/**
 * Renders the email that greets a new account. `sendWelcomeEmail`
 * (`user-service.ts`) sends it after sign-up, in the instance's style and
 * language. Its body is Markdown: the instance's `GERBEUR_WELCOME_EMAIL_BODY`,
 * or the built-in one.
 *
 * @module
 */

import { Marked } from "marked";

import {
  DEFAULT_STYLE,
  EMAIL_LOCALE,
  FRONTEND_URL,
  OG_SITE_NAME,
  WELCOME_EMAIL_BODY,
} from "../config.ts";
import { EmailKit, esc, type RenderedEmail } from "./layout.ts";
import { STRINGS } from "./strings.ts";

/**
 * Returns a Markdown renderer whose blocks are `kit`'s, so the body takes the
 * email's style. Raw HTML in the Markdown passes through: the body comes from
 * whoever runs the instance, never from a user.
 */
function markdownIn(kit: EmailKit): Marked {
  return new Marked({
    renderer: {
      heading({ tokens, depth }) {
        const html = this.parser.parseInline(tokens);
        return depth === 1 ? kit.heading(html, 20) : kit.subhead(html);
      },
      paragraph({ tokens }) {
        return kit.para(this.parser.parseInline(tokens));
      },
      link({ href, tokens }) {
        return kit.link(this.parser.parseInline(tokens), href);
      },
      strong({ tokens }) {
        return `<strong style="font-weight:${
          Math.max(600, kit.style.heavy)
        };">${this.parser.parseInline(tokens)}</strong>`;
      },
    },
  });
}

/**
 * Returns the welcome email of `username`, with `{{username}}` and
 * `{{site_name}}` filled into the body.
 */
export function renderWelcomeEmail(username: string): RenderedEmail {
  const t = STRINGS[EMAIL_LOCALE].welcome;
  const kit = new EmailKit(
    { style: DEFAULT_STYLE, scheme: "auto" },
    EMAIL_LOCALE,
  );
  const markdown = (WELCOME_EMAIL_BODY ?? t.body)
    .replaceAll("{{username}}", username)
    .replaceAll("{{site_name}}", OG_SITE_NAME);
  const subject = t.subject(OG_SITE_NAME);
  const body = markdownIn(kit).parse(markdown, { async: false }) +
    kit.button(esc(t.button(OG_SITE_NAME)), FRONTEND_URL);

  return {
    subject,
    html: kit.document({
      subject,
      preheader: t.preheader,
      body,
      footer: kit.footer(esc(t.reason(OG_SITE_NAME))),
    }),
    text: `${markdown}\n\n${t.button(OG_SITE_NAME)}: ${FRONTEND_URL}\n\n--\n${
      t.reason(OG_SITE_NAME)
    }`,
  };
}