simple Entitas damage system

FireDamageSystem.CS

using Entitas;
using UnityEngine;

public class FireDamageSystem : IExecuteSystem
{
    readonly IGroup<GameEntity> _haveFireEntities;

    public FireDamageSystem(Contexts contexts)
    {
        _haveFireEntities = contexts.game.GetGroup(GameMatcher.Fire);
    }

    public void Execute()
    {
        foreach (GameEntity haveFireEntity in _haveFireEntities.GetEntities())
        {
            haveFireEntity.ReplaceHealth(haveFireEntity.health.Value - haveFireEntity.fire.Strength);
        }
    }
}