From 3a58f2ffc942f6528524b65ff46384aba8e79f26 Mon Sep 17 00:00:00 2001
From: David Dal Busco <david.dalbusco@outlook.com>
Date: Tue, 5 Aug 2025 09:08:25 +0200
Subject: [PATCH] feat: wait command to assert emulator is ready

---
 src/commands/dev.ts               |  4 ++
 src/help/dev.help.ts              |  1 +
 src/services/dev/wait.services.ts | 83 +++++++++++++++++++++++++++++++
 3 files changed, 88 insertions(+)
 create mode 100644 src/services/dev/wait.services.ts

diff --git a/src/commands/dev.ts b/src/commands/dev.ts
index 9abc08fa..1f4043e5 100644
--- a/src/commands/dev.ts
+++ b/src/commands/dev.ts
@@ -5,6 +5,7 @@ import {logHelpFunctionsBuild} from '../help/functions.build.help';
 import {logHelpFunctionsEject} from '../help/functions.eject.help';
 import {start} from '../services/dev/start.services';
 import {stop} from '../services/dev/stop.services';
+import {wait} from '../services/dev/wait.services';
 import {build} from '../services/functions/build/build.services';
 import {eject} from '../services/functions/eject/eject.services';
 
@@ -18,6 +19,9 @@ export const dev = async (args?: string[]) => {
     case 'stop':
       await stop();
       break;
+    case 'wait':
+      await wait();
+      break;
     case 'eject':
       await eject(args);
       break;
diff --git a/src/help/dev.help.ts b/src/help/dev.help.ts
index 85770ef0..0087c498 100644
--- a/src/help/dev.help.ts
+++ b/src/help/dev.help.ts
@@ -8,6 +8,7 @@ const usage = `Usage: ${green('juno')} ${cyan('dev')} ${magenta('<subcommand>')}
 Subcommands:
   ${magenta('start')}               ${DEV_START_DESCRIPTION}
   ${magenta('stop')}                Stop the local network.
+  ${magenta('wait')}                Wait until the emulator is ready.
   ${magenta('build')}               Alias for ${green('juno')} ${cyan('functions')} ${magenta('build')}.
   ${magenta('eject')}               Alias for ${green('juno')} ${cyan('functions')} ${magenta('eject')}.`;
 
diff --git a/src/services/dev/wait.services.ts b/src/services/dev/wait.services.ts
new file mode 100644
index 00000000..b974b03a
--- /dev/null
+++ b/src/services/dev/wait.services.ts
@@ -0,0 +1,83 @@
+import {green, red} from 'kleur';
+import ora from 'ora';
+import {readEmulatorConfig} from '../../configs/emulator.config';
+import type {CliEmulatorConfig} from '../../types/emulator';
+import {dispatchRequest} from '../emulator/emulator.admin.services';
+
+const TIMEOUT_IN_MILLISECONDS = 15000;
+const RETRY_IN_MILLISECONDS = 500;
+
+export const wait = async () => {
+  const parsedResult = await readEmulatorConfig();
+
+  if (!parsedResult.success) {
+    return;
+  }
+
+  const spinner = ora('Waiting for emulator...').start();
+
+  let status: 'ready' | 'timeout' | undefined = undefined;
+
+  try {
+    status = await waitEmulatorReady({
+      count: TIMEOUT_IN_MILLISECONDS / RETRY_IN_MILLISECONDS,
+      config: parsedResult.config
+    });
+  } finally {
+    spinner.stop();
+  }
+
+  if (status === 'timeout') {
+    console.log(red('The emulator is not ready. Operation timed out.'));
+    process.exit(1);
+  }
+
+  console.log(`Emulator is ${green('ready')}.`);
+};
+
+const waitEmulatorReady = async ({
+  count,
+  config
+}: {
+  count: number;
+  config: CliEmulatorConfig;
+}): Promise<'ready' | 'timeout'> => {
+  const ready = await isEmulatorReady({config});
+
+  if (ready) {
+    return 'ready';
+  }
+
+  const nextCount = count - 1;
+
+  if (nextCount === 0) {
+    return 'timeout';
+  }
+
+  // eslint-disable-next-line promise/avoid-new
+  await new Promise((resolve) => setTimeout(resolve, RETRY_IN_MILLISECONDS));
+
+  return await waitEmulatorReady({count: nextCount, config});
+};
+
+// The emulator mounts its internal CLI/admin server as the final step of the startup flow.
+// That's why we can use the health endpoint to check when the emulator is ready.
+// It's also more convenient than pinging something like the satellite version,
+// since initialization, agent creation, or fetching the version may hang until a timeout.
+const isEmulatorReady = async ({config}: {config: CliEmulatorConfig}): Promise<boolean> => {
+  try {
+    const {result} = await dispatchRequest({
+      config,
+      request: 'health'
+    });
+
+    // At the moment, we only check whether the response succeeded.
+    // We don’t verify if the response body is "Ok" or "Unknown command".
+    // Since we don’t have specific use cases yet—other than checking if the server is mounted—
+    // this keeps the command compatible with older versions of the Docker image that didn’t
+    // expose the /health endpoint.
+    return result === 'ok';
+  } catch (_e: unknown) {
+    return false;
+  }
+};