// lib/utils/fit_activity_parser.dart

import 'dart:typed_data';
import 'package:aves/model/activity/activity_track.dart';
import 'package:fit_sdk/fit_sdk.dart' as fit;
import 'package:flutter/foundation.dart';
import 'package:latlong2/latlong.dart';
import 'gps_smoothing.dart';

class FitActivityParser {
  static final Distance _distance = Distance();

  static ActivityTrack parse(
    Uint8List bytes, {
    required String fileName,
  }) {
    final records = <_FitPoint>[];
    double? sessionDistanceMeters;
    Duration? sessionDuration;
    String? sport;

    bool isZepp = false;

    final decoder = fit.Decode();

    decoder.onMesg = (dynamic message) {
      final messageName = '${message.name}'.toLowerCase();
      final fields = <String, dynamic>{};

      for (final dynamic field in message.fields) {
        fields[field.name.toLowerCase()] = field.value;
      }

      // Detect Zepp device
      if (fields['manufacturer'] == 25 ||
          fields['product'] == 25 ||
          fields['serial_number']?.toString().contains('zepp') == true) {
        isZepp = true;
      }

      if (messageName == 'record') {
        final latRaw = _readNumber(fields, const [
          'position_lat',
          'positionlat',
          'lat',
          'latitude',
        ]);

        final lonRaw = _readNumber(fields, const [
          'position_long',
          'positionlong',
          'lon',
          'longitude',
        ]);

        if (latRaw == null || lonRaw == null) return;

        final lat = _toDegrees(latRaw);
        final lon = _toDegrees(lonRaw);

        if (!lat.isFinite || !lon.isFinite) return;
        if (lat.abs() > 90 || lon.abs() > 180) return;

        final elevation = _readNumber(fields, const [
          'enhanced_altitude',
          'altitude',
        ]);

        final time = _readDateTime(fields, const [
          'timestamp',
          'time',
        ]);

        records.add(
          _FitPoint(
            latLng: LatLng(lat, lon),
            elevationMeters: elevation,
            time: time,
            rawFields: fields,
          ),
        );
      }

      if (messageName == 'session') {
        sessionDistanceMeters ??= _readNumber(fields, const [
          'total_distance',
          'distance',
        ]);

        final elapsedSeconds = _readNumber(fields, const [
          'total_elapsed_time',
          'total_timer_time',
        ]);

        if (elapsedSeconds != null) {
          sessionDuration = Duration(seconds: elapsedSeconds.round());
        }

        final sessionSport = fields['sport'];
        if (sessionSport != null) {
          sport = _normalizeSport('$sessionSport');
        }
      }

      if (messageName == 'sport') {
        final sportValue = fields['sport'];
        if (sportValue != null) {
          sport = _normalizeSport('$sportValue');
        }
      }
    };

    decoder.read(bytes);

    final points = records
        .where((p) => p.latLng.latitude.isFinite && p.latLng.longitude.isFinite)
        .toList();

    // Build track
    List<LatLng> track = points.map((p) => p.latLng).toList();

    // Apply smoothing ONLY for Zepp
    if (isZepp) {
      track = GpsSmoothing.douglasPeucker(track, 5.0);
    }

    final activity = ActivityTrack(
      name: fileName,
      format: 'FIT',
      tracks: {track},
      pointCount: track.length,
      distanceMeters: sessionDistanceMeters ?? _computeDistance(track),
      elevationGainMeters: _computeElevation(points),
      duration: sessionDuration ?? _computeDuration(points),
      startTime: points.map((p) => p.time).nonNulls.firstOrNull,
      sport: sport,
    );

    return activity;
  }

  static double? _readNumber(Map<String, dynamic> fields, List<String> names) {
    for (final name in names) {
      final value = fields[name];
      if (value == null) continue;

      if (value is num) return value.toDouble();
      if (value is String) return double.tryParse(value);
    }
    return null;
  }

  static DateTime? _readDateTime(Map<String, dynamic> fields, List<String> names) {
    for (final name in names) {
      final value = fields[name];
      if (value == null) continue;

      if (value is DateTime) return value;

      if (value is int && value > 0) {
        return DateTime.fromMillisecondsSinceEpoch(
          (value + 631065600) * 1000,
          isUtc: true,
        );
      }

      if (value is String) {
        final parsed = DateTime.tryParse(value);
        if (parsed != null) return parsed.toUtc();
      }
    }
    return null;
  }

  static double _toDegrees(num raw) {
    final v = raw.toDouble();
    if (v.abs() <= 180) return v;
    return v * 180.0 / 2147483648.0;
  }

  static double? _computeDistance(List<LatLng> track) {
    if (track.length < 2) return null;

    double dist = 0;
    for (int i = 1; i < track.length; i++) {
      final seg = _distance.as(LengthUnit.Meter, track[i - 1], track[i]);
      if (seg < 0 || seg > 50) continue; // anti‑rumore Zepp
      dist += seg;
    }
    return dist;
  }

  static double? _computeElevation(List<_FitPoint> points) {
    double gain = 0;
    double? prev;

    for (final p in points) {
      final e = p.elevationMeters;
      if (e == null) continue;

      if (prev != null) {
        final delta = e - prev;
        if (delta > 2) gain += delta; // soglia Zepp
      }

      prev = e;
    }

    return gain;
  }

  static Duration? _computeDuration(List<_FitPoint> points) {
    final times = points.map((p) => p.time).nonNulls.toList();
    if (times.length < 2) return null;

    times.sort();
    return times.last.difference(times.first);
  }

  static String _normalizeSport(String raw) {
    final value = raw.trim().toLowerCase();
    final numeric = int.tryParse(value);

    if (numeric != null) {
      switch (numeric) {
        case 1: return 'Corsa';
        case 2: return 'Bici';
        case 5: return 'Nuoto';
        case 6: return 'Camminata';
        case 9: return 'Trekking';
        case 20: return 'Mountain Bike';
        default: return 'Sport $numeric';
      }
    }

    switch (value) {
      case 'running': return 'Corsa';
      case 'cycling': return 'Bici';
      case 'walking': return 'Camminata';
      case 'hiking': return 'Trekking';
      case 'swimming': return 'Nuoto';
      default: return raw.trim();
    }
  }
}

class _FitPoint {
  final LatLng latLng;
  final double? elevationMeters;
  final DateTime? time;
  final Map<String, dynamic> rawFields;

  const _FitPoint({
    required this.latLng,
    this.elevationMeters,
    this.time,
    required this.rawFields,
  });
}

extension _FirstOrNull<E> on Iterable<E> {
  E? get firstOrNull {
    final it = iterator;
    if (!it.moveNext()) return null;
    return it.current;
  }
}