OpenFrontIO/src/core/execution/nation/NationMIRVBehavior.ts

import {
  AllPlayers,
  Difficulty,
  Game,
  Gold,
  Player,
  PlayerID,
  PlayerType,
  Tick,
  UnitType,
} from "../../game/Game";
import { TileRef } from "../../game/GameMap";
import { PseudoRandom } from "../../PseudoRandom";
import { assertNever } from "../../Util";
import { MirvExecution } from "../MIRVExecution";
import { calculateTerritoryCenter } from "../Util";
import {
  EMOJI_NUKE,
  NationEmojiBehavior,
  respondToMIRV,
} from "./NationEmojiBehavior";

// 30 seconds at 10 ticks/second
const MIRV_COOLDOWN_TICKS = 300;

export class NationMIRVBehavior {
  // Shared across all NationMIRVBehavior instances.
  // Tracks the last tick a MIRV was sent at each player, so multiple nations don't pile-on the same target.
  // Especially important for games with very high starting gold settings.
  private static recentMirvTargets = new Map<PlayerID, Tick>();

  constructor(
    private random: PseudoRandom,
    private game: Game,
    private player: Player,
    private emojiBehavior: NationEmojiBehavior,
  ) {}

  private get hesitationOdds(): number {
    const { difficulty } = this.game.config().gameConfig();
    switch (difficulty) {
      case Difficulty.Easy:
        return 2; // More likely to hesitate
      case Difficulty.Medium:
        return 4;
      case Difficulty.Hard:
        return 8;
      case Difficulty.Impossible:
        return 16; // Rarely hesitates
      default:
        assertNever(difficulty);
    }
  }

  private get victoryDenialTeamThreshold(): number {
    const { difficulty } = this.game.config().gameConfig();
    switch (difficulty) {
      case Difficulty.Easy:
        return 0.9; // Only react right before the game ends (95%)
      case Difficulty.Medium:
        return 0.8;
      case Difficulty.Hard:
        return 0.7;
      case Difficulty.Impossible:
        return 0.6; // Reacts early
      default:
        assertNever(difficulty);
    }
  }

  private get victoryDenialIndividualThreshold(): number {
    const { difficulty } = this.game.config().gameConfig();
    switch (difficulty) {
      case Difficulty.Easy:
        return 0.75; // Only react right before the game ends (80%)
      case Difficulty.Medium:
        return 0.65;
      case Difficulty.Hard:
        return 0.55;
      case Difficulty.Impossible:
        return 0.4; // Reacts early
      default:
        assertNever(difficulty);
    }
  }

  private get steamrollCityGapMultiplier(): number {
    const { difficulty } = this.game.config().gameConfig();
    switch (difficulty) {
      case Difficulty.Easy:
        return 1.5; // Needs larger gap to trigger
      case Difficulty.Medium:
        return 1.3;
      case Difficulty.Hard:
        return 1.2;
      case Difficulty.Impossible:
        return 1.15; // Reacts to smaller gaps
      default:
        assertNever(difficulty);
    }
  }

  private get steamrollMinLeaderCities(): number {
    const { difficulty } = this.game.config().gameConfig();
    switch (difficulty) {
      case Difficulty.Easy:
        return 15; // Needs more cities to trigger
      case Difficulty.Medium:
      case Difficulty.Hard:
        return 10;
      case Difficulty.Impossible:
        return 8; // Reacts early
      default:
        assertNever(difficulty);
    }
  }

  considerMIRV(): boolean {
    if (this.player === null) throw new Error("not initialized");
    if (this.player.units(UnitType.MissileSilo).length === 0) {
      return false;
    }
    if (this.player.gold() < this.cost(UnitType.MIRV)) {
      return false;
    }

    if (this.random.chance(this.hesitationOdds)) {
      return false;
    }

    const inboundMIRVSender = this.selectCounterMirvTarget();
    if (inboundMIRVSender && !this.wasRecentlyMirved(inboundMIRVSender)) {
      this.maybeSendMIRV(inboundMIRVSender);
      return true;
    }

    const victoryDenialTarget = this.selectVictoryDenialTarget();
    if (victoryDenialTarget && !this.wasRecentlyMirved(victoryDenialTarget)) {
      this.maybeSendMIRV(victoryDenialTarget);
      return true;
    }

    const steamrollStopTarget = this.selectSteamrollStopTarget();
    if (steamrollStopTarget && !this.wasRecentlyMirved(steamrollStopTarget)) {
      this.maybeSendMIRV(steamrollStopTarget);
      return true;
    }

    return false;
  }

  // MIRV Strategy Methods
  private selectCounterMirvTarget(): Player | null {
    if (this.player === null) throw new Error("not initialized");
    const attackers = this.getValidMirvTargetPlayers().filter((p) =>
      this.isInboundMIRVFrom(p),
    );
    if (attackers.length === 0) return null;
    attackers.sort((a, b) => b.numTilesOwned() - a.numTilesOwned());
    return attackers[0];
  }

