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

import {
  Difficulty,
  Game,
  GameMode,
  Gold,
  Player,
  PlayerType,
  Relation,
  Structures,
  Tick,
  Unit,
  UnitType,
} from "../../game/Game";
import { TileRef, euclDistFN } from "../../game/GameMap";
import { UniversalPathFinding } from "../../pathfinding/PathFinder";
import { PseudoRandom } from "../../PseudoRandom";
import { assertNever, boundingBoxTiles } from "../../Util";
import { NukeExecution } from "../NukeExecution";
import { UpgradeStructureExecution } from "../UpgradeStructureExecution";
import { closestTwoTiles } from "../Util";
import { AiAttackBehavior } from "../utils/AiAttackBehavior";
import { EMOJI_NUKE, NationEmojiBehavior } from "./NationEmojiBehavior";
import { randTerritoryTileArray } from "./NationUtils";

/** Cap on silo levels reachable via maybeDestroyEnemySam's upgrade fallback. */
const MAX_NATION_SILO_UPGRADE_LEVEL = 5;

/**
 * Level-weighted structure density (sum of structure levels per tile owned)
 * above which the richest impossible nation will pre-emptively nuke a player.
 */
const HIGH_DENSITY_NUKE_THRESHOLD = 1 / 75;

/** Minimum sum of structure levels a player needs to qualify as a high-density nuke target. */
const MIN_LEVEL_SUM_FOR_HIGH_DENSITY_NUKE = 5;

export class NationNukeBehavior {
  private readonly recentlySentNukes: [
    Tick,
    TileRef,
    UnitType.AtomBomb | UnitType.HydrogenBomb,
  ][] = [];
  private atomBombsLaunched = 0;
  private atomBombPerceivedCost = this.cost(UnitType.AtomBomb);
  private hydrogenBombsLaunched = 0;
  private hydrogenBombPerceivedCost = this.cost(UnitType.HydrogenBomb);
  // Make 1/3 of nations "hydro-nations" that only throw hydrogen bombs (to reduce atom bomb spam)
  private readonly isHydroNation: boolean = this.random.chance(3);

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

  maybeSendNuke() {
    const silos = this.player.units(UnitType.MissileSilo);
    const config = this.game.config();
    if (
      silos.length === 0 ||
      config.isUnitDisabled(UnitType.MissileSilo) ||
      (config.isUnitDisabled(UnitType.AtomBomb) &&
        config.isUnitDisabled(UnitType.HydrogenBomb))
    ) {
      return;
    }

    const nukeTarget = this.findBestNukeTarget();
    if (nukeTarget === null) {
      return;
    }

    if (
      nukeTarget.type() === PlayerType.Bot || // Don't nuke tribes (as opposed to nations and humans)
      this.player.isOnSameTeam(nukeTarget) ||
      this.attackBehavior.shouldAttack(nukeTarget) === false
    ) {
      return;
    }

    const hydroCost = this.getPerceivedNukeCost(UnitType.HydrogenBomb);
    const atomCost = this.getPerceivedNukeCost(UnitType.AtomBomb);
    let nukeType: UnitType;
    if (
      !this.game.config().isUnitDisabled(UnitType.HydrogenBomb) &&
      this.player.gold() >= hydroCost
    ) {
      nukeType = UnitType.HydrogenBomb;
    } else if (
      !this.game.config().isUnitDisabled(UnitType.AtomBomb) &&
      (!this.isHydroNation || this.isUnderHeavyAttack()) &&
      this.player.gold() >= atomCost
    ) {
      nukeType = UnitType.AtomBomb;
    } else {
      return;
    }
    const range = this.game.config().nukeMagnitudes(nukeType).outer;

    const structures = nukeTarget.units(Structures.types);
    const structureTiles = structures.map((u) => u.tile());
    const difficulty = this.game.config().gameConfig().difficulty;
    // Use more random tiles on Impossible difficulty to improve chances of finding a perfect SAM outranging spot
    const numRandomTiles = difficulty === Difficulty.Impossible ? 30 : 10;
    const randomTiles = randTerritoryTileArray(
      this.random,
      this.game,
      nukeTarget,
      numRandomTiles,
    );
    const allTiles = randomTiles.concat(structureTiles);

    let bestTile: TileRef | null = null;
    let bestValue = -1; // -1 is important, so that we can also nuke land without structures
    this.removeOldNukeEvents();

    outer: for (const tile of new Set(allTiles)) {
      if (tile === null) continue;
      const boundingBox = boundingBoxTiles(this.game, tile, range)
        // Add radius / 2 in case there is a piece of unwanted territory inside the outer radius that we miss.
        .concat(boundingBoxTiles(this.game, tile, Math.floor(range / 2)));
      for (const t of boundingBox) {
        if (!this.isValidNukeTile(t, nukeTarget)) {
          continue outer;
        }
      }
      const spawnTile = this.player.canBuild(nukeType, tile);
      if (spawnTile === false) continue;

