1 files changed, 69 insertions, 0 deletions
diff --git a/testing/web-platform/harness/wptrunner/update/base.py b/testing/web-platform/harness/wptrunner/update/base.py
new file mode 100644
index 000000000..981ae2b70
--- /dev/null
+++ b/testing/web-platform/harness/wptrunner/update/base.py
@@ -0,0 +1,69 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+exit_unclean = object()
+exit_clean = object()
+
+
+class Step(object):
+    provides = []
+
+    def __init__(self, logger):
+        self.logger = logger
+
+    def run(self, step_index, state):
+        """Base class for state-creating steps.
+
+        When a Step is run() the current state is checked to see
+        if the state from this step has already been created. If it
+        has the restore() method is invoked. Otherwise the create()
+        method is invoked with the state object. This is expected to
+        add items with all the keys in __class__.provides to the state
+        object.
+        """
+
+        name = self.__class__.__name__
+
+        try:
+            stored_step = state.steps[step_index]
+        except IndexError:
+            stored_step = None
+
+        if stored_step == name:
+            self.restore(state)
+        elif stored_step is None:
+            self.create(state)
+            assert set(self.provides).issubset(set(state.keys()))
+            state.steps = state.steps + [name]
+        else:
+            raise ValueError("Expected a %s step, got a %s step" % (name, stored_step))
+
+    def create(self, data):
+        raise NotImplementedError
+
+    def restore(self, state):
+        self.logger.debug("Step %s using stored state" % (self.__class__.__name__,))
+        for key in self.provides:
+            assert key in state
+
+
+class StepRunner(object):
+    steps = []
+
+    def __init__(self, logger, state):
+        """Class that runs a specified series of Steps with a common State"""
+        self.state = state
+        self.logger = logger
+        if "steps" not in state:
+            state.steps = []
+
+    def run(self):
+        rv = None
+        for step_index, step in enumerate(self.steps):
+            self.logger.debug("Starting step %s" % step.__name__)
+            rv = step(self.logger).run(step_index, self.state)
+            if rv in (exit_clean, exit_unclean):
+                break
+
+        return rv