refactor(fmt): prepare runner for multiple execution paths

packages/rstack/src/fmt/runner.ts

@@ -1,41 +1,79 @@
-import type { FmtExitCode, FmtFileResult, FmtRunResult, RunFmtFilesOptions } from './types.ts';
+import type {
+  FmtExitCode,
+  FmtFileRequest,
+  FmtFileResult,
+  FmtRunResult,
+  RunFmtFilesOptions,
+} from './types.ts';
 import { formatFileSerial } from './serial.ts';
 
-const runFmtFiles = async ({ files, mode }: RunFmtFilesOptions): Promise<FmtRunResult> => {
+/** Formats one file and reports whether its contents differ. */
+type FormatFile = (file: FmtFileRequest, shouldWrite: boolean) => Promise<boolean>;
+
+/** Converts a formatter outcome into the shared per-file result. */
+const runFmtFile = async (
+  file: FmtFileRequest,
+  shouldWrite: boolean,
+  formatFile: FormatFile,
+): Promise<FmtFileResult> => {
   const startTime = performance.now();
-  const shouldWrite = mode === 'write';
+
+  try {
+    const changed = await formatFile(file, shouldWrite);
+
+    return {
+      path: file.path,
+      status: changed ? (shouldWrite ? 'written' : 'different') : 'unchanged',
+      durationMs: performance.now() - startTime,
+    };
+  } catch (error) {
+    return {
+      path: file.path,
+      status: 'error',
+      error,
+      durationMs: performance.now() - startTime,
+    };
+  }
+};
+
+/** Processes files sequentially while preserving input order. */
+const runFmtFilesSerial = async (
+  files: FmtFileRequest[],
+  shouldWrite: boolean,
+): Promise<FmtFileResult[]> => {
   const results: FmtFileResult[] = [];
+
+  for (const file of files) {
+    results.push(await runFmtFile(file, shouldWrite, formatFileSerial));
+  }
+
+  return results;
+};
+
+/** Maps file results to the Prettier-compatible CLI exit code. */
+const getFmtExitCode = (files: FmtFileResult[]): FmtExitCode => {
   let exitCode: FmtExitCode = 0;
 
   for (const file of files) {
-    const fileStartTime = performance.now();
-
-    try {
-      const changed = await formatFileSerial(file, shouldWrite);
-
-      if (changed && !shouldWrite && exitCode === 0) {
-        exitCode = 1;
-      }
-
-      results.push({
-        path: file.path,
-        status: changed ? (shouldWrite ? 'written' : 'different') : 'unchanged',
-        durationMs: performance.now() - fileStartTime,
-      });
-    } catch (error) {
-      exitCode = 2;
-      results.push({
-        path: file.path,
-        status: 'error',
-        error,
-        durationMs: performance.now() - fileStartTime,
-      });
+    if (file.status === 'error') {
+      return 2;
+    }
+    if (file.status === 'different') {
+      exitCode = 1;
     }
   }
 
+  return exitCode;
+};
+
+/** Runs resolved files and summarizes their outcomes for the CLI. */
+const runFmtFiles = async ({ files, mode }: RunFmtFilesOptions): Promise<FmtRunResult> => {
+  const startTime = performance.now();
+  const results = await runFmtFilesSerial(files, mode === 'write');
+
   return {
     files: results,
-    exitCode,
+    exitCode: getFmtExitCode(results),
     durationMs: performance.now() - startTime,
   };
 };