Add a subsystem manager

Makefile

@@ -1,4 +1,8 @@
-all:
+.PHONY: install publish test
+
+all: install
+
+install:
 	poetry install
 	poetry run mono install
 

app-frame/macrostrat/app_frame/__init__.py

@@ -1,2 +1,4 @@
 from .core import Application
 from .compose import compose
+from .subsystems import SubsystemManager, Subsystem, SubsystemError
+from .exc import ApplicationError

app-frame/macrostrat/app_frame/exc.py

@@ -0,0 +1,4 @@
+class ApplicationError(Exception):
+    """Base class for all errors that should be caught and handled by the application."""
+
+    pass

app-frame/macrostrat/app_frame/subsystems/__init__.py

@@ -0,0 +1,152 @@
+from toposort import toposort_flatten
+from ..core import ApplicationBase
+from packaging.specifiers import InvalidSpecifier, SpecifierSet
+from packaging.version import Version
+from typing import Optional
+
+from macrostrat.utils.logs import get_logger
+
+from .defs import Subsystem, SubsystemError
+
+
+log = get_logger(__name__)
+
+
+class SubsystemManager:
+    """
+    Storage class for plugins. Currently, we enforce a single
+    phase of plugin loading, ended by a call to `finished_loading_plugins`.
+    Hooks can be run afterwards. This removes the risk of some parts of the
+    application performing actions before all plugins are initialized.
+    """
+
+    _hooks_fired = []
+    _app: Optional[ApplicationBase] = None
+    _subsystem_cls: Subsystem = Subsystem
+
+    def __init__(self, subsystem_cls: Subsystem = Subsystem):
+        self._app = None
+        self.__init_store = []
+        self.__store = None
+
+        # Ensure that the plugin class is a subclass of Subsystem
+        assert issubclass(subsystem_cls, Subsystem) or subsystem_cls is Subsystem
+        self._subsystem_cls = subsystem_cls
+
+    def __iter__(self):
+        try:
+            yield from self.__store
+        except TypeError:
+            raise SubsystemError("Cannot list subsystems until loading is finished.")
+
+    @property
+    def is_ready(self):
+        return self.__store is not None
+
+    def _is_compatible(self, sub: Subsystem):
+        """Assess package compatibility: https://packaging.pypa.io/en/latest/specifiers.html"""
+        if sub.app_version is None:
+            return True
+        try:
+            spec = SpecifierSet(sub.app_version, prereleases=True)
+        except InvalidSpecifier:
+            raise SubsystemError(
+                f"Subsystem '{sub.name}' specifies an invalid {self.app.name} compatibility range '{sub.app_version}'"
+            )
+        return Version() in spec
+
+    def add(self, plugin):
+        if not plugin.should_enable(self):
+            return
+        if not self._is_compatible(plugin):
+            _raise_compat_error(plugin)
+            return
+
+        try:
+            self.__init_store.append(plugin)
+        except AttributeError:
+            raise SubsystemError(
+                f"Cannot add subsystems after {self.app.name} is finished loading."
+            )
+        except Exception as err:
+            _raise_load_error(plugin, err)
+
+    def add_module(self, module):
+        for _, obj in module.__dict__.items():
+            try:
+                assert issubclass(obj, Subsystem)
+            except (TypeError, AssertionError):
+                continue
+
+            if obj is Subsystem:
+                continue
+
+            self.add(obj)
+
+    def add_all(self, *plugins):
+        for plugin in plugins:
+            self.add(plugin)
+
+    def order_plugins(self, store=None):
+        store = store or self.__store
+        for p in store:
+            if getattr(p, "name") is None:
+                raise SubsystemError(
+                    f"{self.app.name} subsystem '{p}' must have a name attribute."
+                )
+        struct = {p.name: set(p.dependencies) for p in store}
+        map_ = {p.name: p for p in store}
+        res = toposort_flatten(struct, sort=True)
+        return {map_[k] for k in res}
+
+    def __load_plugin(self, plugin_class, app: ApplicationBase):
+        if not issubclass(plugin_class, Subsystem):
+            raise SubsystemError(
+                f"{app.name} subsystems must be a subclass of Subsystem"
+            )
+        return plugin_class(app)
+
+    def finalize(self, app: ApplicationBase):
+        candidate_store = self.order_plugins(self.__init_store)
+
+        self.__store = []
+        for plugin in candidate_store:
+            self.__store.append(self.__load_plugin(plugin, app))
+
+        self.__init_store = None
+
+    def get(self, name: str) -> Subsystem:
+        """Get a plugin object, given its name."""
+        for plugin in self.__store:
+            if plugin.name == name:
+                return plugin
+        raise AttributeError(f"Subsystem {name} not found")
+
+    def _iter_hooks(self, hook_name):
+        method_name = "on_" + hook_name.replace("-", "_")
+        for plugin in self.__store:
+            method = getattr(plugin, method_name, None)
+            if method is None:
+                continue
+            log.info("  subsystem: " + plugin.name)
+            yield plugin, method
+
+    def run_hook(self, hook_name, *args, **kwargs):
+        self._hooks_fired.append(hook_name)
+        for _, method in self._iter_hooks(hook_name):
+            method(*args, **kwargs)
+
+
+def _raise_compat_error(sub: Subsystem, app: ApplicationBase):
+    _error = (
+        f"Subsystem '{sub.name}' is incompatible with {app.name} "
+        f"version {app.version} (expected {sub.app_version})"
+    )
+    log.error(_error)
+    raise SubsystemError(_error)
+
+
+def _raise_load_error(sub, err):
+    _error = f"Could not load subsystem '{sub.name}': {err}"
+    log.error(_error)
+    raise SubsystemError(_error)

app-frame/macrostrat/app_frame/subsystems/defs.py

@@ -0,0 +1,22 @@
+from ..exc import ApplicationError
+
+
+class SubsystemError(ApplicationError):
+    pass
+
+
+class Subsystem:
+    """A base subsystem
+
+    app_version can be set to a specifier of valid versions of the hosting application.
+    """
+
+    dependencies = []
+    app_version = None
+    name = None
+
+    def __init__(self, app):
+        self.app = app
+
+    def should_enable(self, mgr: "SubsystemManager"):
+        return True

app-frame/pyproject.toml

@@ -6,12 +6,13 @@ packages = [
   {include = "macrostrat"},
   {include = "test_app"},
 ]
-version = "1.1.0"
+version = "1.2.0"
 
 [tool.poetry.dependencies]
 "macrostrat.utils" = "^1.1.0"
 python = "^3.10"
 python-dotenv = "^1.0.0"
+toposort = "^1.5"
 rich = "^13"
 typer = "^0.9.0"