import { replaceEqualById } from '../replace_equal_by_id'

type Record = { type: 'Message'; id: string; text: string; attachments: string[] }
type Pages = { pages: { data: Record[]; links: {}; meta: {} }[]; pageParams: unknown[] }

const record = (id: string, text = id): Record => ({ type: 'Message', id, text, attachments: [] })
const pagesOf = (...pages: Record[][]): Pages => ({
  pages: pages.map(data => ({ data, links: {}, meta: {} })),
  pageParams: pages.map(() => ({})),
})

const share = (prev: Pages, next: Pages) => replaceEqualById(prev, next) as Pages

describe('replaceEqualById', () => {
  it('returns the previous data when nothing changed', () => {
    const prev = pagesOf([record('c'), record('b')], [record('a')])
    const next = pagesOf([record('c'), record('b')], [record('a')])

    expect(share(prev, next)).toBe(prev)
  })

  it('keeps every existing record when one is inserted at the head', () => {
    const [c, b] = [record('c'), record('b')]
    const prev = pagesOf([c, b])
    const next = pagesOf([record('d'), record('c'), record('b')])

    const result = share(prev, next)

    expect(result.pages[0].data[1]).toBe(c)
    expect(result.pages[0].data[2]).toBe(b)
    expect(result.pages[0].data[0].id).toBe('d')
  })

  it('keeps the survivors when a record is removed', () => {
    const [c, b, a] = [record('c'), record('b'), record('a')]
    const prev = pagesOf([c, b, a])
    const next = pagesOf([record('c'), record('a')])

    const result = share(prev, next)

    expect(result.pages[0].data).toEqual([c, a])
    expect(result.pages[0].data[0]).toBe(c)
    expect(result.pages[0].data[1]).toBe(a)
  })

  it('replaces only the changed record and keeps its untouched nested references', () => {
    const b = record('b')
    const prev = pagesOf([record('c'), b])
    const next = pagesOf([record('c'), { ...record('b', 'edited'), attachments: [] }])

    const result = share(prev, next)

    expect(result.pages[0].data[0]).toBe(prev.pages[0].data[0])
    expect(result.pages[0].data[1]).not.toBe(b)
    expect(result.pages[0].data[1].text).toBe('edited')
    expect(result.pages[0].data[1].attachments).toBe(b.attachments)
  })

  it('keeps untouched pages when only another page changed', () => {
    const prev = pagesOf([record('c')], [record('a')])
    const next = pagesOf([record('d'), record('c')], [record('a')])

    const result = share(prev, next)

    expect(result.pages[1]).toBe(prev.pages[1])
  })

  it('returns the new data when there is nothing to share with', () => {
    const next = pagesOf([record('a')])

    expect(replaceEqualById(undefined, next)).toBe(next)
  })
})