      // In team games, avoid nuking the same position as a teammate
      if (
        this.game.config().gameConfig().gameMode === GameMode.Team &&
        difficulty !== Difficulty.Easy &&
        this.isTeammateAlreadyNukingThisSpot(tile, nukeType)
      ) {
        continue;
      }

      // On Hard & Impossible, avoid trajectories that can be intercepted by enemy SAMs
      if (
        (difficulty === Difficulty.Hard ||
          difficulty === Difficulty.Impossible) &&
        this.isTrajectoryInterceptableBySam(spawnTile, tile)
      ) {
        continue;
      }

      // On all difficulties, avoid trajectories that cross impassable terrain
      // (the simulation aborts such launches — see NukeExecution).
      if (this.isTrajectoryBlockedByImpassable(spawnTile, tile)) {
        continue;
      }

      const value = this.nukeTileScore(tile, silos, structures, nukeType);
      if (value > bestValue) {
        bestTile = tile;
        bestValue = value;
      }
    }
    if (
      bestTile !== null &&
      (bestValue > 0 || difficulty !== Difficulty.Impossible)
    ) {
      this.sendNuke(bestTile, nukeType, nukeTarget);
    } else if (difficulty === Difficulty.Impossible) {
      this.maybeDestroyEnemySam(nukeTarget);
    }
  }

  findBestNukeTarget(): Player | null {
    // On Hard & Impossible with only 2 players left, target the only other one
    const { difficulty: diff } = this.game.config().gameConfig();
    if (
      (diff === Difficulty.Hard || diff === Difficulty.Impossible) &&
      this.game.players().length === 2
    ) {
      const other = this.game.players().find((p) => p !== this.player);
      if (other) {
        return other;
      }
    }

    // Retaliate against incoming attacks (Most important!)
    const incomingAttackPlayer = this.attackBehavior.findIncomingAttackPlayer();
    if (incomingAttackPlayer) {
      return incomingAttackPlayer;
    }

    // On Impossible, the richest nation hunts very high structure density targets
    // Restricting to the richest nation prevents every impossible nation
    // from piling onto the same compact player.
    if (
      diff === Difficulty.Impossible &&
      this.isRichestNation() &&
      this.random.chance(2)
    ) {
      const denseTarget = this.findHighDensityTarget();
      if (denseTarget !== null) {
        return denseTarget;
      }
    }

    // On impossible difficulty, prioritize nuking the crown if they have more than 50% of the map
    const { difficulty, gameMode } = this.game.config().gameConfig();
    if (difficulty === Difficulty.Impossible && gameMode === GameMode.FFA) {
      const numTilesWithoutFallout =
        this.game.numLandTiles() - this.game.numTilesWithFallout();
      if (numTilesWithoutFallout > 0) {
        const sortedByTiles = this.game
          .players()
          .slice()
          .sort((a, b) => b.numTilesOwned() - a.numTilesOwned());
        const crown = sortedByTiles[0];

        if (crown && crown !== this.player && !this.player.isFriendly(crown)) {
          const crownShare = crown.numTilesOwned() / numTilesWithoutFallout;
          if (crownShare > 0.5) {
            return crown;
          }
        }
      }
    }

    // Assist allies, check their targets (this is basically the same as in assistAllies, but without sending emojis)
    for (const ally of this.player.allies()) {
      if (ally.targets().length === 0) continue;
      if (this.player.relation(ally) < Relation.Friendly) continue;

      for (const target of ally.targets()) {
        if (target === this.player) continue;
        if (this.player.isFriendly(target)) continue;
        // Found a valid ally target to nuke
        return target;
      }
    }

    // Find the most hated player
    // Ignore much weaker players (we don't need nukes to deal with them)
    const myMaxTroops = this.game.config().maxTroops(this.player);
    for (const relation of this.player.allRelationsSorted()) {
      if (relation.relation !== Relation.Hostile) continue;
      const other = relation.player;
      if (this.player.isFriendly(other)) continue;

      const otherMaxTroops = this.game.config().maxTroops(other);
      if (myMaxTroops >= otherMaxTroops * 2) continue;

      return other;
    }

    // In FFAs, nuke the crown if they're far enough ahead
    const crownTarget = this.findFFACrownTarget();
    if (crownTarget) {
      return crownTarget;
    }

