[FEATURE] Subscription nesting (#747)

Closes Feature Request: #743

Subscriptions support using presets as keys, and using keys to set override variables as values.
For example:

```
tv_show:
  only_recent:
    [News]:
      "Breaking News": "https://www.youtube.com/@SomeBreakingNews"

  [Tech]:
    "Two Minute Papers": "https://www.youtube.com/@TwoMinutePapers"
```
Will create two subscriptions named "Breaking News" and "Two Minute Papers", equivalent to:

```
"Breaking News":
  preset:
    - "tv_show"
    - "only_recent"

  overrides:
    subscription_indent_1: "News"
    subscription_name: "Breaking News"
    subscription_value: "https://www.youtube.com/@SomeBreakingNews"

"Two Minute Papers":
  preset:
    - "tv_show"

  overrides:
    subscription_indent_1: "Tech"
    subscription_name: "Two Minute Papers"     subscription_value: "https://www.youtube.com/@TwoMinutePapers"
```

You can provide as many parent presets in the form of keys, and subscription indents as ``[keys]``.
This can drastically simplify subscription definitions by setting things you want configurable like so in your
parent preset:

```
presets:
  tv_show_name:
    overrides:
      tv_show_name: "{subscription_name}"
      url: "{subscription_value}"
      genre: "{subscription_indent_1}"
```

NOTE!!!
Changing your subscription name from 'legacy' subscriptions will need their download archive file migrated to a new name. A future update will assist in this migration process. Either wait until then or, if you consider yourself a ytdl-sub expert, keep a backup of your subscription file before migrating.

docs/config.rst

@@ -29,7 +29,7 @@ and subscriptions.
 .. autoclass:: ytdl_sub.config.config_validator.ConfigOptions()
   :members:
   :member-order: bysource
-  :exclude-members: persist_logs, experimental
+  :exclude-members: subscription_value, persist_logs, experimental
 
 persist_logs
 """"""""""""
@@ -299,8 +299,66 @@ custom variables: ``{output_directory}``, ``{playlist_name}``, and ``{url}``. Th
 the `parent preset`_ to ``playlist_preset_ex``, and must define the variables ``{playlist_name}``
 and ``{url}`` since the preset did not.
 
+.. _beautifying subscriptions:
+
+Beautifying Subscriptions
+^^^^^^^^^^^^^^^^^^^^^^^^^
+Subscriptions support using presets as keys, and using keys to set override variables as values.
+For example:
+
+.. code-block:: yaml
+  :caption: subscription.yaml
+
+   tv_show:
+     only_recent:
+       [News]:
+         "Breaking News": "https://www.youtube.com/@SomeBreakingNews"
+
+     [Tech]:
+       "Two Minute Papers": "https://www.youtube.com/@TwoMinutePapers"
+
+Will create two subscriptions named "Breaking News" and "Two Minute Papers", equivalent to:
+
+.. code-block:: yaml
+
+  "Breaking News":
+    preset:
+      - "tv_show"
+      - "only_recent"
+
+    overrides:
+      subscription_indent_1: "News"
+      subscription_name: "Breaking News"
+      subscription_value: "https://www.youtube.com/@SomeBreakingNews"
+
+  "Two Minute Papers":
+    preset:
+      - "tv_show"
+
+    overrides:
+      subscription_indent_1: "Tech"
+      subscription_name: "Two Minute Papers"
+      subscription_value: "https://www.youtube.com/@TwoMinutePapers"
+
+You can provide as many parent presets in the form of keys, and subscription indents as ``[keys]``.
+This can drastically simplify subscription definitions by setting things like so in your
+parent preset:
+
+.. code-block:: yaml
+
+  presets:
+    tv_show_name:
+      overrides:
+        tv_show_name: "{subscription_name}"
+        url: "{subscription_value}"
+        genre: "{subscription_indent_1}"
+
+.. _subscription value:
+
 File Preset
 ^^^^^^^^^^^
+NOTE: This is deprecated in favor of using the method in :ref:`beautifying subscriptions`.
+
 You can apply a preset to all subscriptions in the ``subscription.yaml`` file
 by using the file-wide ``__preset__``:
 
@@ -318,10 +376,11 @@ by using the file-wide ``__preset__``:
 This ``subscription.yaml`` is equivalent to the one above it because all
 subscriptions automatically set ``__preset__`` as a `parent preset`_.
 
