using System.Data.Common;
using SQLInsight.Core.Instances;

namespace SQLInsight.Collectors;

/// <summary>
/// Reads one kind of data from a monitored instance. Collectors are stateless; anything they need from the
/// previous run (to compute deltas or continue reading) is passed in <see cref="CollectorContext.Previous"/>.
/// </summary>
public interface ICollector
{
    string Name { get; }

    /// <summary>The type of the collected data, as rules look it up in <c>CollectedData</c>.</summary>
    Type DataType { get; }

    TimeSpan DefaultInterval { get; }

    /// <summary>What the instance must support. If anything is missing, the collector does not run.</summary>
    IReadOnlyCollection<Capability> RequiredCapabilities { get; }

    Task<object> CollectAsync(CollectorContext context);
}

/// <param name="Previous">This collector's result from the previous run on the same instance, if any.</param>
public sealed record CollectorContext(
    DbConnection Connection,
    InstanceInfo Instance,
    InstanceCapabilities Capabilities,
    DateTimeOffset Now,
    object? Previous,
    CancellationToken CancellationToken);

/// <summary>
/// Typed base class for collectors.
/// </summary>
public abstract class Collector<T> : ICollector
    where T : class
{
    public abstract string Name { get; }
    public Type DataType => typeof(T);
    public abstract TimeSpan DefaultInterval { get; }
    public virtual IReadOnlyCollection<Capability> RequiredCapabilities => [];

    async Task<object> ICollector.CollectAsync(CollectorContext context) =>
        await CollectAsync(context, context.Previous as T).ConfigureAwait(false);

    protected abstract Task<T> CollectAsync(CollectorContext context, T? previous);
}