✨ Add low-setup usage

This adds the ability to use moban in an ad-hoc manner
without a config file, like `moban foo.jj2`. This also
adds environment variables as a fallback data source if
the default/specified data files do not exist.

Closes moremoban#133

moban/plugins.py

@@ -46,7 +46,15 @@ def number_of_templated_files(self):
         return self.templated_count
 
     def render_to_file(self, template_file, data_file, output_file):
-        data = self.context.get_data(data_file)
+        try:
+            data = self.context.get_data(data_file)
+        except OSError as exception:
+            # If data file doesn't exist:
+            # 1. Alert the user of their (potential) mistake
+            # 2. Attempt to use environment vars as data
+            reporter.report_error_message(exception)
+            reporter.report_using_env_vars()
+            data = os.environ
         template = self.engine.get_template(template_file)
         template_abs_path = utils.get_template_path(
             self.template_dirs, template_file
@@ -89,7 +97,15 @@ def _render_with_finding_template_first(self, template_file_index):
                 self.template_dirs, template_file
             )
             for (data_file, output) in data_output_pairs:
-                data = self.context.get_data(data_file)
+                try:
+                    data = self.context.get_data(data_file)
+                except OSError as exception:
+                    # If data file doesn't exist:
+                    # 1. Alert the user of their (potential) mistake
+                    # 2. Attempt to use environment vars as data
+                    reporter.report_error_message(exception)
+                    reporter.report_using_env_vars()
+                    data = os.environ
                 flag = self.apply_template(
                     template_abs_path, template, data, output
                 )
@@ -100,7 +116,15 @@ def _render_with_finding_template_first(self, template_file_index):
 
     def _render_with_finding_data_first(self, data_file_index):
         for (data_file, template_output_pairs) in data_file_index.items():
-            data = self.context.get_data(data_file)
+            try:
+                data = self.context.get_data(data_file)
+            except OSError as exception:
+                # If data file doesn't exist:
+                # 1. Alert the user of their (potential) mistake
+                # 2. Attempt to use environment vars as data
+                reporter.report_error_message(exception)
+                reporter.report_using_env_vars()
+                data = os.environ
             for (template_file, output) in template_output_pairs:
                 template = self.engine.get_template(template_file)
                 template_abs_path = utils.get_template_path(

moban/reporter.py

@@ -12,6 +12,7 @@
 MESSAGE_COPIED_ALL = "Copied {0} files."
 MESSAGE_PULLING_REPO = "Updating {0}..."
 MESSAGE_CLONING_REPO = "Cloning {0}..."
+MESSAGE_USING_ENV_VARS = "Attempting to use environment vars as data..."
 
 
 def report_templating(source_file, destination_file):
@@ -89,6 +90,10 @@ def report_git_clone(repo):
     print(MESSAGE_CLONING_REPO.format(colored_repo))
 
 
+def report_using_env_vars():
+    print(crayons.yellow(MESSAGE_USING_ENV_VARS, bold=True))
+
+
 def _format_single(message, count):
     if count == 1:
         return message.replace("files", "file")