feat: modularize flattener tool into separate components with improved project root detection (#417)

tools/flattener/files.js

@@ -0,0 +1,35 @@
+const path = require("node:path");
+const discovery = require("./discovery.js");
+const ignoreRules = require("./ignoreRules.js");
+const { isBinaryFile } = require("./binary.js");
+const { aggregateFileContents } = require("./aggregate.js");
+
+// Backward-compatible signature; delegate to central loader
+async function parseGitignore(gitignorePath) {
+  return await ignoreRules.parseGitignore(gitignorePath);
+}
+
+async function discoverFiles(rootDir) {
+  try {
+    // Delegate to discovery module which respects .gitignore and defaults
+    return await discovery.discoverFiles(rootDir, { preferGit: true });
+  } catch (error) {
+    console.error("Error discovering files:", error.message);
+    return [];
+  }
+}
+
+async function filterFiles(files, rootDir) {
+  const { filter } = await ignoreRules.loadIgnore(rootDir);
+  const relativeFiles = files.map((f) => path.relative(rootDir, f));
+  const filteredRelative = relativeFiles.filter((p) => filter(p));
+  return filteredRelative.map((p) => path.resolve(rootDir, p));
+}
+
+module.exports = {
+  parseGitignore,
+  discoverFiles,
+  isBinaryFile,
+  aggregateFileContents,
+  filterFiles,
+};