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/__init__.py

@@ -1,4 +1,7 @@
 import platform
+from typing import Optional, Sequence, Tuple
+from agame.action import Action
+from agame.dialog import DialogOption
 from .display import Display
 
 if platform.system() in ("Linux", "Darwin", "Unix"):
@@ -14,5 +17,31 @@ class BasicDisplay(Display):
     def line(self, line: str = ""):
         print(line)
 
-    def input(self) -> str:
-        return input("> ")
+    def input(self, prompt: Optional[str] = None) -> str:
+        if prompt is None:
+            prompt = "> "
+        return input(prompt)
+
+    def wait_for_ack(self, prompt: Optional[str] = "Press enter to continue..."):
+        input(prompt or "")
+
+    def dialog_options(self, options: Sequence[DialogOption]) -> DialogOption:
+        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