ENH: Add actions base class

docs/index.rst

@@ -62,6 +62,7 @@ You can contribute to `pypdf on GitHub <https://github.com/py-pdf/pypdf>`_.
    modules/RectangleObject
    modules/Transformation
    modules/XmpInformation
+   modules/actions
    modules/annotations
    modules/constants
    modules/errors

docs/modules/actions.rst

@@ -0,0 +1,7 @@
+Actions
+-------
+
+.. automodule:: pypdf.actions
+    :members:
+    :undoc-members:
+    :show-inheritance:

pypdf/_page.py

@@ -58,6 +58,7 @@
     logger_warning,
     matrix_multiply,
 )
+from .actions import Action
 from .constants import (
     _INLINE_IMAGE_KEY_MAPPING,
     _INLINE_IMAGE_VALUE_MAPPING,
@@ -2168,6 +2169,47 @@ def annotations(self, value: Optional[ArrayObject]) -> None:
         else:
             self[NameObject("/Annots")] = value
 
+    def add_action(self, trigger: str, action: Action) -> None:
+        """
+        Add an action which will launch on the given trigger event of this page.
+
+        Args:
+            trigger: The trigger event.
+            action: An :py:class:`~pypdf.actions.Action` object.
+
+        Example:
+            >>> from pypdf import PdfWriter
+            >>> from pypdf.actions import JavaScript
+            >>> writer = PdfWriter()
+            >>> page = writer.add_blank_page(595, 842)
+            >>> # Display the page number when the page is opened
+            >>> page.add_action("open", JavaScript("app.alert('This is page ' + this.pageNum);"))
+            >>> # Display the page number when the page is closed
+            >>> page.add_action("close", JavaScript("app.alert('This is page ' + this.pageNum);"))
+        """
+        Action._create_new(self, trigger, action)
+
+    def delete_action(self, trigger: str) -> None:
+        """
+        Delete an action associated with an open or close trigger event of this page.
+
+        Args:
+            trigger: "open" or "close" trigger event.
+
+        Example:
+            >>> from pypdf import PdfWriter
+            >>> from pypdf.actions import JavaScript
+            >>> writer = PdfWriter()
+            >>> page = writer.add_blank_page(595, 842)
+            >>> page.add_action("open", JavaScript("app.alert('This is page ' + this.pageNum);"))
+            >>> page.add_action("close", JavaScript("app.alert('This is page ' + this.pageNum);"))
+            >>> # Delete all actions triggered by a page open
+            >>> page.delete_action("open")
+            >>> # Delete all actions triggered by a page close
+            >>> page.delete_action("close")
+        """
+        Action._delete(self, trigger)
+
 
 class _VirtualList(Sequence[PageObject]):
     def __init__(

pypdf/actions/__init__.py

@@ -0,0 +1,17 @@
+"""
+PDF includes a wide variety of standard action types, whose characteristics and
+behaviour are defined by an action dictionary. These are defined in this
+submodule.
+
+Trigger events are the other component of actions, and are specific to their
+associated object.
+"""
+
+
+from ._actions import Action, JavaScript, PageTrigger
+
+__all__ = [
+    "Action",
+    "JavaScript",
+    "PageTrigger",
+]

