using System.Xml.Linq;

namespace Server.WatchBody.Import;

/// <summary>
/// Упрощённый разбор .tcx/.gpx (производные форматы — документ
/// форматов): тип/старт/длительность + пульс-записи; подходов в этих
/// форматах нет. fit_file_id — имя файла (дедупликация).
/// </summary>
public class TcxGpxParser
{
    public ActivityFacts Parse(string path)
    {
        var name = Path.GetFileName(path);
        XDocument doc;
        try
        {
            doc = XDocument.Load(path);
        }
        catch (Exception e)
        {
            throw new FitParseException($"XML не читается: {name} — {e.Message}");
        }

        return doc.Root!.Name.LocalName == "TrainingCenterDatabase"
            ? ParseTcx(doc, name)
            : ParseGpx(doc, name);
    }

    private static ActivityFacts ParseTcx(XDocument doc, string name)
    {
        var ns = doc.Root!.Name.Namespace;
        var activity = doc.Descendants(ns + "Activity").FirstOrDefault()
            ?? throw new FitParseException($"в TCX нет Activity: {name}");
        var id = (string?)activity.Element(ns + "Id");
        var start = ParseStart(id) ?? throw new FitParseException($"в TCX нет Id-старта: {name}");

        var records = activity.Descendants(ns + "Trackpoint")
            .Select(tp => new
            {
                time = DateTime.TryParse((string?)tp.Element(ns + "Time"), out var t)
                    ? t.ToUniversalTime() : (DateTime?)null,
                hr = (int?)tp.Element(ns + "HeartRateBpm")?.Element(ns + "Value"),
            })
            .Where(r => r.time != null && r.hr != null && r.hr > 0)
            .Select(r => (time: r.time!.Value, hr: r.hr!.Value))
            .ToList();

        var durationS = (int)((records.Count > 0 ? records.Max(r => r.time) : start) - start).TotalSeconds;
        var type = (string?)activity.Attribute("Sport") ?? "unknown";
        return Build(name, start, durationS, type.ToLowerInvariant(), records, device: string.Empty);
    }

    private static ActivityFacts ParseGpx(XDocument doc, string name)
    {
        var start = doc.Descendants().FirstOrDefault(e => e.Name.LocalName == "time") is { } t
            ? DateTime.Parse(t.Value).ToUniversalTime()
            : throw new FitParseException($"в GPX нет времени: {name}");
        var records = doc.Descendants()
            .Where(e => e.Name.LocalName is "trkpt" or "wpt")
            .Select(pt => new
            {
                time = pt.Descendants().FirstOrDefault(x => x.Name.LocalName == "time") is { } ptTime &&
                       DateTime.TryParse(ptTime.Value, out var ptParsed)
                    ? ptParsed.ToUniversalTime() : (DateTime?)null,
                hr = pt.Descendants().FirstOrDefault(x => x.Name.LocalName is "hr" or "gpxtpx:hr"
                        || x.Name.LocalName.EndsWith("hr")) is { } hrEl && int.TryParse(hrEl.Value, out var hr)
                    ? hr : (int?)null,
            })
            .Where(r => r.time != null && r.hr != null && r.hr > 0)
            .Select(r => (time: r.time!.Value, hr: r.hr!.Value))
            .ToList();

        var durationS = (int)((records.Count > 0 ? records.Max(r => r.time) : start) - start).TotalSeconds;
        return Build(name, start, durationS, "unknown", records, device: string.Empty);
    }

    internal static ActivityFacts Build(string fileId, DateTime start, int durationS,
        string type, List<(DateTime time, int hr)> records, string device)
    {
        var facts = new Dictionary<string, object?>
        {
            ["schema"] = "workout-facts/1",
            ["session"] = new Dictionary<string, object?>
            {
                ["type"] = type,
                ["start"] = start.ToString("yyyy-MM-dd'T'HH:mm:ss'Z'"),
                ["duration_s"] = durationS,
            },
            ["laps"] = Array.Empty<object>(),
            ["records"] = records.Select(r => new Dictionary<string, object?>
                {
                    ["t_offset_s"] = (int)(r.time - start).TotalSeconds,
                    ["hr"] = r.hr,
                }).ToList(),
            ["sets"] = Array.Empty<object>(),
            ["fit_file_id"] = fileId,
            ["device"] = device,
        };
        int? avgHr = records.Count == 0
            ? null
            : (int)Math.Round(records.Average(r => r.hr), MidpointRounding.AwayFromZero);
        return new ActivityFacts(
            System.Text.Json.JsonSerializer.Serialize(facts),
            start, avgHr, null, fileId, device);
    }

    private static DateTime? ParseStart(string? text) =>
        text != null && DateTime.TryParse(text, out var value) ? value.ToUniversalTime() : null;
}