Extend the webhook to easily support custom subclasses

The design is based on the one used by Buildbot's own GitHubEventHandler.

README.md

@@ -51,6 +51,38 @@ factory.addStep(steps.Gitea(
 ))
 ```
 
+The webhook currently supports pushes and pull requests by default, but you can
+subclass `buildbot_gitea.webhook.GiteaHandler` to add supports for other events,
+and then use your subclass by setting the `class` parameter:
+
+```py
+# myhook.py
+
+from buildbot_gitea.webhook import GiteaHandler
+class MyGiteaHook(GiteaHandler)
+    def process_whatever(self, payload, event_type, codebase):
+        # This should be a list of dicts
+        changes = []
+
+        return changes
+
+# master.cfg
+
+from myhook import MyGiteaHook
+
+c['www'] = {
+    'change_hook_dialects': {
+        'gitea': {
+            'class': MyGiteaHook,
+            # ...
+        }
+    }
+}
+```
+
+Note that the handlers need to be named according to the scheme:
+`process_{event}` (e.g., `process_create`, etc).
+
 # Parameters
 
 ## Change Hook
@@ -61,6 +93,7 @@ The change hook is set as part of the `www` section in the `change_hook_dialects
 | --- | --- |
 | `secret` | The secret, which needs to be set in gitea |
 | `onlyIncludePushCommit` | A push may have more than one commit associated with it. If this is true, only the newest (latest) commit of all received will be added as a change to buildbot. If this is set to false, all commits will inside the push will be added. |
+| `class` | Set this if you want to use your own handler class (see above for details) |
 
 In gitea in your project or organization and add a new webhook of type gitea.
 Set the parameters as follows:

buildbot_gitea/webhook.py

@@ -11,7 +11,7 @@ _HEADER_EVENT_TYPE = 'X-Gitea-Event'
 
 class GiteaHandler(BaseHookHandler):
 
-    def processPushEvent(self, payload, event_type, codebase):
+    def process_push(self, payload, event_type, codebase):
         refname = payload["ref"]
 
         changes = []
@@ -56,7 +56,7 @@ class GiteaHandler(BaseHookHandler):
             changes.append(change)
         return changes
 
-    def processPullRequestEvent(self, payload, event_type, codebase):
+    def process_pull_request(self, payload, event_type, codebase):
         action = payload['action']
 
         # Only handle potential new stuff, ignore close/.
@@ -128,17 +128,30 @@ class GiteaHandler(BaseHookHandler):
         codebases = request.args.get('codebase', [None])
         codebase = bytes2unicode(codebases[0])
         changes = []
-        if event_type == 'push':
-            changes = self.processPushEvent(
-                payload, event_type, codebase)
-        elif event_type == 'pull_request':
-            changes = self.processPullRequestEvent(
-                payload, event_type, codebase)
-        else:
+
+        handler_function = getattr(self, 'process_{}'.format(event_type), None)
+        if not handler_function:
             log.msg("Ignoring gitea event '{}'".format(event_type))
+        else:
+            changes = handler_function(payload, event_type, codebase)
 
         return (changes, 'git')
 
 
+class GiteaHandlerPlugin(BaseHookHandler):
+    def __init__(self, master, options):
+        if not options:
+            options = {}
+        super().__init__(master, options)
+
+        handler_class = options.get('class', GiteaHandler)
+        if 'class' in options:
+            del options['class']
+
+        self.handler = handler_class(master, options)
+
+    def getChanges(self, request):
+        return self.handler.getChanges(request)
+
 # Plugin name
-gitea = GiteaHandler
+gitea = GiteaHandlerPlugin