Add basic builder code

- Takes in config via traitlets
- Pushes image after it is built
- Can run different detectors easily as well
- Single straight up application that runs from start to end,
  no concurrency (woot!)

builder/app.py

@@ -0,0 +1,89 @@
+import json
+import os
+
+
+from traitlets.config import Application, LoggingConfigurable, Unicode, Dict, List
+from traitlets import Type
+import docker
+
+import subprocess
+
+
+from .detectors import BuildPack, PythonBuildPack
+
+class Builder(Application):
+    config_file = Unicode(
+        'builder_config.py',
+        config=True
+    )
+
+    build_name = Unicode(
+        None,
+        allow_none=True,
+        config=True
+    )
+
+    source_url = Unicode(
+        None,
+        allow_none=True,
+        config=True
+    )
+
+    output_image_spec = Unicode(
+        None,
+        allow_none=True,
+        config=True
+    )
+
+    git_workdir = Unicode(
+        "/tmp/git",
+        config=True
+    )
+
+    buildpacks = List(
+        None,
+        [PythonBuildPack],
+        config=True
+    )
+
+    aliases = Dict({
+        'source': 'Builder.source_url',
+        'output': 'Builder.output_image_spec',
+        'f': 'Builder.config_file',
+        'n': 'Builder.build_name'
+    })
+
+
+    def fetch(self, url, ref, output_path):
+        subprocess.check_call([
+            "git", "clone", "--depth", "1",
+            url, output_path
+        ])
+
+
+    def initialize(self, *args, **kwargs):
+        super().initialize(*args, **kwargs)
+
+        self.load_config_file(self.config_file)
+
+    def run(self):
+        output_path = os.path.join(self.git_workdir, self.build_name)
+        self.fetch(
+            self.source_url,
+            'master',
+            output_path
+        )
+        for bp_class in self.buildpacks:
+            bp = bp_class()
+            if bp.detect(output_path):
+                bp.build(output_path, self.output_image_spec)
+
+        client = docker.from_env(version='1.24')
+        for line in client.images.push(self.output_image_spec, stream=True):
+            progress = json.loads(line.decode('utf-8'))
+            print(progress['status'])
+
+if __name__ == '__main__':
+    f = Builder()
+    f.initialize()
+    f.run()

builder/detectors.py

@@ -0,0 +1,51 @@
+import os
+import subprocess
+
+from traitlets import Unicode, Dict
+from traitlets.config import LoggingConfigurable
+
+
+class BuildPack(LoggingConfigurable):
+    def detect(self, workdir):
+        """
+        Return True if app in workdir can be built with this buildpack
+        """
+        pass
+
+    def build(self, workdir, output_image_spec):
+        """
+        Run a command that will take workdir and produce an image ready to be pushed
+        """
+        pass
+
+
+
+class PythonBuildPack(BuildPack):
+    runtime_builder_map = Dict({
+        'python-2.7': 'jupyterhub/singleuser-builder-venv-2.7:v0.1.2',
+        'python-3.5': 'jupyterhub/singleuser-builder-venv-3.5:v0.1.2',
+    })
+
+    runtime = Unicode(
+        'python-3.5',
+        config=True
+    )
+
+    def detect(self, workdir):
+        if os.path.exists(os.path.join(workdir, 'requirements.txt')):
+            try:
+                with open(os.path.join(workdir, 'runtime.txt')) as f:
+                    self.runtime = f.read().strip()
+            except FileNotFoundError:
+                pass
+            return True
+
+    def build(self, workdir, output_image_spec):
+        cmd = [
+            's2i',
+            'build',
+            workdir,
+            self.runtime_builder_map[self.runtime],
+            output_image_spec
+        ]
+        subprocess.check_call(cmd)