import '../models/gps_coordinate.dart';

/// أداة ترميز وفك ترميز Polyline
/// تستخدم خوارزمية Google Encoded Polyline لضغط المسارات بنسبة ~95%
class PolylineUtility {
  /// Encode a list of GPS coordinates to a polyline string
  static String encode(List<GpsCoordinate> coordinates) {
    if (coordinates.isEmpty) return '';

    final buffer = StringBuffer();
    int prevLat = 0;
    int prevLng = 0;

    for (final point in coordinates) {
      int lat = (point.latitude * 1e5).round();
      int lng = (point.longitude * 1e5).round();

      _encodeValue(lat - prevLat, buffer);
      _encodeValue(lng - prevLng, buffer);

      prevLat = lat;
      prevLng = lng;
    }

    return buffer.toString();
  }

  /// Decode a polyline string back to coordinates
  static List<GpsCoordinate> decode(String encoded) {
    if (encoded.isEmpty) return [];

    final coordinates = <GpsCoordinate>[];
    int index = 0;
    int lat = 0;
    int lng = 0;

    while (index < encoded.length) {
      lat += _decodeValue(encoded, index);
      index = _lastIndex;

      if (index >= encoded.length) break;

      lng += _decodeValue(encoded, index);
      index = _lastIndex;

      coordinates.add(GpsCoordinate(
        latitude: lat / 1e5,
        longitude: lng / 1e5,
        timestamp: DateTime.now(), // Polylines don't store timestamps
      ));
    }

    return coordinates;
  }

  // Internal tracking for decode position
  static int _lastIndex = 0;

  static void _encodeValue(int value, StringBuffer buffer) {
    int v = value < 0 ? ~(value << 1) : (value << 1);
    while (v >= 0x20) {
      buffer.writeCharCode((0x20 | (v & 0x1f)) + 63);
      v >>= 5;
    }
    buffer.writeCharCode(v + 63);
  }

  static int _decodeValue(String encoded, int startIndex) {
    int result = 0;
    int shift = 0;
    int index = startIndex;

    while (index < encoded.length) {
      int byte = encoded.codeUnitAt(index) - 63;
      index++;
      result |= (byte & 0x1f) << shift;
      shift += 5;
      if (byte < 0x20) break;
    }

    _lastIndex = index;
    return (result & 1) != 0 ? ~(result >> 1) : (result >> 1);
  }
}