/**
 * Encodes values to be used in mailto protocol.
 *
 * Note that we cannot simply use URLSeachParams because they, for example, encode a space
 * as plus (+), which cannot be used in mailto if we want to have consistent behaviour in
 * all email clients.
 */
function encodeValuesForMailto<T extends object>(object: T) {
  return Object.entries(object)
    .filter(([_, v]) => !!v)
    .map(([key, value]) => `${key}=${encodeURIComponent(value)}`)
    .join("&");
}

function serializeArray(value?: string | string[] | null) {
  return Array.isArray(value) ? value.join(",") : value;
}

type MailtoPayload = {
  body?: string | null;
  subject?: string | null;
  cc?: string | string[] | null;
  bcc?: string | string[] | null;
};

export function mailto(recipient: string | null, payload?: MailtoPayload) {
  // If the recipient is falsy the user can choose who to send the email to.
  const to = recipient ?? "";

  const serialized = payload
    ? `?${encodeValuesForMailto({
        body: payload.body,
        subject: payload.subject,
        cc: serializeArray(payload.cc),
        bcc: serializeArray(payload.bcc),
      })}`
    : "";

  return `mailto:${to}${serialized}`;
}