Update Typescript definition for @turf/line-segment

#727
CC: @dpmcmlxxvi

packages/turf-line-segment/index.d.ts

@@ -1,8 +1,27 @@
-import {LineString, MultiLineString, Polygon, MultiPolygon, LineStrings} from '@turf/helpers'
+/// <reference types="geojson" />
+
+type LineString = GeoJSON.LineString;
+type MultiLineString = GeoJSON.MultiLineString;
+type Polygon = GeoJSON.Polygon;
+type MultiPolygon = GeoJSON.MultiPolygon;
+type GeometryObject = GeoJSON.GeometryObject;
+type GeometryCollection = GeoJSON.GeometryCollection;
+type Feature<Geom extends GeometryObject> = GeoJSON.Feature<Geom>;
+type FeatureCollection<Geom extends GeometryObject> = GeoJSON.FeatureCollection<Geom>;
+type Geoms = LineString | MultiLineString | Polygon | MultiPolygon;
+
+// Not correctly supported in @types/geojson
+interface FeatureGeometryCollection extends Feature<any> {
+  geometry: GeometryCollection
+}
+
+// Input & Output
+type Input = Feature<Geoms> | FeatureCollection<Geoms> | Geoms | GeometryCollection | FeatureGeometryCollection;
+type Output = FeatureCollection<LineString>;
 
 /**
  * http://turfjs.org/docs/#linesegment
  */
-declare function lineSegment(geojson: LineString | MultiLineString | Polygon | MultiPolygon): LineStrings;
+declare function lineSegment(geojson: Input): Output;
 declare namespace lineSegment {}
 export = lineSegment;

packages/turf-line-segment/test/types.ts

@@ -1,8 +1,13 @@
+import {lineString, polygon, featureCollection, geometryCollection} from '@turf/helpers'
 import * as lineSegment from '../'
-import * as path from 'path'
-const load = require('load-json-file')
 
-const polygon: GeoJSON.Feature<GeoJSON.Polygon> = load.sync(path.join(__dirname, 'in', 'polygon.geojson'));
+const poly = polygon([[[-50, 5], [-40, -10], [-50, -10], [-40, 5], [-50, 5]]]);
+const line = lineString([[-50, 5], [-40, -10], [-50, -10], [-40, 5], [-50, 5]]);
+const collection = featureCollection([poly, line]);
+const geomCollection = geometryCollection([poly.geometry, line.geometry]);
 
 // Test Types
-lineSegment(polygon)
+lineSegment(poly)
+lineSegment(line)
+lineSegment(collection)
+lineSegment(geomCollection)