From f775756ad11a64f3f9f840263aa62bf70e432ba6 Mon Sep 17 00:00:00 2001
From: Allon Hadaya <allon@ahadaya.com>
Date: Sun, 26 Apr 2015 16:07:15 -0400
Subject: [PATCH] Alpha attempt at in and out predicates.

---
 query/gremlin/build_iterator.go | 13 +++++++++++++
 query/gremlin/gremlin_test.go   | 14 ++++++++++++++
 query/gremlin/traversals.go     |  2 ++
 3 files changed, 29 insertions(+)

diff --git a/query/gremlin/build_iterator.go b/query/gremlin/build_iterator.go
index e49c2d4..938c428 100644
--- a/query/gremlin/build_iterator.go
+++ b/query/gremlin/build_iterator.go
@@ -139,6 +139,15 @@ func buildInOutIterator(obj *otto.Object, qs graph.QuadStore, base graph.Iterato
 	return iterator.NewHasA(qs, and, out)
 }
 
+func buildInOutPredicateIterator(obj *otto.Object, qs graph.QuadStore, base graph.Iterator, isReverse bool) graph.Iterator {
+	dir := quad.Subject
+	if isReverse {
+		dir = quad.Object
+	}
+	lto := iterator.NewLinksTo(qs, base, dir)
+	return iterator.NewHasA(qs, lto, quad.Predicate)
+}
+
 func buildIteratorTreeHelper(obj *otto.Object, qs graph.QuadStore, base graph.Iterator) graph.Iterator {
 	// TODO: Better error handling
 	var (
@@ -315,6 +324,10 @@ func buildIteratorTreeHelper(obj *otto.Object, qs graph.QuadStore, base graph.It
 		and.AddSubIterator(subIt)
 		and.AddSubIterator(notIt)
 		it = and
+	case "in_predicates":
+		it = buildInOutPredicateIterator(obj, qs, subIt, true)
+	case "out_predicates":
+		it = buildInOutPredicateIterator(obj, qs, subIt, false)
 	}
 	if it == nil {
 		panic("Iterator building does not catch the output iterator in some case.")
diff --git a/query/gremlin/gremlin_test.go b/query/gremlin/gremlin_test.go
index 52269b7..74164a7 100644
--- a/query/gremlin/gremlin_test.go
+++ b/query/gremlin/gremlin_test.go
@@ -250,6 +250,20 @@ var testQueries = []struct {
 		`,
 		expect: []string{"bob", "greg"},
 	},
+	{
+		message: "list all in predicates",
+		query: `
+		  g.V().InPredicates().All()
+		`,
+		expect: []string{"follows", "status"},
+	},
+	{
+		message: "list all out predicates",
+		query: `
+		  g.V().OutPredicates().All()
+		`,
+		expect: []string{"follows", "status"},
+	},
 }
 
 func runQueryGetTag(g []quad.Quad, query string, tag string) []string {
diff --git a/query/gremlin/traversals.go b/query/gremlin/traversals.go
index 1576fc1..8eee050 100644
--- a/query/gremlin/traversals.go
+++ b/query/gremlin/traversals.go
@@ -40,6 +40,8 @@ func (wk *worker) embedTraversals(env *otto.Otto, obj *otto.Object) {
 	obj.Set("SaveR", wk.gremlinFunc("saver", obj, env))
 	obj.Set("Except", wk.gremlinFunc("except", obj, env))
 	obj.Set("Difference", wk.gremlinFunc("except", obj, env))
+	obj.Set("InPredicates", wk.gremlinFunc("in_predicates", obj, env))
+	obj.Set("OutPredicates", wk.gremlinFunc("out_predicates", obj, env))
 }
 
 func (wk *worker) gremlinFunc(kind string, prev *otto.Object, env *otto.Otto) func(otto.FunctionCall) otto.Value {