const sessionIdPattern = /^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;

export const SESSION_PAGE_SIZE = 40;
export const SESSION_PAGE_LIMIT_MIN = 1;
export const SESSION_PAGE_LIMIT_MAX = 100;

export type SessionCursor = {
  readonly updatedAt: string;
  readonly id: string;
};

export function clampSessionLimit(raw: string | null | undefined): number {
  if (raw == null || raw === "") return SESSION_PAGE_SIZE;
  const parsed = Number.parseInt(raw, 10);
  if (!Number.isFinite(parsed)) return SESSION_PAGE_SIZE;
  return Math.min(SESSION_PAGE_LIMIT_MAX, Math.max(SESSION_PAGE_LIMIT_MIN, Math.trunc(parsed)));
}

export function encodeSessionCursor(updatedAt: string, id: string): string {
  return `${updatedAt},${id}`;
}

export function parseSessionCursor(raw: string | null | undefined): SessionCursor | null {
  if (!raw) return null;
  const comma = raw.indexOf(",");
  if (comma <= 0 || comma === raw.length - 1) return null;
  const updatedAt = raw.slice(0, comma);
  const id = raw.slice(comma + 1);
  if (!Number.isFinite(Date.parse(updatedAt))) return null;
  if (!sessionIdPattern.test(id)) return null;
  return { updatedAt, id };
}

export function sessionCursorFilter(cursor: SessionCursor): string {
  const updatedAt = JSON.stringify(cursor.updatedAt);
  const id = JSON.stringify(cursor.id);
  return `updated_at.lt.${updatedAt},and(updated_at.eq.${updatedAt},id.lt.${id})`;
}

export function compareSessionCursor(
  left: SessionCursor,
  right: SessionCursor,
): number {
  const time = Date.parse(right.updatedAt) - Date.parse(left.updatedAt);
  if (time !== 0) return time;
  return left.id < right.id ? 1 : left.id > right.id ? -1 : 0;
}

export function nextSessionCursor(
  rows: readonly { id: string; updated_at?: string; updatedAt?: string }[],
  limit: number,
): string | null {
  if (rows.length <= limit) return null;
  const last = rows[limit - 1];
  if (!last) return null;
  const updatedAt = typeof last.updated_at === "string"
    ? last.updated_at
    : typeof last.updatedAt === "string"
      ? last.updatedAt
      : "";
  if (!updatedAt) return null;
  return encodeSessionCursor(updatedAt, last.id);
}