import { filenameFromUrl } from './fileMeta'

/**
 * Download a remote asset with the desired filename.
 *
 * Tries the same-origin `fetch` → `Blob` → invisible-`<a>.download`
 * route first so the file lands on disk under `filename` instead of
 * navigating the tab to it. When CORS / network errors trip us up we
 * fall back to `window.open` and then to a no-window anchor — the
 * popup-blocker fallback ensures the download still fires even when
 * a browser blocks the `_blank` window.
 *
 * Shared by `DownloadAction` (rendered as an explicit Download button
 * in PDF / image / video viewers) and `MessageAttachment.File` rows
 * (where the entire row is the download trigger). Centralizing here
 * keeps one source of truth for the fallback chain.
 */
export async function triggerDownload(
  url: string,
  filename?: string
): Promise<void> {
  const name = filename ?? filenameFromUrl(url)

  try {
    const res = await fetch(url, { mode: 'cors' })
    if (!res.ok) throw new Error(`HTTP ${res.status}`)
    const blob = await res.blob()
    const objectUrl = URL.createObjectURL(blob)
    const a = document.createElement('a')
    a.href = objectUrl
    a.download = name
    a.style.display = 'none'
    document.body.appendChild(a)
    a.click()
    document.body.removeChild(a)
    URL.revokeObjectURL(objectUrl)
  } catch {
    const fallback = window.open(url, '_blank', 'noopener,noreferrer')
    if (!fallback) {
      // popup blocked — fall back to a non-windowed anchor
      const a = document.createElement('a')
      a.href = url
      a.download = name
      a.target = '_blank'
      a.rel = 'noopener noreferrer'
      a.style.display = 'none'
      document.body.appendChild(a)
      a.click()
      document.body.removeChild(a)
    }
  }
}