Add dialog actions

Rudimentary user input for dialogs has been added.

* Displays must add support for showing dialog options, and receiving
  user input for dialog selections.
* A selected dialog can optionally perform actions, and then directs the
  game into the next dialog state.
* Dialog options may be conditionally shown with variables.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

agame/action.py

@@ -1,10 +1,11 @@
 import dataclasses
 import time
-from typing import Any, Optional, Sequence, Union, TYPE_CHECKING
+from typing import Any, Mapping, Optional, Sequence, Union, TYPE_CHECKING
 import enum
 
 if TYPE_CHECKING:
     from agame.game import Game
+    from agame.dialog import DialogOption
 
 
 __all__ = (
@@ -24,6 +25,7 @@ __all__ = (
     "SetVarAction",
     "RevealItemAction",
     "UnrevealItemAction",
+    "DialogAction",
 )
 
 
@@ -441,3 +443,32 @@ class UnrevealItemAction(Action):
             self.item_id in game.room.items
         ), f"item id {self.item_id} does not exist in the current room {game.room.id}"
         game.room.items[self.item_id].revealed = False
+
+
+@dataclasses.dataclass
+class DialogAction(Action):
+    """
+    Displays a new dialog.
+    """
+
+    dialog: Mapping[str, Sequence["DialogOption"]]
+    start: str
+
+    def act(self, game: "Game"):
+        selection_id: Optional[str] = self.start
+
+        while selection_id:
+            # Figure out which options should appear
+            options = [
+                opt
+                for opt in self.dialog[selection_id]
+                # this is a logical implication
+                # required_var -> (game.vars[opt.required_var])
+                if not opt.required_var
+                or (opt.required_var and game.vars[opt.required_var])
+            ]
+            # Get the selection
+            selection = game.display.dialog_options(options)
+            selection_id = selection.next
+            # Do dialog actions
+            game.do_actions(selection.actions)