webassembly: Implement runCLI() for a Node-based CLI.

This allows running MicroPython webassembly from the command line using:

    node micropython.mjs

Signed-off-by: Damien George <damien@micropython.org>

ports/webassembly/api.js

@@ -154,3 +154,95 @@ export async function loadMicroPython(options) {
 }
 
 globalThis.loadMicroPython = loadMicroPython;
+
+async function runCLI() {
+    const fs = await import("fs");
+    let heap_size = 128 * 1024;
+    let contents = "";
+    let repl = true;
+
+    for (let i = 2; i < process.argv.length; i++) {
+        if (process.argv[i] === "-X" && i < process.argv.length - 1) {
+            if (process.argv[i + 1].includes("heapsize=")) {
+                heap_size = parseInt(process.argv[i + 1].split("heapsize=")[1]);
+                const suffix = process.argv[i + 1].substr(-1).toLowerCase();
+                if (suffix === "k") {
+                    heap_size *= 1024;
+                } else if (suffix === "m") {
+                    heap_size *= 1024 * 1024;
+                }
+                ++i;
+            }
+        } else {
+            contents += fs.readFileSync(process.argv[i], "utf8");
+            repl = false;
+        }
+    }
+
+    if (process.stdin.isTTY === false) {
+        contents = fs.readFileSync(0, "utf8");
+        repl = false;
+    }
+
+    const mp = await loadMicroPython({
+        heapsize: heap_size,
+        stdout: (data) => process.stdout.write(data),
+        linebuffer: false,
+    });
+
+    if (repl) {
+        mp_js_init_repl();
+        process.stdin.setRawMode(true);
+        process.stdin.on("data", (data) => {
+            for (let i = 0; i < data.length; i++) {
+                mp_js_process_char(data[i]).then((result) => {
+                    if (result) {
+                        process.exit();
+                    }
+                });
+            }
+        });
+    } else {
+        try {
+            mp.runPython(contents);
+        } catch (error) {
+            if (error.name === "PythonError") {
+                if (error.type === "SystemExit") {
+                    // SystemExit, this is a valid exception to successfully end a script.
+                } else {
+                    // An unhandled Python exception, print in out.
+                    console.error(error.message);
+                }
+            } else {
+                // A non-Python exception.  Re-raise it.
+                throw error;
+            }
+        }
+    }
+}
+
+// Check if Node is running (equivalent to ENVIRONMENT_IS_NODE).
+if (
+    typeof process === "object" &&
+    typeof process.versions === "object" &&
+    typeof process.versions.node === "string"
+) {
+    // Check if this module is ron from the command line.
+    //
+    // See https://stackoverflow.com/questions/6398196/detect-if-called-through-require-or-directly-by-command-line/66309132#66309132
+    //
+    // Note:
+    // - `resolve()` is used to handle symlinks
+    // - `includes()` is used to handle cases where the file extension was omitted when passed to node
+
+    const path = await import("path");
+    const url = await import("url");
+
+    const pathToThisFile = path.resolve(url.fileURLToPath(import.meta.url));
+    const pathPassedToNode = path.resolve(process.argv[1]);
+    const isThisFileBeingRunViaCLI = pathToThisFile.includes(pathPassedToNode);
+
+    if (isThisFileBeingRunViaCLI) {
+        runCLI();
+    }
+}