DPE-2655 profile limit option (#244)

* port over from k8s

* fix unit tests

Author: paulomach

config.yaml

@@ -34,3 +34,9 @@ options:
       minimal running performance.
    type: string
    default: production
+  profile-limit-memory:
+    type: int
+    description: |
+      Amount of memory in Megabytes to limit PostgreSQL and associated process to.
+      If unset, this will be decided according to the default memory limit in the selected profile.
+      Only comes into effect when the `production` profile is selected.

lib/charms/data_platform_libs/v0/data_models.py

@@ -0,0 +1,354 @@
+# Copyright 2023 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+r"""Library to provide simple API for promoting typed, validated and structured dataclass in charms.
+
+Dict-like data structure are often used in charms. They are used for config, action parameters
+and databag. This library aims at providing simple API for using pydantic BaseModel-derived class
+in charms, in order to enhance:
+* Validation, by embedding custom business logic to validate single parameters or even have
+  validators that acts across different fields
+* Parsing, by loading data into pydantic object we can both allow for other types (e.g. float) to
+  be used in configuration/parameters as well as specify even nested complex objects for databags
+* Static typing checks, by moving from dict-like object to classes with typed-annotated properties,
+  that can be statically checked using mypy to ensure that the code is correct.
+
+Pydantic models can be used on:
+
+* Charm Configuration (as defined in config.yaml)
+* Actions parameters (as defined in actions.yaml)
+* Application/Unit Databag Information (thus making it more structured and encoded)
+
+
+## Creating models
+
+Any data-structure can be modeled using dataclasses instead of dict-like objects (e.g.  storing
+config, action parameters and databags). Within pydantic, we can define dataclasses that provides
+also parsing and validation on standard dataclass implementation:
+
+```python
+
+from charms.data_platform_libs.v0.data_models import BaseConfigModel
+
+class MyConfig(BaseConfigModel):
+
+    my_key: int
+
+    @validator("my_key")
+     def is_lower_than_100(cls, v: int):
+         if v > 100:
+             raise ValueError("Too high")
+
+```
+
+This should allow to collapse both parsing and validation as the dataclass object is parsed and
+created:
+
+```python
+dataclass = MyConfig(my_key="1")
+
+dataclass.my_key # this returns 1 (int)
+dataclass["my_key"] # this returns 1 (int)
+
+dataclass = MyConfig(my_key="102") # this returns a ValueError("Too High")
+```
+
+## Charm Configuration Model
+
+Using the class above, we can implement parsing and validation of configuration by simply
+extending our charms using the `TypedCharmBase` class, as shown below.
+
+```python
+class MyCharm(TypedCharmBase[MyConfig]):
+    config_type = MyConfig
+
+     # everywhere in the code you will have config property already parsed and validate
+     def my_method(self):
+         self.config: MyConfig
+```
+
+## Action parameters
+
+In order to parse action parameters, we can use a decorator to be applied to action event
+callbacks, as shown below.
+
+```python
+@validate_params(PullActionModel)
+def _pull_site_action(
+    self, event: ActionEvent,
+    params: Optional[Union[PullActionModel, ValidationError]] = None
+):
+    if isinstance(params, ValidationError):
+        # handle errors
+    else:
+        # do stuff
+```
+
+Note that this changes the signature of the callbacks by adding an extra parameter with the parsed
+counterpart of the `event.params` dict-like field. If validation fails, we return (not throw!) the
+exception, to be handled (or raised) in the callback.
+
+## Databag
+
+In order to parse databag fields, we define a decorator to be applied to base relation event
+callbacks.
+
+```python
+@parse_relation_data(app_model=AppDataModel, unit_model=UnitDataModel)
+def _on_cluster_relation_joined(
+        self, event: RelationEvent,
+        app_data: Optional[Union[AppDataModel, ValidationError]] = None,
+        unit_data: Optional[Union[UnitDataModel, ValidationError]] = None
+) -> None:
+    ...
+```
+
+The parameters `app_data` and `unit_data` refers to the databag of the entity which fired the
+RelationEvent.
+
+When we want to access to a relation databag outsides of an action, it can be useful also to
+compact multiple databags into a single object (if there are no conflicting fields), e.g.
+
+```python
+
+class ProviderDataBag(BaseClass):
+    provider_key: str
+
+class RequirerDataBag(BaseClass):
+    requirer_key: str
+
+class MergedDataBag(ProviderDataBag, RequirerDataBag):
+    pass
+
+merged_data = get_relation_data_as(
+    MergedDataBag, relation.data[self.app], relation.data[relation.app]
+)
+
+merged_data.requirer_key
+merged_data.provider_key
+
+```
+
+The above code can be generalized to other kinds of merged objects, e.g. application and unit, and
+it can be extended to multiple sources beyond 2:
+
+```python
+merged_data = get_relation_data_as(
+    MergedDataBag, relation.data[self.app], relation.data[relation.app], ...
+)
+```
+
+"""
+
+import json
+from functools import reduce, wraps
+from typing import Callable, Generic, MutableMapping, Optional, Type, TypeVar, Union
+
+import pydantic
+from ops.charm import ActionEvent, CharmBase, RelationEvent
+from ops.model import RelationDataContent
+from pydantic import BaseModel, ValidationError
+
+# The unique Charmhub library identifier, never change it
+LIBID = "cb2094c5b07d47e1bf346aaee0fcfcfe"
+
+# Increment this major API version when introducing breaking changes
+LIBAPI = 0
+
+# Increment this PATCH version before using `charmcraft publish-lib` or reset
+# to 0 if you are raising the major API version
+LIBPATCH = 4
+
+PYDEPS = ["ops>=2.0.0", "pydantic>=1.10,<2"]
+
+G = TypeVar("G")
+T = TypeVar("T", bound=BaseModel)
+AppModel = TypeVar("AppModel", bound=BaseModel)
+UnitModel = TypeVar("UnitModel", bound=BaseModel)
