using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace Jellyfin.Plugin.Enigma2;

/// <summary>Keep DVB page/region/object versions distinct across independently muxed status and live clips.</summary>
public sealed class DvbSubtitleVersions
{
    private readonly HashSet<int> pids;
    private readonly Dictionary<(int Pid, int Type, int Id), int> versions = new();
    private readonly Dictionary<long, List<(int Position, byte Value)>> plans = new();
    public DvbSubtitleVersions(BroadcastTracks tracks) => pids = tracks.Output.Select((s, i) => (s.Codec, Pid: 256 + i)).Where(s => s.Codec == "DVBSUB").Select(s => s.Pid).ToHashSet();
    public void Apply(byte[] transport, long sequence)
    {
        if (pids.Count == 0) return;
        if (plans.TryGetValue(sequence, out var known)) { foreach (var edit in known) transport[edit.Position] = edit.Value; return; }
        var edits = new List<(int, byte)>();
        var packets = new Dictionary<int, List<int>>();
        void Flush(int pid, List<int> positions)
        {
            if (positions.Count < 14) return;
            byte At(int index) => transport[positions[index]];
            if (At(0) != 0 || At(1) != 0 || At(2) != 1 || At(3) != 189) return;
            var length = (At(4) << 8) | At(5);
            var end = length > 0 ? Math.Min(positions.Count, length + 6) : positions.Count;
            var p = 9 + At(8);
            if (p + 2 > end || At(p) != 32) return; p += 2;
            while (p + 6 <= end && At(p) == 15)
            {
                var type = At(p + 1); var size = (At(p + 4) << 8) | At(p + 5); var data = p + 6;
                if (data + size > end) break;
                var field = type switch { 16 => 1, 17 => 1, 18 => 1, 19 => 2, 20 => 0, _ => -1 };
                if (field >= 0 && size > field)
                {
                    var id = type switch { 17 or 18 => At(data), 19 => (At(data) << 8) | At(data + 1), _ => 0 };
                    var key = (pid, (int)type, id);
                    if (!versions.ContainsKey(key) && versions.Count >= 4096) throw new InvalidDataException("Too many DVB subtitle objects");
                    versions.TryGetValue(key, out var next); versions[key] = next + 1;
                    var index = positions[data + field]; var value = (byte)((transport[index] & 15) | ((next & 15) << 4));
                    transport[index] = value; edits.Add((index, value));
                }
                p = data + size;
            }
        }
        for (var start = 0; start + 188 <= transport.Length; start += 188)
        {
            var pid = ((transport[start + 1] & 31) << 8) | transport[start + 2]; if (!pids.Contains(pid)) continue;
            if ((transport[start + 3] & 16) == 0) continue;
            var payload = start + 4 + ((transport[start + 3] & 32) != 0 ? transport[start + 4] + 1 : 0);
            if (payload >= start + 188) continue;
            if ((transport[start + 1] & 64) != 0)
            {
                if (packets.TryGetValue(pid, out var previous)) Flush(pid, previous);
                packets[pid] = new();
            }
            if (!packets.TryGetValue(pid, out var positions)) continue;
            if (positions.Count + 188 > 512 * 1024) throw new InvalidDataException("Oversized DVB subtitle PES");
            for (var p = payload; p < start + 188; p++) positions.Add(p);
        }
        foreach (var packet in packets) Flush(packet.Key, packet.Value);
        plans[sequence] = edits;
        foreach (var old in plans.Keys.Order().Take(Math.Max(0, plans.Count - 8)).ToArray()) plans.Remove(old);
    }
}