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/display/display.py

@@ -1,5 +1,10 @@
 import abc
-from typing import Optional
+from typing import Optional, Sequence, Tuple, TYPE_CHECKING
+from agame.action import Action
+from agame.dialog import DialogOption
+
+if TYPE_CHECKING:
+    from agame.game import Game
 
 
 class Display(metaclass=abc.ABCMeta):
@@ -14,7 +19,7 @@ class Display(metaclass=abc.ABCMeta):
         "Print a single line to the display."
 
     @abc.abstractmethod
-    def input(self) -> str:
+    def input(self, prompt: Optional[str] = None) -> str:
         "Get player input."
 
     @abc.abstractmethod
@@ -28,5 +33,31 @@ class Display(metaclass=abc.ABCMeta):
         user.
         """
 
+    def dialog_options(self, options: Sequence[DialogOption]) -> DialogOption:
+        """
+        Displays, and gets, an answer from a list of dialog options.
+
+        Returns the selected DialogOption.next value and actions.
+        """
+        valid_opts = range(1, len(options) + 1)
+
+        def print_opts():
+            for i, opt in enumerate(options):
+                self.line(f"{i}. {opt.text}")
+
+        print_opts()
+        while True:
+            got = self.input("? ")
+            try:
+                choice = int(got)
+            except ValueError:
+                print_opts()
+                continue
+            if choice in valid_opts:
+                break
+        index = choice - 1
+        selection = options[index]
+        return selection
+
     def finish(self):
         "Final cleanup code for this display."