plugin: add custom command support

bebop/browser/browser.py

@@ -358,6 +358,14 @@ class Browser:
             return
 
         command = words[0]
+
+        # Check for plugin registered commands first.
+        for plugin in self.plugins:
+            if command in map(lambda c: c.name, plugin.commands):
+                plugin.use_command(self, command, command_text)
+                return
+
+        # Then built-in commands without args.
         if num_words == 1:
             if command == "help":
                 self.open_help()
@@ -368,6 +376,8 @@ class Browser:
             elif command in ("i", "info"):
                 self.show_page_info()
             return
+
+        # And commands with one or more args.
         if command in ("o", "open"):
             self.open_url(words[1])
         elif command == "forget-certificate":

bebop/plugins.py

@@ -18,15 +18,58 @@ There is at least one plugin in this repository in the `plugins` directory.
 """
 
 from abc import ABC, abstractmethod
+from dataclasses import dataclass
 from typing import Optional
 
 from bebop.browser.browser import Browser
 
 
-class SchemePlugin(ABC):
-    """Plugin for URL scheme management."""
+@dataclass
+class PluginCommand:
+    """A descriptor for a plugin command.
+
+    Attributes:
+    - name: the command name.
+    - description: a very short description of the command; should start lower
+      case and does not need a period at the end.
+    """
+    name: str
+    description: str
+
+
+class Plugin(ABC):
+    """Base class for plugins.
+
+    Attributes:
+    - commands: list of PluginCommand provided by the plugin.
+    """
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.commands = []
+
+    def use_command(self, browser: Browser, name: str, text: str):
+        """Use a command presented by this plugin.
+
+        Plugins that do not use custom commands can leave this method
+        unimplemented.
+
+        Attributes:
+        - name: the command used as it is in the commands list.
+        - text: the whole command text, including the command name.
+        """
+        pass
+
+
+class SchemePlugin(Plugin):
+    """Plugin for URL scheme management.
+
+    If you want to create a plugin that can handle new schemes, create a plugin
+    inheriting this class.
+    """
 
     def __init__(self, scheme: str) -> None:
+        super().__init__()
         self.scheme = scheme
 
     @abstractmethod