plugins/figlet: error out when figlet doesn't exist

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

plugins/figlet.py

@@ -11,15 +11,35 @@ Say something in a Chat tab.
 .. note:: Can create fun things when used with :ref:`The rainbow plugin <rainbow-plugin>`.
 
 """
-from poezio.plugin import BasePlugin
+
 import subprocess
+from poezio.plugin import BasePlugin
+
+
+def is_figlet() -> bool:
+    """Ensure figlet exists"""
+    process = subprocess.Popen(
+        ['which', 'figlet'],
+        stdout=subprocess.DEVNULL,
+        stderr=subprocess.DEVNULL,
+    )
+    return process.wait() == 0
 
 
 class Plugin(BasePlugin):
     def init(self):
+        if not is_figlet():
+            self.api.information(
+                'Couldn\'t find the figlet program. '
+                'Please install it and reload the plugin.',
+                'Error',
+            )
+            return None
+
         self.api.add_event_handler('muc_say', self.figletize)
         self.api.add_event_handler('conversation_say', self.figletize)
         self.api.add_event_handler('private_say', self.figletize)
+        return None
 
     def figletize(self, msg, tab):
         process = subprocess.Popen(