slime/src/systems/MovementSystem.ts

import { System } from '../core/System.ts';
import { SystemName, ComponentType } from '../core/Constants.ts';
import type { Entity } from '../core/Entity.ts';
import type { Position } from '../components/Position.ts';
import type { Velocity } from '../components/Velocity.ts';
import type { Health } from '../components/Health.ts';

/**
 * System responsible for moving entities based on their velocity and handling collisions.
 */
export class MovementSystem extends System {
  constructor() {
    super(SystemName.MOVEMENT);
    this.requiredComponents = [ComponentType.POSITION, ComponentType.VELOCITY];
    this.priority = 10;
  }

  /**
   * Update the position of entities based on their velocity, applying friction and collision detection.
   * @param deltaTime - Time elapsed since last frame in seconds
   * @param entities - Entities matching system requirements
   */
  process(deltaTime: number, entities: Entity[]): void {
    entities.forEach((entity) => {
      const position = entity.getComponent<Position>(ComponentType.POSITION);
      const velocity = entity.getComponent<Velocity>(ComponentType.VELOCITY);
      const health = entity.getComponent<Health>(ComponentType.HEALTH);

      if (!position || !velocity) return;

      if (velocity.lockTimer > 0) {
        velocity.lockTimer -= deltaTime;
        if (velocity.lockTimer <= 0) {
          velocity.lockTimer = 0;
          velocity.isLocked = false;
        }
      }

      const isProjectile = health && health.isProjectile;

      if (!isProjectile && !velocity.isLocked) {
        const speed = Math.sqrt(velocity.vx * velocity.vx + velocity.vy * velocity.vy);
        if (speed > velocity.maxSpeed) {
          const factor = velocity.maxSpeed / speed;
          velocity.vx *= factor;
          velocity.vy *= factor;
        }
      }

      const tileMap = this.engine.tileMap;

      const nextX = position.x + velocity.vx * deltaTime;
      if (tileMap && tileMap.isSolid(nextX, position.y)) {
        velocity.vx = 0;
        if (velocity.isLocked) {
          velocity.lockTimer = 0;
          velocity.isLocked = false;
        }
      } else {
        position.x = nextX;
      }

      const nextY = position.y + velocity.vy * deltaTime;
      if (tileMap && tileMap.isSolid(position.x, nextY)) {
        velocity.vy = 0;
        if (velocity.isLocked) {
          velocity.lockTimer = 0;
          velocity.isLocked = false;
        }
      } else {
        position.y = nextY;
      }

      if (!isProjectile) {
        const friction = velocity.isLocked ? 0.98 : 0.9;
        velocity.vx *= Math.pow(friction, deltaTime * 60);
        velocity.vy *= Math.pow(friction, deltaTime * 60);
      }

      if (tileMap) {
        const mapWidth = tileMap.cols * tileMap.tileSize;
        const mapHeight = tileMap.rows * tileMap.tileSize;

        if (position.x < 0) {
          position.x = 0;
          velocity.vx = 0;
        } else if (position.x > mapWidth) {
          position.x = mapWidth;
          velocity.vx = 0;
        }

        if (position.y < 0) {
          position.y = 0;
          velocity.vy = 0;
        } else if (position.y > mapHeight) {
          position.y = mapHeight;
          velocity.vy = 0;
        }
      } else {
        const canvas = this.engine.canvas;
        if (position.x < 0) {
          position.x = 0;
          velocity.vx = 0;
        } else if (position.x > canvas.width) {
          position.x = canvas.width;
          velocity.vx = 0;
        }

        if (position.y < 0) {
          position.y = 0;
          velocity.vy = 0;
        } else if (position.y > canvas.height) {
          position.y = canvas.height;
          velocity.vy = 0;
        }
      }
    });
  }
}