using Dynastream.Fit;
using FitDateTime = Dynastream.Fit.DateTime;

namespace Server.WatchBody.Import;

/// <summary>Разобранные факты активности (.fit / TCX / GPX) — единый
/// вход WorkoutImporter (spec 01/02 m06).</summary>
public sealed record ActivityFacts(
    string FactsJson,
    System.DateTime StartedAt,
    int? AvgHr,
    int? HrRecoveryS,
    string FitFileId,
    string Device);

/// <summary>Файл не активность или повреждён (spec 01 §1).</summary>
public class FitParseException(string message) : Exception(message);

/// <summary>
/// Потоковый разбор .fit — официальный FIT SDK (tech-req разд. 5):
/// события Decode.MesgEvent, файл читается один раз. Результат —
/// канонический факт workout-facts/1 (tech-req 2.3).
/// </summary>
public class FitParser
{
    private readonly decimal _restingHr; // порог возврата пульса (Р3-А)

    public FitParser(decimal restingHrSitting = 90) => _restingHr = restingHrSitting;

    public ActivityFacts Parse(string path)
    {
        var session = new SessionAccumulator();
        var bytes = System.IO.File.ReadAllBytes(path);
        using (var probe = new MemoryStream(bytes))
        {
            if (!new Decode().IsFIT(probe))
                throw new FitParseException($"файл не .fit: {path}");
            probe.Position = 0;
            if (!new Decode().CheckIntegrity(probe))
                throw new FitParseException($"контрольная сумма .fit не сошлась: {path}");
        }
        var decode = new Decode();
        decode.MesgEvent += (_, e) => session.OnMesg(e.mesg);
        using var stream = new MemoryStream(bytes);
        if (!decode.Read(stream))
            throw new FitParseException($"файл не прочитан: {path}");
        return session.Build(_restingHr);
    }

    /// <summary>Генерация .fit для тест-фикстур (spec 01 §4) —
    /// энкодер SDK; порядок FileId → DeviceInfo → Record* → Lap* →
    /// Set* → Session.</summary>
    public static void WriteTestFile(
        string path, System.DateTime startUtc,
        (int offsetS, int hr)[] records,
        (int index, int offsetS, int durationS)[] laps,
        (int reps, decimal? weightKg)[] sets,
        string? serial = null)
    {
        var encode = new Encode(ProtocolVersion.V20);
        using var output = new FileStream(path, FileMode.Create);
        encode.Open(output);

        var fileId = new FileIdMesg();
        fileId.SetTimeCreated(new FitDateTime(startUtc));
        if (serial != null) fileId.SetSerialNumber(uint.Parse(serial));
        encode.Write(fileId);

        var device = new DeviceInfoMesg();
        device.SetTimestamp(new FitDateTime(startUtc));
        device.SetGarminProduct(GarminProduct.Fenix6sAsia);
        encode.Write(device);

        foreach (var (offsetS, hr) in records)
        {
            var record = new RecordMesg();
            record.SetTimestamp(new FitDateTime(startUtc.AddSeconds(offsetS)));
            record.SetHeartRate((byte)hr);
            encode.Write(record);
        }
        foreach (var (index, offsetS, durationS) in laps)
        {
            var lap = new LapMesg();
            lap.SetStartTime(new FitDateTime(startUtc.AddSeconds(offsetS)));
            lap.SetTotalTimerTime((float)durationS);
            encode.Write(lap);
        }
        foreach (var (reps, weightKg) in sets)
        {
            var set = new SetMesg();
            set.SetStartTime(new FitDateTime(startUtc));
            set.SetRepetitions((ushort)reps);
            if (weightKg != null) set.SetWeight((float)weightKg);
            encode.Write(set);
        }

        var session = new SessionMesg();
        session.SetStartTime(new FitDateTime(startUtc));
        session.SetTotalTimerTime((float)(records.Length > 0 ? records[^1].offsetS + 60 : 3600));
        session.SetSport(Sport.Training);
        encode.Write(session);
        encode.Close();
    }

    private sealed class SessionAccumulator
    {
        private FileIdMesg? _fileId;
        private SessionMesg? _session;
        private readonly List<LapMesg> _laps = [];
        private readonly List<(System.DateTime time, int hr)> _records = [];
        private readonly List<SetMesg> _sets = [];
        private DeviceInfoMesg? _device;

        public void OnMesg(Mesg mesg)
        {
            // SDK доставляет базовый Mesg — типизированные классы
            // конструируются из него по Num
            switch (mesg.Num)
            {
                case MesgNum.FileId: _fileId = new FileIdMesg(mesg); break;
                case MesgNum.Session: _session = new SessionMesg(mesg); break;
                case MesgNum.Lap: _laps.Add(new LapMesg(mesg)); break;
                case MesgNum.Record:
                {
                    var record = new RecordMesg(mesg);
                    if (record.GetHeartRate().HasValue && record.GetHeartRate().Value > 0 &&
                        record.GetTimestamp() != null)
                        _records.Add((record.GetTimestamp().GetDateTime().ToUniversalTime(),
                            record.GetHeartRate().Value));
                    break;
                }
                case MesgNum.Set: _sets.Add(new SetMesg(mesg)); break;
                case MesgNum.DeviceInfo:
                {
                    var device = new DeviceInfoMesg(mesg);
                    if (device.GetTimestamp() != null &&
                        (_device == null ||
                         device.GetTimestamp().GetDateTime() >= _device.GetTimestamp().GetDateTime()))
                        _device = device;
                    break;
                }
            }
        }

