jenkins: Add Jenkins webhook

Using the [Generic Event Plugin][0], we can receive a notification from
Jenkins when builds start and finish.  We'll relay these to *ntfy* on a
unique topic that I will subscribe to on my desktop.  That way, I can
get desktop notifications about jobs while I am working, which will be
particularly useful while developing and troubleshooting pipelines.

[0]: https://plugins.jenkins.io/generic-event/

dch_webhooks.py

@@ -1,3 +1,4 @@
+import base64
 import datetime
 import importlib.metadata
 import logging
@@ -44,6 +45,7 @@ MAX_DOCUMENT_SIZE = int(
         50 * 2**20,
     )
 )
+NTFY_URL = os.environ.get('NTFY_URL', 'http://ntfy.ntfy:2586')
 PAPERLESS_URL = os.environ.get(
     'PAPERLESS_URL',
     'http://paperless-ngx',
@@ -308,6 +310,55 @@ def response_filename(response: httpx.Response) -> str:
     return response.url.path.rstrip('/').rsplit('/', 1)[-1]
 
 
+async def ntfy(
+    message: Optional[str],
+    topic: str,
+    title: Optional[str] = None,
+    tags: Optional[str] = None,
+    attach: Optional[bytes] = None,
+    filename: Optional[str] = None,
+) -> None:
+    assert message or attach
+    headers = {
+    }
+    if title:
+        headers['Title'] = title
+    if tags:
+        headers['Tags'] = tags
+    url = f'{NTFY_URL}/{topic}'
+    client = httpx.AsyncClient()
+    if attach:
+        if filename:
+            headers['Filename'] = filename
+        if message:
+            try:
+                message.encode("ascii")
+            except UnicodeEncodeError:
+                message = rfc2047_base64encode(message)
+            else:
+                message = message.replace('\n', '\\n')
+            headers['Message'] = message
+        r = await client.put(
+            url,
+            headers=headers,
+            content=attach,
+        )
+    else:
+        r = await client.post(
+            url,
+            headers=headers,
+            content=message,
+        )
+    r.raise_for_status()
+
+
+def rfc2047_base64encode(
+    message: str,
+) -> str:
+    encoded = base64.b64encode(message.encode("utf-8")).decode("ascii")
+    return f"=?UTF-8?B?{encoded}?="
+
+
 app = fastapi.FastAPI(
     name=DIST['Name'],
     version=DIST['Version'],
@@ -331,3 +382,46 @@ def status() -> str:
 @app.post('/hooks/firefly-iii/create')
 async def firefly_iii_create(hook: FireflyIIIWebhook) -> None:
     await handle_firefly_transaction(hook.content)
+
+
+@app.post('/hooks/jenkins')
+async def jenkins_notify(request: fastapi.Request) -> None:
+    body = await request.json()
+    data = body.get('data', {})
+    if body['type'] == 'run.started':
+        title = 'Build started'
+        tag = 'building_construction'
+        build_cause = None
+        for action in data.get('actions', []):
+            for cause in action.get('causes', []):
+                if build_cause := cause.get('shortDescription'):
+                    break
+            else:
+                continue
+            break
+        message = f'Build started: {data["fullDisplayName"]}'
+        if build_cause:
+            message = f'{message} ({build_cause})'
+    elif body['type'] == 'run.finalized':
+        message = f'{data["fullDisplayName"]} {data["result"]}'
+        title = 'Build finished'
+        match data['result']:
+            case 'FAILURE':
+                tag = 'red_circle'
+            case 'SUCCESS':
+                tag = 'green_circle'
+            case 'UNSTABLE':
+                tag = 'yellow_circle'
+            case 'NOT_BUILT':
+                tag = 'large_blue_circle'
+            case 'ABORTED':
+                tag = 'black_circle'
+            case _:
+                tag = 'white_circle'
+    else:
+        return
+
+    try:
+        await ntfy(message, 'jenkins', title, tag)
+    except httpx.HTTPError:
+        log.exception('Failed to send notification:')