automation: pull up terraform funcs to abstract class

see #1

app/terraform/terraform.py

@@ -0,0 +1,93 @@
+import json
+import subprocess
+from typing import Dict, Any, Optional
+
+import jinja2
+
+from app.terraform import BaseAutomation
+
+
+class TerraformAutomation(BaseAutomation):
+    """
+    An abstract class to be extended by automation plugins using Terraform
+    providers to deploy resources.
+    """
+
+    parallelism = 10
+    """
+    Default parallelism for remote API calls.
+    """
+
+    def automate(self):
+        self.tf_prehook()
+        self.tf_generate()
+        self.tf_init()
+        self.tf_apply(refresh=False)
+        self.tf_posthook()
+
+    def tf_apply(self, refresh: bool = True, parallelism: Optional[int] = None):
+        if not parallelism:
+            parallelism = self.parallelism
+        subprocess.run(
+            ['terraform', 'apply', f'-refresh={str(refresh).lower()}', '-auto-approve',
+             f'-parallelism={str(parallelism)}'],
+            cwd=self.working_directory())
+
+    def tf_generate(self):
+        raise NotImplementedError()
+
+    def tf_init(self):
+        subprocess.run(
+            ['terraform', 'init'],
+            cwd=self.working_directory())
+
+    def tf_output(self) -> Dict[str, Any]:
+        tf = subprocess.run(
+            ['terraform', 'output', '-json'],
+            cwd=self.working_directory(),
+            stdout=subprocess.PIPE)
+        return json.loads(tf.stdout)
+
+    def tf_plan(self):
+        tf = subprocess.run(
+            ['terraform', 'plan'],
+            cwd=self.working_directory())
+        # TODO: looks like terraform has a -json output mode here but it's
+        # more like JSON-ND, task is to figure out how to yield those records
+        # as plan runs, the same is probably also true for apply
+
+    def tf_posthook(self, prehook_result: Any = None) -> None:
+        """
+        This hook function is called as part of normal automation, after the
+        completion of :func:`tf_apply`.
+
+        The default, if not overridden by a subclass, is to do nothing.
+
+        :param prehook_result: the returned value of :func:`tf_prehook`
+        :return: None
+        """
+        pass
+
+    def tf_prehook(self) -> Optional[Any]:
+        """
+        This hook function is called as part of normal automation, before generating
+        the terraform configuration file. The return value will be passed to
+        :func:`tf_posthook` but is otherwise ignored.
+
+        The default, if not overridden by a subclass, is to do nothing.
+
+        :return: state that is useful to :func:`tf_posthook`, if required
+        """
+        pass
+
+    def tf_show(self) -> Dict[str, Any]:
+        terraform = subprocess.run(
+            ['terraform', 'show', '-json'],
+            cwd=self.working_directory(),
+            stdout=subprocess.PIPE)
+        return json.loads(terraform.stdout)
+
+    def tf_write(self, template: str, **kwargs):
+        tmpl = jinja2.Template(template)
+        with open(self.working_directory("main.tf"), 'w') as tf:
+            tf.write(tmpl.render(**kwargs))