/**
 * Flattens the Markdown users write into one line of plain text, where a
 * quote of it can't render markup: the chat's reply previews, the digest
 * email's quotes of a comment or a note, and the line of a description on a
 * playlist's card and on a user in the search results.
 *
 * @module
 */

/**
 * Returns the Markdown `md` as one line of plain text. Images become their alt
 * text, or `imageLabel` without one, and links their text. It also takes a
 * body cut short, possibly inside a link, as the server cuts a chat message's
 * `replyToBody`: the unfinished link then shows as its text, without half a
 * URL.
 */
export function markdownToPlainText(md: string, imageLabel: string): string {
  return md
    // An image or link cut short at the end loses its unfinished target.
    .replace(/!\[([^\]]*)\]\([^)]*$/, (_, alt: string) => alt || imageLabel)
    .replace(/(^|[^!])\[([^\]]*)\]\([^)]*$/, "$1$2")
    .replace(/!\[[^\]]*$/, "")
    .replace(/!\[([^\]]*)\]\([^)]*\)/g, (_, alt: string) => alt || imageLabel)
    .replace(/\[([^\]]*)\]\([^)]*\)/g, "$1")
    .replace(/^\s{0,3}(#{1,6}|>|[-*+]|\d+\.)\s+/gm, "")
    .replace(/```\w*|\*\*|__|~~|[*`]/g, "")
    .replace(/\s+/g, " ")
    .trim();
}