export const MENTION_CUSTOM_TYPE = 'chi.messaging.mentions';

export type HumanIdentity = {
  id: `github:${string}`;
  handle: string;
};

export type MentionMarker = {
  schemaVersion: 1;
  actor: HumanIdentity;
  recipients: HumanIdentity[];
  target: { sessionId: string; entryId: string };
};

const HANDLE = /^[A-Za-z0-9](?:[A-Za-z0-9-]{0,37}[A-Za-z0-9])?$/;

export function identityFromOwnerId(ownerId: string): HumanIdentity | null {
  const match = /^github:(.+)$/i.exec(ownerId.trim());
  const handle = match?.[1] ?? '';
  if (!HANDLE.test(handle)) return null;
  return { id: `github:${handle.toLowerCase()}`, handle };
}

export function mentionHandles(text: string): string[] {
  const handles: string[] = [];
  const seen = new Set<string>();
  for (const match of text.matchAll(/(?:^|[\s(])@([A-Za-z0-9](?:[A-Za-z0-9-]{0,37}[A-Za-z0-9])?)(?=$|[\s),.!?:;])/g)) {
    const handle = match[1]!;
    const key = handle.toLowerCase();
    if (!seen.has(key)) handles.push(handle);
    seen.add(key);
  }
  return handles;
}

export function recipientsOf(text: string, participants: readonly HumanIdentity[]): HumanIdentity[] {
  const byHandle = new Map(participants.map((participant) => [participant.handle.toLowerCase(), participant]));
  return mentionHandles(text).flatMap((handle) => {
    const participant = byHandle.get(handle.toLowerCase());
    return participant ? [participant] : [];
  });
}

export function markerFor(actor: HumanIdentity, recipients: readonly HumanIdentity[], sessionId: string, entryId: string): MentionMarker {
  return {
    schemaVersion: 1,
    actor,
    recipients: [...recipients].sort((left, right) => left.id.localeCompare(right.id)),
    target: { sessionId, entryId },
  };
}