    // In Teams, nuke the strongest team
    const teamTarget = this.findStrongestTeamTarget();
    if (teamTarget) {
      return teamTarget;
    }

    return null;
  }

  private isRichestNation(): boolean {
    const myGold = this.player.gold();
    for (const other of this.game.players()) {
      if (other === this.player) continue;
      if (other.type() !== PlayerType.Nation) continue;
      if (other.gold() > myGold) return false;
    }
    return true;
  }

  private findHighDensityTarget(): Player | null {
    let bestTarget: Player | null = null;
    let bestDensity = HIGH_DENSITY_NUKE_THRESHOLD;
    for (const other of this.game.players()) {
      if (other === this.player) continue;
      if (other.type() === PlayerType.Bot) continue;
      if (this.player.isFriendly(other)) continue;
      const tilesOwned = other.numTilesOwned();
      if (tilesOwned === 0) continue;
      const structures = other.units(Structures.types);
      let levelSum = 0;
      for (const s of structures) levelSum += s.level();
      // Skip players with too few structures regardless of density
      if (levelSum < MIN_LEVEL_SUM_FOR_HIGH_DENSITY_NUKE) continue;
      const density = levelSum / tilesOwned;
      if (density > bestDensity) {
        bestDensity = density;
        bestTarget = other;
      }
    }
    return bestTarget;
  }

  private findFFACrownTarget(): Player | null {
    const { difficulty, gameMode } = this.game.config().gameConfig();
    if (gameMode !== GameMode.FFA) {
      return null;
    }

    if (this.game.players().length <= 1) {
      return null;
    }

    const sortedByTiles = this.game
      .players()
      .slice()
      .sort((a, b) => b.numTilesOwned() - a.numTilesOwned());
    const firstPlace = sortedByTiles[0];

    // If we're the crown on Impossible difficulty, target 2nd place
    if (
      difficulty === Difficulty.Impossible &&
      firstPlace === this.player &&
      sortedByTiles.length >= 2
    ) {
      const secondPlace = sortedByTiles[1];
      if (!this.player.isFriendly(secondPlace)) {
        return secondPlace;
      }
    }

    // Don't target ourselves or allies
    if (firstPlace === this.player || this.player.isFriendly(firstPlace)) {
      return null;
    }

    const numTilesWithoutFallout =
      this.game.numLandTiles() - this.game.numTilesWithFallout();
    if (numTilesWithoutFallout <= 0) {
      return null;
    }

    const firstPlaceShare = firstPlace.numTilesOwned() / numTilesWithoutFallout;
    const myShare = this.player.numTilesOwned() / numTilesWithoutFallout;

    let threshold: number;
    switch (difficulty) {
      case Difficulty.Easy:
        threshold = 0.4; // 40%
        break;
      case Difficulty.Medium:
        threshold = 0.3; // 30%
        break;
      case Difficulty.Hard:
        threshold = 0.2; // 20%
        break;
      case Difficulty.Impossible:
        threshold = 0.1; // 10%
        break;
      default:
        assertNever(difficulty);
    }

    // Check if first place has threshold% more tile-percentage of the map than us
    if (firstPlaceShare - myShare > threshold) {
      return firstPlace;
    }

    return null;
  }

  private findStrongestTeamTarget(): Player | null {
    if (this.game.config().gameConfig().gameMode !== GameMode.Team) {
      return null;
    }

    if (this.game.players().length <= 1) {
      return null;
    }

    const teamTiles = new Map<string, number>();
    const teamPlayers = new Map<string, Player[]>();

    for (const p of this.game.players()) {
      const team = p.team();
      if (team === null) continue;

      teamTiles.set(team, (teamTiles.get(team) ?? 0) + p.numTilesOwned());
      let players = teamPlayers.get(team);
      if (!players) {
        players = [];
        teamPlayers.set(team, players);
      }
      players.push(p);
    }

    const sortedTeams = Array.from(teamTiles.entries()).sort(
      (a, b) => b[1] - a[1],
    );

    if (sortedTeams.length === 0) {
      return null;
    }

    let strongestTeam = sortedTeams[0][0];
    if (strongestTeam === this.player.team()) {
      if (sortedTeams.length > 1) {
        strongestTeam = sortedTeams[1][0];
      } else {
        return null;
      }
    }

    const targetTeamPlayers = teamPlayers.get(strongestTeam)!;

    // Filter out friendly players
    const validTargets = targetTeamPlayers.filter(
      (p) => !this.player.isFriendly(p),
    );

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

    if (this.random.chance(2)) {
      // Strongest player
      return validTargets.reduce((prev, current) =>
        this.game.config().maxTroops(prev) >
        this.game.config().maxTroops(current)
          ? prev
          : current,
      );
    } else {
      // Random player
      return this.random.randElement(validTargets);
    }
  }

  // Simulate saving up for a MIRV
  private getPerceivedNukeCost(type: UnitType): Gold {
    // If only 2 players left, use actual cost (no point saving for MIRV)
    if (this.game.players().length === 2) {
      return this.cost(type);
    }

    // If MIRVs are disabled, return the actual cost
    if (this.game.config().isUnitDisabled(UnitType.MIRV)) {
      return this.cost(type);
    }