+
+DataBagNativeTypes = (int, str, float)
+
+
+class BaseConfigModel(BaseModel):
+    """Class to be used for defining the structured configuration options."""
+
+    def __getitem__(self, x):
+        """Return the item using the notation instance[key]."""
+        return getattr(self, x.replace("-", "_"))
+
+
+class TypedCharmBase(CharmBase, Generic[T]):
+    """Class to be used for extending config-typed charms."""
+
+    config_type: Type[T]
+
+    @property
+    def config(self) -> T:
+        """Return a config instance validated and parsed using the provided pydantic class."""
+        translated_keys = {k.replace("-", "_"): v for k, v in self.model.config.items()}
+        return self.config_type(**translated_keys)
+
+
+def validate_params(cls: Type[T]):
+    """Return a decorator to allow pydantic parsing of action parameters.
+
+    Args:
+        cls: Pydantic class representing the model to be used for parsing the content of the
+             action parameter
+    """
+
+    def decorator(
+        f: Callable[[CharmBase, ActionEvent, Union[T, ValidationError]], G]
+    ) -> Callable[[CharmBase, ActionEvent], G]:
+        @wraps(f)
+        def event_wrapper(self: CharmBase, event: ActionEvent):
+            try:
+                params = cls(
+                    **{key.replace("-", "_"): value for key, value in event.params.items()}
+                )
+            except ValidationError as e:
+                params = e
+            return f(self, event, params)
+
+        return event_wrapper
+
+    return decorator
+
+
+def write(relation_data: RelationDataContent, model: BaseModel):
+    """Write the data contained in a domain object to the relation databag.
+
+    Args:
+        relation_data: pointer to the relation databag
+        model: instance of pydantic model to be written
+    """
+    for key, value in model.dict(exclude_none=False).items():
+        if value:
+            relation_data[key.replace("_", "-")] = (
+                str(value)
+                if any(isinstance(value, _type) for _type in DataBagNativeTypes)
+                else json.dumps(value)
+            )
+        else:
+            relation_data[key.replace("_", "-")] = ""
+
+
+def read(relation_data: MutableMapping[str, str], obj: Type[T]) -> T:
+    """Read data from a relation databag and parse it into a domain object.
+
+    Args:
+        relation_data: pointer to the relation databag
+        obj: pydantic class representing the model to be used for parsing
+    """
+    return obj(
+        **{
+            field_name: (
+                relation_data[parsed_key]
+                if field.outer_type_ in DataBagNativeTypes
+                else json.loads(relation_data[parsed_key])
+            )
+            for field_name, field in obj.__fields__.items()
+            # pyright: ignore[reportGeneralTypeIssues]
+            if (parsed_key := field_name.replace("_", "-")) in relation_data
+            if relation_data[parsed_key]
+        }
+    )
+
+
+def parse_relation_data(
+    app_model: Optional[Type[AppModel]] = None, unit_model: Optional[Type[UnitModel]] = None
+):
+    """Return a decorator to allow pydantic parsing of the app and unit databags.
+
+    Args:
+        app_model: Pydantic class representing the model to be used for parsing the content of the
+            app databag. None if no parsing ought to be done.
+        unit_model: Pydantic class representing the model to be used for parsing the content of the
+            unit databag. None if no parsing ought to be done.
+    """
+
+    def decorator(
+        f: Callable[
+            [
+                CharmBase,
+                RelationEvent,
+                Optional[Union[AppModel, ValidationError]],
+                Optional[Union[UnitModel, ValidationError]],
+            ],
+            G,
+        ]
+    ) -> Callable[[CharmBase, RelationEvent], G]:
+        @wraps(f)
+        def event_wrapper(self: CharmBase, event: RelationEvent):
+            try:
+                app_data = (
+                    read(event.relation.data[event.app], app_model)
+                    if app_model is not None and event.app
+                    else None
+                )
+            except pydantic.ValidationError as e:
+                app_data = e
+
+            try:
+                unit_data = (
+                    read(event.relation.data[event.unit], unit_model)
+                    if unit_model is not None and event.unit
+                    else None
+                )
+            except pydantic.ValidationError as e:
+                unit_data = e
+
+            return f(self, event, app_data, unit_data)
+
+        return event_wrapper
+
+    return decorator
+
+
+class RelationDataModel(BaseModel):
+    """Base class to be used for creating data models to be used for relation databags."""
+
+    def write(self, relation_data: RelationDataContent):
+        """Write data to a relation databag.
+
+        Args:
+            relation_data: pointer to the relation databag
+        """
+        return write(relation_data, self)
+
+    @classmethod
+    def read(cls, relation_data: RelationDataContent) -> "RelationDataModel":
+        """Read data from a relation databag and parse it as an instance of the pydantic class.
+
+        Args:
+            relation_data: pointer to the relation databag
+        """
+        return read(relation_data, cls)
+
+
+def get_relation_data_as(
+    model_type: Type[AppModel],
+    *relation_data: RelationDataContent,
+) -> Union[AppModel, ValidationError]:
+    """Return a merged representation of the provider and requirer databag into a single object.
+
+    Args:
+        model_type: pydantic class representing the merged databag
+        relation_data: list of RelationDataContent of provider/requirer/unit sides
+    """
+    try:
+        app_data = read(reduce(lambda x, y: dict(x) | dict(y), relation_data, {}), model_type)
+    except pydantic.ValidationError as e:
+        app_data = e
+    return app_data