feat: implement Markdown domain in GitHub API simulator

github/package.json

@@ -20,6 +20,7 @@
   "devDependencies": {
     "eslint": "^9.39.4",
     "prettier": "^3.8.3",
+    "tsx": "^4.23.1",
     "typescript-eslint": "^8.60.0"
   }
 }

github/routes/_.context.ts

@@ -8,6 +8,7 @@ import type { simple_user } from "../types/components/schemas/simple-user.js";
 import type { Context as GistsContext } from "./gists/_.context.js";
 import type { Context as EmojisContext } from "./emojis/_.context.js";
 import type { Context as LicensesContext } from "./licenses/_.context.js";
+import type { Context as MarkdownContext } from "./markdown/_.context.js";
 import type { Context as ReposContext } from "./repos/_.context.js";
 import type { Context as UsersContext } from "./users/_.context.js";
 
@@ -30,6 +31,10 @@ export class Context {
     return this.loadContext("/licenses") as LicensesContext;
   }
 
+  private markdownContext(): MarkdownContext {
+    return this.loadContext("/markdown") as MarkdownContext;
+  }
+
   saveEmoji(...args: Parameters<EmojisContext["saveEmoji"]>) {
     return this.emojisContext().saveEmoji(...args);
   }
@@ -50,6 +55,17 @@ export class Context {
     return this.licensesContext().listLicenses(...args);
   }
 
+  renderMarkdown(...args: Parameters<MarkdownContext["renderMarkdown"]>) {
+    return this.markdownContext().renderMarkdown(...args);
+  }
+
+  renderRaw(...args: Parameters<MarkdownContext["renderRaw"]>) {
+    return this.markdownContext().renderRaw(...args);
+  }
+
+  commonMarkerVersion() {
+    return this.markdownContext().commonMarkerVersion();
+  }
   private usersContext(): UsersContext {
     return this.loadContext("/users") as UsersContext;
   }

github/routes/markdown.ts

@@ -1,5 +1,15 @@
 import type { markdownRender } from "../types/paths/markdown.types.js";
 
 export const POST: markdownRender = async ($) => {
-  return $.response[200].random();
+  const html = $.context.renderMarkdown(
+    $.body.text,
+    $.body.mode,
+    $.body.context,
+  );
+  const version = $.context.commonMarkerVersion();
+  return $.response[200]
+    .header("Content-Type", "text/html; charset=utf-8")
+    .header("Content-Length", String(Buffer.byteLength(html, "utf8")))
+    .header("X-CommonMarker-Version", version)
+    .html(html);
 };

