God-awful code

-- what's on screen is sent by other systems to this sytem, then what's done is acquired by other systems from this system
-- eg: inventory gets what's on the ground that can be picked up, sends that to ui, ui handles any inputs, wills takes those inputs and makes them into actions and then inventory takes those actions and makes them work

local concord = require("lib.concord")
local ui = concord.system({camera = {"camera", "inventory"}})

function ui:update(dt)
    local camera = self.camera[1]

    self.inventoryGrids = {}

    if camera then
        local cameraInventoryItems = {}
        for i, v in ipairs(camera.inventory.items) do
            cameraInventoryItems[i] = v
        end
        self.inventoryGrids.cameraInventory = {128, 20, 10, 10, cameraInventoryItems, camera.inventory.capacity}
    end
    if self.cameraPickupables then
        self.inventoryGrids.cameraPickupables = {20, 20, 10, 10, self.cameraPickupables, #self.cameraPickupables}
    end

    if not camera or not (camera and camera.inventory.isOpen) then
        self.currentInventoryGrid, self.currentInventoryGridSelector, self.selectedItem, self.selectedItemPos = nil
    end
    if self.changeGrid or not self.currentInventoryGrid then
        if camera and camera.inventory.isOpen then
            if not self.currentInventoryGridSelector then
                self.currentInventoryGridSelector = self.inventoryGrids.cameraInventory and "main"
            elseif self.currentInventoryGridSelector == "main" then
                if self.inventoryGrids.cameraPickupables then
                    self.currentInventoryGridSelector = "pickupables"
                    self.selectedItem, self.selectedItemPos = nil
                end
            elseif self.currentInventoryGridSelector == "pickupables" then
                if self.inventoryGrids.cameraInventory then
                    self.currentInventoryGridSelector = "main"
                    self.selectedItem, self.selectedItemPos = nil
                end
            end
        end
    end

    if self.currentInventoryGridSelector == "main" then
        self.currentInventoryGrid = self.inventoryGrids.cameraInventory
    elseif self.currentInventoryGridSelector == "pickupables" then
        self.currentInventoryGrid = self.inventoryGrids.cameraPickupables
    else
        self.currentInventoryGrid = nil
    end

    if self.currentInventoryGrid then
        if #self.currentInventoryGrid[5] == 0 then
            self.selectedItemPos = nil
            self.selectedItem = nil
        else
            if self.selectedItem then
                self.selectedItemPos = nil
                for i, v in ipairs(self.currentInventoryGrid[5]) do
                    if v == self.selectedItem then
                        self.selectedItemPos = i
                    end
                end
                if not self.selectedItemPos then
                    self.selectedItem = nil
                end
            end
            if not self.selectedItemPos then
                -- if self.selectorMove then
                    self.selectedItemPos = 1
                -- end
            elseif self.selectorMove == "up" then
                self.selectedItemPos = math.max(self.selectedItemPos - self.currentInventoryGrid[1], 1)
            elseif self.selectorMove == "down" then
                self.selectedItemPos = math.min(self.selectedItemPos + self.currentInventoryGrid[1], #self.currentInventoryGrid[5])
            elseif self.selectorMove == "left" then
                self.selectedItemPos = math.max(self.selectedItemPos - 1, 1)
            elseif self.selectorMove == "right" then
                self.selectedItemPos = math.min(self.selectedItemPos + 1, #self.currentInventoryGrid[5])
            end
            if self.selectedItemPos then
                self.selectedItem = self.currentInventoryGrid[5][self.selectedItemPos]
            end
        end
    end

    if self.select and self.selectedItem then
        local moved = false
        if self.currentInventoryGridSelector == "pickupables" then
            if self:getWorld().inventory:giveItem(camera, self.selectedItem) then
                self:getWorld():removeEntity(self.selectedItem)
                moved = true
            end
        elseif self.currentInventoryGridSelector == "main" then
            if camera.position then
                local item = self:getWorld().inventory:takeItem(camera, self.selectedItem)
                self:getWorld().map:addItemToWorld(camera.position.x, camera.position.y, item)
                moved = true
            end
        end
        if moved then
            table.remove(self.currentInventoryGrid[5], self.selectedItemPos)
            self.selectedItem.moved = true -- necessary?
            if #self.currentInventoryGrid[5] > 0 then
                self.selectedItemPos = math.min(self.selectedItemPos, #self.currentInventoryGrid[5])
                self.selectedItem = self.currentInventoryGrid[5][self.selectedItemPos]
            else
                self.selectedItem = nil
                self.selectedItemPos = nil
            end
        end
    end

    if self.selectedItemPos then
        self.currentInventoryGrid[7] = self.selectedItemPos
    end

    for _, v in pairs(self.inventoryGrids) do
        v[8] = v == self.currentInventoryGrid
    end

    self.cameraPickupables = nil
    self.changeGrid = nil
    self.selectorMove = nil
    self.select = nil
end

return ui