message, string? source = null)
    {
        _diagnostics.Add(new Diagnostic { Severity = DiagnosticSeverity.Info, Message = message, Source = source });
    }
}