Guncircle.io/packages/server/src/validation.ts

// ═══════════════════════════════════════════════════════════════════════════════
// GunCircle.io — Input Validator (Anti-cheat)
// ═══════════════════════════════════════════════════════════════════════════════

import {
  type Player,
  type GunConfig,
  type PlayerInput,
  PLAYER_BASE_SPEED,
  PLAYER_ACCELERATION,
  ARENA_WIDTH,
  ARENA_HEIGHT,
  STAT_MAX_LEVEL,
  STAT_COUNT,
  Stat,
  AIM_ANGLE_TOLERANCE,
  MAX_LEVEL,
} from '@guncircle/shared';

// ─── InputValidator ──────────────────────────────────────────────────────────

export class InputValidator {
  /** Maximum position change per tick at max speed */
  private readonly maxDistPerTick: number;

  constructor() {
    // At 60Hz, max distance per tick = speed / 60 + small tolerance
    this.maxDistPerTick = PLAYER_BASE_SPEED / 60 + 2;
  }

  /**
   * Validate movement input. Speed must not exceed base * (1 + moveSpeedStat).
   * Returns clamped (newX, newY) that are within allowed bounds.
   */
  validateMovement(
    player: Player,
    moveAngle: number,
    dt: number
  ): { x: number; y: number; valid: boolean } {
    if (moveAngle < -0.5) {
      // -1 or negative means no movement input
      return { x: player.x, y: player.y, valid: true };
    }

    const moveSpeedStat: number = player.stats[Stat.MovementSpeed] ?? 0;
    const maxSpeed: number = PLAYER_BASE_SPEED * (1 + moveSpeedStat * 0.05);
    const maxStep: number = maxSpeed * dt;

    // Validate position delta from current position
    const requestedVx: number = Math.cos(moveAngle) * maxSpeed;
    const requestedVy: number = Math.sin(moveAngle) * maxSpeed;

    const newX: number = player.x + requestedVx * dt;
    const newY: number = player.y + requestedVy * dt;

    // Clamp to arena
    const clampedX: number = Math.max(
      player.radius,
      Math.min(ARENA_WIDTH - player.radius, newX)
    );
    const clampedY: number = Math.max(
      player.radius,
      Math.min(ARENA_HEIGHT - player.radius, newY)
    );

    // Check if the step size is reasonable
    const dx: number = clampedX - player.x;
    const dy: number = clampedY - player.y;
    const stepSize: number = Math.sqrt(dx * dx + dy * dy);

    if (stepSize > maxStep * 1.5) {
      // Possible speed hack — reject movement
      return { x: player.x, y: player.y, valid: false };
    }

    return { x: clampedX, y: clampedY, valid: true };
  }

  /**
   * Validate aim angle change. Change per tick must be within tolerance.
   */
  validateAimAngle(oldAngle: number, newAngle: number): { angle: number; valid: boolean } {
    let diff: number = newAngle - oldAngle;
    // Normalize to [-PI, PI]
    while (diff > Math.PI) diff -= Math.PI * 2;
    while (diff < -Math.PI) diff += Math.PI * 2;

    const absDiff: number = Math.abs(diff);
    if (absDiff > AIM_ANGLE_TOLERANCE * 10) {
      // Suspiciously large angle change — could be aimbot
      // Cap it to max allowed
      const cappedDiff: number = Math.sign(diff) * AIM_ANGLE_TOLERANCE * 10;
      let cappedAngle: number = oldAngle + cappedDiff;
      while (cappedAngle > Math.PI) cappedAngle -= Math.PI * 2;
      while (cappedAngle < -Math.PI) cappedAngle += Math.PI * 2;
      return { angle: cappedAngle, valid: false };
    }

    return { angle: newAngle, valid: true };
  }

  /**
   * Validate fire rate: time since last shot must be >= cooldown.
   * Returns true if firing is allowed.
   */
  validateFireRate(
    lastShotTime: number,
    currentTime: number,
    gun: GunConfig,
    reloadSpdStat: number
  ): boolean {
    const baseCooldown: number = 1000 / gun.fireRate;
    const reloadBonus: number = 1 + reloadSpdStat * 0.1;
    const adjustedCooldown: number = baseCooldown / reloadBonus;

    const elapsed: number = currentTime - lastShotTime;
    return elapsed >= adjustedCooldown - 5; // 5ms tolerance for network jitter
  }

  /**
   * Validate stat upgrade choice. Returns true if the player can make this upgrade.
   */
  validateUpgrade(player: Player, choice: number): { valid: boolean; reason: string } {
    // Must have upgrade points
    if (player.upgradePoints <= 0) {
      return { valid: false, reason: 'No upgrade points available' };
    }

    // Choice must be a valid stat index
    if (choice < 0 || choice >= STAT_COUNT) {
      return { valid: false, reason: 'Invalid stat index' };
    }

    // Stat must not be maxed
    const currentLevel: number = player.stats[choice] ?? 0;
    if (currentLevel >= STAT_MAX_LEVEL) {
      return { valid: false, reason: 'Stat already at max level' };
    }

    return { valid: true, reason: '' };
  }

  /**
   * Validate branch selection choice. Returns true if branch is valid for player.
   */
  validateBranchChoice(
    player: Player,
    branchIndex: number,
    availableBranches: number[]
  ): { valid: boolean; reason: string } {
    if (branchIndex < 0 || branchIndex >= availableBranches.length) {
      return { valid: false, reason: 'Invalid branch selection' };
    }

    if (player.upgradePoints <= 0) {
      return { valid: false, reason: 'No upgrade points available' };
    }

    return { valid: true, reason: '' };
  }

  /**
   * Validate general input bounds. Clamp numeric values to reasonable ranges.
   */
  sanitizeInput(input: PlayerInput): PlayerInput {
    return {
      seq: Math.max(0, input.seq | 0),
      moveAngle: isNaN(input.moveAngle) ? -1 : input.moveAngle,
      aimAngle: isNaN(input.aimAngle) ? 0 : input.aimAngle,
      isShooting: Boolean(input.isShooting),
      upgradeChoice:
        input.upgradeChoice !== undefined ? Math.max(0, input.upgradeChoice | 0) : undefined,
    };
  }

  /**
   * Check if a position is within arena bounds.
   */
  isInArena(x: number, y: number, radius: number = 0): boolean {
    return (
      x >= radius &&
      x <= ARENA_WIDTH - radius &&
      y >= radius &&
      y <= ARENA_HEIGHT - radius
    );
  }

  /**
   * Validate that velocity is within reasonable bounds.
   */
  validateVelocity(vx: number, vy: number, maxSpeed: number): { vx: number; vy: number } {
    const speedSq: number = vx * vx + vy * vy;
    const maxSpeedSq: number = maxSpeed * maxSpeed;

    if (speedSq > maxSpeedSq * 4) {
      // Suspicious velocity — cap it
      const speed: number = Math.sqrt(speedSq);
      const scale: number = (maxSpeed * 2) / speed;
      return { vx: vx * scale, vy: vy * scale };
    }

    return { vx, vy };
  }
}