Add hooks

.pylintrc

@@ -75,6 +75,7 @@ disable=fixme,
         unnecessary-lambda-assignment,
         broad-exception-raised,
         consider-using-generator,
+        too-many-ancestors
 
 
 # Enable the message, report, category or checker with the given id(s). You can

dash/__init__.py

@@ -41,6 +41,8 @@
 from ._patch import Patch  # noqa: F401,E402
 from ._jupyter import jupyter_dash  # noqa: F401,E402
 
+from ._hooks import hooks  # noqa: F401,E402
+
 ctx = callback_context
 
 

dash/_callback.py

@@ -1,14 +1,17 @@
 import collections
 import hashlib
 from functools import wraps
-from typing import Callable, Optional, Any, List, Tuple
+
+from typing import Callable, Optional, Any, List, Tuple, Union
+
 
 import flask
 
 from .dependencies import (
     handle_callback_args,
     handle_grouped_callback_args,
     Output,
+    ClientsideFunction,
     Input,
 )
 from .development.base_component import ComponentRegistry
@@ -210,7 +213,10 @@ def validate_long_inputs(deps):
             )
 
 
-def clientside_callback(clientside_function, *args, **kwargs):
+ClientsideFuncType = Union[str, ClientsideFunction]
+
+
+def clientside_callback(clientside_function: ClientsideFuncType, *args, **kwargs):
     return register_clientside_callback(
         GLOBAL_CALLBACK_LIST,
         GLOBAL_CALLBACK_MAP,
@@ -597,7 +603,7 @@ def register_clientside_callback(
     callback_map,
     config_prevent_initial_callbacks,
     inline_scripts,
-    clientside_function,
+    clientside_function: ClientsideFuncType,
     *args,
     **kwargs,
 ):

