using System.Text.Json;
using Microsoft.Extensions.Logging;

namespace VFXReviewWorker;

/// <summary>
/// Durable lifecycle reports (§7.6): fail/complete reports are written to the
/// spool directory before the first send attempt and replayed strictly in
/// order with exponential backoff (1 s → 60 s). Rendering continues during
/// server downtime; a report is deleted only once the server accepts it (or
/// permanently rejects it as contradictory).
/// </summary>
public sealed class ReportSpooler
{
    private readonly ApiClient _api;
    private readonly ILogger<ReportSpooler> _log;
    private readonly string _dir;
    private readonly SemaphoreSlim _wake = new(0);
    private long _seq;

    public ReportSpooler(ApiClient api, ILogger<ReportSpooler> log, string? dir = null)
    {
        _api = api;
        _log = log;
        _dir = dir ?? WorkerOptions.SpoolDir;
        Directory.CreateDirectory(_dir);
    }

    public void Enqueue(string kind, string jobId, Dictionary<string, object?> payload)
    {
        var report = new SpooledReport { Kind = kind, JobId = jobId, Payload = payload };
        var name = $"{DateTimeOffset.UtcNow.UtcTicks:D20}_{Interlocked.Increment(ref _seq):D6}.json";
        var tmp = Path.Combine(_dir, name + ".tmp");
        var final = Path.Combine(_dir, name);
        File.WriteAllText(tmp, JsonSerializer.Serialize(report, WorkerOptions.JsonOpts));
        File.Move(tmp, final);
        _wake.Release();
    }

    public bool HasPending => Directory.EnumerateFiles(_dir, "*.json").Any();

    /// <summary>Long-running replay loop; started once by the worker service.</summary>
    public async Task RunAsync(CancellationToken ct)
    {
        var backoff = TimeSpan.FromSeconds(1);
        while (!ct.IsCancellationRequested)
        {
            var next = Directory.EnumerateFiles(_dir, "*.json").OrderBy(f => f, StringComparer.Ordinal).FirstOrDefault();
            if (next is null)
            {
                try { await _wake.WaitAsync(TimeSpan.FromSeconds(5), ct); } catch (OperationCanceledException) { break; }
                continue;
            }

            bool done;
            try
            {
                var report = JsonSerializer.Deserialize<SpooledReport>(File.ReadAllText(next), WorkerOptions.JsonOpts);
                if (report is null || string.IsNullOrEmpty(report.JobId))
                {
                    _log.LogWarning("Discarding unreadable spool file {File}", next);
                    done = true;
                }
                else
                {
                    done = await _api.SendLifecycleAsync(report.Kind, report.JobId, report.Payload, ct);
                }
            }
            catch (OperationCanceledException)
            {
                break;
            }
            catch (Exception ex)
            {
                _log.LogWarning(ex, "Spool replay attempt failed for {File}", next);
                done = false;
            }

            if (done)
            {
                try { File.Delete(next); } catch { /* re-sent next pass; server side is idempotent */ }
                backoff = TimeSpan.FromSeconds(1);
            }
            else
            {
                try { await Task.Delay(backoff, ct); } catch (OperationCanceledException) { break; }
                backoff = TimeSpan.FromSeconds(Math.Min(backoff.TotalSeconds * 2, 60));
            }
        }
    }
}