feature(client): Add helper function to convert enum into string

lib/asn1.js

@@ -484,8 +484,10 @@ const bacappEncodeApplicationData = module.exports.bacappEncodeApplicationData =
     case baEnum.ApplicationTags.READ_ACCESS_SPECIFICATION:
       encodeReadAccessSpecification(buffer, value.value);
       break;
+    case undefined:
+      throw new Error('Cannot encode a value if the type has not been specified');
     default:
-      throw 'Unknown type';
+      throw 'Unknown ApplicationTags type: ' + baEnum.getEnumName(baEnum.ApplicationTags, value.type);
   }
 };
 

lib/enum.js

@@ -1,5 +1,29 @@
 'use strict';
 
+/**
+ * Turn an enum into a string suitable for debugging.
+ *
+ * @param object group
+ *   Enum group, e.g. bacnet.enum.ConfirmedServiceChoice.
+ *
+ * @param Number value
+ *   Enum value, e.g. 1.  Note that this *must* be an integer value, so you may
+ *   need to use parseInt().  Non-integer values will result in an exception.
+ *
+ * @example
+ * const s = bacnet.enum.getEnumName(
+ *   bacnet.enum.PropertyIdentifier,
+ *   bacnet.enum.PropertyIdentifier.PRESENT_VALUE
+ * );
+ * console.log(s); // "PRESENT_VALUE(85)"
+ */
+module.exports.getEnumName = function(group, value) {
+	if (!Number.isInteger(value)) {
+		throw new Error('getEnumName() can only be passed an integer value, was given "' + value + '"');
+	}
+	return Object.keys(group).find(key => group[key] === value) + '(' + value + ')';
+}
+
 module.exports.PDU_TYPE_MASK = 0xF0;
 module.exports.ASN1_MAX_OBJECT = 0x3FF;
 module.exports.ASN1_INSTANCE_BITS = 22;