using System;
using Svrnty.CQRS.Events.Abstractions.Storage;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Svrnty.CQRS.Events.Abstractions;

namespace Svrnty.CQRS.Events.PostgreSQL.Retention;

/// <summary>
/// Background service that automatically enforces retention policies.
/// Periodically cleans up events that exceed configured retention limits.
/// </summary>
public class RetentionPolicyService : BackgroundService
{
    private readonly IRetentionPolicyStore _policyStore;
    private readonly RetentionServiceOptions _options;
    private readonly ILogger<RetentionPolicyService> _logger;

    public RetentionPolicyService(
        IRetentionPolicyStore policyStore,
        IOptions<RetentionServiceOptions> options,
        ILogger<RetentionPolicyService> logger)
    {
        _policyStore = policyStore ?? throw new ArgumentNullException(nameof(policyStore));
        _options = options?.Value ?? throw new ArgumentNullException(nameof(options));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));

        _options.Validate();
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        if (!_options.Enabled)
        {
            _logger.LogInformation("Retention policy service is disabled");
            return;
        }

        _logger.LogInformation(
            "Retention policy service started. Cleanup interval: {CleanupInterval}, Window: {WindowStart}-{WindowEnd} UTC, UseWindow: {UseWindow}",
            _options.CleanupInterval,
            _options.CleanupWindowStart,
            _options.CleanupWindowEnd,
            _options.UseCleanupWindow);

        using var timer = new PeriodicTimer(_options.CleanupInterval);

        try
        {
            while (await timer.WaitForNextTickAsync(stoppingToken))
            {
                await RunCleanupCycleAsync(stoppingToken);
            }
        }
        catch (OperationCanceledException)
        {
            _logger.LogInformation("Retention policy service stopping");
        }
        catch (Exception ex)
        {
            _logger.LogCritical(ex, "Retention policy service encountered a fatal error");
            throw;
        }
    }

    private async Task RunCleanupCycleAsync(CancellationToken cancellationToken)
    {
        try
        {
            // Check if we're in the cleanup window
            if (_options.UseCleanupWindow && !IsInCleanupWindow())
            {
                _logger.LogDebug(
                    "Outside cleanup window ({WindowStart}-{WindowEnd} UTC), skipping retention enforcement",
                    _options.CleanupWindowStart,
                    _options.CleanupWindowEnd);
                return;
            }

            _logger.LogInformation("Starting retention policy enforcement cycle");

            var result = await _policyStore.ApplyRetentionPoliciesAsync(cancellationToken);

            if (result.EventsDeleted > 0)
            {
                _logger.LogInformation(
                    "Retention cleanup complete: {StreamsProcessed} streams processed, {EventsDeleted} events deleted in {Duration}",
                    result.StreamsProcessed,
                    result.EventsDeleted,
                    result.Duration);

                // Log per-stream details at Debug level
                if (result.EventsDeletedPerStream != null)
                {
                    foreach (var (streamName, count) in result.EventsDeletedPerStream)
                    {
                        _logger.LogDebug(
                            "Stream {StreamName}: {EventsDeleted} events deleted",
                            streamName,
                            count);
                    }
                }
            }
            else
            {
                _logger.LogDebug(
                    "Retention cleanup complete: No events needed cleanup (processed {StreamsProcessed} streams in {Duration})",
                    result.StreamsProcessed,
                    result.Duration);
            }
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error during retention policy enforcement cycle");
            // Don't rethrow - we want the service to continue running
        }
    }

    private bool IsInCleanupWindow()
    {
        var now = DateTime.UtcNow.TimeOfDay;

        // Handle window that crosses midnight
        if (_options.CleanupWindowEnd < _options.CleanupWindowStart)
        {
            // Window spans midnight (e.g., 22:00 - 02:00)
            return now >= _options.CleanupWindowStart || now <= _options.CleanupWindowEnd;
        }
        else
        {
            // Normal window (e.g., 02:00 - 06:00)
            return now >= _options.CleanupWindowStart && now <= _options.CleanupWindowEnd;
        }
    }

    public override async Task StopAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("Retention policy service is stopping");
        await base.StopAsync(cancellationToken);
    }
}