Camera = {
    pan = {
        x = 0,
        y = 0,
    },
}

expireBelowScreenSystem = filteredSystem("expireBelowScreen", { position = T.XyPair, expireBelowScreenBy = T.number })

local focusPriority = {}

cameraPanSystem = filteredSystem("cameraPan", { focusPriority = T.number, position = T.XyPair }, function(e, _)
    if e.focusPriority >= focusPriority.priority then
        focusPriority.position = e.position
    end
end)

function cameraPanSystem.preProcess()
    focusPriority.priority = 0
    focusPriority.position = { x = 0, y = 0 }
end

function cameraPanSystem:postProcess()
    Camera.pan.x = math.max(0, focusPriority.position.x - 200)
    Camera.pan.y = math.min(0, focusPriority.position.y - 120)
    -- TODO: set draw offset

    for _, entity in pairs(expireBelowScreenSystem.entities) do
        if entity.position.y - (Camera.pan.y + 240) > entity.expireBelowScreenBy then
            self.world:removeEntity(entity)
        end
    end
end

local cameraTopIsh, cameraBottomIsh

local enableNearCameraY = filteredSystem(
    "enableNearCameraY",
    { enableNearCameraY = Arr(T.Entity) },
    function(e, _, system)
        if e.position.y > cameraTopIsh and e.position.y < cameraBottomIsh then
            for _, enable in ipairs(e.enableNearCameraY) do
                enable.velocity = e.velocity
                system.world:addEntity(enable)
            end
            system.world:removeEntity(e)
        end
    end
)

local within = 1000
function enableNearCameraY:preProcess()
    cameraTopIsh = Camera.pan.y - within
    cameraBottomIsh = Camera.pan.y + 240 + within
end