    // Save up a limited amount in team games, synced with NationStructureBehavior
    // Saving up for a MIRV is not relevant
    if (
      this.game.config().gameConfig().gameMode === GameMode.Team &&
      this.player.gold() > this.cost(UnitType.HydrogenBomb)
    ) {
      return this.cost(type);
    }

    // Return the actual cost if we already have enough gold to buy both a MIRV and a hydro
    if (
      this.player.gold() >
      this.cost(UnitType.MIRV) + this.cost(UnitType.HydrogenBomb)
    ) {
      return this.cost(type);
    }

    // On Hard & Impossible, ignore perceived cost when under heavy attack
    // The nation is probably going to get destroyed soon, so go all-in on nukes
    const difficulty = this.game.config().gameConfig().difficulty;
    if (
      (difficulty === Difficulty.Hard ||
        difficulty === Difficulty.Impossible) &&
      this.isUnderHeavyAttack()
    ) {
      return this.cost(type);
    }

    if (type === UnitType.AtomBomb) {
      return this.atomBombPerceivedCost;
    } else {
      return this.hydrogenBombPerceivedCost;
    }
  }

  private isUnderHeavyAttack(): boolean {
    // Get the total incoming attack troops
    const incomingAttacks = this.player.incomingAttacks();
    let totalIncomingTroops = 0;
    for (const attack of incomingAttacks) {
      totalIncomingTroops += attack.troops();
    }

    const myTroops = this.player.troops();

    return totalIncomingTroops >= myTroops;
  }

  private removeOldNukeEvents() {
    const maxAge = 600; // 600 ticks = 1 minute
    const tick = this.game.ticks();
    while (
      this.recentlySentNukes.length > 0 &&
      this.recentlySentNukes[0][0] + maxAge < tick
    ) {
      this.recentlySentNukes.shift();
    }
  }

  private isTeammateAlreadyNukingThisSpot(
    tile: TileRef,
    nukeType: UnitType.AtomBomb | UnitType.HydrogenBomb,
  ): boolean {
    // Get the inner radius for our nuke type
    const ourInnerRadius = this.game.config().nukeMagnitudes(nukeType).inner;

    // Get all active nukes in the game
    const activeNukes = this.game.units(
      UnitType.AtomBomb,
      UnitType.HydrogenBomb,
    );

    // Check if any teammate's nuke blast radius overlaps with ours
    for (const nuke of activeNukes) {
      const nukeOwner = nuke.owner();

      // Skip our own nukes and non-teammate nukes
      if (nukeOwner === this.player || !this.player.isFriendly(nukeOwner)) {
        continue;
      }

      // Get the target tile of the teammate's nuke
      const targetTile = nuke.targetTile();
      if (!targetTile) continue;

      // Get the blast radius of the teammate's nuke
      const teammateInnerRadius = this.game
        .config()
        .nukeMagnitudes(nuke.type()).inner;

      // Check if the blast zones overlap
      // They overlap if distance between targets < sum of the two radii
      const distSquared = this.game.euclideanDistSquared(tile, targetTile);
      const sumRadius = ourInnerRadius + teammateInnerRadius;
      const sumRadiusSquared = sumRadius * sumRadius;

      if (distSquared <= sumRadiusSquared) {
        return true;
      }
    }

    return false;
  }

  // mirroring NukeTrajectoryPreviewLayer.ts logic a bit
  private isTrajectoryInterceptableBySam(
    spawnTile: TileRef,
    targetTile: TileRef,
    excludedSamIds?: Set<number>,
  ): boolean {
    const speed = this.game.config().defaultNukeSpeed();
    const pathFinder = UniversalPathFinding.Parabola(this.game, {
      increment: speed,
      distanceBasedHeight: true, // Atom/Hydrogen bombs use distance-based height
      directionUp: true, // AI nukes always go "up" for now
    });

    const trajectory = pathFinder.findPath(spawnTile, targetTile) ?? [];
    if (trajectory.length === 0) {
      return false;
    }

    const targetRangeSquared =
      this.game.config().defaultNukeTargetableRange() ** 2;

    let untargetableStart = -1;
    let untargetableEnd = -1;
    for (let i = 0; i < trajectory.length; i++) {
      const tile = trajectory[i];
      if (untargetableStart === -1) {
        if (
          this.game.euclideanDistSquared(tile, spawnTile) > targetRangeSquared
        ) {
          if (
            this.game.euclideanDistSquared(tile, targetTile) <
            targetRangeSquared
          ) {
            // Overlapping spawn & target range – no untargetable segment.
            break;
          } else {
            untargetableStart = i;
          }
        }
      } else if (
        this.game.euclideanDistSquared(tile, targetTile) < targetRangeSquared
      ) {
        untargetableEnd = i;
        break;
      }
    }

