feat: articles pagination

web/src/lib/__tests__/pagination.spec.ts

@@ -0,0 +1,42 @@
+import { describe, expect, it } from 'vitest'
+import { pageItems, pageCountFor, rangeFor } from '@/lib/pagination'
+
+describe('pageItems', () => {
+	it('lists every page when there are seven or fewer', () => {
+		expect(pageItems(3, 7)).toEqual([1, 2, 3, 4, 5, 6, 7])
+		expect(pageItems(1, 1)).toEqual([1])
+	})
+
+	it('marks the skipped range after the first page', () => {
+		expect(pageItems(1, 13)).toEqual([1, 2, 'gap', 13])
+	})
+
+	it('marks skipped ranges on both sides of a middle page', () => {
+		expect(pageItems(7, 13)).toEqual([1, 'gap', 6, 7, 8, 'gap', 13])
+	})
+
+	it('marks the skipped range before the last page', () => {
+		expect(pageItems(13, 13)).toEqual([1, 'gap', 12, 13])
+	})
+
+	it('does not mark a gap between adjacent pages', () => {
+		expect(pageItems(3, 13)).toEqual([1, 2, 3, 4, 'gap', 13])
+	})
+})
+
+describe('pageCountFor', () => {
+	it('rounds up and never drops below one', () => {
+		expect(pageCountFor(312, 25)).toBe(13)
+		expect(pageCountFor(6, 25)).toBe(1)
+		expect(pageCountFor(0, 25)).toBe(1)
+	})
+})
+
+describe('rangeFor', () => {
+	it('computes the shown range', () => {
+		expect(rangeFor(1, 25, 312)).toEqual({ from: 1, to: 25 })
+		expect(rangeFor(7, 25, 312)).toEqual({ from: 151, to: 175 })
+		expect(rangeFor(13, 25, 312)).toEqual({ from: 301, to: 312 })
+		expect(rangeFor(1, 25, 0)).toEqual({ from: 0, to: 0 })
+	})
+})