feat(endo): Add import

The import function most directly models the Node.js command line:
pass the path to the entry module and the capability to read files on
the corresponding file system.
Importing a module creates a compartment graph and executes the entry
module of the root compartment.

packages/endo/src/import.js

@@ -0,0 +1,57 @@
+/* global StaticModuleRecord */
+/* eslint no-shadow: 0 */
+
+import { compartmentMapForNodeModules } from "./compartmap.js";
+import { search } from "./search.js";
+import { assemble } from "./assemble.js";
+
+const decoder = new TextDecoder();
+
+const resolve = (rel, abs) => new URL(rel, abs).toString();
+
+const makeImportHookMaker = (read, rootLocation) => packagePath => {
+  const packageLocation = resolve(packagePath, rootLocation);
+  return async moduleSpecifier => {
+    const moduleLocation = resolve(moduleSpecifier, packageLocation);
+    const moduleBytes = await read(moduleLocation);
+    const moduleSource = decoder.decode(moduleBytes);
+    return new StaticModuleRecord(moduleSource, moduleLocation);
+  };
+};
+
+export const loadPath = async (read, modulePath) => {
+  const { packagePath, packageDescriptorText, moduleSpecifier } = await search(
+    read,
+    modulePath
+  );
+
+  const packageDescriptor = JSON.parse(packageDescriptorText);
+  const compartmentMap = await compartmentMapForNodeModules(
+    read,
+    packagePath,
+    [],
+    packageDescriptor
+  );
+
+  const { compartments, main } = compartmentMap;
+
+  const makeImportHook = makeImportHookMaker(read, packagePath);
+
+  const execute = async (endowments, modules) => {
+    const compartment = assemble({
+      name: main,
+      compartments,
+      makeImportHook,
+      endowments,
+      modules
+    });
+    return compartment.import(moduleSpecifier);
+  };
+
+  return { execute };
+};
+
+export const importPath = async (read, modulePath, endowments, modules) => {
+  const application = await loadPath(read, modulePath, endowments, modules);
+  return application.execute(endowments, modules);
+};