buildbucket: add longest_pending_time API

appengine/cr-buildbucket/service.py

Index: appengine/cr-buildbucket/service.py
diff --git a/appengine/cr-buildbucket/service.py b/appengine/cr-buildbucket/service.py
index 9678ef0b18eff6adbea2f3e0d0e222b685108d68..9749d7a04456bece0786eeb8837cd83e03afcae7 100644
--- a/appengine/cr-buildbucket/service.py
+++ b/appengine/cr-buildbucket/service.py
@@ -833,3 +833,30 @@ def parse_identity(identity):
     except ValueError as ex:
       raise errors.InvalidInputError('Invalid identity identity: %s' % ex)
   return identity
+
+
+def longest_pending_time(bucket, builder):
+  """Returns longest waiting time among SCHEDULED builds of a builder.
+
+  |builder| is a value of "builder" tag.
+
+  Returns a datetime.timedelta.
+  """
+  if not bucket:
+    raise errors.InvalidInputError('no bucket')
+  if not acl.can_access_bucket(bucket):
+    raise acl.current_identity_cannot('access bucket %s', bucket)
+  if not builder:
+    raise errors.InvalidInputError('no builder')
+
+  # Find the oldest, still SCHEDULED build in this builder.
+  q = model.Build.query(
+      model.Build.bucket == bucket,
+      model.Build.tags == ('builder:%s' % builder),
+      model.Build.status == model.BuildStatus.SCHEDULED,
+      projection=[model.Build.create_time])
+  q = q.order(model.Build.create_time)
+  result = q.fetch(1)
+  if not result:
+    return datetime.timedelta(0)
+  return utils.utcnow() - result[0].create_time