From baad3e1dac5467fc5a8488f4bbe67706c606e13c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adina=20=C8=9Aeudan?= <adina@devplant.ro>
Date: Wed, 8 Feb 2023 17:20:13 +0200
Subject: [PATCH] Shift click selection logic

---
 src/lib/listing/services/listing.service.ts | 75 +++++++++++++++++++--
 1 file changed, 68 insertions(+), 7 deletions(-)

diff --git a/src/lib/listing/services/listing.service.ts b/src/lib/listing/services/listing.service.ts
index de765de..740771c 100644
--- a/src/lib/listing/services/listing.service.ts
+++ b/src/lib/listing/services/listing.service.ts
@@ -19,9 +19,13 @@ export class ListingService<Class extends IListable<PrimaryKey>, PrimaryKey exte
     readonly selectedEntities$: Observable<Class[]>;
     readonly selectedLength$: Observable<number>;
     readonly sortedDisplayedEntities$: Observable<Class[]>;
+
     private _displayed: Class[] = [];
     private readonly _selected$ = new BehaviorSubject<PrimaryKey[]>([]);
-    readonly #sortedDisplayedEntities$ = new BehaviorSubject<Class[]>([]);
+
+    private _anchor: Class | undefined = undefined;
+    private _focus: Class | undefined = undefined;
+    private _sortedDisplayed: Class[] = [];
 
     constructor(
         protected readonly _filterService: FilterService,
@@ -98,6 +102,10 @@ export class ListingService<Class extends IListable<PrimaryKey>, PrimaryKey exte
     setSelected(newEntities: Class[]): void {
         const selectedIds = newEntities.map(e => e.id);
         this._selected$.next(selectedIds);
+
+        if (this._anchor && !newEntities.includes(this._anchor)) {
+            this._anchor = undefined;
+        }
     }
 
     isSelected(entity: Class): boolean {
@@ -121,13 +129,20 @@ export class ListingService<Class extends IListable<PrimaryKey>, PrimaryKey exte
     select(entity: Class, withShift = false): void {
         const currentlySelected = this.selected;
         const currentEntityIdx = currentlySelected.indexOf(entity);
+        const isCurrentlySelected = currentEntityIdx !== -1;
 
-        if (currentEntityIdx === -1) {
-            // Entity is not previously selected, select it
-            this.setSelected([...currentlySelected, entity]);
+        if (!withShift) {
+            if (!isCurrentlySelected) {
+                this.setSelected([...currentlySelected, entity]);
+                this._anchor = entity;
+                this._focus = entity;
+            } else {
+                // Entity is previously selected, deselect it
+                this.setSelected(currentlySelected.slice(0, currentEntityIdx).concat(currentlySelected.slice(currentEntityIdx + 1)));
+                this.#moveAnchorAfterDeselect(entity);
+            }
         } else {
-            // Entity is previously selected, deselect it
-            this.setSelected(currentlySelected.slice(0, currentEntityIdx).concat(currentlySelected.slice(currentEntityIdx + 1)));
+            this.#shiftClick(entity);
         }
     }
 
@@ -137,6 +152,52 @@ export class ListingService<Class extends IListable<PrimaryKey>, PrimaryKey exte
         this.setSelected(this.selected.filter(el => !entitiesIds.includes(el.id)));
     }
 
+    /** Move anchor & focus to next selected, or previous selected, or undefined */
+    #moveAnchorAfterDeselect(entity: Class): void {
+        const entityIdx = this._sortedDisplayed.indexOf(entity);
+
+        let newAnchorIdx = entityIdx + 1;
+        let increment = 1;
+        do {
+            if (this.isSelected(this._sortedDisplayed[newAnchorIdx])) {
+                break;
+            }
+
+            newAnchorIdx += increment;
+            if (newAnchorIdx === this._sortedDisplayed.length) {
+                newAnchorIdx = entityIdx - 1;
+                increment = -1;
+            }
+        } while (newAnchorIdx > 0);
+
+        this._anchor = this._sortedDisplayed[newAnchorIdx];
+        this._focus = this._sortedDisplayed[newAnchorIdx];
+    }
+
+    #shiftClick(entity: Class): void {
+        const entityIdx = this._sortedDisplayed.indexOf(entity);
+
+        if (!this._anchor || !this._focus) {
+            this._anchor = this._sortedDisplayed[0];
+            this._focus = this._sortedDisplayed[0];
+        }
+
+        const anchorIdx = this._sortedDisplayed.indexOf(this._anchor);
+        const focusIdx = this._sortedDisplayed.indexOf(this._focus);
+
+        // Deselect entities between anchor and previous focus
+        const remove = this._sortedDisplayed.slice(Math.min(anchorIdx, focusIdx), Math.max(anchorIdx, focusIdx) + 1);
+
+        // Update focus
+        this._focus = entity;
+
+        // Select entities between anchor and new focus
+        const intervalEntities = this._sortedDisplayed.slice(Math.min(anchorIdx, entityIdx), Math.max(anchorIdx, entityIdx) + 1);
+
+        const newSelected = [...intervalEntities, ...this.selected.filter(e => !intervalEntities.includes(e) && !remove.includes(e))];
+        this.setSelected(newSelected);
+    }
+
     private _updateSelection(): void {
         const items = this._displayed.filter(item => this.selected.includes(item));
         this.setSelected(items);
@@ -148,7 +209,7 @@ export class ListingService<Class extends IListable<PrimaryKey>, PrimaryKey exte
         return this._sortingService.sortingOption$.pipe(
             switchMap(() => sortedEntities$),
             tap(sortedEntities => {
-                this.#sortedDisplayedEntities$.next(sortedEntities);
+                this._sortedDisplayed = sortedEntities;
             }),
             shareDistinctLast(),
         );