Port meta segment functions & lineSegment

lib/src/line_segment.dart

@@ -0,0 +1,87 @@
+// TODO implement https://github.com/Turfjs/turf/blob/fcdaa939c905e6cfa80cca11a0e7cbb851ad1a47/packages/turf-meta/index.js#L886
+// TODO implement https://github.com/Turfjs/turf/blob/fcdaa939c905e6cfa80cca11a0e7cbb851ad1a47/packages/turf-meta/index.js#L1001
+import 'geojson.dart';
+import 'invariant.dart';
+import 'meta.dart';
+
+// export default lineSegment;
+
+/// Creates a [FeatureCollection] of 2-vertex [LineString] segments from a
+/// [LineString] or [MultiLineString] or [Polygon] and [MultiPolygon]
+/// Returns [FeatureCollection<LineString>] 2-vertex line segments
+/// For example:
+///
+/// ```dart
+/// var polygon = Polygon.fromJson({
+///     'coordinates': [
+///       [
+///         [0, 0],
+///         [1, 1],
+///         [0, 1],
+///         [0, 0],
+///       ],
+///     ];
+/// var segments = lineSegment(polygon);
+/// //addToMap
+/// var addToMap = [polygon, segments]
+
+FeatureCollection<LineString> lineSegment(GeometryObject geoJson) {
+  List<Feature<LineString>> features = [];
+  if (geoJson is! LineString &&
+      geoJson is! MultiLineString &&
+      geoJson is! MultiPolygon &&
+      geoJson is! Polygon &&
+      geoJson is! Feature &&
+      geoJson is! FeatureCollection) {
+    throw Exception('Unsupported GeoJSONObject type');
+  } else {
+    flattenEach(geoJson,
+        (Feature currentFeature, int featureIndex, int multiFeatureIndex) {
+      lineSegmentFeature(geoJson, features); //
+    });
+  }
+  return FeatureCollection(features: features);
+}
+
+createSegments(List<Position> coord, properties) {
+  List<Feature<LineString>> segments = [];
+  coord.reduce((previousCoords, currentCoords) {
+    Feature<LineString> segment = Feature<LineString>(
+        geometry: LineString(coordinates: [previousCoords, currentCoords]),
+        properties: properties,
+        bbox: BBox.named(
+            lat1: previousCoords.lat,
+            lat2: currentCoords.lat,
+            lng1: previousCoords.lng,
+            lng2: currentCoords.lng));
+
+    segments.add(segment);
+    return currentCoords;
+  });
+  return segments;
+}
+
+lineSegmentFeature(GeoJSONObject geoJson, List<Feature<LineString>> results) {
+  var coords = [];
+  bool isFeature = geoJson is Feature && geoJson is FeatureCollection;
+  var geometry =
+      isFeature ? geoJson.geometry : (geoJson as GeometryType).coordinates;
+  if (geometry != null) {
+    switch (geometry.type) {
+      case GeoJSONObjectType.lineString:
+        coords.add(getCoords(geometry));
+        break;
+      default:
+        coords = getCoords(geometry);
+        break;
+    }
+    for (List<Position> coord in coords) {
+      var segments =
+          createSegments(coord, isFeature ? geoJson.properties : null);
+      segments.forEach((segment) {
+        segment.id = results.length;
+        results.add(segment);
+      });
+    }
+  }
+}