rewrite if/then/else as oneOf: [allOf: [X, Y], allOf: [not: X, Z]]

Author: MikeRalphson

index.js

@@ -30,6 +30,7 @@ function convertSchema(schema, path, parent, parentPath) {
 	schema = stripIllegalKeywords(schema);
 	schema = convertTypes(schema);
 	schema = convertDependencies(schema);
+	schema = rewriteIfThenElse(schema);
 
 	if (typeof schema['patternProperties'] === 'object') {
 		schema = convertPatternProperties(schema);
@@ -140,4 +141,27 @@ function convertPatternProperties(schema) {
 	return schema;
 }
 
+function rewriteIfThenElse(schema) {
+/* @handrews https://github.com/OAI/OpenAPI-Specification/pull/1766#issuecomment-442652805
+if and the *Of keywords
+
+There is a really easy solution for implementations, which is that
+
+if: X, then: Y, else: Z
+
+is equivalent to
+
+oneOf: [allOf: [X, Y], allOf: [not: X, Z]]
+*/
+	if (schema.if && schema.then) {
+		schema.oneOf = [ { allOf: [ schema.if, schema.then ] },
+				 { allOf: [ { not: schema.if }, schema.else ] } ];
+		delete schema.if;
+		delete schema.then;
+		delete schema.else;
+	}
+	return schema;
+}
+
 module.exports = convert;
+

test/if-then-else.test.js

@@ -0,0 +1,24 @@
+'use strict';
+
+const convert = require('../');
+const should = require('should');
+
+it('if-then-else', () => {
+	const schema = {
+		$schema: 'http://json-schema.org/draft-04/schema#',
+		if: { type: 'object' },
+                then: { properties: { id: { type: 'string' } } },
+                else: { format: 'uuid' }
+	};
+
+	const result = convert(schema);
+
+	const expected = {
+		oneOf: [
+			{ allOf: [ { type: 'object' }, { properties: { id: { type: 'string' } } } ] },
+			{ allOf: [ { not: { type: 'object' } }, { format: 'uuid' } ] }
+                ]
+	};
+
+	should(result).deepEqual(expected, 'converted');
+});