using System;
using Svrnty.CQRS.Events.Abstractions.Subscriptions;
using Svrnty.Sample.Events;
using Svrnty.CQRS.Events.Abstractions.EventStore;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using Svrnty.CQRS.Events.Abstractions.Projections;

namespace Svrnty.Sample.Projections;

/// <summary>
/// Projection that builds user statistics from UserAddedEvent and UserRemovedEvent.
/// Demonstrates dynamic projection handling multiple event types.
/// </summary>
/// <remarks>
/// <para>
/// This projection maintains a simple in-memory read model tracking:
/// - Total users added
/// - Total users removed
/// - Current user count
/// - Last user details
/// </para>
/// <para>
/// In production, this would typically update a database, cache, or other persistent store.
/// </para>
/// </remarks>
public sealed class UserStatisticsProjection : IDynamicProjection, IResettableProjection
{
    private readonly UserStatistics _statistics;
    private readonly ILogger<UserStatisticsProjection> _logger;

    public UserStatisticsProjection(
        UserStatistics statistics,
        ILogger<UserStatisticsProjection> logger)
    {
        _statistics = statistics ?? throw new ArgumentNullException(nameof(statistics));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    /// <summary>
    /// Gets the current statistics (for querying).
    /// </summary>
    public UserStatistics Statistics => _statistics;

    /// <inheritdoc />
    public Task HandleAsync(ICorrelatedEvent @event, CancellationToken cancellationToken = default)
    {
        switch (@event)
        {
            case UserAddedEvent added:
                return HandleUserAddedAsync(added, cancellationToken);

            case UserRemovedEvent removed:
                return HandleUserRemovedAsync(removed, cancellationToken);

            default:
                // Unknown event type - skip
                _logger.LogWarning("Received unknown event type: {EventType}", @event.GetType().Name);
                return Task.CompletedTask;
        }
    }

    /// <inheritdoc />
    public Task ResetAsync(CancellationToken cancellationToken = default)
    {
        _logger.LogInformation("Resetting user statistics projection");

        _statistics.TotalUsersAdded = 0;
        _statistics.TotalUsersRemoved = 0;
        _statistics.LastUserId = 0;
        _statistics.LastUserName = string.Empty;
        _statistics.LastUserEmail = string.Empty;
        _statistics.LastUpdated = DateTimeOffset.MinValue;

        return Task.CompletedTask;
    }

    private Task HandleUserAddedAsync(UserAddedEvent @event, CancellationToken cancellationToken)
    {
        _statistics.TotalUsersAdded++;
        _statistics.LastUserId = @event.UserId;
        _statistics.LastUserName = @event.Name;
        _statistics.LastUserEmail = @event.Email;
        _statistics.LastUpdated = @event.OccurredAt;

        _logger.LogInformation(
            "User added: {UserId} ({Name}). Total users: {Total}",
            @event.UserId, @event.Name, _statistics.CurrentUserCount);

        return Task.CompletedTask;
    }

    private Task HandleUserRemovedAsync(UserRemovedEvent @event, CancellationToken cancellationToken)
    {
        _statistics.TotalUsersRemoved++;
        _statistics.LastUpdated = @event.OccurredAt;

        _logger.LogInformation(
            "User removed: {UserId}. Total users: {Total}",
            @event.UserId, _statistics.CurrentUserCount);

        return Task.CompletedTask;
    }
}