dash/_hooks.py

@@ -0,0 +1,231 @@
+import typing as _t
+
+from importlib import metadata as _importlib_metadata
+
+import typing_extensions as _tx
+import flask as _f
+
+from .exceptions import HookError
+from .resources import ResourceType
+from ._callback import ClientsideFuncType
+
+if _t.TYPE_CHECKING:
+    from .dash import Dash
+    from .development.base_component import Component
+
+    ComponentType = _t.TypeVar("ComponentType", bound=Component)
+    LayoutType = _t.Union[ComponentType, _t.List[ComponentType]]
+else:
+    LayoutType = None
+    ComponentType = None
+    Dash = None
+
+
+HookDataType = _tx.TypeVar("HookDataType")
+
+
+# pylint: disable=too-few-public-methods
+class _Hook(_tx.Generic[HookDataType]):
+    def __init__(self, func, priority=0, final=False, data: HookDataType = None):
+        self.func = func
+        self.final = final
+        self.data = data
+        self.priority = priority
+
+    def __call__(self, *args, **kwargs):
+        return self.func(*args, **kwargs)
+
+
+class _Hooks:
+    def __init__(self) -> None:
+        self._ns = {
+            "setup": [],
+            "layout": [],
+            "routes": [],
+            "error": [],
+            "callback": [],
+            "index": [],
+        }
+        self._js_dist = []
+        self._css_dist = []
+        self._clientside_callbacks: _t.List[
+            _t.Tuple[ClientsideFuncType, _t.Any, _t.Any]
+        ] = []
+
+        # final hooks are a single hook added to the end of regular hooks.
+        self._finals = {}
+
+    def add_hook(
+        self,
+        hook: str,
+        func: _t.Callable,
+        priority: _t.Optional[int] = None,
+        final=False,
+        data=None,
+    ):
+        if final:
+            existing = self._finals.get(hook)
+            if existing:
+                raise HookError("Final hook already present")
+            self._finals[hook] = _Hook(func, final, data=data)
+            return
+        hks = self._ns.get(hook, [])
+
+        p = 0
+        if not priority and len(hks):
+            priority_max = max(h.priority for h in hks)
+            p = priority_max - 1
+
+        hks.append(_Hook(func, priority=p, data=data))
+        self._ns[hook] = sorted(hks, reverse=True, key=lambda h: h.priority)
+
+    def get_hooks(self, hook: str) -> _t.List[_Hook]:
+        final = self._finals.get(hook, None)
+        if final:
+            final = [final]
+        else:
+            final = []
+        return self._ns.get(hook, []) + final
+
+    def layout(self, priority: _t.Optional[int] = None, final: bool = False):
+        """
+        Run a function when serving the layout, the return value
+        will be used as the layout.
+        """
+
+        def _wrap(func: _t.Callable[[LayoutType], LayoutType]):
+            self.add_hook("layout", func, priority=priority, final=final)
+            return func
+
+        return _wrap
+
+    def setup(self, priority: _t.Optional[int] = None, final: bool = False):
+        """
+        Can be used to get a reference to the app after it is instantiated.
+        """
+
+        def _setup(func: _t.Callable[[Dash], None]):
+            self.add_hook("setup", func, priority=priority, final=final)
+            return func
+
+        return _setup
+
+    def route(
+        self,
+        name: _t.Optional[str] = None,
+        methods: _t.Sequence[str] = ("GET",),
+        priority: _t.Optional[int] = None,
+        final=False,
+    ):
+        """
+        Add a route to the Dash server.
+        """
+
+        def wrap(func: _t.Callable[[], _f.Response]):
+            _name = name or func.__name__
+            self.add_hook(
+                "routes",
+                func,
+                priority=priority,
+                final=final,
+                data=dict(name=_name, methods=methods),
+            )
+            return func
+
+        return wrap
+
+    def error(self, priority: _t.Optional[int] = None, final=False):
+        """Automatically add an error handler to the dash app."""
+
+        def _error(func: _t.Callable[[Exception], _t.Any]):
+            self.add_hook("error", func, priority=priority, final=final)
+            return func
+
+        return _error
+
+    def callback(self, *args, priority: _t.Optional[int] = None, final=False, **kwargs):
+        """
+        Add a callback to all the apps with the hook installed.
+        """
+
+        def wrap(func):
+            self.add_hook(
+                "callback",
+                func,
+                priority=priority,
+                final=final,
+                data=(list(args), dict(kwargs)),
+            )
+            return func
+
+        return wrap
+
+    def clientside_callback(
+        self, clientside_function: ClientsideFuncType, *args, **kwargs
+    ):
+        """
+        Add a callback to all the apps with the hook installed.
+        """
+        self._clientside_callbacks.append((clientside_function, args, kwargs))
+
+    def script(self, distribution: _t.List[ResourceType]):
+        """Add js scripts to the page."""
+        self._js_dist.extend(distribution)
+
+    def stylesheet(self, distribution: _t.List[ResourceType]):
+        """Add stylesheets to the page."""
+        self._css_dist.extend(distribution)
+
+    def index(self, priority: _t.Optional[int] = None, final=False):
+        """Modify the index of the apps."""
+
+        def wrap(func):
+            self.add_hook(
+                "index",
+                func,
+                priority=priority,
+                final=final,
+            )
+            return func
+
+        return wrap
+
+
+hooks = _Hooks()
+
+
+class HooksManager:
+    # Flag to only run `register_setuptools` once
+    _registered = False
+    hooks = hooks
+
+    # pylint: disable=too-few-public-methods
+    class HookErrorHandler:
+        def __init__(self, original):
+            self.original = original
+
+        def __call__(self, err: Exception):
+            result = None
+            if self.original:
+                result = self.original(err)
+            hook_result = None
+            for hook in HooksManager.get_hooks("error"):
+                hook_result = hook(err)
+            return result or hook_result
+
+    @classmethod
+    def get_hooks(cls, hook: str):
+        return cls.hooks.get_hooks(hook)
+
+    @classmethod
+    def register_setuptools(cls):
+        if cls._registered:
+            # Only have to register once.
+            return
+
+        for dist in _importlib_metadata.distributions():
+            for entry in dist.entry_points:
+                # Look for setup.py entry points named `dash-hooks`
+                if entry.group != "dash-hooks":
+                    continue
+                entry.load()

dash/dash.py

@@ -567,6 +567,8 @@ def __init__(  # pylint: disable=too-many-statements
             for plugin in plugins:
                 plugin.plug(self)
 
