fix: telegram html formatting (#435, thanks @RandyVentures)

src/telegram/format.ts

@@ -0,0 +1,141 @@
+import MarkdownIt from "markdown-it";
+
+type ListState = {
+  type: "bullet" | "ordered";
+  index: number;
+};
+
+type RenderEnv = {
+  telegramListStack?: ListState[];
+  telegramLinkStack?: boolean[];
+};
+
+const md = new MarkdownIt({
+  html: false,
+  linkify: true,
+  breaks: false,
+  typographer: false,
+});
+
+md.enable("strikethrough");
+
+const { escapeHtml } = md.utils;
+
+function getListStack(env: RenderEnv): ListState[] {
+  if (!env.telegramListStack) env.telegramListStack = [];
+  return env.telegramListStack;
+}
+
+function getLinkStack(env: RenderEnv): boolean[] {
+  if (!env.telegramLinkStack) env.telegramLinkStack = [];
+  return env.telegramLinkStack;
+}
+
+md.renderer.rules.text = (tokens, idx) =>
+  escapeHtml(tokens[idx]?.content ?? "");
+
+md.renderer.rules.softbreak = () => "\n";
+md.renderer.rules.hardbreak = () => "\n";
+
+md.renderer.rules.paragraph_open = () => "";
+md.renderer.rules.paragraph_close = (_tokens, _idx, _opts, env) => {
+  const stack = getListStack(env as RenderEnv);
+  return stack.length ? "" : "\n\n";
+};
+
+md.renderer.rules.heading_open = () => "";
+md.renderer.rules.heading_close = () => "\n\n";
+
+md.renderer.rules.blockquote_open = () => "";
+md.renderer.rules.blockquote_close = () => "\n";
+
+md.renderer.rules.bullet_list_open = (_tokens, _idx, _opts, env) => {
+  getListStack(env as RenderEnv).push({ type: "bullet", index: 0 });
+  return "";
+};
+md.renderer.rules.bullet_list_close = (_tokens, _idx, _opts, env) => {
+  getListStack(env as RenderEnv).pop();
+  return "";
+};
+md.renderer.rules.ordered_list_open = (tokens, idx, _opts, env) => {
+  const start = Number(tokens[idx]?.attrGet("start") ?? "1");
+  getListStack(env as RenderEnv).push({ type: "ordered", index: start - 1 });
+  return "";
+};
+md.renderer.rules.ordered_list_close = (_tokens, _idx, _opts, env) => {
+  getListStack(env as RenderEnv).pop();
+  return "";
+};
+md.renderer.rules.list_item_open = (_tokens, _idx, _opts, env) => {
+  const stack = getListStack(env as RenderEnv);
+  const top = stack[stack.length - 1];
+  if (!top) return "";
+  top.index += 1;
+  const indent = "  ".repeat(Math.max(0, stack.length - 1));
+  const prefix = top.type === "ordered" ? `${top.index}. ` : "• ";
+  return `${indent}${prefix}`;
+};
+md.renderer.rules.list_item_close = () => "\n";
+
+md.renderer.rules.em_open = () => "<i>";
+md.renderer.rules.em_close = () => "</i>";
+md.renderer.rules.strong_open = () => "<b>";
+md.renderer.rules.strong_close = () => "</b>";
+md.renderer.rules.s_open = () => "<s>";
+md.renderer.rules.s_close = () => "</s>";
+
+md.renderer.rules.code_inline = (tokens, idx) =>
+  `<code>${escapeHtml(tokens[idx]?.content ?? "")}</code>`;
+md.renderer.rules.code_block = (tokens, idx) =>
+  `<pre><code>${escapeHtml(tokens[idx]?.content ?? "")}</code></pre>\n`;
+md.renderer.rules.fence = (tokens, idx) =>
+  `<pre><code>${escapeHtml(tokens[idx]?.content ?? "")}</code></pre>\n`;
+
+md.renderer.rules.link_open = (tokens, idx, _opts, env) => {
+  const href = tokens[idx]?.attrGet("href") ?? "";
+  const safeHref = escapeHtml(href);
+  const stack = getLinkStack(env as RenderEnv);
+  const hasHref = Boolean(safeHref);
+  stack.push(hasHref);
+  return hasHref ? `<a href="${safeHref}">` : "";
+};
+md.renderer.rules.link_close = (_tokens, _idx, _opts, env) => {
+  const stack = getLinkStack(env as RenderEnv);
+  const hasHref = stack.pop();
+  return hasHref ? "</a>" : "";
+};
+
+md.renderer.rules.image = (tokens, idx) => {
+  const alt = tokens[idx]?.content ?? "";
+  return escapeHtml(alt);
+};
+
+md.renderer.rules.html_block = (tokens, idx) =>
+  escapeHtml(tokens[idx]?.content ?? "");
+md.renderer.rules.html_inline = (tokens, idx) =>
+  escapeHtml(tokens[idx]?.content ?? "");
+
+md.renderer.rules.table_open = () => "";
+md.renderer.rules.table_close = () => "";
+md.renderer.rules.thead_open = () => "";
+md.renderer.rules.thead_close = () => "";
+md.renderer.rules.tbody_open = () => "";
+md.renderer.rules.tbody_close = () => "";
+md.renderer.rules.tr_open = () => "";
+md.renderer.rules.tr_close = () => "\n";
+md.renderer.rules.th_open = () => "";
+md.renderer.rules.th_close = () => "\t";
+md.renderer.rules.td_open = () => "";
+md.renderer.rules.td_close = () => "\t";
+
+md.renderer.rules.hr = () => "\n";
+
+export function markdownToTelegramHtml(markdown: string): string {
+  const env: RenderEnv = {};
+  const rendered = md.render(markdown ?? "", env);
+  return rendered
+    .replace(/[ \t]+\n/g, "\n")
+    .replace(/\t+\n/g, "\n")
+    .replace(/\n{3,}/g, "\n\n")
+    .trimEnd();
+}