Refactor Nations AI (#427)

## Description:

Refactor AI troop management and strategic behavior based around two key
values: a trigger ratio and a reserve ratio.
- Reserve ratio: This determines the portion of the population the AI
will keep in reserve and will not send on attacks.
- Trigger ratio: This is the threshold at which the bot will initiate an
attack.

Additionally, when an incoming attack is detected, bots will now
prioritize retaliating by switching targets to the largest incoming
attacker.

Fixes #470 

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

fake.neo

---------

Co-authored-by: Scott Anderson <662325+scottanderson@users.noreply.github.com>

src/core/execution/BotExecution.ts

@@ -6,15 +6,21 @@ import { BotBehavior } from "./utils/BotBehavior";
 export class BotExecution implements Execution {
   private active = true;
   private random: PseudoRandom;
-  private attackRate: number;
   private mg: Game;
   private neighborsTerraNullius = true;
 
   private behavior: BotBehavior | null = null;
+  private attackRate: number;
+  private attackTick: number;
+  private triggerRatio: number;
+  private reserveRatio: number;
 
   constructor(private bot: Player) {
     this.random = new PseudoRandom(simpleHash(bot.id()));
-    this.attackRate = this.random.nextInt(10, 50);
+    this.attackRate = this.random.nextInt(40, 80);
+    this.attackTick = this.random.nextInt(0, this.attackRate);
+    this.triggerRatio = this.random.nextInt(60, 90) / 100;
+    this.reserveRatio = this.random.nextInt(30, 60) / 100;
   }
 
   activeDuringSpawnPhase(): boolean {
@@ -27,17 +33,21 @@ export class BotExecution implements Execution {
   }
 
   tick(ticks: number) {
+    if (ticks % this.attackRate != this.attackTick) return;
+
     if (!this.bot.isAlive()) {
       this.active = false;
       return;
     }
 
-    if (ticks % this.attackRate != 0) {
-      return;
-    }
-
     if (this.behavior === null) {
-      this.behavior = new BotBehavior(this.random, this.mg, this.bot, 1 / 20);
+      this.behavior = new BotBehavior(
+        this.random,
+        this.mg,
+        this.bot,
+        this.triggerRatio,
+        this.reserveRatio,
+      );
     }
 
     this.behavior.handleAllianceRequests();
@@ -65,15 +75,14 @@ export class BotExecution implements Execution {
       this.neighborsTerraNullius = false;
     }
 
+    this.behavior.forgetOldEnemies();
+    this.behavior.checkIncomingAttacks();
     const enemy = this.behavior.selectRandomEnemy();
     if (!enemy) return;
+    if (!this.bot.sharesBorderWith(enemy)) return;
     this.behavior.sendAttack(enemy);
   }
 
-  owner(): Player {
-    return this.bot;
-  }
-
   isActive(): boolean {
     return this.active;
   }