Implement backend and frontend loading

This system lets a server modularly load backend and frontend and allows
hosting each of the parts on separate services.

package.json

@@ -34,6 +34,8 @@
   "devDependencies": {
     "@types/chai": "^4.2.22",
     "@types/chai-as-promised": "^7.1.4",
+    "@types/compression": "^1.7.2",
+    "@types/express": "^4.17.13",
     "@types/fs-extra": "^9.0.13",
     "@types/mocha": "^9.0.0",
     "@types/node": "^16.11.10",
@@ -52,6 +54,8 @@
     "typescript": "^4.5.2"
   },
   "dependencies": {
-    "commander": "^8.3.0"
+    "commander": "^8.3.0",
+    "compression": "^1.7.4",
+    "express": "^4.17.2"
   }
 }

src/backend.ts

@@ -0,0 +1,7 @@
+"use strict";
+
+import { Router } from "express";
+
+export default function init(router: Router): void {
+
+}

src/frontend.ts

@@ -0,0 +1,6 @@
+"use strict";
+import { Router } from "express";
+
+export default function init(router: Router): void {
+    
+}

src/main.ts

@@ -1,13 +1,47 @@
 #!/usr/bin/env node
 "use strict";
-
 import loadConfig from "./config-loader";
 import { program } from "commander";
+import express from "express";
+import compression from "compression";
+import { resolve } from "path";
 
 async function main(): Promise<void> {
     await loadConfig([
+        ["--no-frontend", "Do not start the frontend server"],
+        ["--no-backend", "Do not start the backend server"],
+        ["-p, --port <port>", "Port to listen on", (port: any) => parseInt(port), 6969],
+        ["--backend-base-url <url>", "Base URL for the backend server", null],
     ], ".poll-horse-config");
     const opts = program.opts();
+
+    const app = express();
+    app.use(express.json());
+    app.use(compression());
+
+    if (opts.backend) {
+        console.log(`Mounting backend`);
+        const backendRouter = express.Router();
+
+        const backend = await import("./backend");
+        await backend.default(backendRouter);
+
+        app.use("/_backend/", backendRouter);
+    }
+
+    if (opts.frontend) {
+        console.log(`Mounting frontend`);
+        const frontendRouter = express.Router();
+        const frontend = await import("./frontend");
+        await frontend.default(frontendRouter);
+
+        app.use("/static", express.static(resolve(__dirname, "../frontend/static")));
+        app.use("/", frontendRouter);
+    }
+
+    app.listen(opts.port, () => {
+        console.log(`Listening on port ${opts.port}`);
+    });
 }
 
 main();