collidingEntities = filteredSystem("collidingEntitites", {
    velocity = T.XyPair,
    position = T.XyPair,
    size = T.XyPair,
    canCollideWith = T.BitMask,
    isSolid = Maybe(T.bool),
})

filteredSystem(
    "collisionDetection",
    { position = T.XyPair, size = T.XyPair, canBeCollidedBy = T.BitMask, isSolid = Maybe(T.bool) },
    -- Here, the entity, e, refers to some entity that a moving object may be colliding *into*
    function(e, _, system)
        for _, collider in pairs(collidingEntities.entities) do
            if
                (e ~= collider)
                and collider.canCollideWith
                and e.canBeCollidedBy
                and bit.band(collider.canCollideWith, e.canBeCollidedBy) ~= 0
            then
                local colliderTop = collider.position.y
                local colliderBottom = collider.position.y + collider.size.y
                local entityTop = e.position.y
                local entityBottom = entityTop + e.size.y

                local withinY = (entityTop > colliderTop and entityTop < colliderBottom)
                    or (entityBottom > colliderTop and entityBottom < colliderBottom)

                if
                    withinY
                    and collider.position.x < e.position.x + e.size.x
                    and collider.position.x + collider.size.x > e.position.x
                then
                    system.world:addEntity({ collisionBetween = { e, collider } })
                end
            end
        end
    end
)