    for (let i = 0; i < trajectory.length; i++) {
      // Skip the mid-air untargetable portion
      if (
        untargetableStart !== -1 &&
        untargetableEnd !== -1 &&
        i === untargetableStart
      ) {
        i = untargetableEnd - 1;
        continue;
      }

      const tile = trajectory[i];
      const nearbySams = this.game.nearbyUnits(
        tile,
        this.game.config().maxSamRange(),
        UnitType.SAMLauncher,
      );

      for (const sam of nearbySams) {
        const owner = sam.unit.owner();
        if (owner === this.player || this.player.isFriendly(owner)) {
          continue;
        }
        // Skip SAMs we're intentionally overwhelming
        if (excludedSamIds?.has(sam.unit.id())) {
          continue;
        }
        const rangeSquared = this.game.config().samRange(sam.unit.level()) ** 2;
        if (sam.distSquared <= rangeSquared) {
          return true;
        }
      }
    }

    return false;
  }

  /**
   * Check if the parabolic nuke trajectory from spawnTile to targetTile
   * crosses any impassable terrain. Mirrors the check in NukeExecution that
   * aborts such launches
   */
  private isTrajectoryBlockedByImpassable(
    spawnTile: TileRef,
    targetTile: TileRef,
  ): boolean {
    const pathFinder = UniversalPathFinding.Parabola(this.game, {
      increment: this.game.config().defaultNukeSpeed(),
      distanceBasedHeight: true,
      directionUp: true,
    });
    const path = pathFinder.findPath(spawnTile, targetTile) ?? [];
    for (const tile of path) {
      if (this.game.isImpassable(tile)) {
        return true;
      }
    }
    return false;
  }

  private isValidNukeTile(t: TileRef, nukeTarget: Player | null): boolean {
    const difficulty = this.game.config().gameConfig().difficulty;

    const owner = this.game.owner(t);
    if (owner === nukeTarget) return true;
    // On Hard & Impossible, allow TerraNullius (hit small islands) and in team games other non-friendly players
    if (
      (difficulty === Difficulty.Hard ||
        difficulty === Difficulty.Impossible) &&
      (!owner.isPlayer() ||
        (this.game.config().gameConfig().gameMode === GameMode.Team &&
          owner.isPlayer() &&
          !this.player.isFriendly(owner)))
    ) {
      return true;
    }
    // On Easy & Medium, only allow tiles owned by the target player (=> nuke away from the border) to reduce nuke usage
    return false;
  }

  private nukeTileScore(
    tile: TileRef,
    silos: Unit[],
    targets: Unit[],
    nukeType: UnitType.AtomBomb | UnitType.HydrogenBomb,
  ): number {
    const magnitude = this.game.config().nukeMagnitudes(nukeType);
    const dist = euclDistFN(tile, magnitude.outer, false);
    let tileValue = targets
      .filter((unit) => dist(this.game, unit.tile()))
      .map((unit): number => {
        const level = unit.level();
        switch (unit.type()) {
          case UnitType.City:
            return 25_000 * level;
          case UnitType.DefensePost:
            return 5_000 * level;
          case UnitType.MissileSilo:
            return 50_000 * level;
          case UnitType.Port:
            return 15_000 * level;
          case UnitType.Factory:
            return 15_000 * level;
          default:
            return 0;
        }
      })
      .reduce((prev, cur) => prev + cur, 0);

    const difficulty = this.game.config().gameConfig().difficulty;
    // On Easy, ignore SAMs entirely.
    // On Medium, apply a simple local SAM penalty.
    // On Hard & Impossible we rely on trajectory-based interception checks instead. See maybeSendNuke().
    if (difficulty === Difficulty.Medium) {
      const dist50 = euclDistFN(tile, 50, false);
      const hasSam = targets.some(
        (unit) =>
          unit.type() === UnitType.SAMLauncher &&
          dist50(this.game, unit.tile()),
      );
      if (hasSam) return -1;
    }

    // On Impossible difficulty and a hydrogen bomb, add value for SAMs that can be outranged
    if (
      difficulty === Difficulty.Impossible &&
      nukeType === UnitType.HydrogenBomb
    ) {
      const hydroMagnitude = this.game
        .config()
        .nukeMagnitudes(UnitType.HydrogenBomb);
      const nearbySams = this.game.nearbyUnits(
        tile,
        hydroMagnitude.outer,
        UnitType.SAMLauncher,
      );

      for (const sam of nearbySams) {
        const samLevel = sam.unit.level();
        if (samLevel >= 5) continue; // Can't outrange level 5+ SAMs

        const samRange = this.game.config().samRange(samLevel);
        const distToSam = Math.sqrt(
          this.game.euclideanDistSquared(tile, sam.unit.tile()),
        );

