import type { Communication } from 'fhir/r4';
import { READ_RECEIPT_EXTENSION_URLS } from './messageStatus';

export const hasReadReceiptForReference = (
  message: Communication,
  recipientReference: string,
): boolean => {
  const readReceiptExtensions = (message.extension || []).filter(
    (extension) =>
      !!extension?.url && READ_RECEIPT_EXTENSION_URLS.includes(extension.url),
  );

  return readReceiptExtensions.some((extension) => {
    const childExtensions = extension.extension || [];
    const receiptRecipient = childExtensions.find(
      (child) => child.url === "recipient",
    )?.valueReference?.reference;
    const readAt =
      childExtensions.find((child) => child.url === "readAt")?.valueInstant ||
      childExtensions.find((child) => child.url === "readAt")?.valueDateTime ||
      childExtensions.find((child) => child.url === "readAt")?.valueString;

    return receiptRecipient === recipientReference && !!readAt;
  });
};

export const addReadReceiptForReference = (
  message: Communication,
  recipientReference: string,
  readAt: string,
): Communication => {
  if (hasReadReceiptForReference(message, recipientReference)) {
    return message;
  }

  return {
    ...message,
    extension: [
      ...(message.extension || []),
      {
        url: READ_RECEIPT_EXTENSION_URLS[0],
        extension: [
          {
            url: "recipient",
            valueReference: { reference: recipientReference },
          },
          {
            url: "readAt",
            valueInstant: readAt,
          },
        ],
      },
    ],
  };
};

const unreadBy = (messages: Communication[], reader: string): Communication[] =>
  messages.filter((message) => message.sender?.reference !== reader && !hasReadReceiptForReference(message, reader));

/** Messages from someone else with no receipt for this reader. Undefined when the reader is unknown, since no count is then readable. */
export const threadUnreadCount = (messages: Communication[], reader: string | null | undefined): number | undefined =>
  reader ? unreadBy(messages, reader).length : undefined;

/** The unread messages, each carrying this reader's receipt, ready to save. */
export const withReadReceipts = (messages: Communication[], reader: string, readAt: string): Communication[] =>
  unreadBy(messages, reader).map((message) => addReadReceiptForReference(message, reader, readAt));