lib/engine/Collision.ts

// Collision detection system

import { PlayerState, Block, Enemy, Position } from './types';
import { GAME_CONFIG } from '../constants';

const { TILE_SIZE } = GAME_CONFIG;

export interface CollisionResult {
    collided: boolean;
    side?: 'top' | 'bottom' | 'left' | 'right';
    block?: Block;
}

export class Collision {
    // AABB collision check between two rectangles
    checkAABB(
        a: { x: number; y: number; width: number; height: number },
        b: { x: number; y: number; width: number; height: number }
    ): boolean {
        return (
            a.x < b.x + b.width &&
            a.x + a.width > b.x &&
            a.y < b.y + b.height &&
            a.y + a.height > b.y
        );
    }

    // Determine collision side
    getCollisionSide(
        player: PlayerState,
        block: Block,
        prevY: number
    ): 'top' | 'bottom' | 'left' | 'right' {
        const playerBottom = player.y + player.height;
        const playerTop = player.y;
        const blockBottom = block.y + block.height;
        const blockTop = block.y;

        // Check if landing on top
        if (prevY + player.height <= block.y + 2 && player.vy >= 0) {
            return 'top';
        }

        // Check if hitting from below
        if (prevY >= blockBottom - 2 && player.vy < 0) {
            return 'bottom';
        }

        // Determine left/right based on position
        const playerCenterX = player.x + player.width / 2;
        const blockCenterX = block.x + block.width / 2;

        return playerCenterX < blockCenterX ? 'right' : 'left';
    }

    // Check player collision with blocks
    checkPlayerBlockCollision(
        player: PlayerState,
        blocks: Block[],
        prevY: number
    ): { grounded: boolean; hitBlock?: Block } {
        let grounded = false;
        let hitBlock: Block | undefined;

        for (const block of blocks) {
            // Skip coins - they have separate handling
            if (block.type === 'coin') continue;

            if (this.checkAABB(player, block)) {
                const side = this.getCollisionSide(player, block, prevY);

                switch (side) {
                    case 'top':
                        player.y = block.y - player.height;
                        player.vy = 0;
                        player.isJumping = false;
                        player.isFalling = false;
                        grounded = true;
                        break;
                    case 'bottom':
                        player.y = block.y + block.height;
                        player.vy = 1; // Small downward velocity
                        if (block.type === 'question' && !block.isHit) {
                            hitBlock = block;
                        }
                        break;
                    case 'left':
                        player.x = block.x + block.width;
                        player.vx = 0;
                        break;
                    case 'right':
                        player.x = block.x - player.width;
                        player.vx = 0;
                        break;
                }
            }
        }

        return { grounded, hitBlock };
    }

    // Check enemy collision with blocks (ground only)
    checkEnemyBlockCollision(enemy: Enemy, blocks: Block[]): void {
        for (const block of blocks) {
            if (block.type === 'coin') continue;

            if (this.checkAABB(enemy, block)) {
                // Land on top
                if (enemy.vy > 0) {
                    enemy.y = block.y - enemy.height;
                    enemy.vy = 0;
                }
                // Side collision - reverse direction
                if (
                    enemy.x + enemy.width > block.x &&
                    enemy.x < block.x + block.width
                ) {
                    if (enemy.y + enemy.height > block.y + 4) {
                        enemy.direction *= -1;
                    }
                }
            }
        }
    }

    // Check player collision with enemy
    checkPlayerEnemyCollision(
        player: PlayerState,
        enemy: Enemy
    ): { killed: boolean; playerHit: boolean } {
        if (!enemy.isAlive || !player.isAlive) {
            return { killed: false, playerHit: false };
        }

        if (this.checkAABB(player, enemy)) {
            // Check if player is landing on enemy (stomping)
            if (player.vy > 0 && player.y + player.height < enemy.y + enemy.height / 2) {
                return { killed: true, playerHit: false };
            } else {
                return { killed: false, playerHit: true };
            }
        }

        return { killed: false, playerHit: false };
    }

    // Check player collision with coin
    checkCoinCollision(player: PlayerState, blocks: Block[]): Block[] {
        const collectedCoins: Block[] = [];

        blocks.forEach((block, index) => {
            if (block.type === 'coin' && this.checkAABB(player, block)) {
                collectedCoins.push(block);
            }
        });

        return collectedCoins;
    }

    // Check if player reached the flag
    checkFlagCollision(player: PlayerState, flagPosition: Position): boolean {
        return (
            player.x + player.width >= flagPosition.x &&
            player.x <= flagPosition.x + 50 &&
            player.y <= flagPosition.y + 100
        );
    }

    // Check if player fell off the level
    checkFallDeath(player: PlayerState, levelHeight: number): boolean {
        return player.y > levelHeight + 100;
    }
}