dotnet-cqrs/Svrnty.CQRS.Events/Projections/ProjectionServiceCollectionExtensions.cs

using System;
using Svrnty.CQRS.Events.Abstractions.EventStore;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;
using Svrnty.CQRS.Events.Abstractions;
using Svrnty.CQRS.Events.Abstractions.Projections;

namespace Svrnty.CQRS.Events.Projections;

/// <summary>
/// Extension methods for registering event sourcing projections.
/// </summary>
public static class ProjectionServiceCollectionExtensions
{
    /// <summary>
    /// Adds projection infrastructure services to the service collection.
    /// </summary>
    /// <param name="services">The service collection.</param>
    /// <param name="useInMemoryCheckpoints">
    /// If true, uses in-memory checkpoint storage (for development/testing).
    /// If false, requires PostgresProjectionCheckpointStore or custom implementation.
    /// </param>
    /// <returns>The service collection for chaining.</returns>
    public static IServiceCollection AddProjections(
        this IServiceCollection services,
        bool useInMemoryCheckpoints = false)
    {
        // Register core services
        services.TryAddSingleton<IProjectionRegistry, ProjectionRegistry>();
        services.TryAddSingleton<IProjectionEngine, ProjectionEngine>();

        // Register checkpoint store
        if (useInMemoryCheckpoints)
        {
            services.TryAddSingleton<IProjectionCheckpointStore, InMemoryProjectionCheckpointStore>();
        }

        // Register hosted service for auto-start projections
        services.AddHostedService<ProjectionHostedService>();

        return services;
    }

    /// <summary>
    /// Registers a projection with the projection engine.
    /// </summary>
    /// <typeparam name="TProjection">The type of the projection implementation.</typeparam>
    /// <typeparam name="TEvent">The type of event the projection handles.</typeparam>
    /// <param name="services">The service collection.</param>
    /// <param name="projectionName">The unique name of the projection.</param>
    /// <param name="streamName">The name of the stream to consume from.</param>
    /// <param name="configure">Optional configuration for projection options.</param>
    /// <returns>The service collection for chaining.</returns>
    /// <remarks>
    /// <para>
    /// <strong>Example:</strong>
    /// <code>
    /// services.AddProjection&lt;UserStatisticsProjection, UserRegisteredEvent&gt;(
    ///     projectionName: "user-statistics",
    ///     streamName: "user-events",
    ///     configure: options =>
    ///     {
    ///         options.BatchSize = 100;
    ///         options.AutoStart = true;
    ///     });
    /// </code>
    /// </para>
    /// </remarks>
    public static IServiceCollection AddProjection<TProjection, TEvent>(
        this IServiceCollection services,
        string projectionName,
        string streamName,
        Action<ProjectionOptions>? configure = null)
        where TProjection : class, IProjection<TEvent>
        where TEvent : ICorrelatedEvent
    {
        if (string.IsNullOrWhiteSpace(projectionName))
            throw new ArgumentException("Projection name cannot be null or empty", nameof(projectionName));

        if (string.IsNullOrWhiteSpace(streamName))
            throw new ArgumentException("Stream name cannot be null or empty", nameof(streamName));

        // Register projection implementation in DI
        services.TryAddScoped<TProjection>();

        // Build options
        var options = new ProjectionOptions();
        configure?.Invoke(options);

        // Register projection definition
        services.AddSingleton(sp =>
        {
            var registry = sp.GetRequiredService<IProjectionRegistry>();

            var definition = new ProjectionDefinition
            {
                ProjectionName = projectionName,
                StreamName = streamName,
                ProjectionType = typeof(TProjection),
                EventType = typeof(TEvent),
                Options = options,
                Description = $"Projection '{projectionName}' consuming {typeof(TEvent).Name} from '{streamName}'"
            };

            registry.Register(definition);

            return definition;
        });

        return services;
    }

    /// <summary>
    /// Registers a dynamic projection that can handle multiple event types.
    /// </summary>
    /// <typeparam name="TProjection">The type of the projection implementation.</typeparam>
    /// <param name="services">The service collection.</param>
    /// <param name="projectionName">The unique name of the projection.</param>
    /// <param name="streamName">The name of the stream to consume from.</param>
    /// <param name="configure">Optional configuration for projection options.</param>
    /// <returns>The service collection for chaining.</returns>
    public static IServiceCollection AddDynamicProjection<TProjection>(
        this IServiceCollection services,
        string projectionName,
        string streamName,
        Action<ProjectionOptions>? configure = null)
        where TProjection : class, IDynamicProjection
    {
        if (string.IsNullOrWhiteSpace(projectionName))
            throw new ArgumentException("Projection name cannot be null or empty", nameof(projectionName));

        if (string.IsNullOrWhiteSpace(streamName))
            throw new ArgumentException("Stream name cannot be null or empty", nameof(streamName));

        // Register projection implementation in DI
        services.TryAddScoped<TProjection>();

        // Build options
        var options = new ProjectionOptions();
        configure?.Invoke(options);

        // Register projection definition
        services.AddSingleton(sp =>
        {
            var registry = sp.GetRequiredService<IProjectionRegistry>();

            var definition = new ProjectionDefinition
            {
                ProjectionName = projectionName,
                StreamName = streamName,
                ProjectionType = typeof(TProjection),
                EventType = null, // Dynamic projections don't have a specific event type
                Options = options,
                Description = $"Dynamic projection '{projectionName}' consuming from '{streamName}'"
            };

            registry.Register(definition);

            return definition;
        });

        return services;
    }
}