/**
 * A bullet (or plasma bolt) tracked in world space. Unlike classic Wolf3D
 * hitscan, shots fly at the weapon's bulletSpeed and only deal damage when
 * they actually collide with a wall, an enemy, or the player. Shots deviate
 * from the aim direction by the weapon's spread (scaled up for low-skill
 * enemies), so accuracy is emergent: a wide shot simply misses. Weapons with
 * an `explosion` def (rocket launcher) also splash-damage everything around
 * their impact point — see explode().
 *
 * Quacks like a renderable for SpriteRenderer: { x, y, active, isEnemy,
 * def: { tex, scale, anchor: 'center' } } — drawn as a small billboard at
 * eye height, occluded by walls via the zBuffer like any sprite.
 */

/** Max cells a projectile may advance per collision sample. Smaller than the
 *  hit radii and any wall tile, so fast bullets can't tunnel through either. */
const MAX_STEP = 0.25;

/** Collision radii (cells): entities are torso-sized, the player a bit
 *  slimmer so incoming fire is dodgeable. */
const ENEMY_HIT_RADIUS = 0.35;
const PLAYER_HIT_RADIUS = 0.3;

// --- Skill (1–10) → shooting-quality helpers. One source of truth, used by
// --- Entity (enemy fire) and available to tests.

/** Spread multiplier: skill 10 shoots at the weapon's listed spread,
 *  skill 1 at ~4.15×. */
export function skillSpreadMult(skill) {
  return 1 + (10 - skill) * 0.35;
}

/** Delay between spotting the player and the first shot. */
export function skillReactionMs(skill) {
  return (11 - skill) * 120;
}

/** Low-skill enemies also fire slower than the weapon allows. */
export function skillCooldownMs(weapon, skill) {
  return weapon.cooldownMs * (1 + (10 - skill) * 0.15);
}

/** Rotate the unit vector (dirX, dirY) by a uniform random angle within
 *  ±spreadDeg × spreadMult degrees. */
export function spreadDir(dirX, dirY, spreadDeg, spreadMult = 1) {
  const maxRad = (spreadDeg * spreadMult * Math.PI) / 180;
  if (maxRad === 0) return { x: dirX, y: dirY };
  const a = (Math.random() * 2 - 1) * maxRad;
  const c = Math.cos(a);
  const s = Math.sin(a);
  return { x: dirX * c - dirY * s, y: dirX * s + dirY * c };
}

export class Projectile {
  /** owner is the shooter (the Player or an Entity): it selects the target
   *  set — player bullets hit enemies, enemy bullets hit the player — which
   *  also inherently prevents self-hits and enemy friendly fire. */
  constructor({ x, y, dirX, dirY, weapon, owner, spreadMult = 1, spreadDeg = weapon.spreadDeg }) {
    const dir = spreadDir(dirX, dirY, spreadDeg, spreadMult);
    // Muzzle offset along the true aim so the bolt doesn't clip the shooter.
    this.x = x + dirX * 0.3;
    this.y = y + dirY * 0.3;
    this.dx = dir.x;
    this.dy = dir.y;
    this.speed = weapon.bulletSpeed;
    this.damage = weapon.damage;
    this.rangeLeft = weapon.range;
    this.owner = owner;
    this.fromPlayer = !!owner?.cam;
    this.active = true;

    // Splash spec ({ radius, damage } or null) and the blast art, both from
    // the weapon def. Explosive shots detonate wherever they stop.
    this.explosion = weapon.explosion ?? null;
    this.explosionTex = weapon.explosionTex ?? null;

    // SpriteRenderer contract (anchor 'center' = eye height, not floor).
    this.isEnemy = false;
    this.def = { tex: weapon.projTex, scale: weapon.projectile?.size ?? 0.08, anchor: 'center' };

    // Set when this projectile hits something, for GameScene to react to.
    // Arrays/totals because one explosion can kill several enemies and hurt
    // the player (splash ignores ownership — even the shooter isn't safe).
    this.kills = []; // enemies killed by this shot, for score credit
    this.playerDamage = 0; // total damage dealt to the player
    this.exploded = null; // { x, y, radius } once detonated, for the blast VFX
  }

  /** Advance by dt seconds through `world` = { map, entities, player },
   *  substepped so no sample exceeds MAX_STEP cells. */
  update(dt, world) {
    if (!this.active) return;
    const travel = Math.min(this.speed * dt, this.rangeLeft);
    const steps = Math.max(1, Math.ceil(travel / MAX_STEP));
    const stepLen = travel / steps;

    for (let i = 0; i < steps; i++) {
      this.x += this.dx * stepLen;
      this.y += this.dy * stepLen;
      this.rangeLeft -= stepLen;

      if (world.map.isWall(this.x, this.y)) {
        // Back out of the wall so a detonation isn't buried inside the cell
        // (hasLineOfSight from within a wall would block all its splash).
        this.x -= this.dx * stepLen;
        this.y -= this.dy * stepLen;
        this.impact(world);
        return;
      }

      if (this.fromPlayer) {
        for (const e of world.entities) {
          if (!e.alive) continue; // corpses and dying enemies don't soak hits
          if (Math.hypot(e.x - this.x, e.y - this.y) >= ENEMY_HIT_RADIUS) continue;
          if (e.damage(this.damage)) this.kills.push(e);
          this.impact(world);
          return;
        }
      } else {
        const { cam } = world.player;
        if (Math.hypot(cam.posX - this.x, cam.posY - this.y) < PLAYER_HIT_RADIUS) {
          this.playerDamage += this.damage;
          this.impact(world);
          return;
        }
      }
    }

    if (this.rangeLeft <= 0) this.impact(world);
  }

  /** Stop here; direct-hit damage was already applied by the caller. Explosive
   *  warheads add their splash on top (a direct hit deals both). */
  impact(world) {
    this.active = false;
    if (this.explosion) this.explode(world);
  }

  /** Splash damage to everything alive within the blast radius — enemies and
   *  the player alike, shooter included — falling off linearly from full
   *  damage at the center to zero at the edge. Walls (and closed doors)
   *  shield anything without line of sight to the blast. */
  explode(world) {
    const { radius, damage } = this.explosion;
    this.exploded = { x: this.x, y: this.y, radius };

    const splash = (tx, ty) => {
      const d = Math.hypot(tx - this.x, ty - this.y);
      if (d >= radius || !world.map.hasLineOfSight(this.x, this.y, tx, ty)) return 0;
      return Math.round(damage * (1 - d / radius));
    };

    for (const e of world.entities) {
      if (!e.alive) continue;
      const dmg = splash(e.x, e.y);
      if (dmg > 0 && e.damage(dmg)) this.kills.push(e);
    }
    const { cam } = world.player;
    this.playerDamage += splash(cam.posX, cam.posY);
  }
}