github/routes/markdown/_.context.ts

@@ -0,0 +1,172 @@
+import type { Context$ } from "../../types/_.context.js";
+
+const COMMONMARKER_VERSION = "0.23.4";
+
+const escapeHtml = (text: string): string =>
+  text
+    .replace(/&/g, "&")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;");
+
+const renderInline = (text: string): string =>
+  text
+    .replace(
+      /`([^`]+)`/g,
+      (_, code: string) => `<code>${escapeHtml(code)}</code>`,
+    )
+    .replace(/\*\*([^*]+)\*\*/g, "<strong>$1</strong>")
+    .replace(/__([^_]+)__/g, "<strong>$1</strong>")
+    .replace(/\*([^*]+)\*/g, "<em>$1</em>")
+    .replace(/_([^_]+)_/g, "<em>$1</em>")
+    .replace(/~~([^~]+)~~/g, "<del>$1</del>")
+    .replace(
+      /!\[([^\]]*)\]\(([^)]+)\)/g,
+      (_, alt: string, src: string) =>
+        `<img src="${escapeHtml(src)}" alt="${escapeHtml(alt)}">`,
+    )
+    .replace(
+      /\[([^\]]+)\]\(([^)]+)\)/g,
+      (_, label: string, href: string) =>
+        `<a href="${escapeHtml(href)}">${label}</a>`,
+    );
+
+const renderIssueReferences = (text: string, repoContext: string): string =>
+  text.replace(/#(\d+)/g, (_, num: string) => {
+    const url = `https://github.com/${repoContext}/issues/${num}`;
+    return `<a href="${url}">#${num}</a>`;
+  });
+
+const renderBlock = (
+  lines: string[],
+  mode: "markdown" | "gfm",
+  repoContext?: string,
+): string => {
+  const result: string[] = [];
+  let index = 0;
+
+  while (index < lines.length) {
+    const line = lines[index] ?? "";
+
+    // Fenced code block
+    const fenceMatch = /^(`{3,}|~{3,})(.*)$/.exec(line);
+    if (fenceMatch) {
+      const fence = fenceMatch[1] ?? "";
+      const lang = (fenceMatch[2] ?? "").trim();
+      const codeLines: string[] = [];
+      index++;
+      while (index < lines.length && !lines[index]?.startsWith(fence)) {
+        codeLines.push(lines[index] ?? "");
+        index++;
+      }
+      index++;
+      const langAttr = lang ? ` class="language-${escapeHtml(lang)}"` : "";
+      result.push(
+        `<pre><code${langAttr}>${escapeHtml(codeLines.join("\n"))}</code></pre>`,
+      );
+      continue;
+    }
+
+    // ATX headings
+    const headingMatch = /^(#{1,6})\s+(.+)$/.exec(line);
+    if (headingMatch) {
+      const level = (headingMatch[1] ?? "").length;
+      const content = headingMatch[2] ?? "";
+      result.push(`<h${level}>${renderInline(content)}</h${level}>`);
+      index++;
+      continue;
+    }
+
+    // Horizontal rule
+    if (/^(?:-{3,}|_{3,}|\*{3,})$/.test(line.trim())) {
+      result.push("<hr>");
+      index++;
+      continue;
+    }
+
+    // Blockquote
+    if (line.startsWith("> ")) {
+      const quoteLines: string[] = [];
+      while (
+        index < lines.length &&
+        (lines[index]?.startsWith("> ") ?? false)
+      ) {
+        quoteLines.push((lines[index] ?? "").slice(2));
+        index++;
+      }
+      result.push(
+        `<blockquote>\n${renderBlock(quoteLines, mode, repoContext)}\n</blockquote>`,
+      );
+      continue;
+    }
+
+    // Unordered list
+    if (/^[*\-+]\s+/.test(line)) {
+      const listItems: string[] = [];
+      while (index < lines.length && /^[*\-+]\s+/.test(lines[index] ?? "")) {
+        listItems.push((lines[index] ?? "").replace(/^[*\-+]\s+/, ""));
+        index++;
+      }
+      const items = listItems
+        .map((item) => `<li>${renderInline(item)}</li>`)
+        .join("\n");
+      result.push(`<ul>\n${items}\n</ul>`);
+      continue;
+    }
+
+    // Ordered list
+    if (/^\d+\.\s+/.test(line)) {
+      const listItems: string[] = [];
+      while (index < lines.length && /^\d+\.\s+/.test(lines[index] ?? "")) {
+        listItems.push((lines[index] ?? "").replace(/^\d+\.\s+/, ""));
+        index++;
+      }
+      const items = listItems
+        .map((item) => `<li>${renderInline(item)}</li>`)
+        .join("\n");
+      result.push(`<ol>\n${items}\n</ol>`);
+      continue;
+    }
+
+    // Blank line — skip
+    if (line.trim() === "") {
+      index++;
+      continue;
+    }
+
+    // Paragraph — collect until blank line
+    const paraLines: string[] = [];
+    while (index < lines.length && (lines[index]?.trim() ?? "") !== "") {
+      paraLines.push(lines[index] ?? "");
+      index++;
+    }
+    let paraText = paraLines.join(" ");
+    if (mode === "gfm" && repoContext) {
+      paraText = renderIssueReferences(paraText, repoContext);
+    }
+    result.push(`<p>${renderInline(paraText)}</p>`);
+  }
+
+  return result.join("\n");
+};
+
+export class Context {
+  constructor(private readonly $: Context$) {}
+
+  renderMarkdown(
+    text: string,
+    mode: "markdown" | "gfm" = "markdown",
+    repoContext?: string,
+  ): string {
+    const lines = text.split("\n");
+    return renderBlock(lines, mode, repoContext);
+  }
+
+  renderRaw(text: string): string {
+    return this.renderMarkdown(text, "markdown");
+  }
+
+  commonMarkerVersion(): string {
+    return COMMONMARKER_VERSION;
+  }
+}

github/routes/markdown/raw.ts

@@ -1,5 +1,8 @@
 import type { markdownRenderRaw } from "../../types/paths/markdown/raw.types.js";
 
 export const POST: markdownRenderRaw = async ($) => {
-  return $.response[200].random();
+  const text = ($ as unknown as { body: string }).body ?? "";
+  const html = $.context.renderRaw(text);
+  const version = $.context.commonMarkerVersion();
+  return $.response[200].header("X-CommonMarker-Version", version).html(html);
 };

github/test-support/create-context.ts

@@ -3,6 +3,7 @@ import { Context } from "../routes/_.context.ts";
 import { Context as EmojisContext } from "../routes/emojis/_.context.ts";
 import { Context as GistsContext } from "../routes/gists/_.context.ts";
 import { Context as LicensesContext } from "../routes/licenses/_.context.ts";
+import { Context as MarkdownContext } from "../routes/markdown/_.context.ts";
 import { Context as ReposContext } from "../routes/repos/_.context.ts";
 import { Context as UsersContext } from "../routes/users/_.context.ts";
 
@@ -40,6 +41,12 @@ export const createContextHarness = () => {
           readJson: async () => ({}),
         });
         break;
+      case "/markdown":
+        created = new MarkdownContext({
+          loadContext,
+          readJson: async () => ({}),
+        });
+        break;
       case "/users":
         created = new UsersContext({ loadContext, readJson: async () => ({}) });
         break;

github/test-support/create-response.ts

@@ -0,0 +1,32 @@
+type RouteResult = {
+  status: number;
+  body?: unknown;
+  headers: Record<string, string>;
+};
+
+export const createResponse = () => {
+  const makeBuilder = (
+    status: number,
+    headers: Record<string, string> = {},
+  ): never => {
+    const builder = {
+      status,
+      headers,
+      header: (name: string, value: string) =>
+        makeBuilder(status, { ...headers, [name]: value }),
+      html: (body: unknown): RouteResult => ({ status, headers, body }),
+      text: (body: unknown): RouteResult => ({ status, headers, body }),
+      json: (body: unknown): RouteResult => ({ status, headers, body }),
+      empty: (): RouteResult => ({ status, headers }),
+      random: (): RouteResult => ({ status, headers }),
+    };
+    return builder as never;
+  };
+
+  return new Proxy(
+    {},
+    {
+      get: (_, key) => makeBuilder(Number(key)),
+    },
+  ) as never;
+};