feature: add dedicated Expo CLI entrypoint (#22)

cli.d.ts

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+export * from './build/src/cli';

cli.js

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+module.exports = require('./build/src/cli');

src/cli.ts

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+import type { ConfigT as MetroConfig } from 'metro-config';
+
+import { MetroGraphSource } from './data/MetroGraphSource';
+import { createAtlasMiddleware } from './utils/middleware';
+
+/**
+ * Iniitalize Expo Atlas to gather statistics from Metro when exporting bundles.
+ * This function adds the required Metro config, and should be used inside the Expo CLI.
+ *
+ * @example ```js
+ *   const atlasFromProject = requireFrom(projectRoot, 'expo-atlas/cli');
+ *
+ *   if (atlasFromProject) {
+ *     middleware.use('/_expo/atlas', atlasFromProject.middleware);
+ *   }
+ * ```
+ */
+export function createExpoAtlasMiddleware(config: MetroConfig) {
+  const projectRoot = config.projectRoot;
+
+  const source = new MetroGraphSource();
+  const middleware = createAtlasMiddleware(source);
+
+  const metroCustomSerializer = config.serializer?.customSerializer ?? (() => {});
+  const metroExtensions = {
+    source: config.resolver?.sourceExts,
+    asset: config.resolver?.assetExts,
+  };
+
+  // @ts-expect-error Should still be writable at this stage
+  config.serializer.customSerializer = (entryPoint, preModules, graph, options) => {
+    source.onSerializeGraph({
+      projectRoot,
+      entryPoint,
+      preModules,
+      graph,
+      options,
+      extensions: metroExtensions,
+    });
+
+    return metroCustomSerializer(entryPoint, preModules, graph, options);
+  };
+
+  return { source, middleware };
+}