refactored to use reducer instead of explicit state change in component

src/routePlanner/index.tsx

@@ -1,96 +1,71 @@
-import { nanoid } from 'nanoid';
-import { useCallback, useState } from 'preact/hooks';
-import { reorderElements } from '../shared/collections';
+import { useCallback, useReducer } from 'preact/hooks';
 import { Coordinates } from '../shared/types';
 import { ExportComponent } from './export';
 import { MapComponent } from './map';
 import { MarkersComponent } from './markers';
-import { Marker, ReorderMarkersParams } from './types';
+import { ReorderMarkersParams } from './types';
 
 import './style.css';
+import { markersReducer } from './reducer';
 
 export const RoutePlanner = () => {
-    const [markers, setMarkers] = useState<Marker[]>([]);
+    const [markers, dispatchMarkers] = useReducer(markersReducer, []);
 
-    const onMarkersReorder = useCallback(
+    const reorderMarkers = useCallback(
         ({ oldIndex, newIndex }: ReorderMarkersParams): void =>
-            setMarkers((oldMarkers) => {
-                console.log(
-                    `Reordering markers: from ${oldIndex} to ${newIndex}`,
-                );
-                const newMarkers = reorderElements(
-                    oldMarkers,
-                    oldIndex,
-                    newIndex,
-                );
-                return newMarkers.map((marker, i) => ({
-                    ...marker,
-                    label: `${i + 1}`,
-                    remove: () =>
-                        onMarkersReorder({
-                            oldIndex: i,
-                            newIndex: -1,
-                        }),
-                    ...(i - 1 >= 0 && {
-                        moveDown: () =>
-                            onMarkersReorder({
-                                oldIndex: i,
-                                newIndex: i - 1,
-                            }),
-                    }),
-                    ...(i + 1 < newMarkers.length && {
-                        moveUp: () =>
-                            onMarkersReorder({
-                                oldIndex: i,
-                                newIndex: i + 1,
-                            }),
-                    }),
-                }));
+            dispatchMarkers({
+                type: 'reorder',
+                data: { oldIndex, newIndex },
             }),
         [],
     );
 
-    const onMapClick = useCallback(
-        (coordinates: Coordinates) => {
-            setMarkers((markers) => [
-                ...markers.slice(0, markers.length - 1),
-                ...markers
-                    .slice(markers.length - 1, markers.length)
-                    .map((marker) => ({
-                        ...marker,
-                        moveUp: () =>
-                            onMarkersReorder({
-                                oldIndex: markers.length - 1,
-                                newIndex: markers.length,
-                            }),
-                    })),
-                {
-                    key: nanoid(10),
-                    label: `${markers.length + 1}`,
-                    remove: () =>
-                        onMarkersReorder({
-                            oldIndex: markers.length,
-                            newIndex: -1,
-                        }),
-                    ...(markers.length && {
-                        moveDown: () =>
-                            onMarkersReorder({
-                                oldIndex: markers.length,
-                                newIndex: markers.length - 1,
-                            }),
-                    }),
+    const moveMarkerUp = useCallback(
+        (key: string) =>
+            dispatchMarkers({
+                type: 'moveUp',
+                data: { key },
+            }),
+        [],
+    );
+
+    const moveMarkerDown = useCallback(
+        (key: string) =>
+            dispatchMarkers({
+                type: 'moveDown',
+                data: { key },
+            }),
+        [],
+    );
+
+    const removeMarker = useCallback(
+        (key: string) =>
+            dispatchMarkers({
+                type: 'remove',
+                data: { key },
+            }),
+        [],
+    );
+
+    const addMarker = useCallback(
+        (coordinates: Coordinates) =>
+            dispatchMarkers({
+                type: 'add',
+                data: {
                     coordinates,
+                    moveUp: moveMarkerUp,
+                    moveDown: moveMarkerDown,
+                    remove: removeMarker,
                 },
-            ]);
-        },
-        [onMarkersReorder],
+            }),
+        [moveMarkerUp, moveMarkerDown, removeMarker],
     );
 
