using System.Diagnostics;
using System.Text;

namespace VFXReviewWorker;

/// <summary>
/// Renews a job's lease with progress reports while the worker does something
/// long that reports nothing on its own — the High quality encode and the
/// uploads can each outlast a 300 s lease, and an expired lease lets the
/// reaper hand the job to another machine mid-upload.
///
/// Each report also replaces the job's log tail with what the worker is doing
/// now ("Uploading High quality MP4: 12.0 / 34.0 MB…"). Without it the app
/// keeps showing aerender's last frame line and a busy job looks hung.
/// </summary>
internal sealed class LeaseKeepAlive : IAsyncDisposable
{
    private readonly ApiClient _api;
    private readonly string _jobId;
    private readonly string _machineId;
    private readonly CancellationTokenSource _cts;
    private readonly SemaphoreSlim _wake = new(0);
    private readonly Task _loop;
    private readonly object _lock = new();
    private readonly List<string> _lines = new();
    private string? _current;

    public LeaseKeepAlive(ApiClient api, string jobId, string machineId, TimeSpan interval, CancellationToken shutdown)
    {
        _api = api;
        _jobId = jobId;
        _machineId = machineId;
        _cts = CancellationTokenSource.CreateLinkedTokenSource(shutdown);
        var token = _cts.Token;
        _loop = Task.Run(async () =>
        {
            try
            {
                while (!token.IsCancellationRequested)
                {
                    // Best-effort by contract (ApiClient.ProgressAsync never throws
                    // on transport errors); progress stays at 1.0 — the render is done.
                    await _api.ProgressAsync(_jobId, _machineId, 1.0, null, null, null, Render(), token);
                    await _wake.WaitAsync(interval, token);
                }
            }
            catch (OperationCanceledException)
            {
                // stopped
            }
        });
    }

    /// <summary>Adds a finished step to the status shown in the app.</summary>
    public void Line(string text)
    {
        lock (_lock)
        {
            _current = null;
            _lines.Add($"{DateTime.Now:HH:mm:ss} {text}");
        }
        _wake.Release();
    }

    /// <summary>
    /// Progress callback for <see cref="ApiClient.UploadArtifactAsync"/>: keeps
    /// one live line ("Uploading X: 12.0 / 34.0 MB (35%, 2.1 MB/s)") up to date.
    /// </summary>
    public Action<long> Track(string label, string filePath)
    {
        long total = File.Exists(filePath) ? new FileInfo(filePath).Length : 0;
        var sw = Stopwatch.StartNew();
        lock (_lock) _current = $"Uploading {label}: 0.0 / {Mb(total)} MB";
        _wake.Release();
        return sent =>
        {
            var pct = total > 0 ? 100.0 * sent / total : 0;
            var speed = sent / 1048576.0 / Math.Max(0.001, sw.Elapsed.TotalSeconds);
            lock (_lock) _current = $"Uploading {label}: {Mb(sent)} / {Mb(total)} MB ({pct:F0}%, {speed:F1} MB/s)";
        };
    }

    private static string Mb(long bytes) => (bytes / 1048576.0).ToString("F1");

    private string Render()
    {
        lock (_lock)
        {
            var sb = new StringBuilder();
            foreach (var l in _lines) sb.AppendLine(l);
            if (_current is not null) sb.AppendLine($"{DateTime.Now:HH:mm:ss} {_current}");
            return sb.ToString();
        }
    }

    public async ValueTask DisposeAsync()
    {
        _cts.Cancel();
        try { await _loop; } catch { /* already reported */ }
        _cts.Dispose();
        _wake.Dispose();
    }
}