-.. _subscription value:
 
 Subscription Value
 ^^^^^^^^^^^^^^^^^^^
+NOTE: This is deprecated in favor of using the method in :ref:`beautifying subscriptions`.
+
 With a clever config and use of ``__preset__``, your subscriptions can typically boil
 down to a name and url. You can set ``__value__`` to the name of an override variable,
 and use the override variable ``subscription_name`` to achieve one-liner subscriptions.

docs/deprecation_notices.rst

@@ -1,6 +1,14 @@
 Deprecation Notices
 ===================
 
+Oct 2023
+--------
+
+subscription preset and value
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+The use of ``__value__`` will go away in Dec 2023 in favor of the method found in
+:ref:`beautifying subscriptions`. ``__preset__`` will still be supported for the time being.
+
 July 2023
 ---------
 

src/ytdl_sub/subscriptions/subscription.py

@@ -1,18 +1,23 @@
 import copy
+from typing import Any
 from typing import Dict
 from typing import List
 from typing import Optional
 
 from ytdl_sub.config.config_file import ConfigFile
 from ytdl_sub.config.preset import Preset
 from ytdl_sub.subscriptions.subscription_download import SubscriptionDownload
+from ytdl_sub.subscriptions.subscription_validators import SubscriptionValidator
 from ytdl_sub.utils.exceptions import ValidationException
+from ytdl_sub.utils.logger import Logger
 from ytdl_sub.utils.yaml import load_yaml
 from ytdl_sub.validators.validators import LiteralDictValidator
 
 FILE_PRESET_APPLY_KEY = "__preset__"
 FILE_SUBSCRIPTION_VALUE_KEY = "__value__"
 
+logger = Logger.get("subscription")
+
 
 class Subscription(SubscriptionDownload):
     @classmethod
@@ -68,15 +73,23 @@ def from_dict(cls, config: ConfigFile, preset_name: str, preset_dict: Dict) -> "
     def _maybe_get_subscription_value(
         cls, config: ConfigFile, subscription_dict: Dict
     ) -> Optional[str]:
+        subscription_value_key: Optional[str] = config.config_options.subscription_value
         if FILE_SUBSCRIPTION_VALUE_KEY in subscription_dict:
             if not isinstance(subscription_dict[FILE_SUBSCRIPTION_VALUE_KEY], str):
                 raise ValidationException(
                     f"Using {FILE_SUBSCRIPTION_VALUE_KEY} in a subscription"
                     f"must be a string that corresponds to an override variable"
                 )
-            return subscription_dict[FILE_SUBSCRIPTION_VALUE_KEY]
 
-        return config.config_options.subscription_value  # can be None
+            subscription_value_key = subscription_dict[FILE_SUBSCRIPTION_VALUE_KEY]
+
+        if subscription_value_key is not None:
+            logger.warning(
+                "Using %s in a subscription will eventually be deprecated in favor of writing "
+                "to the override variable `subscription_value`. Please update by Dec 2023.",
+                FILE_SUBSCRIPTION_VALUE_KEY,
+            )
+        return subscription_value_key
 
     @classmethod
     def from_file_path(cls, config: ConfigFile, subscription_path: str) -> List["Subscription"]:
@@ -121,39 +134,22 @@ def from_file_path(cls, config: ConfigFile, subscription_path: str) -> List["Sub
             config = copy.deepcopy(config)
             config.presets.dict[FILE_PRESET_APPLY_KEY] = file_preset.dict
 
-        for subscription_key, subscription_object in subscription_dict.items():
+        subscriptions_dict: Dict[str, Any] = {
+            key: obj
+            for key, obj in subscription_dict.items()
+            if key not in [FILE_PRESET_APPLY_KEY, FILE_SUBSCRIPTION_VALUE_KEY]
+        }
 
-            # Skip file preset or value
-            if subscription_key in [FILE_PRESET_APPLY_KEY, FILE_SUBSCRIPTION_VALUE_KEY]:
-                continue
-
-            # If the subscription obj is just a string, set it to the override variable
-            # defined in FILE_SUBSCRIPTION_VALUE_KEY
-            if isinstance(subscription_object, str) and file_subscription_value:
-                subscription_object = {"overrides": {file_subscription_value: subscription_object}}
-            elif isinstance(subscription_object, dict):
-                pass
-            elif isinstance(subscription_object, str) and not file_subscription_value:
-                raise ValidationException(
-                    f"Subscription {subscription_key} is a string, but the subscription value "
-                    f"is not set to an override variable"
-                )
-            else:
-                raise ValidationException(
-                    f"Subscription {subscription_key} should be in the form of a preset"
-                )
-
-            # If it has file_preset, inject it as a parent preset
-            if has_file_preset:
-                parent_preset = subscription_object.get("preset", [])
-                # Preset can be a single string
-                if isinstance(parent_preset, str):
-                    parent_preset = [parent_preset]
-
-                # If it's not a string or list, it will fail downstream
-                if isinstance(parent_preset, list):
-                    subscription_object["preset"] = parent_preset + [FILE_PRESET_APPLY_KEY]
+        subscriptions_dicts = SubscriptionValidator(
+            name="",
+            value=subscriptions_dict,
+            config=config,
+            presets=[FILE_PRESET_APPLY_KEY] if has_file_preset else [],
+            indent_overrides=[],
+            subscription_value=file_subscription_value,
+        ).subscription_dicts()
 
+        for subscription_key, subscription_object in subscriptions_dicts.items():
             subscriptions.append(
                 cls.from_dict(
                     config=config,