feat(api): Create a paginate method

apps/api/src/common/paginate.spec.ts

@@ -0,0 +1,93 @@
+import { paginate } from './paginate'
+
+describe('paginate', () => {
+  it('should paginate without default query', () => {
+    const totalCount = 100
+    const relativeUrl = '/items'
+    const query = { page: 2, limit: 10 }
+
+    const result = paginate(totalCount, relativeUrl, query)
+
+    expect(result).toBeDefined()
+    expect(result).toEqual(
+      expect.objectContaining({
+        page: 2,
+        perPage: 10,
+        pageCount: 10,
+        totalCount: 100
+      })
+    )
+    expect(result.links.self).toEqual('/items?page=2&limit=10')
+    expect(result.links.first).toEqual('/items?page=0&limit=10')
+    expect(result.links.previous).toEqual('/items?page=1&limit=10')
+    expect(result.links.next).toEqual('/items?page=3&limit=10')
+    expect(result.links.last).toEqual('/items?page=9&limit=10')
+  })
+
+  it('should paginate with default query', () => {
+    const totalCount = 100
+    const relativeUrl = '/items'
+    const query = { page: 5, limit: 10 }
+    const defaultQuery = { pricing: 'pro', filter: 'admin' }
+
+    const result = paginate(totalCount, relativeUrl, query, defaultQuery)
+
+    expect(result).toBeDefined()
+    expect(result).toEqual(
+      expect.objectContaining({
+        page: 5,
+        perPage: 10,
+        pageCount: 10,
+        totalCount: 100
+      })
+    )
+    expect(result.links.self).toEqual(
+      '/items?filter=admin&pricing=pro&page=5&limit=10'
+    )
+    expect(result.links.first).toEqual(
+      '/items?filter=admin&pricing=pro&page=0&limit=10'
+    )
+    expect(result.links.previous).toEqual(
+      '/items?filter=admin&pricing=pro&page=4&limit=10'
+    )
+    expect(result.links.next).toEqual(
+      '/items?filter=admin&pricing=pro&page=6&limit=10'
+    )
+    expect(result.links.last).toEqual(
+      '/items?filter=admin&pricing=pro&page=9&limit=10'
+    )
+  })
+
+  it('should paginate correctly edge cases where pervious or next is null', () => {
+    const totalCount = 10
+    const relativeUrl = '/items'
+    const query = { page: 0, limit: 10 }
+
+    const result = paginate(totalCount, relativeUrl, query)
+
+    expect(result).toBeDefined()
+    expect(result).toEqual(
+      expect.objectContaining({
+        page: 0,
+        perPage: 10,
+        pageCount: 1,
+        totalCount: 10
+      })
+    )
+    expect(result.links.self).toEqual('/items?page=0&limit=10')
+    expect(result.links.first).toEqual('/items?page=0&limit=10')
+    expect(result.links.previous).toBeNull()
+    expect(result.links.next).toBeNull()
+    expect(result.links.last).toEqual('/items?page=0&limit=10')
+  })
+
+  it('should not be able to paginate when limit is 0 or undefined', () => {
+    const totalCount = 10
+    const relativeUrl = '/items'
+    const query = { page: 0, limit: 0 }
+
+    expect(() => paginate(totalCount, relativeUrl, query)).toThrow(
+      'Limit is required'
+    )
+  })
+})

apps/api/src/common/paginate.ts

@@ -0,0 +1,75 @@
+export interface PaginatedMetadata {
+  page: number
+  perPage: number
+  pageCount: number
+  totalCount: number
+  links: {
+    self: string
+    first: string
+    previous: string | null
+    next: string | null
+    last: string
+  }
+}
+
+interface QueryOptions {
+  page: number
+  limit: number
+  sort?: string
+  order?: string
+  search?: string
+}
+
+//convert query object to query string to use in links
+const getQueryString = (query: QueryOptions) => {
+  return Object.keys(query)
+    .map((key) => `${key}=${query[key]}`)
+    .join('&')
+}
+
+export const paginate = (
+  totalCount: number,
+  relativeUrl: string,
+  query: QueryOptions,
+  defaultQuery?: Record<string, any>
+) => {
+  //query.limit cannot be 0 or undefined
+  if (!query.limit) throw new Error('Limit is required')
+  let defaultQueryStr = ''
+  if (defaultQuery) {
+    //sorting entries to make sure the order is consistent and predictable during tests
+    const sortedEntries = Object.entries(defaultQuery).sort(([keyA], [keyB]) =>
+      keyA.localeCompare(keyB)
+    )
+    //ignore keys with undefined values. Undefined values may occur when qury params are optional
+    defaultQueryStr = sortedEntries.reduce((res, [key, value]) => {
+      if (value !== undefined) {
+        res += `${key}=${value}&`
+      }
+      return res
+    }, '')
+  }
+
+  const metadata = {} as PaginatedMetadata
+  metadata.page = query.page
+  metadata.perPage = query.limit
+  metadata.pageCount = Math.ceil(totalCount / query.limit)
+  metadata.totalCount = totalCount
+
+  //create links from relativeUrl , defalutQueryStr and query of type QueryOptions
+  metadata.links = {
+    self: `${relativeUrl}?${defaultQueryStr + getQueryString(query)}`,
+    first: `${relativeUrl}?${defaultQueryStr + getQueryString({ ...query, page: 0 })}`,
+    previous:
+      query.page === 0
+        ? null
+        : `${relativeUrl}?${defaultQueryStr + getQueryString({ ...query, page: query.page - 1 })}`,
+    next:
+      query.page === metadata.pageCount - 1
+        ? null
+        : `${relativeUrl}?${defaultQueryStr + getQueryString({ ...query, page: query.page + 1 })}`,
+    last: `${relativeUrl}?${defaultQueryStr + getQueryString({ ...query, page: metadata.pageCount - 1 })}`
+  }
+
+  return metadata
+}