        // Check if we can outrange this SAM
        if (distToSam > samRange) {
          // Add significant value for destroying a SAM that we can outrange
          tileValue += 100_000 * samLevel;
        }
      }
    }

    // Prefer tiles that are closer to a silo (but preserve structure value)
    const siloTiles = silos.map((u) => u.tile());
    const result = closestTwoTiles(this.game, siloTiles, [tile]);
    if (result === null) throw new Error("Missing result");
    const { x: closestSilo } = result;
    const distanceSquared = this.game.euclideanDistSquared(tile, closestSilo);
    const distanceToClosestSilo = Math.sqrt(distanceSquared);
    const distancePenalty = distanceToClosestSilo * 30;
    const baseTileValue = tileValue;
    tileValue = Math.max(baseTileValue * 0.2, tileValue - distancePenalty); // Keep at least 20% of structure value

    // Don't target near recent targets
    tileValue -= this.recentlySentNukes
      .filter(([_tick, recentTile, recentNukeType]) => {
        const recentInnerRadius = this.game
          .config()
          .nukeMagnitudes(recentNukeType).inner;
        const distSquared = this.game.euclideanDistSquared(tile, recentTile);
        return distSquared <= recentInnerRadius * recentInnerRadius;
      })
      .map((_) => 1_000_000)
      .reduce((prev, cur) => prev + cur, 0);

    return tileValue;
  }

  private sendNuke(
    tile: TileRef,
    nukeType: UnitType.AtomBomb | UnitType.HydrogenBomb,
    targetPlayer: Player,
    waitTicks = 0,
  ) {
    const tick = this.game.ticks();
    this.recentlySentNukes.push([tick, tile, nukeType]);
    if (nukeType === UnitType.AtomBomb) {
      this.atomBombsLaunched++;
      // Increase perceived cost by 50% each time to simulate saving up for a MIRV (higher than hydro to make atom bombs less attractive for the lategame)
      this.atomBombPerceivedCost = (this.atomBombPerceivedCost * 150n) / 100n;
    } else if (nukeType === UnitType.HydrogenBomb) {
      this.hydrogenBombsLaunched++;
      // Increase perceived cost by 25% each time to simulate saving up for a MIRV
      this.hydrogenBombPerceivedCost =
        (this.hydrogenBombPerceivedCost * 125n) / 100n;
    }
    this.game.addExecution(
      new NukeExecution(nukeType, this.player, tile, null, -1, waitTicks),
    );
    this.emojiBehavior.maybeSendEmoji(targetPlayer, EMOJI_NUKE);
  }

  /**
   * On Impossible difficulty, when no good nuke target is available (score <= 0),
   * attempt to destroy enemy SAMs by overwhelming them with atom bombs.
   * A SAM of level N can intercept N nukes before going on cooldown,
   * so we need N+1 bombs to destroy it (accounting for all covering SAMs).
   */
  private maybeDestroyEnemySam(nukeTarget: Player): void {
    if (this.game.config().isUnitDisabled(UnitType.AtomBomb)) {
      return;
    }

    // Don't launch another salvo if we already have atom bombs in flight
    const ourAtomBombs = this.player.units(UnitType.AtomBomb);
    if (ourAtomBombs.length > 0) {
      return;
    }

    const atomCost = this.cost(UnitType.AtomBomb);
    const enemySams = nukeTarget.units(UnitType.SAMLauncher);
    if (enemySams.length === 0) {
      return;
    }

    const ourSilos = this.player
      .units(UnitType.MissileSilo)
      .filter((silo) => !silo.isUnderConstruction());
    if (ourSilos.length === 0) {
      return;
    }

    // Try each enemy SAM as a target, easiest (lowest level) first
    const sortedSams = enemySams.slice().sort((a, b) => a.level() - b.level());
    let needsMoreSilos = false;
    // Track the first failed attempt so we can upgrade a silo that would
    // actually have helped that plan (rather than an unrelated silo).
    let failedTarget: {
      targetTile: TileRef;
      coveringSamIds: Set<number>;
      totalBombs: number;
    } | null = null;

    for (const targetSam of sortedSams) {
      const targetTile = targetSam.tile();

      // Find all enemy SAMs whose range covers the target tile (they will all try to intercept)
      const coveringSams = this.findEnemySamsCoveringTile(targetTile);
      const coveringSamIds = new Set(coveringSams.map((s) => s.id()));

      // Total interception capacity = sum of covering SAM levels
      const totalInterceptions = coveringSams.reduce(
        (sum, sam) => sum + sam.level(),
        0,
      );
      const bombsNeeded = totalInterceptions + 1;

