// `#N` and `@user` in text the user is typing (spec §6.2): what is being
// completed at the cursor, and which reference a position sits on. No
// vscode imports, so it is tested with plain Node.

/** A reference being typed: `#12` (issue or proposal) or `@an` (a user). */
export type Typing = { kind: "number"; prefix: string; start: number } | { kind: "user"; prefix: string; start: number };

/**
 * What the text before the cursor is in the middle of typing, if anything.
 * A reference starts a word: after the line start, whitespace or an
 * opening bracket, so `a#1` and `mail@host` are not references.
 */
export function typingAt(before: string): Typing | undefined {
  const n = /(^|[\s([{])#(\d*)$/.exec(before);
  if (n) {
    return { kind: "number", prefix: n[2], start: before.length - n[2].length - 1 };
  }
  const u = /(^|[\s([{])@([A-Za-z0-9][A-Za-z0-9_-]*|)$/.exec(before);
  if (u) {
    return { kind: "user", prefix: u[2], start: before.length - u[2].length - 1 };
  }
  return undefined;
}

/** The `#N` reference covering `column` of `line`, with its span. */
export function numberAt(line: string, column: number): { number: number; start: number; end: number } | undefined {
  const re = /(^|[\s([{])#(\d+)\b/g;
  for (let m = re.exec(line); m; m = re.exec(line)) {
    const start = m.index + m[1].length;
    const end = start + 1 + m[2].length;
    if (column >= start && column <= end) {
      return { number: Number(m[2]), start, end };
    }
  }
  return undefined;
}

/** A repository root named by an SCM input box's URI query (`rootUri=file:///…`). */
export function rootFromScmQuery(query: string): string | undefined {
  const raw = new URLSearchParams(query).get("rootUri");
  if (!raw) {
    return undefined;
  }
  try {
    return decodeURIComponent(new URL(raw).pathname);
  } catch {
    return undefined;
  }
}