botfights/frontend/src/game/arcade/combat.ts

import type { FighterInstance, Hitbox } from './types'
import {
  HURTBOX_WIDTH, HURTBOX_HEIGHT, CROUCH_HURTBOX_HEIGHT,
  CHIP_DAMAGE_RATIO, COMBO_DAMAGE_SCALING,
} from './constants'
import { MOVES } from './moves'

export interface HitResult {
  type: 'hit' | 'blocked'
  damage: number
  hitstun: number
  blockstun: number
  knockbackX: number
  knockbackY: number
  hitbox: Hitbox
}

/**
 * Check all active hitboxes of the attacker's current move against the defender.
 * Returns HitResult if any hitbox connects, null otherwise.
 */
export function checkHit(attacker: FighterInstance, defender: FighterInstance): HitResult | null {
  const { combat, physics, obj } = attacker
  if (!combat.currentMove || combat.hasHitThisAttack) return null

  const move = MOVES[combat.currentMove]
  if (!move) return null

  const frame = combat.attackFrame

  for (const hitbox of move.hitboxes) {
    if (frame < hitbox.activeFrames[0] || frame > hitbox.activeFrames[1]) continue

    const result = testHitbox(attacker, defender, hitbox)
    if (result) return result
  }

  return null
}

function testHitbox(
  attacker: FighterInstance,
  defender: FighterInstance,
  hitbox: Hitbox,
): HitResult | null {
  const dir = attacker.physics.facingRight ? 1 : -1

  // Hitbox world position
  const hx = attacker.obj.pos.x + hitbox.offsetX * dir
  const hy = attacker.obj.pos.y + hitbox.offsetY
  const hLeft = hx - hitbox.width / 2
  const hRight = hx + hitbox.width / 2
  const hTop = hy - hitbox.height / 2
  const hBottom = hy + hitbox.height / 2

  // Defender hurtbox (centered on position, extends upward)
  const isCrouching = defender.combat.state === 'crouching' || defender.combat.state === 'blocking'
  const hurtH = isCrouching ? CROUCH_HURTBOX_HEIGHT : HURTBOX_HEIGHT
  const dLeft = defender.obj.pos.x - HURTBOX_WIDTH / 2
  const dRight = defender.obj.pos.x + HURTBOX_WIDTH / 2
  const dTop = defender.obj.pos.y - hurtH
  const dBottom = defender.obj.pos.y

  // AABB overlap test
  if (hRight < dLeft || hLeft > dRight || hBottom < dTop || hTop > dBottom) {
    return null
  }

  // Check if defender is blocking
  const isBlocking = isDefenderBlocking(attacker, defender)

  if (isBlocking) {
    return {
      type: 'blocked',
      damage: Math.round(hitbox.damage * CHIP_DAMAGE_RATIO),
      hitstun: 0,
      blockstun: hitbox.blockstun,
      knockbackX: hitbox.knockbackX * 0.3,
      knockbackY: 0,
      hitbox,
    }
  }

  // Apply combo damage scaling
  const comboScale = Math.pow(COMBO_DAMAGE_SCALING, defender.combat.comboCount)
  const scaledDamage = Math.round(hitbox.damage * comboScale)

  return {
    type: 'hit',
    damage: scaledDamage,
    hitstun: hitbox.hitstun,
    blockstun: 0,
    knockbackX: hitbox.knockbackX,
    knockbackY: hitbox.knockbackY,
    hitbox,
  }
}

function isDefenderBlocking(attacker: FighterInstance, defender: FighterInstance): boolean {
  if (defender.combat.state !== 'blocking') return false
  if (!defender.physics.grounded) return false

  // Must be holding direction away from attacker
  const holdingBack = defender.physics.facingRight
    ? defender.input.left && !defender.input.right
    : defender.input.right && !defender.input.left

  return holdingBack
}

/**
 * Apply hit result to the defender. Mutates defender state.
 */
export function applyHit(
  attacker: FighterInstance,
  defender: FighterInstance,
  result: HitResult,
): void {
  // Deal damage
  defender.combat.hp = Math.max(0, defender.combat.hp - result.damage)

  // Mark attacker's attack as having connected (prevent multi-hit per hitbox window)
  attacker.combat.hasHitThisAttack = true

  if (result.type === 'hit') {
    // Increment combo counter
    attacker.combat.comboCount++
    attacker.combat.comboDamage += result.damage
  }
}

/**
 * Reset combo counter (called when the opponent recovers from hitstun).
 */
export function resetCombo(fighter: FighterInstance): void {
  fighter.combat.comboCount = 0
  fighter.combat.comboDamage = 0
}