Move variables and triggers to be defined in the database

* Variables are now defined in the database, rather than the game
  itself.
* Triggers are now defined in the database, rather than hidden away in a
  method in the game. Custom triggers can now be added as well, in case
  a game needs more complex behavior that isn't necessarily available in
  the base library.

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

agame/game.py

@@ -1,6 +1,6 @@
 import dataclasses
 import textwrap
-from typing import Any, MutableMapping, Match, Optional, Sequence
+from typing import Any, MutableMapping, List, Match, Optional, Sequence
 from agame.action import Action
 from agame.color import colorize
 from agame.item import Item, ItemInst
@@ -20,6 +20,21 @@ class Database:
     items: MutableMapping[str, Item] = dataclasses.field(default_factory=dict)
     # All rooms available to the game.
     rooms: MutableMapping[str, Room] = dataclasses.field(default_factory=dict)
+    # All variables available to the game.
+    vars: MutableMapping[str, Any] = dataclasses.field(default_factory=dict)
+    # All triggers available to the game.
+    triggers: List[Trigger] = dataclasses.field(
+        default_factory=lambda: [
+            GetTrigger(),
+            UseTrigger(),
+            PutTrigger(),
+            LookTrigger(),
+            ReadTrigger(),
+            OpenTrigger(),
+            CloseTrigger(),
+            GoTrigger(),
+        ]
+    )
 
     def add_item(self, item: Item):
         self.items[item.id] = item
@@ -35,6 +50,12 @@ class Database:
         for room in rooms:
             self.add_room(room)
 
+    def add_var(self, var: str, value: Any):
+        self.vars[var] = value
+
+    def add_trigger(self, trigger: Trigger):
+        self.triggers += [trigger]
+
 
 @dataclasses.dataclass
 class Game:
@@ -44,28 +65,15 @@ class Game:
     room: Room
     # Player inventory.
     inventory: MutableMapping[str, ItemInst] = dataclasses.field(default_factory=dict)
-    # Variables.
-    vars: MutableMapping[str, Any] = dataclasses.field(default_factory=dict)
 
     def run_command(self, line: str):
         line = line.strip()
         if not line:
             return
 
-        triggers: Sequence[Trigger] = [
-            GetTrigger(),
-            UseTrigger(),
-            PutTrigger(),
-            LookTrigger(),
-            ReadTrigger(),
-            OpenTrigger(),
-            CloseTrigger(),
-            GoTrigger(),
-        ]
-
         trigger = None
         match: Optional[Match] = None
-        for t in triggers:
+        for t in self.database.triggers:
             match = t.pattern().fullmatch(line)
             if match:
                 trigger = t
@@ -128,3 +136,8 @@ class Game:
     def items(self):
         "Shortcut property for `game.database.items`."
         return self.database.items
+
+    @property
+    def vars(self):
+        "Shortcut property for `game.database.vars`."
+        return self.database.vars