From 641b9f3ee4133352fef6cfab43e4f85e3de4e8eb Mon Sep 17 00:00:00 2001
From: Armon Dadgar <armon.dadgar@gmail.com>
Date: Sun, 11 Oct 2015 15:57:06 -0400
Subject: [PATCH] scheduler: support lexical ordering constraints

---
 scheduler/feasible.go      | 29 ++++++++++++++++++++++--
 scheduler/feasible_test.go | 45 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/scheduler/feasible.go b/scheduler/feasible.go
index 5ecfbedab..7482a953d 100644
--- a/scheduler/feasible.go
+++ b/scheduler/feasible.go
@@ -250,8 +250,7 @@ func checkConstraint(operand string, lVal, rVal interface{}) bool {
 	case "!=", "not":
 		return !reflect.DeepEqual(lVal, rVal)
 	case "<", "<=", ">", ">=":
-		// TODO: Implement
-		return false
+		return checkLexicalOrder(operand, lVal, rVal)
 	case "version":
 		return checkVersionConstraint(lVal, rVal)
 	case "regexp":
@@ -261,6 +260,32 @@ func checkConstraint(operand string, lVal, rVal interface{}) bool {
 	}
 }
 
+// checkLexicalOrder is used to check for lexical ordering
+func checkLexicalOrder(op string, lVal, rVal interface{}) bool {
+	// Ensure the values are strings
+	lStr, ok := lVal.(string)
+	if !ok {
+		return false
+	}
+	rStr, ok := rVal.(string)
+	if !ok {
+		return false
+	}
+
+	switch op {
+	case "<":
+		return lStr < rStr
+	case "<=":
+		return lStr <= rStr
+	case ">":
+		return lStr > rStr
+	case ">=":
+		return lStr >= rStr
+	default:
+		return false
+	}
+}
+
 // checkVersionConstraint is used to compare a version on the
 // left hand side with a set of constraints on the right hand side
 func checkVersionConstraint(lVal, rVal interface{}) bool {
diff --git a/scheduler/feasible_test.go b/scheduler/feasible_test.go
index 8ee3c6dc5..a69b4c8ce 100644
--- a/scheduler/feasible_test.go
+++ b/scheduler/feasible_test.go
@@ -254,6 +254,11 @@ func TestCheckConstraint(t *testing.T) {
 			lVal: "foobarbaz", rVal: "[\\w]+",
 			result: true,
 		},
+		{
+			op:   "<",
+			lVal: "foo", rVal: "bar",
+			result: false,
+		},
 	}
 
 	for _, tc := range cases {
@@ -263,6 +268,46 @@ func TestCheckConstraint(t *testing.T) {
 	}
 }
 
+func TestCheckLexicalOrder(t *testing.T) {
+	type tcase struct {
+		op         string
+		lVal, rVal interface{}
+		result     bool
+	}
+	cases := []tcase{
+		{
+			op:   "<",
+			lVal: "bar", rVal: "foo",
+			result: true,
+		},
+		{
+			op:   "<=",
+			lVal: "foo", rVal: "foo",
+			result: true,
+		},
+		{
+			op:   ">",
+			lVal: "bar", rVal: "foo",
+			result: false,
+		},
+		{
+			op:   ">=",
+			lVal: "bar", rVal: "bar",
+			result: true,
+		},
+		{
+			op:   ">",
+			lVal: 1, rVal: "foo",
+			result: false,
+		},
+	}
+	for _, tc := range cases {
+		if res := checkLexicalOrder(tc.op, tc.lVal, tc.rVal); res != tc.result {
+			t.Fatalf("TC: %#v, Result: %v", tc, res)
+		}
+	}
+}
+
 func TestCheckVersionConstraint(t *testing.T) {
 	type tcase struct {
 		lVal, rVal interface{}