// Streaming SSR, proven at two levels: raw chunk timing over HTTP, and
// progressive DOM construction in real Chromium.

import { test, before, after } from 'node:test'
import assert from 'node:assert'
import { chromium } from 'playwright'

import { startServer } from './serve.js'

const DELAY = 500

let browser, srv

before(async () => {
  srv = await startServer()
  browser = await chromium.launch()
})

after(async () => {
  await browser?.close()
  await srv?.close()
})

test('HTTP level: shell bytes arrive before the slow section resolves', async () => {
  const started = performance.now()
  const res = await fetch(`${srv.origin}/stream?delay=${DELAY}`)
  const decoder = new TextDecoder()

  let sawShellAt = null
  let text = ''
  for await (const chunk of res.body) {
    text += decoder.decode(chunk, { stream: true })
    if (sawShellAt === null && text.includes('<h1>choo streams</h1>')) {
      sawShellAt = performance.now() - started
      assert.ok(!text.includes('id="slow"'), 'slow section not in the early bytes')
    }
  }

  assert.ok(sawShellAt !== null, 'shell was seen')
  assert.ok(sawShellAt < DELAY, `shell arrived at ${sawShellAt.toFixed(0)}ms, before the ${DELAY}ms hole`)
  assert.match(text, /id="slow"/, 'slow section arrived in the same response')
  assert.match(text, /<\/html>/, 'document completed')
})

test('browser level: Chromium builds the shell DOM before the stream ends', async () => {
  const page = await browser.newPage()
  await page.goto(`${srv.origin}/stream?delay=${DELAY}`, { waitUntil: 'commit' })

  // the shell must be in the DOM while the slow section is still absent
  await page.waitForSelector('h1', { timeout: DELAY - 100 })
  assert.strictEqual(await page.$('#slow'), null, 'slow section not parsed yet')

  // then the same document grows the slow section without navigation
  await page.waitForSelector('#slow', { timeout: DELAY * 4 })
  assert.match(await page.textContent('#slow'), /500ms later/)
  await page.close()
})