feat(backend): add csv_analysis_config validator

backend/src/lib/csvConfigValidation.js

@@ -0,0 +1,51 @@
+const REQUIRED_DEFAULT_BUCKETS = ['Success', 'Failure', 'Other'];
+const ALLOWED_TYPES = new Set(['note', 'numerical']);
+
+/**
+ * Validate a csv_analysis_config payload.
+ * @param {unknown} body
+ * @returns {string|null} error message, or null if valid.
+ */
+function validateCsvConfig(body) {
+  if (body === null || typeof body !== 'object' || Array.isArray(body)) {
+    return 'Body must be an object';
+  }
+  const { buckets } = body;
+  if (!Array.isArray(buckets)) {
+    return 'buckets must be an array';
+  }
+
+  const seenNames = new Set();
+  for (const b of buckets) {
+    if (b === null || typeof b !== 'object' || Array.isArray(b)) {
+      return 'Each bucket must be an object';
+    }
+    if (typeof b.name !== 'string' || b.name.trim() === '') {
+      return 'Each bucket must have a non-empty name';
+    }
+    if (seenNames.has(b.name)) {
+      return `Duplicate bucket name: ${b.name}`;
+    }
+    seenNames.add(b.name);
+
+    if (!ALLOWED_TYPES.has(b.type)) {
+      return `Invalid type for bucket ${b.name}: ${b.type}`;
+    }
+    if (!Array.isArray(b.notes)) {
+      return `notes must be an array for bucket ${b.name}`;
+    }
+    if (!b.notes.every((n) => typeof n === 'string')) {
+      return `notes must be an array of strings for bucket ${b.name}`;
+    }
+  }
+
+  for (const required of REQUIRED_DEFAULT_BUCKETS) {
+    if (!seenNames.has(required)) {
+      return `Missing required default bucket: ${required}`;
+    }
+  }
+
+  return null;
+}
+
+module.exports = { validateCsvConfig, REQUIRED_DEFAULT_BUCKETS };