using System.Text.Json;

namespace Server.WatchBody.Web.Services;

/// <summary>
/// Таймлайн тренировки из facts_json (spec 03 §2 m08): по Lap —
/// длительность/avg/peak пульс/отдых; пульсограмма records с
/// прореживанием до 600 точек.
/// </summary>
public static class FactsTimeline
{
    public static (List<Dictionary<string, object?>> Timeline, List<Dictionary<string, int>> Curve) Parse(
        string? factsJson, int sessionDurationS)
    {
        var timeline = new List<Dictionary<string, object?>>();
        var curve = new List<Dictionary<string, int>>();
        if (string.IsNullOrWhiteSpace(factsJson)) return (timeline, curve);
        try
        {
            using var doc = JsonDocument.Parse(factsJson);
            var root = doc.RootElement;

            var records = new List<(int t, int hr)>();
            if (root.TryGetProperty("records", out var recordNodes))
                foreach (var r in recordNodes.EnumerateArray())
                    if (r.TryGetProperty("t_offset_s", out var t) && r.TryGetProperty("hr", out var hr))
                        records.Add((t.GetInt32(), hr.GetInt32()));

            // пульсограмма: не более 600 точек
            if (records.Count > 0)
            {
                var step = Math.Max(1, (int)Math.Ceiling(records.Count / 600.0));
                for (var i = 0; i < records.Count; i += step)
                    curve.Add(new Dictionary<string, int> { ["t"] = records[i].t, ["hr"] = records[i].hr });
            }

            if (!root.TryGetProperty("laps", out var lapNodes)) return (timeline, curve);
            var laps = new List<(DateTime start, int durationS)>();
            foreach (var l in lapNodes.EnumerateArray())
                if (l.TryGetProperty("start", out var s) && l.TryGetProperty("duration_s", out var d) &&
                    DateTime.TryParse(s.GetString(), null, System.Globalization.DateTimeStyles.AssumeUniversal |
                        System.Globalization.DateTimeStyles.AdjustToUniversal, out var start))
                    laps.Add((start, d.GetInt32()));
            var sessionStart = laps.Count > 0 ? laps.Min(l => l.start)
                : records.Count > 0 ? DateTime.MinValue : DateTime.MinValue;

            for (var i = 0; i < laps.Count; i++)
            {
                var offset = (int)(laps[i].start - sessionStart).TotalSeconds;
                var end = offset + laps[i].durationS;
                var nextStart = i + 1 < laps.Count ? (int)(laps[i + 1].start - sessionStart).TotalSeconds : end;
                var inLap = records.Where(r => r.t >= offset && r.t <= end).Select(r => r.hr).ToList();
                timeline.Add(new Dictionary<string, object?>
                {
                    ["index"] = i,
                    ["startOffsetS"] = offset,
                    ["durationS"] = laps[i].durationS,
                    ["avgHr"] = inLap.Count > 0 ? (int)Math.Round(inLap.Average(), MidpointRounding.AwayFromZero) : null,
                    ["peakHr"] = inLap.Count > 0 ? inLap.Max() : null,
                    ["restAfterS"] = Math.Max(0, nextStart - end),
                });
            }
        }
        catch (JsonException)
        {
            // битые факты — пустой таймлайн
        }
        return (timeline, curve);
    }
}