using System;
using System.Collections.Generic;

namespace Svrnty.CQRS.Events.Abstractions.Sagas;

/// <summary>
/// Registry for saga definitions.
/// </summary>
public interface ISagaRegistry
{
    /// <summary>
    /// Register a saga definition.
    /// </summary>
    /// <typeparam name="TSaga">The saga type.</typeparam>
    /// <param name="definition">The saga definition.</param>
    void Register<TSaga>(SagaDefinition definition) where TSaga : ISaga;

    /// <summary>
    /// Get saga definition by type.
    /// </summary>
    /// <typeparam name="TSaga">The saga type.</typeparam>
    /// <returns>The saga definition, or null if not found.</returns>
    SagaDefinition? GetDefinition<TSaga>() where TSaga : ISaga;

    /// <summary>
    /// Get saga definition by name.
    /// </summary>
    /// <param name="sagaName">The saga name.</param>
    /// <returns>The saga definition, or null if not found.</returns>
    SagaDefinition? GetDefinitionByName(string sagaName);

    /// <summary>
    /// Get saga type by name.
    /// </summary>
    /// <param name="sagaName">The saga name.</param>
    /// <returns>The saga type, or null if not found.</returns>
    Type? GetSagaType(string sagaName);
}

/// <summary>
/// Saga definition with steps.
/// </summary>
public sealed class SagaDefinition
{
    private readonly List<ISagaStep> _steps = new();

    public SagaDefinition(string sagaName)
    {
        if (string.IsNullOrWhiteSpace(sagaName))
            throw new ArgumentException("Saga name cannot be null or empty", nameof(sagaName));

        SagaName = sagaName;
    }

    /// <summary>
    /// Saga name.
    /// </summary>
    public string SagaName { get; }

    /// <summary>
    /// Saga steps in execution order.
    /// </summary>
    public IReadOnlyList<ISagaStep> Steps => _steps.AsReadOnly();

    /// <summary>
    /// Add a step to the saga.
    /// </summary>
    public SagaDefinition AddStep(ISagaStep step)
    {
        if (step == null)
            throw new ArgumentNullException(nameof(step));

        _steps.Add(step);
        return this;
    }

    /// <summary>
    /// Add a step using lambdas.
    /// </summary>
    public SagaDefinition AddStep(
        string stepName,
        Func<ISagaContext, System.Threading.CancellationToken, System.Threading.Tasks.Task> execute,
        Func<ISagaContext, System.Threading.CancellationToken, System.Threading.Tasks.Task> compensate)
    {
        if (string.IsNullOrWhiteSpace(stepName))
            throw new ArgumentException("Step name cannot be null or empty", nameof(stepName));
        if (execute == null)
            throw new ArgumentNullException(nameof(execute));
        if (compensate == null)
            throw new ArgumentNullException(nameof(compensate));

        _steps.Add(new LambdaSagaStep(stepName, execute, compensate));
        return this;
    }
}

/// <summary>
/// Saga step implemented with lambda functions.
/// </summary>
internal sealed class LambdaSagaStep : ISagaStep
{
    private readonly Func<ISagaContext, System.Threading.CancellationToken, System.Threading.Tasks.Task> _execute;
    private readonly Func<ISagaContext, System.Threading.CancellationToken, System.Threading.Tasks.Task> _compensate;

    public LambdaSagaStep(
        string stepName,
        Func<ISagaContext, System.Threading.CancellationToken, System.Threading.Tasks.Task> execute,
        Func<ISagaContext, System.Threading.CancellationToken, System.Threading.Tasks.Task> compensate)
    {
        StepName = stepName ?? throw new ArgumentNullException(nameof(stepName));
        _execute = execute ?? throw new ArgumentNullException(nameof(execute));
        _compensate = compensate ?? throw new ArgumentNullException(nameof(compensate));
    }

    public string StepName { get; }

    public System.Threading.Tasks.Task ExecuteAsync(ISagaContext context, System.Threading.CancellationToken cancellationToken = default)
    {
        return _execute(context, cancellationToken);
    }

    public System.Threading.Tasks.Task CompensateAsync(ISagaContext context, System.Threading.CancellationToken cancellationToken = default)
    {
        return _compensate(context, cancellationToken);
    }
}