using Serilog;
using System.Threading.Channels;
using TriliumMind.Models;
using TriliumMind.Services;
using TriliumMind.Services.Mappers;

namespace TriliumMind.Workers;

public class AppDbWorker : BackgroundService
{
    private readonly Serilog.ILogger _log;
    private readonly AppConfigs _configs;
    private readonly IServiceScopeFactory _scopeFactory; // Singleton services cannot directly inject Scoped services.
    private readonly Channel<Issue> _issueChannel;

    private readonly int _batchSize;
    private readonly TimeSpan _batchTimeout;

    public AppDbWorker(AppConfigs configs, IServiceScopeFactory scopeFactory, Channel<Issue> issueChannel)
    {
        _log = Log.ForContext<AppDbWorker>();
        _configs = configs;
        _scopeFactory = scopeFactory;
        _issueChannel = issueChannel;

        _batchSize = 50;
        _batchTimeout = TimeSpan.FromSeconds(5);
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _log.Information("AppDbWorker started");

        var batch = new List<Issue>();
        try
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                try
                {
                    using var timeoutCts = CancellationTokenSource.CreateLinkedTokenSource(stoppingToken);
                    timeoutCts.CancelAfter(_batchTimeout);

                    while (batch.Count < _batchSize && !stoppingToken.IsCancellationRequested)
                    {
                        try
                        {
                            if (_issueChannel.Reader.TryRead(out var issue))
                            {
                                batch.Add(issue);
                            }
                            else
                            {
                                // Wait if channel is empty
                                var readTask = _issueChannel.Reader.WaitToReadAsync(timeoutCts.Token);
                                if (await readTask.ConfigureAwait(false))
                                {
                                    if (_issueChannel.Reader.TryRead(out issue))
                                    {
                                        batch.Add(issue);
                                    }
                                }
                                else
                                {
                                    break; // Channel is closed.
                                }
                            }
                        }
                        catch (OperationCanceledException) when (timeoutCts.IsCancellationRequested && !stoppingToken.IsCancellationRequested)
                        {
                            break; // Timeout
                        }
                    }

                    if (batch.Count > 0)
                    {
                        using var scope = _scopeFactory.CreateScope();
                        var db = scope.ServiceProvider.GetRequiredService<AppDbService>();
                        var jiraIssues = batch.Select(i => i.ToEntity()).ToList();
                        await db.UpsertJiraIssuesBatchAsync(jiraIssues, stoppingToken);
                        _log.Information("Processed batch of {count} Jira issues", batch.Count);
                        batch.Clear();
                    }
                }
                catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
                {
                    break;
                }
                catch (Exception ex)
                {
                    _log.Error(ex, "Error processing batch");
                    batch.Clear();
                    await Task.Delay(TimeSpan.FromSeconds(1), stoppingToken);
                }
            }

            // Process any remaining issues in the batch
            if (batch.Count > 0)
            {
                using var scope = _scopeFactory.CreateScope();
                var db = scope.ServiceProvider.GetRequiredService<AppDbService>();
                var jiraIssues = batch.Select(i => i.ToEntity()).ToList();
                await db.UpsertJiraIssuesBatchAsync(jiraIssues, CancellationToken.None);
                _log.Information("Processed final batch of {count} Jira issues", batch.Count);
            }
        }
        catch (Exception ex)
        {
            _log.Error(ex, "Fatal error in JiraDbWorker");
        }
        _log.Information("AppDbWorker stopped");
    }
}