feat: pluggable reply/forward quote header #295

lib/plugin-hooks.ts

@@ -222,6 +222,12 @@ export const emailHooks = {
   onBeforeReply: new HookBus(),
   onBeforeReplyAll: new HookBus(),
   onBeforeForward: new HookBus(),
+  // Transform hook - lets plugins replace the quote header block ("On X,
+  // Y wrote:" / "---------- Forwarded message ----------") used when opening
+  // a reply or forward. Initial value: QuoteHeader (host default), second
+  // argument: QuoteHeaderContext. Handlers return a QuoteHeader (or
+  // undefined to pass through). Fires once per composer open.
+  onBuildQuoteHeader: new HookBus(),
   // Intercept hook fired before a file is added to the composer as an
   // attachment. Handler receives AttachmentInfo (size/type/name only - the
   // raw file is not exposed). Return false to refuse the upload.

lib/plugin-types.ts

@@ -645,6 +645,52 @@ export interface ReplyContext {
   mode: 'reply' | 'reply-all' | 'forward';
 }
 
+/**
+ * Second argument to onBuildQuoteHeader transform handlers. Describes the
+ * original message and how the host plans to render the quote header so
+ * plugins can produce a replacement block (e.g. an Outlook-style
+ * From/Sent/To/Cc/Subject section).
+ */
+export interface QuoteHeaderContext {
+  mode: 'reply' | 'replyAll' | 'forward';
+  /** Recipients of the new outgoing message (already resolved by the host). */
+  newTo: string[];
+  newCc: string[];
+  /** Original message metadata. */
+  from: { name?: string; email: string } | null;
+  to: { name?: string; email: string }[];
+  cc: { name?: string; email: string }[];
+  subject: string;
+  /** Pre-formatted date string the host already produced (locale-aware). */
+  date: string;
+  /** Raw ISO datetime, in case the plugin wants to reformat. */
+  receivedAt?: string;
+  /** Active UI locale (BCP-47), useful for Intl.DateTimeFormat in plugins. */
+  locale: string;
+}
+
+/**
+ * Initial value for the onBuildQuoteHeader transform hook. Plugins return a
+ * replacement; returning undefined falls through to the next handler or the
+ * default. The composer splices `html` into HTML drafts and `text` into
+ * plain-text drafts.
+ *
+ * For HTML, returning a header that includes its own surrounding wrapper
+ * (`<div>...</div>`) is fine; the composer does not add extra wrappers.
+ * For text, the host appends the quoted body after the header.
+ */
+export interface QuoteHeader {
+  html: string;
+  text: string;
+  /**
+   * When false, the composer skips its default blockquote wrapping around the
+   * quoted body (HTML mode only). Use this for the Outlook style where the
+   * quoted message is intended to follow the header without indentation.
+   * Defaults to true (preserve the existing blockquote wrapping).
+   */
+  wrapInBlockquote?: boolean;
+}
+
 /**
  * Describes an attachment crossing an attachment hook (upload, download, preview).
  */

lib/quote-header.ts

@@ -0,0 +1,82 @@
+// Builds the default reply/forward quote header and runs it through the
+// emailHooks.onBuildQuoteHeader transform so plugins can replace it (e.g.
+// with an Outlook-style From/Sent/To/Cc/Subject block).
+//
+// This module is the single source of truth for the default header strings -
+// the composer keeps the same defaults inline as a fallback, but production
+// flow goes through here.
+
+import { formatDateTime } from "@/lib/utils";
+import { emailHooks } from "@/lib/plugin-hooks";
+import type { QuoteHeader, QuoteHeaderContext } from "@/lib/plugin-types";
+
+interface BuildArgs {
+  mode: "reply" | "replyAll" | "forward";
+  email: {
+    from?: { email?: string; name?: string }[];
+    to?: { email?: string; name?: string }[];
+    cc?: { email?: string; name?: string }[];
+    subject?: string;
+    receivedAt?: string;
+  };
+  newTo: string[];
+  newCc: string[];
+  locale: string;
+  timeFormat: "12h" | "24h";
+  unknownLabel: string;
+}
+
+function defaultHeader(args: BuildArgs): QuoteHeader {
+  const { mode, email, timeFormat, unknownLabel } = args;
+  const date = email.receivedAt
+    ? formatDateTime(email.receivedAt, timeFormat, {
+        weekday: "short",
+        year: "numeric",
+        month: "short",
+        day: "numeric",
+      })
+    : "";
+  const from = email.from?.[0];
+  const fromStr = from ? `${from.name || from.email}` : unknownLabel;
+  const subject = email.subject || "";
+
+  if (mode === "forward") {
+    const text = `---------- Forwarded message ----------\nFrom: ${fromStr}\nDate: ${date}\nSubject: ${subject}\n`;
+    const html = `<div>---------- Forwarded message ----------<br>From: ${fromStr}<br>Date: ${date}<br>Subject: ${subject}<br><br></div>`;
+    return { html, text, wrapInBlockquote: false };
+  }
+
+  const text = `On ${date}, ${fromStr} wrote:\n`;
+  const html = `<div>On ${date}, ${fromStr} wrote:<br></div>`;
+  return { html, text, wrapInBlockquote: true };
+}
+
+export async function buildQuoteHeader(args: BuildArgs): Promise<QuoteHeader> {
+  const def = defaultHeader(args);
+  const ctx: QuoteHeaderContext = {
+    mode: args.mode,
+    newTo: args.newTo,
+    newCc: args.newCc,
+    from: args.email.from?.[0]?.email
+      ? { name: args.email.from[0].name, email: args.email.from[0].email }
+      : null,
+    to: (args.email.to ?? [])
+      .filter((r): r is { email: string; name?: string } => !!r.email)
+      .map((r) => ({ name: r.name, email: r.email })),
+    cc: (args.email.cc ?? [])
+      .filter((r): r is { email: string; name?: string } => !!r.email)
+      .map((r) => ({ name: r.name, email: r.email })),
+    subject: args.email.subject ?? "",
+    date: args.email.receivedAt
+      ? formatDateTime(args.email.receivedAt, args.timeFormat, {
+          weekday: "short",
+          year: "numeric",
+          month: "short",
+          day: "numeric",
+        })
+      : "",
+    receivedAt: args.email.receivedAt,
+    locale: args.locale,
+  };
+  return emailHooks.onBuildQuoteHeader.transform<QuoteHeader>(def, ctx);
+}