      // NukeExecution always picks the closest non-cooldown silo by Manhattan
      // distance to target (via nukeSpawn). Our planning must mirror that order.
      // Silos with interceptable trajectories will still be picked first by
      // NukeExecution — their bombs launch but get intercepted, "wasting" slots.
      const nukeSpeed = this.game.config().defaultNukeSpeed();
      const allAvailableSilos: {
        silo: Unit;
        slots: number;
        flightTicks: number;
        interceptable: boolean;
      }[] = [];
      for (const silo of ourSilos) {
        const availableSlots = silo.level() - silo.missileTimerQueue().length;
        if (availableSlots <= 0) {
          continue;
        }
        const interceptable = this.isTrajectoryInterceptableBySam(
          silo.tile(),
          targetTile,
          coveringSamIds,
        );
        // Compute actual parabolic flight time in ticks
        const pathFinder = UniversalPathFinding.Parabola(this.game, {
          increment: nukeSpeed,
          distanceBasedHeight: true,
          directionUp: true,
        });
        const trajectory = pathFinder.findPath(silo.tile(), targetTile) ?? [];
        if (trajectory.length === 0) continue;
        // Skip silos whose trajectory crosses impassable terrain — the
        // simulation would abort these launches (see NukeExecution).
        if (this.isTrajectoryBlockedByImpassable(silo.tile(), targetTile))
          continue;
        allAvailableSilos.push({
          silo,
          slots: availableSlots,
          flightTicks: trajectory.length,
          interceptable,
        });
      }

      // Sort by Manhattan distance to target (matching nukeSpawn's pick order)
      allAvailableSilos.sort(
        (a, b) =>
          this.game.manhattanDist(a.silo.tile(), targetTile) -
          this.game.manhattanDist(b.silo.tile(), targetTile),
      );

      // Flatten into a per-bomb launch sequence matching NukeExecution's order.
      // Each silo contributes `slots` consecutive bombs before NukeExecution
      // moves to the next silo.
      const launchSequence: {
        flightTicks: number;
        interceptable: boolean;
      }[] = [];
      for (const entry of allAvailableSilos) {
        for (let s = 0; s < entry.slots; s++) {
          launchSequence.push({
            flightTicks: entry.flightTicks,
            interceptable: entry.interceptable,
          });
        }
      }

      // Use half the SAM cooldown as the max total arrival spread to be safe.
      const samCooldown = this.game.config().SAMCooldown();
      const maxTotalArrivalSpread = Math.floor(samCooldown / 2);

      // Add extra bombs: 1 for every 5 to account for enemy building more SAMs
      // while our bombs are in flight
      const extraBombs = Math.floor(bombsNeeded / 5);
      const totalBombs = bombsNeeded + extraBombs;

      // Collect bombs from silos whose trajectory to the target is NOT blocked
      // by enemy SAMs other than the covering SAMs we're trying to overwhelm.
      const unblockedBombs: { index: number; flightTicks: number }[] = [];
      for (let i = 0; i < launchSequence.length; i++) {
        if (!launchSequence[i].interceptable) {
          unblockedBombs.push({
            index: i,
            flightTicks: launchSequence[i].flightTicks,
          });
        }
      }

      if (unblockedBombs.length < totalBombs) {
        failedTarget ??= { targetTile, coveringSamIds, totalBombs };
        needsMoreSilos = true;
        continue;
      }

      // Sort unblocked bombs by flight time to find a sliding window
      // of maxTotalArrivalSpread that captures the most bombs.
      const sortedByFlight = [...unblockedBombs].sort(
        (a, b) => a.flightTicks - b.flightTicks,
      );

      let bestWindowStart = 0;
      let bestWindowCount = 0;
      for (let start = 0; start < sortedByFlight.length; start++) {
        let end = start;
        while (
          end < sortedByFlight.length &&
          sortedByFlight[end].flightTicks - sortedByFlight[start].flightTicks <=
            maxTotalArrivalSpread
        ) {
          end++;
        }
        if (end - start > bestWindowCount) {
          bestWindowCount = end - start;
          bestWindowStart = start;
        }
      }

      if (bestWindowCount < totalBombs) {
        failedTarget ??= { targetTile, coveringSamIds, totalBombs };
        needsMoreSilos = true;
        continue;
      }

      // From the window, pick totalBombs with the lowest launch-sequence
      // indices to minimise how many bombs we need to fire (minimise gold cost).
      const windowBombs = sortedByFlight.slice(
        bestWindowStart,
        bestWindowStart + bestWindowCount,
      );
      const windowByIndex = [...windowBombs].sort((a, b) => a.index - b.index);
      const selected = windowByIndex.slice(0, totalBombs);
      const selectedSet = new Set(selected.map((b) => b.index));
      const lastSelectedIndex = selected[selected.length - 1].index;
      const bombsToFire = lastSelectedIndex + 1;

