using System.Collections.Concurrent;
using System.Threading.Channels;
using Microsoft.Extensions.Options;
using ScrapperAPI.Enums;
using ScrapperAPI.Interfaces;
using ScrapperAPI.Options;
using ScrapperAPI.Records;

namespace ScrapperAPI.Workers;

public sealed class ScrapeCoordinator : BackgroundService, IScrapeCoordinator
{
    private readonly IServiceScopeFactory _scopeFactory;
    private readonly IHttpClientFactory _httpClientFactory;
    private readonly ILogger<ScrapeCoordinator> _logger;
    private readonly IScraperHttpClient _scraperHttp;
    private readonly IScrapeEventBus _events;
    private readonly ScraperOptions _opts;
    private readonly WorkerOptions _workerOpts;

    private readonly Channel<int> _startRequests = Channel.CreateUnbounded<int>(
        new UnboundedChannelOptions { SingleReader = true, SingleWriter = false });

    private readonly ConcurrentDictionary<int, Runner> _runners = new();
    
    private static readonly ThreadLocal<Random> _rng =
        new(() => new Random());

    public ScrapeCoordinator(
        IServiceScopeFactory scopeFactory,
        IHttpClientFactory httpClientFactory,
        ILogger<ScrapeCoordinator> logger,
        IOptions<ScraperOptions> options,
        IOptions<WorkerOptions> workerOptions,
        IScraperHttpClient scraperHttp,
        IScrapeEventBus events)
    {
        _scopeFactory = scopeFactory;
        _httpClientFactory = httpClientFactory;
        _logger = logger;
        _opts = options.Value;
        _workerOpts = workerOptions.Value;
        _scraperHttp = scraperHttp;
        _events = events;
    }

    public async Task StartAsync(int sessionId, CancellationToken ct = default)
    {
        var runner = _runners.GetOrAdd(sessionId, id => new Runner(id));
        runner.RequestStart();

        await _events.PublishAsync(new ScrapeEvent(
            ScrapeEventType.SessionStarted, sessionId, DateTimeOffset.UtcNow
        ), ct);

        await _startRequests.Writer.WriteAsync(sessionId, ct);
    }

    public Task StopAsync(int sessionId)
    {
        if (_runners.TryGetValue(sessionId, out var runner))
        {
            runner.RequestStop();
            _ = _events.PublishAsync(new ScrapeEvent(
                ScrapeEventType.SessionStopRequested, sessionId, DateTimeOffset.UtcNow
            ));
        }
        return Task.CompletedTask;
    }

    public ScrapeRuntimeStatus GetRuntimeStatus(int sessionId)
    {
        if (!_runners.TryGetValue(sessionId, out var r))
            return new(sessionId, false, false, null, null, null);

        return new(sessionId, r.IsRunning, r.StopRequested, r.CurrentQueueId, r.CurrentUrl, r.CurrentStartedAt);
    }

    public IReadOnlyCollection<ScrapeRuntimeStatus> ListRunningSessions()
        => _runners.Values
            .Where(r => r.IsRunning)
            .Select(r => new ScrapeRuntimeStatus(r.SessionId, r.IsRunning, r.StopRequested, r.CurrentQueueId, r.CurrentUrl, r.CurrentStartedAt))
            .ToList();

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("ScrapeCoordinator started.");

        while (!stoppingToken.IsCancellationRequested)
        {
            int sessionId;
            try
            {
                sessionId = await _startRequests.Reader.ReadAsync(stoppingToken);
            }
            catch (OperationCanceledException) { break; }

            var runner = _runners.GetOrAdd(sessionId, id => new Runner(id));
            runner.RequestStart();

            _ = RunSessionLoopAsync(runner, stoppingToken);
        }
    }
    
    private Task PoliteDelayAsync(CancellationToken ct)
    {
        var min = _opts.DelayMinMs;
        var max = _opts.DelayMaxMs;

        if (min < 0) min = 0;
        if (max < min) max = min;

        var delayMs = Random.Shared.Next(min, max + 1);
        return Task.Delay(delayMs, ct);
    }

    private async Task RunSessionLoopAsync(Runner runner, CancellationToken hostToken)
    {
        if (!runner.TryEnterLoop())
            return;

        runner.MarkRunning(true);

        try
        {
            if (!_workerOpts.Local.Enabled)
                return;

            var http = _httpClientFactory.CreateClient("scraper");

            // When PreferAgents: only run local if no agent was recently seen.
            while (!hostToken.IsCancellationRequested)
            {
                if (_workerOpts.Mode == DistributedMode.PreferAgents)
                {
                    var noAgents = await NoAgentsRecentlySeenAsync(_workerOpts.Local.PreferAgentsGraceSeconds, hostToken);
                    if (!noAgents)
                    {
                        await Task.Delay(TimeSpan.FromSeconds(2), hostToken);
                        continue;
                    }
                }