pypdf/actions/_actions.py

@@ -0,0 +1,174 @@
+"""Action types"""
+import sys
+from abc import ABC
+from enum import Enum, unique
+from typing import (
+    TYPE_CHECKING,
+    cast,
+)
+
+from .._utils import logger_warning
+from ..generic import (
+    ArrayObject,
+    DictionaryObject,
+    NameObject,
+    NullObject,
+    TextStringObject,
+    is_null_or_none,
+)
+
+if sys.version_info >= (3, 11):
+    from enum import StrEnum
+else:
+    class StrEnum(str, Enum):
+        def __str__(self) -> str:
+            return str(self.value)
+
+if TYPE_CHECKING:
+    from .._page import PageObject
+
+
+@unique
+class PageTrigger(StrEnum):
+    """Trigger event entries in a page object's additional-actions dictionary."""
+
+    OPEN = "open"  # An action that shall be performed when the page is opened
+    CLOSE = "close"  # An action that shall be performed when the page is closed
+
+
+class Action(DictionaryObject, ABC):
+    """An action dictionary defines the characteristics and behaviour of an action."""
+    def __init__(self) -> None:
+        super().__init__()
+        self[NameObject("/Type")] = NameObject("/Action")
+        # The next action or sequence of actions that shall be performed after the action
+        # represented by this dictionary. The value is either a single action dictionary
+        # or an array of action dictionaries that shall be performed in order.
+        self[NameObject("/Next")] = NullObject()  # Optional
+
+    @classmethod
+    def _create_new(cls, page: "PageObject", trigger: str, action: "Action") -> None:
+        """
+        Create a new action and add it to the page.
+
+        Args:
+            page: The page to add the action.
+            trigger: The trigger event.
+            action: An :py:class:`~pypdf.actions.Action` object.
+        """
+        valid_values = [trigger.value for trigger in PageTrigger]
+
+        if trigger not in valid_values:
+            raise ValueError(f"The trigger must be one of {valid_values}")
+
+        trigger_name = NameObject("/O") if PageTrigger(trigger).value == PageTrigger.OPEN else NameObject("/C")
+
+        if "/AA" not in page:
+            # Additional actions key not present
+            page[NameObject("/AA")] = DictionaryObject(
+                {trigger_name: action}
+            )
+            return
+
+        if isinstance(page["/AA"], NullObject):
+            page[NameObject("/AA")] = DictionaryObject()
+
+        if not isinstance(page["/AA"], DictionaryObject):
+            if page.pdf is not None and hasattr(page.pdf, "strict") and page.pdf.strict:
+                raise ValueError("The PageObject has an AA entry whose value is not a DictionaryObject.")
+            logger_warning(
+                "The PageObject has an AA entry whose value is not a DictionaryObject.",
+                source=__name__,
+            )
+            return
+
+        additional_actions: DictionaryObject = page["/AA"]
+
+        if is_null_or_none(additional_actions.get(trigger_name)):
+            additional_actions.update({trigger_name: action})
+            return
+
+        """
+        The action dictionary's Next entry allows sequences of actions to be
+        chained together. For example, the effect of clicking a link
+        annotation with the mouse can be to play a sound, jump to a new
+        page, and start up a movie. Note that the Next entry is not
+        restricted to a single action but can contain an array of actions,
+        each of which in turn can have a Next entry of its own.
+        §12.6.2 Action dictionaries ISO 32000-2:2020
+        """
+        head = current = additional_actions.get(trigger_name)
+        if not isinstance(head, DictionaryObject):
+            raise TypeError(
+                f"The type in a page object's additional-actions key must be a DictionaryObject: "
+                f"received type {type(head)}"
+            )
+        current = cast(DictionaryObject, current)
+
+        visited = set()
+        while True:
+            next_ = current.get("/Next", None)
+
+            if is_null_or_none(next_):
+                break
+
+            if not isinstance(next_, (ArrayObject, DictionaryObject)):
+                raise TypeError(
+                    f"An action dictionary’s Next entry must be an Action dictionary "
+                    f"or an array of Action dictionaries: received type {type(next_)}"
+                )
+
+            id_ = id(next_)
+            if id_ in visited:
+                logger_warning("Detected cycle in the action tree for %(current)s", source=__name__, current=current)
+                break
+            visited.add(id_)
+
+            if isinstance(next_, ArrayObject):
+                current = next_[-1]
+            else:
+                current = next_
+
+        if not is_null_or_none(next_ := current.get("/Next")) and id(next_) in visited:
+            logger_warning("Detected cycle in the action tree for %(current)s", source=__name__, current=current)
+
+        current[NameObject("/Next")] = action
+        additional_actions.update({trigger_name: head})
+
+    @classmethod
+    def _delete(cls, page: "PageObject", trigger: str) -> None:
+        valid_values = [trigger.value for trigger in PageTrigger]
+
+        if trigger not in valid_values:
+            raise ValueError(f"The trigger must be one of {valid_values}")
+
+        trigger_name = NameObject("/O") if PageTrigger(trigger).value == PageTrigger.OPEN else NameObject("/C")
+
+        if "/AA" not in page:
+            return
+
+        additional_actions: DictionaryObject = cast(DictionaryObject, page["/AA"])
+
+        if trigger_name in additional_actions:
+            del additional_actions[trigger_name]
+
+            if not additional_actions:
+                del page["/AA"]
+
+
+class JavaScript(Action):
+    """
+    Upon invocation of an ECMAScript action, a PDF processor shall execute a
+    script that is written in the ECMAScript programming language. ECMAScript
+    extensions described in ISO/DIS 21757-1 shall also be allowed.
+    """
+    def __init__(self, js: str) -> None:
+        """
+        Initialize JavaScript with a string.
+
+        Args:
+            js (str): A text string containing the ECMAScript script to be executed.
+        """
+        super().__init__()
+        self[NameObject("/S")] = NameObject("/JavaScript")
+        self[NameObject("/JS")] = TextStringObject(js)

pypdf/constants.py

@@ -1,11 +1,14 @@
 """Various constants, enums, and flags to aid readability."""
 
+import sys
 from enum import Enum, IntFlag, auto, unique
 
-
-class StrEnum(str, Enum):  # Once we are on Python 3.11+: enum.StrEnum
-    def __str__(self) -> str:
-        return str(self.value)
+if sys.version_info >= (3, 11):
+    from enum import StrEnum
+else:
+    class StrEnum(str, Enum):
+        def __str__(self) -> str:
+            return str(self.value)
 
 
 class Core:

pypdf/types.py

@@ -78,3 +78,7 @@
     "/Projection",
     "/RichMedia",
 ]
+
+ActionSubtype: TypeAlias = Literal[
+    "/JavaScript",
+]