      // Compute per-bomb waitTicks so all selected bombs arrive in the window.
      // Target: spread arrivals evenly, anchored at the earliest flight time
      // in the selected set.
      const selectedFlightMin = Math.min(...selected.map((b) => b.flightTicks));
      const staggerInterval = Math.max(
        1,
        Math.floor(maxTotalArrivalSpread / totalBombs),
      );
      let selectedIdx = 0;
      const waitTicksPerBomb: number[] = [];
      for (let i = 0; i < bombsToFire; i++) {
        if (selectedSet.has(i)) {
          const targetArrival =
            selectedFlightMin + selectedIdx * staggerInterval;
          waitTicksPerBomb.push(
            Math.max(0, targetArrival - launchSequence[i].flightTicks),
          );
          selectedIdx++;
        } else {
          // Wasted bomb (interceptable or out-of-window) — launch immediately
          waitTicksPerBomb.push(0);
        }
      }

      // Check gold for all fired bombs (including wasted ones)
      const totalCost = atomCost * BigInt(bombsToFire);
      if (this.player.gold() < totalCost) {
        continue;
      }

      // Fire the salvo — NukeExecution will pick silos in the same
      // Manhattan distance order we planned.
      for (let i = 0; i < bombsToFire; i++) {
        this.sendNuke(
          targetTile,
          UnitType.AtomBomb,
          nukeTarget,
          waitTicksPerBomb[i],
        );
      }
      return;
    }

    // Couldn't destroy any SAM — upgrade silos only if capacity was the bottleneck.
    // If we only lack gold, don't waste it upgrading silos — just wait and save.
    if (needsMoreSilos && failedTarget !== null) {
      this.maybeUpgradeHelpfulSilo(failedTarget);
    }
  }

  /**
   * Find all enemy SAMs whose range covers a given tile.
   */
  private findEnemySamsCoveringTile(tile: TileRef): Unit[] {
    const nearbySams = this.game.nearbyUnits(
      tile,
      this.game.config().maxSamRange(),
      UnitType.SAMLauncher,
    );

    const result: Unit[] = [];
    for (const sam of nearbySams) {
      const owner = sam.unit.owner();
      if (owner === this.player || this.player.isFriendly(owner)) {
        continue;
      }
      const range = this.game.config().samRange(sam.unit.level());
      if (sam.distSquared <= range * range) {
        result.push(sam.unit);
      }
    }
    return result;
  }

  /**
   * Upgrade a missile silo that would actually have helped the failed
   * overwhelm attempt: trajectory to the failed target is not blocked by
   * non-covering enemy SAMs, and the silo is below the upgrade cap. Among
   * those, picks the one best protected by our own SAMs.
   */
  private maybeUpgradeHelpfulSilo(failedTarget: {
    targetTile: TileRef;
    coveringSamIds: Set<number>;
    totalBombs: number;
  }): void {
    const silos = this.player.units(UnitType.MissileSilo);
    if (silos.length === 0) return;

    // First pass: find silos with an unblocked trajectory to the failed
    // target. Only these contribute slots to the overwhelm plan.
    // "Unblocked" means not interceptable by non-covering enemy SAMs AND
    // not crossing impassable terrain (the sim aborts those launches).
    const unblockedSilos: Unit[] = [];
    for (const silo of silos) {
      if (
        !this.isTrajectoryInterceptableBySam(
          silo.tile(),
          failedTarget.targetTile,
          failedTarget.coveringSamIds,
        ) &&
        !this.isTrajectoryBlockedByImpassable(
          silo.tile(),
          failedTarget.targetTile,
        )
      ) {
        unblockedSilos.push(silo);
      }
    }
    if (unblockedSilos.length === 0) return;

    // Bail out if the target is unreachable even at max silo level —
    // crazy amounts of covering SAMs, upgrading is wasted gold.
    const maxAchievableSlots =
      unblockedSilos.length * MAX_NATION_SILO_UPGRADE_LEVEL;
    if (maxAchievableSlots < failedTarget.totalBombs) return;

    const ourSams = this.player.units(UnitType.SAMLauncher);
    let bestSilo: Unit | null = null;
    let bestProtection = -1;

    for (const silo of unblockedSilos) {
      if (silo.level() >= MAX_NATION_SILO_UPGRADE_LEVEL) continue;
      if (!this.player.canUpgradeUnit(silo)) continue;

      let protection = 0;
      for (const sam of ourSams) {
        const range = this.game.config().samRange(sam.level());
        const distSquared = this.game.euclideanDistSquared(
          silo.tile(),
          sam.tile(),
        );
        if (distSquared <= range * range) {
          protection += sam.level();
        }
      }

      if (protection > bestProtection) {
        bestProtection = protection;
        bestSilo = silo;
      }
    }

    if (bestSilo !== null) {
      this.game.addExecution(
        new UpgradeStructureExecution(this.player, bestSilo.id()),
      );
    }
  }

  private cost(type: UnitType): Gold {
    return this.game.unitInfo(type).cost(this.game, this.player);
  }
}