boolean_clockwise.dart

import 'package:turf/src/invariant.dart';

import '../../helpers.dart';

/// Takes a ring and return [true] or [false] whether or not the ring is clockwise
/// or counter-clockwise.
/// Takes a [Feature<LineString>] or[LineString] or a [List<Position>] to be
/// evaluated.
/// example:
/// ```dart
/// var clockwiseRing = LineString(
///   coordinates: [
///     Position.of([0, 0]),
///     Position.of([1, 1]),
///     Position.of([1, 0]),
///     Position.of([0, 0])
///   ],
/// );
/// var counterClockwiseRing = LineString(
///   coordinates: [
///     Position.of([0, 0]),
///     Position.of([1, 0]),
///     Position.of([1, 1]),
///     Position.of([0, 0])
///   ],
/// );
///
/// booleanClockwise(clockwiseRing);
/// //=true
/// booleanClockwise(counterClockwiseRing);
/// //=false
/// ```
bool booleanClockwise(LineString line) {
  var ring = getCoords(line) as List<Position>;
  num sum = 0;
  int i = 1;
  Position prev;
  Position? cur;

  while (i < ring.length) {
    prev = cur ?? ring[0];
    cur = ring[i];
    sum += (cur[0]! - prev[0]!) * (cur[1]! + prev[1]!);
    i++;
  }
  return sum > 0;
}