implemented toPairs

src/routePlanner/hooks/useMarkersOnMap/getLayersForMarkers.ts

@@ -1,4 +1,5 @@
 import leaflet from 'leaflet';
+import { toPairs } from '../../../shared/collections';
 import type { Marker } from '../../types';
 
 export type MarkerLayersStyle = {
@@ -10,19 +11,9 @@ export const getLayersForMarkers = (
     markerLayersStyle: MarkerLayersStyle,
 ) => [
     // lines
-    ...markers.flatMap((thisMarker, i) => {
-        const previousMarker = markers[i - 1];
-        if (!previousMarker) {
-            return [];
-        }
-
-        return [
-            leaflet.polyline([
-                previousMarker.coordinates,
-                thisMarker.coordinates,
-            ]),
-        ];
-    }),
+    ...toPairs(markers).map(([a, b]) =>
+        leaflet.polyline([a.coordinates, b.coordinates]),
+    ),
     // circles and labels
     ...markers.map((marker) =>
         leaflet

src/shared/collections.test.ts

@@ -1,5 +1,5 @@
 import t from 'tap';
-import { reorderElements } from './collections.js';
+import { reorderElements, toPairs } from './collections.js';
 
 void t.test('reorderElements', (t) => {
     const checkReordering = (
@@ -40,3 +40,35 @@ void t.test('reorderElements', (t) => {
     checkReordering(4, 4, 'abcde');
     t.end();
 });
+
+void t.test('toPairs', (t) => {
+    t.matchOnlyStrict(toPairs([]), []);
+    t.matchOnlyStrict(toPairs(['a']), []);
+    t.matchOnlyStrict(toPairs(['a', 'b']), [['a', 'b']]);
+    t.matchOnlyStrict(toPairs(['a', 'b', 'c']), [
+        ['a', 'b'],
+        ['b', 'c'],
+    ]);
+    t.matchOnlyStrict(toPairs(['a', 'b', 'c', 'd']), [
+        ['a', 'b'],
+        ['b', 'c'],
+        ['c', 'd'],
+    ]);
+    t.matchOnlyStrict(toPairs([undefined, 'b', 'c']), [
+        [undefined, 'b'],
+        ['b', 'c'],
+    ]);
+    t.matchOnlyStrict(toPairs(['a', undefined, 'c']), [
+        ['a', undefined],
+        [undefined, 'c'],
+    ]);
+    t.matchOnlyStrict(toPairs(['a', 'b', undefined]), [
+        ['a', 'b'],
+        ['b', undefined],
+    ]);
+    t.matchOnlyStrict(toPairs([undefined, undefined, undefined]), [
+        [undefined, undefined],
+        [undefined, undefined],
+    ]);
+    t.end();
+});

src/shared/collections.ts

@@ -22,3 +22,15 @@ export const reorderElements = <T>(
 
     return collection;
 };
+
+export const toPairs = <T>(collection: T[]): [T, T][] =>
+    collection.flatMap((element, index, collection) => {
+        if (!index) {
+            return [];
+        }
+
+        const previousElement = collection[index - 1];
+        // We just checked that index of the previous element is inside array bounds
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        return [[previousElement!, element]];
+    });

src/shared/routes.ts

@@ -1,19 +1,8 @@
 import haversineDistance from 'haversine-distance';
+import { toPairs } from './collections';
 import { Waypoint } from './types';
 
-export const getRouteLength = (points: Waypoint[]) => {
-    let result = 0;
-    for (let i = 0; i < points.length; i++) {
-        const currentPoint = points[i];
-        const previousPoint = points[i - 1];
-        if (!currentPoint || !previousPoint) {
-            continue;
-        }
-        result += haversineDistance(
-            previousPoint.coordinates,
-            currentPoint.coordinates,
-        );
-    }
-
-    return result;
-};
+export const getRouteLength = (points: Waypoint[]) =>
+    toPairs(points)
+        .map(([a, b]) => haversineDistance(a.coordinates, b.coordinates))
+        .reduce((sum, value) => sum + value, 0);