webmail/lib/plugin-sandbox/assistant/b.list-selection.ts

// Area b of the assistant's host APIs: the messages ticked in the list, as
// the reader panel's `listSelection` prop, so the assistant can work on
// several at once ("summarise these").

import { useMemo, useRef } from 'react';
import type { IJMAPClient } from '@/lib/jmap/client-interface';
import { resolveEmailBlobContext, resolveSelectedEmails, useEmailStore } from '@/stores/email-store';
import { useAuthStore } from '@/stores/auth-store';
import type { ListSelectionView } from './b.types';

/** Most messages the prop names; `total` still counts them all. */
export const MAX_LIST_SELECTION = 50;

type SelectionState = Parameters<typeof resolveSelectedEmails>[0];

/**
 * The ticked messages when two or more are, else null. Each names the
 * account it is in, so api.email.get and getThread read it from there.
 * Rows of another connected login are left out of `emails` (this login
 * can't read them) but counted in `total`.
 */
export function listSelectionOf(state: SelectionState, client: IJMAPClient | null): ListSelectionView | null {
  const total = state.selectedEmailKeys.size;
  if (total < 2) return null;
  const emails: ListSelectionView['emails'] = [];
  for (const email of resolveSelectedEmails(state)) {
    if (emails.length >= MAX_LIST_SELECTION) break;
    const owner = client ? resolveEmailBlobContext(email, client) : null;
    if (owner && owner.client !== client) continue;
    const accountId = owner?.accountId ?? email.sourceAccountId ?? client?.getAccountId();
    emails.push({ id: email.id, ...(accountId ? { accountId } : {}) });
  }
  return { emails, total };
}

/** listSelectionOf for the list on screen; the same object while the selection stays the same. */
export function useListSelection(): ListSelectionView | null {
  const selectedEmailKeys = useEmailStore((s) => s.selectedEmailKeys);
  const emails = useEmailStore((s) => s.emails);
  const threadEmailsCache = useEmailStore((s) => s.threadEmailsCache);
  const client = useAuthStore((s) => s.client);
  const last = useRef<{ key: string; value: ListSelectionView | null }>({ key: 'null', value: null });
  return useMemo(() => {
    const value = listSelectionOf({ selectedEmailKeys, emails, threadEmailsCache }, client);
    const key = JSON.stringify(value);
    // New mail arriving re-renders the list; the panel only hears of a new selection.
    if (key !== last.current.key) last.current = { key, value };
    return last.current.value;
  }, [selectedEmailKeys, emails, threadEmailsCache, client]);
}