  private selectVictoryDenialTarget(): Player | null {
    if (this.player === null) throw new Error("not initialized");
    const totalLand = this.game.numLandTiles();
    if (totalLand === 0) return null;
    let best: { p: Player; severity: number } | null = null;
    for (const p of this.getValidMirvTargetPlayers()) {
      let severity = 0;
      const team = p.team();
      if (team !== null) {
        const teamMembers = this.game
          .players()
          .filter((x) => x.team() === team && x.isPlayer());
        const teamTerritory = teamMembers
          .map((x) => x.numTilesOwned())
          .reduce((a, b) => a + b, 0);
        const teamShare = teamTerritory / totalLand;
        if (teamShare >= this.victoryDenialTeamThreshold) {
          // Only consider the largest team member as the target when team exceeds threshold
          let largestMember: Player | null = null;
          let largestTiles = -1;
          for (const member of teamMembers) {
            const tiles = member.numTilesOwned();
            if (tiles > largestTiles) {
              largestTiles = tiles;
              largestMember = member;
            }
          }
          if (largestMember === p) {
            severity = teamShare;
          } else {
            severity = 0; // Skip non-largest members
          }
        }
      } else {
        const share = p.numTilesOwned() / totalLand;
        if (share >= this.victoryDenialIndividualThreshold) severity = share;
      }
      if (severity > 0) {
        if (best === null || severity > best.severity) best = { p, severity };
      }
    }
    return best ? best.p : null;
  }

  private selectSteamrollStopTarget(): Player | null {
    if (this.player === null) throw new Error("not initialized");
    const validTargets = this.getValidMirvTargetPlayers();

    if (validTargets.length === 0) return null;

    const allPlayers = this.game
      .players()
      .filter((p) => p.isPlayer())
      .map((p) => ({ p, cityCount: this.countCities(p) }))
      .sort((a, b) => b.cityCount - a.cityCount);

    if (allPlayers.length < 2) return null;

    const topPlayer = allPlayers[0];

    if (topPlayer.cityCount <= this.steamrollMinLeaderCities) return null;

    const secondHighest = allPlayers[1].cityCount;

    const threshold = secondHighest * this.steamrollCityGapMultiplier;

    if (topPlayer.cityCount >= threshold) {
      return validTargets.some((p) => p === topPlayer.p) ? topPlayer.p : null;
    }

    return null;
  }

  // MIRV Cooldown Methods
  private wasRecentlyMirved(target: Player): boolean {
    const lastTick = NationMIRVBehavior.recentMirvTargets.get(target.id());
    if (lastTick === undefined) return false;
    return this.game.ticks() - lastTick < MIRV_COOLDOWN_TICKS;
  }

  private recordMirvHit(target: Player): void {
    NationMIRVBehavior.recentMirvTargets.set(target.id(), this.game.ticks());
  }

  // MIRV Helper Methods
  private getValidMirvTargetPlayers(): Player[] {
    if (this.player === null) throw new Error("not initialized");

    return this.game.players().filter((p) => {
      return (
        p !== this.player &&
        p.isPlayer() &&
        p.type() !== PlayerType.Bot &&
        !this.player!.isOnSameTeam(p)
      );
    });
  }

  private isInboundMIRVFrom(attacker: Player): boolean {
    if (this.player === null) throw new Error("not initialized");
    const enemyMirvs = attacker.units(UnitType.MIRV);
    for (const mirv of enemyMirvs) {
      const dst = mirv.targetTile();
      if (!dst) continue;
      if (!this.game.hasOwner(dst)) continue;
      const owner = this.game.owner(dst);
      if (owner === this.player) {
        return true;
      }
    }
    return false;
  }

  // MIRV Execution Methods
  private maybeSendMIRV(enemy: Player): void {
    if (this.player === null) throw new Error("not initialized");

    this.emojiBehavior.maybeSendAttackEmoji(enemy);

    const centerTile = this.calculateTerritoryCenter(enemy);
    if (centerTile && this.player.canBuild(UnitType.MIRV, centerTile)) {
      this.game.addExecution(new MirvExecution(this.player, centerTile));
      this.recordMirvHit(enemy);
      this.emojiBehavior.sendEmoji(AllPlayers, EMOJI_NUKE);
      respondToMIRV(this.game, this.random, enemy);
    }
  }

  private countCities(p: Player): number {
    return p.unitCount(UnitType.City);
  }

  private calculateTerritoryCenter(target: Player): TileRef | null {
    return calculateTerritoryCenter(this.game, target);
  }

  private cost(type: UnitType): Gold {
    if (this.player === null) throw new Error("not initialized");
    return this.game.unitInfo(type).cost(this.game, this.player);
  }
}