+        self._setup_hooks()
+
         # tracks internally if a function already handled at least one request.
         self._got_first_request = {"pages": False, "setup_server": False}
 
@@ -582,6 +584,38 @@ def __init__(  # pylint: disable=too-many-statements
             )
         self.setup_startup_routes()
 
+    def _setup_hooks(self):
+        # pylint: disable=import-outside-toplevel,protected-access
+        from ._hooks import HooksManager
+
+        self._hooks = HooksManager
+        self._hooks.register_setuptools()
+
+        for setup in self._hooks.get_hooks("setup"):
+            setup(self)
+
+        for hook in self._hooks.get_hooks("callback"):
+            callback_args, callback_kwargs = hook.data
+            self.callback(*callback_args, **callback_kwargs)(hook.func)
+
+        for (
+            clientside_function,
+            args,
+            kwargs,
+        ) in self._hooks.hooks._clientside_callbacks:
+            _callback.register_clientside_callback(
+                self._callback_list,
+                self.callback_map,
+                self.config.prevent_initial_callbacks,
+                self._inline_scripts,
+                clientside_function,
+                *args,
+                **kwargs,
+            )
+
+        if self._hooks.get_hooks("error"):
+            self._on_error = self._hooks.HookErrorHandler(self._on_error)
+
     def init_app(self, app=None, **kwargs):
         """Initialize the parts of Dash that require a flask app."""
 
@@ -682,6 +716,9 @@ def _setup_routes(self):
                 "_alive_" + jupyter_dash.alive_token, jupyter_dash.serve_alive
             )
 
+        for hook in self._hooks.get_hooks("routes"):
+            self._add_url(hook.data["name"], hook.func, hook.data["methods"])
+
         # catch-all for front-end routes, used by dcc.Location
         self._add_url("<path:path>", self.index)
 
@@ -748,6 +785,9 @@ def index_string(self, value):
     def serve_layout(self):
         layout = self._layout_value()
 
+        for hook in self._hooks.get_hooks("layout"):
+            layout = hook(layout)
+
         # TODO - Set browser cache limit - pass hash into frontend
         return flask.Response(
             to_json(layout),
@@ -890,9 +930,13 @@ def _relative_url_path(relative_package_path="", namespace=""):
 
         return srcs
 
+    # pylint: disable=protected-access
     def _generate_css_dist_html(self):
         external_links = self.config.external_stylesheets
-        links = self._collect_and_register_resources(self.css.get_all_css())
+        links = self._collect_and_register_resources(
+            self.css.get_all_css()
+            + self.css._resources._filter_resources(self._hooks.hooks._css_dist)
+        )
 
         return "\n".join(
             [
@@ -941,6 +985,9 @@ def _generate_scripts_html(self):
                 + self.scripts._resources._filter_resources(
                     dash_table._js_dist, dev_bundles=dev
                 )
+                + self.scripts._resources._filter_resources(
+                    self._hooks.hooks._js_dist, dev_bundles=dev
+                )
             )
         )
 
@@ -1064,6 +1111,9 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
             renderer=renderer,
         )
 
+        for hook in self._hooks.get_hooks("index"):
+            index = hook(index)
+
         checks = (
             _re_index_entry_id,
             _re_index_config_id,

dash/exceptions.py

@@ -101,3 +101,7 @@ class PageError(DashException):
 
 class ImportedInsideCallbackError(DashException):
     pass
+
+
+class HookError(DashException):
+    pass