Lightweight ninja writer in Python

Summary:
- Create python classes for ninja vocbulary in `ninja_syntax.py`. These
  classes will be serialized to a ninja file
- Create a Writer class in `ninja_writer.py`. The current API supports
  adding variables,rules,build actions, etc. This can be extended in the
  future (See `test_ninja_writer.py` for examples)

Future Work:
 - Update the `Subninja` class once chDir is supported (aosp/2064612)
 - Support a width parameter that will be used to wrap long lines of
   text. This will improve readability of the generated files

Expected Use Case: Multi-tree build orchestrator

Test: python ./test_ninja_syntax.py
Test: python ./test_ninja_writer.py

Change-Id: I90c7ee69ddeb7c20c3fd4fca5a911dddbf2253bd
diff --git a/orchestrator/ninja/ninja_writer.py b/orchestrator/ninja/ninja_writer.py
new file mode 100644
index 0000000..e3070bb
--- /dev/null
+++ b/orchestrator/ninja/ninja_writer.py
@@ -0,0 +1,55 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2022 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ninja_syntax import Variable, BuildAction, Rule, Pool, Subninja, Line
+
+# TODO: Format the output according to a configurable width variable
+# This will ensure that the generated content fits on a screen and does not
+# require horizontal scrolling
+class Writer:
+
+  def __init__(self, file):
+    self.file = file
+    self.nodes = [] # type Node
+
+  def add_variable(self, variable: Variable):
+    self.nodes.append(variable)
+
+  def add_rule(self, rule: Rule):
+    self.nodes.append(rule)
+
+  def add_build_action(self, build_action: BuildAction):
+    self.nodes.append(build_action)
+
+  def add_pool(self, pool: Pool):
+    self.nodes.append(pool)
+
+  def add_comment(self, comment: str):
+    self.nodes.append(Line(value=f"# {comment}"))
+
+  def add_default(self, default: str):
+    self.nodes.append(Line(value=f"default {default}"))
+
+  def add_newline(self):
+    self.nodes.append(Line(value=""))
+
+  def add_subninja(self, subninja: Subninja):
+    self.nodes.append(subninja)
+
+  def write(self):
+    for node in self.nodes:
+      for line in node.stream():
+        print(line, file=self.file)