2 files changed, 73 insertions, 0 deletions
diff --git a/src/lib/shared/group-by-category.test.ts b/src/lib/shared/group-by-category.test.ts
new file mode 100644
index 0000000..d9bb379
--- /dev/null
+++ b/src/lib/shared/group-by-category.test.ts
@@ -0,0 +1,50 @@
+import { describe, it, expect } from 'vitest';
+import { groupByCategory } from './group-by-category';
+
+type Item = { id: number; name: string; categoryName: string | null };
+type Cat = { id: number; name: string };
+
+describe('groupByCategory', () => {
+	const categories: Cat[] = [
+		{ id: 1, name: 'Laitier' },
+		{ id: 2, name: 'Fruits' },
+		{ id: 3, name: 'Boulangerie' },
+	];
+
+	it('groups items by category, ordered by category order', () => {
+		const items: Item[] = [
+			{ id: 1, name: 'banane', categoryName: 'Fruits' },
+			{ id: 2, name: 'lait', categoryName: 'Laitier' },
+			{ id: 3, name: 'pomme', categoryName: 'Fruits' },
+		];
+
+		const result = groupByCategory(items, categories);
+
+		expect(result.map(([cat]) => cat)).toEqual(['Laitier', 'Fruits']);
+		expect(result[0][1].map((i) => i.name)).toEqual(['lait']);
+		expect(result[1][1].map((i) => i.name)).toEqual(['banane', 'pomme']);
+	});
+
+	it('prepends a non-catégorisé group for items without a category', () => {
+		const items: Item[] = [
+			{ id: 1, name: 'miel', categoryName: null },
+			{ id: 2, name: 'lait', categoryName: 'Laitier' },
+		];
+
+		const result = groupByCategory(items, categories);
+
+		expect(result.map(([cat]) => cat)).toEqual(['Non catégorisé', 'Laitier']);
+	});
+
+	it('omits categories without any item', () => {
+		const items: Item[] = [{ id: 1, name: 'lait', categoryName: 'Laitier' }];
+
+		const result = groupByCategory(items, categories);
+
+		expect(result.map(([cat]) => cat)).toEqual(['Laitier']);
+	});
+
+	it('returns no groups for empty items', () => {
+		expect(groupByCategory([], categories)).toEqual([]);
+	});
+});
diff --git a/src/lib/shared/group-by-category.ts b/src/lib/shared/group-by-category.ts
new file mode 100644
index 0000000..e9b0acd
--- /dev/null
+++ b/src/lib/shared/group-by-category.ts
@@ -0,0 +1,23 @@
+export function groupByCategory<
+	TItem extends { categoryName: string | null },
+	TCategory extends { name: string },
+>(items: TItem[], categories: TCategory[]): [string, TItem[]][] {
+	const groups = new Map<string, TItem[]>();
+	for (const item of items) {
+		const key = item.categoryName ?? 'Non catégorisé';
+		const list = groups.get(key);
+		if (list) list.push(item);
+		else groups.set(key, [item]);
+	}
+
+	const result: [string, TItem[]][] = [];
+	for (const cat of categories) {
+		const list = groups.get(cat.name);
+		if (list?.length) result.push([cat.name, list]);
+	}
+	const uncategorized = groups.get('Non catégorisé');
+	if (uncategorized?.length) {
+		result.unshift(['Non catégorisé', uncategorized]);
+	}
+	return result;
+}