Add date-based loadout restriction.

Follow up work:

* Data entry. I plan to do the air-to-air missiles in the near term. I
  covered some variants of the AIM-120, AIM-7, and AIM-9 here, but there
  are variants of those weapons for each mounting rack that need to be
  done still, as well as all the non-US weapons.
* Arbitrary start dates.

https://github.com/Khopa/dcs_liberation/issues/490

game/data/weapons.py

@@ -1,11 +1,15 @@
 from __future__ import annotations
 
+import datetime
 import inspect
+import logging
+from collections import defaultdict
 from dataclasses import dataclass
-from typing import Dict, Iterator, Set, Tuple, Type, Union, cast
+from typing import Dict, Iterator, Optional, Set, Tuple, Type, Union, cast
 
 from dcs.unitgroup import FlyingGroup
 from dcs.unittype import FlyingType
+from dcs.weapons_data import Weapons, weapon_ids
 
 
 PydcsWeapon = Dict[str, Union[int, str]]
@@ -20,6 +24,14 @@ class Weapon:
     name: str
     weight: int
 
+    def available_on(self, date: datetime.date) -> bool:
+        introduction_year = WEAPON_INTRODUCTION_YEARS.get(self)
+        if introduction_year is None:
+            logging.warning(
+                f"No introduction year for {self}, assuming always available")
+            return True
+        return date >= datetime.date(introduction_year, 1, 1)
+
     @property
     def as_pydcs(self) -> PydcsWeapon:
         return {
@@ -28,6 +40,13 @@ class Weapon:
             "weight": self.weight,
         }
 
+    @property
+    def fallbacks(self) -> Iterator[Weapon]:
+        yield self
+        fallback = WEAPON_FALLBACK_MAP[self]
+        if fallback is not None:
+            yield from fallback.fallbacks
+
     @classmethod
     def from_pydcs(cls, weapon_data: PydcsWeapon) -> Weapon:
         return cls(
@@ -36,6 +55,13 @@ class Weapon:
             cast(int, weapon_data["weight"])
         )
 
+    @classmethod
+    def from_clsid(cls, clsid: str) -> Optional[Weapon]:
+        data = weapon_ids.get(clsid)
+        if data is None:
+            return None
+        return cls.from_pydcs(data)
+
 
 @dataclass(frozen=True)
 class Pylon:
@@ -53,6 +79,11 @@ class Pylon:
     def make_pydcs_assignment(self, weapon: Weapon) -> PydcsWeaponAssignment:
         return self.number, weapon.as_pydcs
 
+    def available_on(self, date: datetime.date) -> Iterator[Weapon]:
+        for weapon in self.allowed:
+            if weapon.available_on(date):
+                yield weapon
+
     @classmethod
     def for_aircraft(cls, aircraft: Type[FlyingType], number: int) -> Pylon:
         # In pydcs these are all arbitrary inner classes of the aircraft type.
@@ -78,3 +109,37 @@ class Pylon:
     def iter_pylons(cls, aircraft: Type[FlyingType]) -> Iterator[Pylon]:
         for pylon in sorted(list(aircraft.pylons)):
             yield cls.for_aircraft(aircraft, pylon)
+
+
+_WEAPON_FALLBACKS = [
+    (Weapons.AIM_120C, Weapons.AIM_120B),
+    (Weapons.AIM_120B, Weapons.AIM_7MH),
+    (Weapons.AIM_7MH, Weapons.AIM_7M),
+    (Weapons.AIM_7M, Weapons.AIM_7F),
+    (Weapons.AIM_7F, Weapons.AIM_7E),
+    (Weapons.AIM_7M, Weapons.AIM_9X_Sidewinder_IR_AAM),
+    (Weapons.AIM_9X_Sidewinder_IR_AAM, Weapons.AIM_9P5_Sidewinder_IR_AAM),
+    (Weapons.AIM_9P5_Sidewinder_IR_AAM, Weapons.AIM_9P_Sidewinder_IR_AAM),
+    (Weapons.AIM_9P_Sidewinder_IR_AAM, Weapons.AIM_9M_Sidewinder_IR_AAM),
+    (Weapons.AIM_9M_Sidewinder_IR_AAM, Weapons.AIM_9L_Sidewinder_IR_AAM),
+]
+
+WEAPON_FALLBACK_MAP: Dict[Weapon, Optional[Weapon]] = defaultdict(
+    lambda: cast(Optional[Weapon], None),
+    ((Weapon.from_pydcs(a), Weapon.from_pydcs(b))
+     for a, b in _WEAPON_FALLBACKS))
+
+
+WEAPON_INTRODUCTION_YEARS = {
+    Weapon.from_pydcs(Weapons.AIM_120C): 1996,
+    Weapon.from_pydcs(Weapons.AIM_120B): 1994,
+    Weapon.from_pydcs(Weapons.AIM_7MH): 1987,
+    Weapon.from_pydcs(Weapons.AIM_7M): 1982,
+    Weapon.from_pydcs(Weapons.AIM_7F): 1976,
+    Weapon.from_pydcs(Weapons.AIM_7E): 1963,
+    Weapon.from_pydcs(Weapons.AIM_9X_Sidewinder_IR_AAM): 2003,
+    Weapon.from_pydcs(Weapons.AIM_9P5_Sidewinder_IR_AAM): 1963,
+    Weapon.from_pydcs(Weapons.AIM_9P_Sidewinder_IR_AAM): 1978,
+    Weapon.from_pydcs(Weapons.AIM_9M_Sidewinder_IR_AAM): 1983,
+    Weapon.from_pydcs(Weapons.AIM_9L_Sidewinder_IR_AAM): 1977,
+}