From 2da1728c7046c227a9442dcf36df630ab64cd054 Mon Sep 17 00:00:00 2001
From: Brad Rydzewski <brad.rydzewski@gmail.com>
Date: Wed, 11 May 2016 21:28:49 -0700
Subject: [PATCH] enabled "change" status

---
 agent/agent.go           |  3 +++
 yaml/transform/filter.go | 17 +++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/agent/agent.go b/agent/agent.go
index c76eca72a..88106d5ca 100644
--- a/agent/agent.go
+++ b/agent/agent.go
@@ -133,6 +133,9 @@ func (a *Agent) prep(w *queue.Work) (*yaml.Config, error) {
 	transform.Clone(conf, w.Repo.Kind)
 	transform.Environ(conf, envs)
 	transform.DefaultFilter(conf)
+	if w.BuildLast != nil {
+		transform.ChangeFilter(conf, w.BuildLast.Status)
+	}
 
 	transform.ImageSecrets(conf, secrets, w.Build.Event)
 	transform.Identifier(conf)
diff --git a/yaml/transform/filter.go b/yaml/transform/filter.go
index 9a36245e9..1d1ecb478 100644
--- a/yaml/transform/filter.go
+++ b/yaml/transform/filter.go
@@ -5,6 +5,23 @@ import (
 	"github.com/drone/drone/yaml"
 )
 
+// ChangeFilter is a transform function that alters status constraints set to
+// change and replaces with the opposite of the prior status.
+func ChangeFilter(conf *yaml.Config, prev string) {
+	for _, step := range conf.Pipeline {
+		for i, status := range step.Constraints.Status.Include {
+			if status != "change" && status != "changed" {
+				continue
+			}
+			if prev == model.StatusFailure {
+				step.Constraints.Status.Include[i] = model.StatusSuccess
+			} else {
+				step.Constraints.Status.Include[i] = model.StatusFailure
+			}
+		}
+	}
+}
+
 // DefaultFilter is a transform function that applies default Filters to each
 // step in the Yaml specification file.
 func DefaultFilter(conf *yaml.Config) {