109 lines
3.4 KiB
TypeScript
109 lines
3.4 KiB
TypeScript
export interface ReplyAddress {
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email?: string;
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name?: string;
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}
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export interface ReplySource {
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from?: ReplyAddress[];
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/** Addresses from the original message's Reply-To header. */
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replyToAddresses?: ReplyAddress[];
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to?: ReplyAddress[];
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cc?: ReplyAddress[];
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}
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export interface ReplyRecipientsResult {
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to: ReplyAddress[];
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cc: ReplyAddress[];
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}
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function normalize(email: string): string {
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return email.trim().toLowerCase();
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}
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function normalizeBase(email: string): string {
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const normalized = normalize(email);
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const at = normalized.indexOf('@');
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if (at <= 0) return normalized;
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const local = normalized.slice(0, at);
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const domain = normalized.slice(at + 1);
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const plus = local.indexOf('+');
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return `${plus >= 0 ? local.slice(0, plus) : local}@${domain}`;
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}
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/**
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* Does `email` belong to the user? Matches exactly first, then with `+tag`
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* sub-addressing stripped (info+news@ is still info@).
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*/
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function isOwnAddress(email: string | undefined, ownEmails: string[]): boolean {
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if (!email?.trim()) return false;
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const exact = normalize(email);
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if (ownEmails.some((own) => normalize(own) === exact)) return true;
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const base = normalizeBase(email);
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return ownEmails.some((own) => normalizeBase(own) === base);
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}
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/**
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* Is this a message the user themself sent? True when the From address is one
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* of their own identities - the case that shows up when browsing a thread and
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* replying to your own last message.
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*/
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export function isSelfSent(source: ReplySource | undefined, ownEmails: string[]): boolean {
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return isOwnAddress(source?.from?.[0]?.email, ownEmails);
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}
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/**
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* Work out the To/Cc a reply should open with.
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*
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* Normal case: reply goes to the Reply-To header if the original carried one,
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* else to From (RFC 5322). Reply-all adds the other original recipients,
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* minus the user's own addresses.
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*
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* Self-sent case (#703): replying to your own message inside a thread must
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* continue the conversation, not mail yourself. Gmail and Thunderbird address
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* the reply to the message's original recipients instead, so that's what we do
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* - the original To for reply, plus the original Cc for reply-all. Those
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* addresses were the user's own choice, so they're kept verbatim (no self-
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* filtering) and the Reply-To header is ignored, since answering your own
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* Reply-To would land the mail back in your inbox again.
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*
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* A self-sent message with no visible recipients (Bcc-only) has nothing to
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* continue to, so it falls back to the normal behaviour.
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*/
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export function buildReplyRecipients(
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source: ReplySource | undefined,
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mode: 'reply' | 'replyAll',
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ownEmails: string[],
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): ReplyRecipientsResult {
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if (!source) return { to: [], cc: [] };
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const withEmail = (list: ReplyAddress[] | undefined) => (list ?? []).filter((r) => Boolean(r.email));
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if (isSelfSent(source, ownEmails)) {
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const originalTo = withEmail(source.to);
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if (originalTo.length > 0) {
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return {
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to: originalTo,
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cc: mode === 'replyAll' ? withEmail(source.cc) : [],
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};
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}
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}
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const replyTarget = withEmail(source.replyToAddresses).length
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? withEmail(source.replyToAddresses)
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: (source.from?.[0]?.email ? [source.from[0]] : []);
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if (mode === 'reply') {
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return { to: replyTarget, cc: [] };
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}
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const others = (list: ReplyAddress[] | undefined) =>
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withEmail(list).filter((r) => !isOwnAddress(r.email, ownEmails));
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return {
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to: [...replyTarget, ...others(source.to)],
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cc: others(source.cc),
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};
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}
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