        public ActivityFacts Build(decimal restingHr)
        {
            if (_session?.GetStartTime() == null)
                throw new FitParseException("в файле нет Session — это не активность");

            var start = _session.GetStartTime().GetDateTime().ToUniversalTime();
            var durationS = _session.GetTotalTimerTime() != null
                ? (int)Math.Round(_session.GetTotalTimerTime().Value, MidpointRounding.AwayFromZero)
                : 0;

            var lapsJson = _laps
                .Where(l => l.GetStartTime() != null)
                .Select((l, i) => new Dictionary<string, object?>
                {
                    ["index"] = i,
                    ["start"] = l.GetStartTime().GetDateTime().ToUniversalTime()
                        .ToString("yyyy-MM-dd'T'HH:mm:ss'Z'"),
                    ["duration_s"] = l.GetTotalTimerTime() != null
                        ? (int)Math.Round(l.GetTotalTimerTime().Value, MidpointRounding.AwayFromZero)
                        : 0,
                })
                .ToList();

            var recordsJson = _records
                .Select(r => new Dictionary<string, object?>
                {
                    ["t_offset_s"] = (int)(r.time - start).TotalSeconds,
                    ["hr"] = r.hr,
                })
                .ToList();

            var setsJson = _sets
                .Where(s => s.GetRepetitions().HasValue && s.GetRepetitions().Value > 0)
                .Select((s, i) =>
                {
                    var item = new Dictionary<string, object?>
                    {
                        ["index"] = i,
                        ["reps"] = s.GetRepetitions().Value,
                    };
                    if (s.GetWeight().HasValue && s.GetWeight().Value > 0)
                        item["weight_kg"] = Math.Round((decimal)s.GetWeight().Value, 1,
                            MidpointRounding.AwayFromZero);
                    return item;
                })
                .ToList();

            var fitFileId = ComposeFileId();
            var device = _device == null
                ? string.Empty
                : _device.GetGarminProduct().HasValue
                    ? _device.GetGarminProduct().Value.ToString()
                    : _device.GetProduct()?.ToString() ?? string.Empty;

            var facts = new Dictionary<string, object?>
            {
                ["schema"] = "workout-facts/1",
                ["session"] = new Dictionary<string, object?>
                {
                    ["type"] = _session.GetSport().ToString(),
                    ["start"] = start.ToString("yyyy-MM-dd'T'HH:mm:ss'Z'"),
                    ["duration_s"] = durationS,
                },
                ["laps"] = lapsJson,
                ["records"] = recordsJson,
                ["sets"] = setsJson,
                ["fit_file_id"] = fitFileId,
                ["device"] = device,
            };

            int? avgHr = recordsJson.Count == 0
                ? null
                : (int)Math.Round(recordsJson.Average(r => (int)r["hr"]!),
                    MidpointRounding.AwayFromZero);
            var lapEnds = _laps
                .Where(l => l.GetStartTime() != null && l.GetTotalTimerTime() != null)
                .Select(l => l.GetStartTime().GetDateTime().ToUniversalTime()
                    .AddSeconds(l.GetTotalTimerTime().Value))
                .ToList();
            var recovery = HrRecovery(lapEnds, _records, restingHr);

            return new ActivityFacts(
                System.Text.Json.JsonSerializer.Serialize(facts),
                start, avgHr, recovery, fitFileId, device);
        }

        /// <summary>Конец последнего Lap → первый Record строго после
        /// него с hr ниже порога (Ф-13.4, spec 01 §3); нет записей или
        /// не опустился — null.</summary>
        private static int? HrRecovery(
            List<System.DateTime> lapEnds, List<(System.DateTime time, int hr)> records, decimal restingHr)
        {
            if (lapEnds.Count == 0) return null;
            var lastEnd = lapEnds.Max();
            var after = records
                .Where(r => r.time > lastEnd)
                .OrderBy(r => r.time)
                .ToList();
            var hit = after.FirstOrDefault(r => r.hr < restingHr);
            if (hit == default) return null;
            return (int)Math.Round((hit.time - lastEnd).TotalSeconds, MidpointRounding.AwayFromZero);
        }

        private string ComposeFileId() =>
            _fileId == null
                ? throw new FitParseException("в файле нет FileId — не Garmin-экспорт")
                : _fileId.GetTimeCreated() == null
                    ? throw new FitParseException("FileId без TimeCreated")
                    : $"{(_fileId.GetSerialNumber()?.ToString() ?? "nosn")}-" +
                      $"{_fileId.GetTimeCreated().GetDateTime().ToUniversalTime():yyyyMMdd'T'HHmmss'Z'}";

    }
}