import puppeteer, { type Browser } from 'puppeteer'

/**
 * HTML → PDF via puppeteer. The browser is a lazy module-level singleton:
 * launch costs ~1s, so it starts on first render and is reused after.
 * Guarding with a promise (not the Browser) makes concurrent first calls
 * share one launch instead of racing two Chromes.
 */
let browserPromise: Promise<Browser> | null = null

function getBrowser(): Promise<Browser> {
  browserPromise ??= puppeteer.launch()
  return browserPromise
}

export async function renderPdf(html: string): Promise<Buffer> {
  const page = await (await getBrowser()).newPage()
  try {
    await page.setContent(html, { waitUntil: 'load' })
    const bytes = await page.pdf({ format: 'A4', printBackground: true })
    return Buffer.from(bytes)
  } finally {
    await page.close()
  }
}

/** For tests/scripts that must let the process exit; the server never calls it. */
export async function closePdfBrowser(): Promise<void> {
  if (browserPromise === null) return
  const b = await browserPromise
  browserPromise = null
  await b.close()
}