                // STOP GRACIOSO: não pega próxima URL
                if (runner.StopRequested)
                    break;
                var concurrency = Math.Max(1, _workerOpts.Local.Concurrency);
                var leaseFor = TimeSpan.FromSeconds(Math.Max(5, _workerOpts.LeaseSeconds));

                var tasks = Enumerable.Range(0, concurrency)
                    .Select(i => RunLocalWorkerLoopAsync(runner, workerId: $"local:{Environment.MachineName}:{i}", leaseFor, hostToken))
                    .ToArray();

                await Task.WhenAll(tasks);
                break; // no more work (or stop requested)
            }
        }
        finally
        {
            runner.MarkRunning(false);
            await _events.PublishAsync(new ScrapeEvent(
                ScrapeEventType.SessionStopped,
                runner.SessionId,
                DateTimeOffset.UtcNow
            ), hostToken);
            runner.ExitLoop();
        }
    }

    private async Task RunLocalWorkerLoopAsync(Runner runner, string workerId, TimeSpan leaseFor, CancellationToken hostToken)
    {
        while (!hostToken.IsCancellationRequested && !runner.StopRequested)
        {
            using var scope = _scopeFactory.CreateScope();
            var queue = scope.ServiceProvider.GetRequiredService<IQueueRepository>();
            var content = scope.ServiceProvider.GetRequiredService<IContentRepository>();

            var item = await queue.TryDequeueAsync(runner.SessionId, workerId, leaseFor, hostToken);
            if (item is null)
                return;

            runner.SetCurrent(item.Id, item.Url);

            await _events.PublishAsync(new ScrapeEvent(
                ScrapeEventType.ItemStarted,
                runner.SessionId,
                DateTimeOffset.UtcNow,
                QueueId: item.Id,
                Url: item.Url
            ), hostToken);

            try
            {
                var html = await _scraperHttp.GetStringWithRetryAsync(item.Url, hostToken);

                await content.SaveAsync(item.Id, html, hostToken);
                await queue.MarkDoneAsync(item.Id, workerId, hostToken);

                await _events.PublishAsync(new ScrapeEvent(
                    ScrapeEventType.ItemSucceeded,
                    runner.SessionId,
                    DateTimeOffset.UtcNow,
                    QueueId: item.Id,
                    Url: item.Url
                ), hostToken);
            }
            catch (Exception ex)
            {
                await queue.MarkFailedAsync(item.Id, workerId, Truncate(ex.ToString(), 8000), hostToken);

                await _events.PublishAsync(new ScrapeEvent(
                    ScrapeEventType.ItemFailed,
                    runner.SessionId,
                    DateTimeOffset.UtcNow,
                    QueueId: item.Id,
                    Url: item.Url,
                    Error: ex.Message
                ), hostToken);
            }
            finally
            {
                var counts = await queue.GetCountsAsync(runner.SessionId, hostToken);
                var percent = counts.Total == 0 ? 0 : (double)counts.Done * 100.0 / (double)counts.Total;

                await _events.PublishAsync(new ScrapeEvent(
                    ScrapeEventType.Progress,
                    runner.SessionId,
                    DateTimeOffset.UtcNow,
                    Total: counts.Total,
                    Done: counts.Done,
                    Pending: counts.Pending,
                    Processing: counts.Processing,
                    Failed: counts.Failed,
                    Percent: percent
                ), hostToken);

                runner.ClearCurrent();

                if (!runner.StopRequested && !hostToken.IsCancellationRequested)
                    await PoliteDelayAsync(hostToken);
            }
        }
    }

    private async Task<bool> NoAgentsRecentlySeenAsync(int withinSeconds, CancellationToken ct)
    {
        try
        {
            using var scope = _scopeFactory.CreateScope();
            var agents = scope.ServiceProvider.GetRequiredService<IAgentRepository>();
            var active = await agents.CountActiveAsync(TimeSpan.FromSeconds(Math.Max(1, withinSeconds)), ct);
            return active == 0;
        }
        catch
        {
            // If agents table isn't configured yet, default to "no agents".
            return true;
        }
    }

    private static async Task<string> FetchHtmlAsync(HttpClient http, string url, CancellationToken ct)
    {
        using var req = new HttpRequestMessage(HttpMethod.Get, url);
        req.Headers.UserAgent.ParseAdd("webscrapper/1.0");
        using var resp = await http.SendAsync(req, HttpCompletionOption.ResponseHeadersRead, ct);
        resp.EnsureSuccessStatusCode();
        return await resp.Content.ReadAsStringAsync(ct);
    }

    private static string Truncate(string s, int max) => s.Length <= max ? s : s[..max];

    private sealed class Runner
    {
        private int _loopEntered;

        public int SessionId { get; }
        public bool IsRunning { get; private set; }
        public bool StopRequested { get; private set; }

        public int? CurrentQueueId { get; private set; }
        public string? CurrentUrl { get; private set; }
        public DateTimeOffset? CurrentStartedAt { get; private set; }

        public Runner(int sessionId) => SessionId = sessionId;

        public void RequestStart() => StopRequested = false;
        public void RequestStop() => StopRequested = true;

        public bool TryEnterLoop() => Interlocked.CompareExchange(ref _loopEntered, 1, 0) == 0;
        public void ExitLoop() => Interlocked.Exchange(ref _loopEntered, 0);
        public void MarkRunning(bool running) => IsRunning = running;

        public void SetCurrent(int queueId, string url)
        {
            CurrentQueueId = queueId;
            CurrentUrl = url;
            CurrentStartedAt = DateTimeOffset.UtcNow;
        }

        public void ClearCurrent()
        {
            CurrentQueueId = null;
            CurrentUrl = null;
            CurrentStartedAt = null;
        }
    }
}