import { Fragment, type ReactNode } from "react";

// Known platform → profile base URL, for "<platform>: @handle" mentions in descriptions.
const PLATFORMS: Record<string, string> = {
  x: "https://x.com/",
  twitter: "https://x.com/",
  instagram: "https://instagram.com/",
  insta: "https://instagram.com/",
  ig: "https://instagram.com/",
  facebook: "https://facebook.com/",
  fb: "https://facebook.com/",
  tiktok: "https://www.tiktok.com/@",
  youtube: "https://www.youtube.com/@",
  yt: "https://www.youtube.com/@",
  twitch: "https://www.twitch.tv/",
  threads: "https://www.threads.net/@",
  telegram: "https://t.me/",
  soundcloud: "https://soundcloud.com/",
};

// Two link shapes, combined into one scanner:
//   URL — explicit http(s):// URLs, www.* hosts, or domain.tld/path bare URLs (required path +
//         letters-only TLD keep version numbers / file names out). Non-http gets an https:// href.
//   MENTION — "<platform>: @handle" where <platform> is one of the known keys above. The colon/arrow
//         separator is REQUIRED, so a stray "x" in prose won't match. Only the @handle is linked
//         (to the platform's profile URL); the "<platform>: " label stays as text. Bare @handles
//         with no platform, and #hashtags, are left plain.
const URL_SOURCE =
  "(?:https?://|www\\.)[^\\s<]+[^\\s<.,!?;:)\\]}\"']|[a-z0-9-]+(?:\\.[a-z0-9-]+)*\\.[a-z]{2,}/[^\\s<]*[^\\s<.,!?;:)\\]}\"']";
const MENTION_SOURCE =
  "\\b(" +
  Object.keys(PLATFORMS).join("|") +
  ")\\b[ \\t]*[:：►▶▸]+[ \\t]*@([a-z0-9_](?:[a-z0-9_.]{0,28}[a-z0-9_])?)";
const TOKEN_RE = new RegExp("(" + URL_SOURCE + ")|" + MENTION_SOURCE, "gi");

/**
 * Turn links inside a plain-text string into clickable <a>s that open in a new tab (safe rel):
 * bare URLs (http(s)/www/domain.tld/path) and "<platform>: @handle" social mentions. Everything
 * else is returned as text, so it composes with `whitespace-pre-wrap` (line breaks preserved).
 */
export function linkify(text: string): ReactNode[] {
  const out: ReactNode[] = [];
  let last = 0;
  let key = 0;
  TOKEN_RE.lastIndex = 0;
  const link = (href: string, label: string) => (
    <a
      key={key++}
      href={href}
      target="_blank"
      rel="noopener noreferrer"
      className="text-accent hover:underline break-all"
    >
      {label}
    </a>
  );
  let m: RegExpExecArray | null;
  while ((m = TOKEN_RE.exec(text)) !== null) {
    if (m.index > last) out.push(<Fragment key={key++}>{text.slice(last, m.index)}</Fragment>);
    if (m[1]) {
      // Plain URL.
      const raw = m[1];
      out.push(link(/^https?:\/\//i.test(raw) ? raw : `https://${raw}`, raw));
    } else {
      // Reached only when the MENTION alternative matched, so its groups are present: m[2] is the
      // platform (always one of PLATFORMS' own keys — the pattern is built from them) and m[3] the
      // handle. "<platform>: @handle" — keep the "<platform>: " prefix as text, link only the handle.
      const platform = m[2]!;
      const handle = m[3]!;
      const base = PLATFORMS[platform.toLowerCase()]!;
      out.push(<Fragment key={key++}>{m[0].slice(0, m[0].length - handle.length - 1)}</Fragment>);
      out.push(link(base + handle, "@" + handle));
    }
    last = m.index + m[0].length;
  }
  if (last < text.length) out.push(<Fragment key={key++}>{text.slice(last)}</Fragment>);
  return out;
}