update docs

docs/concepts/extending-cmd-task.md

@@ -2,4 +2,127 @@
 
 # Extending CmdTask
 
+Aside from all methods described in the [Extending Task Section](extending-task.md), there are some other methods you can use to extend CmdTask:
+
+- `get_cmd_script(self, *args: Any, **kwargs: Any)`
+
+
+## SlackPrintTask
+
+```python
+from typing import Any, Optional, Iterable, Union, Callable
+from zrb import (
+    runner, Group, AnyTask, CmdTask, AnyInput, StrInput, Env, EnvFile
+)
+
+import jsons
+import os
+
+
+class SlackPrintTask(CmdTask):
+
+    def __init__(
+        self,
+        name: str,
+        group: Optional[Group] = None,
+        inputs: Iterable[AnyInput] = [],
+        envs: Iterable[Env] = [],
+        env_files: Iterable[EnvFile] = [],
+        icon: Optional[str] = None,
+        color: Optional[str] = None,
+        description: str = '',
+        slack_channel_id: str = '',
+        slack_app_token: str = '',
+        message: str = '',
+        upstreams: Iterable[AnyTask] = [],
+        checkers: Iterable[AnyTask] = [],
+        checking_interval: Union[float, int] = 0,
+        retry: int = 2,
+        retry_interval: Union[float, int] = 1,
+        should_execute: Union[bool, str, Callable[..., bool]] = True,
+    ):
+        CmdTask.__init__(
+            self,
+            name=name,
+            group=group,
+            inputs=inputs,
+            envs=envs,
+            env_files=env_files,
+            icon=icon,
+            color=color,
+            description=description,
+            upstreams=upstreams,
+            checkers=checkers,
+            checking_interval=checking_interval,
+            retry=retry,
+            retry_interval=retry_interval,
+            should_execute=should_execute
+        )
+        self._slack_channel_id = slack_channel_id
+        self._slack_app_token = slack_app_token
+        self._message = message
+
+    def inject_envs(self):
+        self.add_env(
+            Env(
+                name='CHANNEL_ID', os_name='',
+                default=self.render_str(self._slack_channel_id)
+            ),
+            Env(
+                name='TOKEN', os_name='',
+                default=self.render_str(self._slack_app_token)
+            ),
+            Env(
+                name='MESSAGE', os_name='',
+                default=self.render_str(self._message)
+            )
+        )
+
+    def get_cmd_script(self, *args: Any, **kwargs: Any):
+        # contruct json payload and replace all `"` with `\\"`
+        json_payload = jsons.dumps({
+            'channel': '$CHANNEL_ID',
+            'blocks': [{
+                'type': 'section',
+                'text': {
+                    'type': 'mrkdwn',
+                    'text': '$MESSAGE'
+                }
+            }]
+        }).replace('"', '\\"')
+        # send payload to slack API
+        return ' '.join([
+            'curl -H "Content-type: application/json"',
+            f'--data "{json_payload}"',
+            '-H "Authorization: Bearer $TOKEN"',
+            '-X POST https://slack.com/api/chat.postMessage'
+        ])
+```
+
+Here is how you can use `SlackPrintTask`:
+
+```python
+say_hi = SlackPrintTask(
+    name='say-hi',
+    inputs=[
+        StrInput(name='message', default='Hello world')
+    ],
+    slack_channel_id=os.getenv('SLACK_CHANNEL_ID'),
+    slack_app_token=os.getenv('SLACK_APP_TOKEN'),
+    message='{{ input.message }}',
+)
+runner.register(say_hi)
+```
+
+You can run the Task by invoking the following command.
+
+```bash
+zrb say-hi
+```
+
+# TODO
+
+Add more examples.
+
+
 🔖 [Table of Contents](../README.md) / [Concepts](README.md)

docs/concepts/extending-task.md

@@ -211,4 +211,8 @@ To run again: zrb search --keyword "hakuna matata" --max-results "5"
 
 Add more examples.
 
+# Next
+
+Next you can see how you can [extend CmdTask](extending-cmd-task.md).
+
 🔖 [Table of Contents](../README.md) / [Concepts](README.md)