     return (
         <section class="route-planner">
             <section class="markers">
                 <MarkersComponent
-                    onMarkersReorder={onMarkersReorder}
+                    onMarkersReorder={reorderMarkers}
                     markers={markers}
                 />
             </section>
@@ -98,7 +73,7 @@ export const RoutePlanner = () => {
                 <ExportComponent markers={markers} />
             </section>
             <section class="map">
-                <MapComponent onMapClick={onMapClick} markers={markers} />
+                <MapComponent onMapClick={addMarker} markers={markers} />
             </section>
         </section>
     );

src/routePlanner/marker.tsx

@@ -5,10 +5,10 @@ export const MarkerComponent = ({ marker }: MarkerProps) => {
         <li key={marker.key}>
             {`Waypoint ${marker.label} (${marker.key.substring(0, 4)})`}
             <span class="buttons">
-                <button onClick={marker.moveDown} disabled={!marker.moveDown}>
+                <button onClick={marker.moveUp} disabled={!marker.moveUp}>
                     🔼
                 </button>
-                <button onClick={marker.moveUp} disabled={!marker.moveUp}>
+                <button onClick={marker.moveDown} disabled={!marker.moveDown}>
                     🔽
                 </button>
                 <button onClick={marker.remove}>🗑️</button>

src/routePlanner/reducer.ts

@@ -0,0 +1,79 @@
+import { nanoid } from 'nanoid';
+import { Marker, ReducerAction } from './types';
+import { reorderElements } from '../shared/collections';
+
+const reindexMarkers = (markers: Marker[]) =>
+    markers.map((marker, i) => {
+        const newLabel = `${i + 1}`;
+        if (marker.label === newLabel) {
+            return marker;
+        }
+
+        return {
+            ...marker,
+            label: newLabel,
+        };
+    });
+
+export const markersReducer = (
+    markers: Marker[],
+    action: ReducerAction,
+): Marker[] => {
+    const type = action.type;
+    switch (action.type) {
+        case 'add': {
+            const key = nanoid(10);
+            return reindexMarkers([
+                ...markers,
+                {
+                    key,
+                    label: 'placeholder',
+                    remove: () => action.data.remove(key),
+                    moveUp: () => action.data.moveUp(key),
+                    moveDown: () => action.data.moveDown(key),
+                    coordinates: action.data.coordinates,
+                },
+            ]);
+        }
+        case 'remove': {
+            return reindexMarkers([
+                ...markers.filter(({ key }) => key !== action.data.key),
+            ]);
+        }
+        case 'moveUp': {
+            const oldIndex = markers.findIndex(
+                ({ key }) => key === action.data.key,
+            );
+            if (oldIndex < 1) {
+                return markers;
+            }
+
+            return reindexMarkers(
+                reorderElements(markers, oldIndex, oldIndex - 1),
+            );
+        }
+        case 'moveDown': {
+            const oldIndex = markers.findIndex(
+                ({ key }) => key === action.data.key,
+            );
+            if (oldIndex < 0 || oldIndex + 1 >= markers.length) {
+                return markers;
+            }
+
+            return reindexMarkers(
+                reorderElements(markers, oldIndex, oldIndex + 1),
+            );
+        }
+        case 'reorder': {
+            return reindexMarkers(
+                reorderElements(
+                    markers,
+                    action.data.oldIndex,
+                    action.data.newIndex,
+                ),
+            );
+        }
+        default:
+            throw new Error(`Unsupported type ${type}`);
+    }
+};

src/routePlanner/types.ts

@@ -8,6 +8,26 @@ export type Marker = Waypoint & {
     label: string;
 };
 
+type GenericReducerAction<TType extends string, TData> = {
+    type: TType;
+    data: TData;
+};
+
+export type ReducerAction =
+    | GenericReducerAction<
+          'add',
+          {
+              coordinates: Coordinates;
+              remove: (key: string) => void;
+              moveUp: (key: string) => void;
+              moveDown: (key: string) => void;
+          }
+      >
+    | GenericReducerAction<'remove', { key: string }>
+    | GenericReducerAction<'moveUp', { key: string }>
+    | GenericReducerAction<'moveDown', { key: string }>
+    | GenericReducerAction<'reorder', { oldIndex: number; newIndex: number }>;
+
 export type ReorderMarkersParams = {
     oldIndex: number;
     newIndex: number;