using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;

namespace Jellyfin.Plugin.Enigma2;

/// <summary>Bounded, never-ending HLS timeline shared by language-specific viewers.</summary>
public sealed class ContinuityTimeline
{
    // 112 frames at 50 Hz == 105 AAC frames at 48 kHz: exact AV boundary.
    public const double SegmentSeconds = 2.24;
    public sealed record Segment(long Sequence, long DiscontinuitiesBefore, bool Discontinuity, double Duration, byte[] Video, string Slate, long Start90k, long? ClockOffset90k = null);
    private readonly double slateSeconds;
    private readonly List<Segment> segments = new();
    private readonly object gate = new();
    private long next, discontinuities;
    private long clock90k = 126000;
    private string previousEpoch;
    private string clockEpoch;
    private long sourceOffset90k, sourceWrap90k, lastDecode90k;
    private DateTime lastAppend, lastLive;
    public ContinuityTimeline(DateTime now, bool withSlates = true, double slateSeconds = SegmentSeconds) { this.slateSeconds = slateSeconds; lastAppend = now; lastLive = DateTime.MinValue; if (!withSlates) return; Add(null, "waiting", "slate", slateSeconds, now); Add(null, "waiting", "slate", slateSeconds, now); }
    private void Add(byte[] video, string slate, string epoch, double duration, DateTime now, long? offset = null, long? start = null, long? end = null)
    {
        var discontinuity = next > 0 && (slate != null || previousEpoch != epoch);
        segments.Add(new(next++, discontinuities, discontinuity, duration, video, slate, start ?? clock90k, offset));
        clock90k = end ?? clock90k + (long)Math.Round(duration * 90000);
        if (discontinuity) discontinuities++;
        previousEpoch = epoch; lastAppend = now;
        while (segments.Count > 8) segments.RemoveAt(0);
    }
    public void Live(byte[] video, string epoch, double duration, DateTime now)
    {
        if (video == null || video.Length == 0 || video.Length > 32 * 1024 * 1024 || duration <= 0 || duration > 30) throw new ArgumentException("Invalid live segment");
        lock (gate)
        {
            lastLive = now;
            var bounds = TransportStreamClock.ClockBounds(video);
            if (bounds == null) { Add(video, null, epoch, duration, now); return; }
            var times = bounds.Value;
            // Keep one offset for an entire producer epoch. Anchoring each segment
            // to its first PTS corrupts DTS order when copied video has B-frames.
            if (clockEpoch != epoch || previousEpoch != epoch)
            { clockEpoch = epoch; sourceWrap90k = 0; sourceOffset90k = clock90k + 9000 - times.Earliest; }
            else if (times.Decode + sourceWrap90k < lastDecode90k - (1L << 32)) sourceWrap90k += 1L << 33;
            lastDecode90k = times.Decode + sourceWrap90k;
            var offset = sourceOffset90k + sourceWrap90k;
            var end = Math.Max(times.Decode + (long)Math.Round(duration * 90000), times.Latest + 9000) + offset;
            Add(video, null, epoch, duration, now, offset, times.Decode + offset, end);
        }
    }
    public void Tick(DateTime now, bool retrying)
    {
        lock (gate)
            if ((now - lastAppend).TotalSeconds >= 2 && (now - lastLive).TotalSeconds >= 5)
                Add(null, retrying ? "retrying" : "waiting", "slate", slateSeconds, now);
    }
    public Segment Find(long sequence) { lock (gate) return segments.FirstOrDefault(s => s.Sequence == sequence); }
    public string Playlist()
    {
        lock (gate)
        {
            var window = segments.TakeLast(4).ToArray();
            var text = new StringBuilder($"#EXTM3U\n#EXT-X-VERSION:3\n#EXT-X-TARGETDURATION:{Math.Max(5, Math.Ceiling(window.Select(s => s.Duration).DefaultIfEmpty(5).Max()))}\n");
            if (window.Length == 0) return text.ToString();
            text.Append("#EXT-X-MEDIA-SEQUENCE:").Append(window[0].Sequence).Append('\n');
            text.Append("#EXT-X-DISCONTINUITY-SEQUENCE:").Append(window[0].DiscontinuitiesBefore).Append('\n');
            foreach (var segment in window)
            {
                if (segment.Discontinuity) text.Append("#EXT-X-DISCONTINUITY\n");
                text.Append("#EXTINF:").Append(segment.Duration.ToString("0.000000", CultureInfo.InvariantCulture)).Append(",\n");
                text.Append(segment.Sequence).Append(".ts\n");
            }
            return text.ToString(); // Never ENDLIST: only the viewer closes playback.
        }
    }
}