import { afterEach, beforeEach, describe, expect, it } from 'vitest'
import { fetchPack } from '../../server/utils/git-wire/upload-pack'
import { fakeGithubFetch, GitFixture, localReceivePackFactory } from '../utils/git-wire'
import { ReceivePackSession } from '../../server/utils/git-wire/receive-pack'
import { ZERO_SHA } from '../../server/utils/git-wire/refs'

async function drain(gen: AsyncGenerator<Buffer>): Promise<Buffer> {
  const parts: Buffer[] = []
  for await (const c of gen) parts.push(c)
  return Buffer.concat(parts)
}

describe('fetchPack negotiation edge cases', () => {
  let fx: GitFixture
  let realFetch: typeof globalThis.fetch

  beforeEach(() => {
    fx = new GitFixture()
    realFetch = globalThis.fetch
  })

  afterEach(() => {
    globalThis.fetch = realFetch
    fx.cleanup()
  })

  function firstBytes(buf: Buffer, n = 4): string {
    return buf.subarray(0, n).toString('ascii')
  }

  it('pack begins with the PACK signature when a have is a real common commit', async () => {
    const gh = fx.initBare('gh.git')
    const work = fx.initWork('work')
    const base = fx.commit(work, 'a.txt', 'hello')
    fx.pushTo(work, gh, 'HEAD:refs/heads/main')
    const head = fx.commit(work, 'b.txt', 'world')
    fx.pushTo(work, gh, 'HEAD:refs/heads/main')

    globalThis.fetch = fakeGithubFetch(new Map([['owner/repo', gh]])) as unknown as typeof globalThis.fetch
    const { pack } = await fetchPack({ repoFullName: 'owner/repo', token: 't', want: head, haves: [base], maxBytes: 1 << 30 })
    expect(firstBytes(await drain(pack))).toBe('PACK')
  })

  it('pack begins with PACK when a have is unknown to GitHub (diverged knot ref)', async () => {
    const gh = fx.initBare('gh.git')
    const work = fx.initWork('work')
    const base = fx.commit(work, 'a.txt', 'hello')
    fx.pushTo(work, gh, 'HEAD:refs/heads/main')
    const head = fx.commit(work, 'b.txt', 'world')
    fx.pushTo(work, gh, 'HEAD:refs/heads/main')

    // A commit GitHub has never seen (exists only on a throwaway repo). The
    // knot could advertise such a tip; we must not let it corrupt the stream.
    const other = fx.initWork('other')
    const stranger = fx.commit(other, 'x.txt', 'stranger')

    globalThis.fetch = fakeGithubFetch(new Map([['owner/repo', gh]])) as unknown as typeof globalThis.fetch
    const { pack } = await fetchPack({ repoFullName: 'owner/repo', token: 't', want: head, haves: [stranger, base], maxBytes: 1 << 30 })
    expect(firstBytes(await drain(pack))).toBe('PACK')
  })

  it('pushes into a knot that advertises a stranger tip alongside the base', async () => {
    const gh = fx.initBare('gh.git')
    const work = fx.initWork('work')
    const base = fx.commit(work, 'a.txt', 'hello')
    fx.pushTo(work, gh, 'HEAD:refs/heads/main')
    const head = fx.commit(work, 'b.txt', 'world')
    fx.pushTo(work, gh, 'HEAD:refs/heads/main')

    // Knot has the base on main plus an unrelated tip on another ref, so its
    // advertisement (and therefore our have-set) mixes a real common commit
    // with one GitHub can't resolve.
    const knot = fx.initBare('knot.git')
    fx.pushTo(work, knot, `${base}:refs/heads/main`)
    const other = fx.initWork('other')
    const stranger = fx.commit(other, 'x.txt', 'stranger')
    fx.pushTo(other, knot, `${stranger}:refs/heads/wip`)

    globalThis.fetch = fakeGithubFetch(new Map([['owner/repo', gh]])) as unknown as typeof globalThis.fetch

    const session = await ReceivePackSession.open(localReceivePackFactory(knot))
    const haves = [...new Set(session.tips.values())].filter(s => s !== ZERO_SHA)
    const { pack } = await fetchPack({ repoFullName: 'owner/repo', token: 't', want: head, haves, maxBytes: 1 << 30 })
    await session.push([{ ref: 'refs/heads/main', old: base, next: head }], pack)

    expect(fx.revParse(knot, 'refs/heads/main')).toBe(head)
  })
})