COMPUTERCRAFT: Point of sale machine for potato vending machine

pos.lua

-- Globals
STATES = {}
CURRENT_STATE = nil

NUM_SLOTS = 16

PRICES = {
    ["minecraft:coal"] = 1,
    ["minecraft:iron_ingot"] = 6,
    ["minecraft:diamond"] = 45,
    ["minecraft:netherite_ingot"] = 100,
    ["minecraft:bone_meal"] = 2,
    ["minecraft:arrow"] = 4

}

-- Utils
function succ()
    for i = 1, NUM_SLOTS, 1 do
        turtle.suck()
    end
end

function empty_inventory()
    for i = 1, NUM_SLOTS, 1 do
        turtle.select(i)
        turtle.drop()
    end
end

-- State machine
function sm_switch_states(new_state, args)
    
    if (CURRENT_STATE ~= nil) then
        CURRENT_STATE:exit()
    end

    CURRENT_STATE = new_state
    CURRENT_STATE:enter(args)
end

-- States

-- Idle: Waits for someone to throw it items
IDLE_STATE = {}

function IDLE_STATE:enter(args)
    empty_inventory()
end

function IDLE_STATE:execute()
    -- Succ then check inventory for changes. Can't use event because it is blocking.
    succ()

    for i = 1, NUM_SLOTS, 1 do
        local x = turtle.getItemDetail(i)
        if (x ~= nil) then
            sm_switch_states(STATES['exchange'], nil);
            return
        end
    end

    os.sleep(0.25)
end

function IDLE_STATE:exit()
    -- Do nothing
end

-- Exchange: Calculates the value of items in inventory and drops them into store chest
EXCHANGE_STATE = {}

function EXCHANGE_STATE:enter(args)
    -- Do nothing
end

function EXCHANGE_STATE:execute()
    -- Go through inventory and calculate value
    local value = 0 

    for i = 1, NUM_SLOTS, 1 do
        x = turtle.getItemDetail(i)
        if (x ~= nil) then

            if PRICES[x["name"]] ~= nil then
                value = value + (x['count'] * PRICES[x["name"]])
                turtle.dropDown()
            else
                turtle.drop()
            end
        end
    end

    if (value > 0) then 
        sm_switch_states(STATES['dispense'], value)
        return
    else
        sm_switch_states(STATES['idle'], nil)
        return
    end
end

function EXCHANGE_STATE:exit()
    -- Make sure inventory is empty
    empty_inventory()
end

-- Dispense: Grab potatoes from the chest and dispense them
DISPENSE_STATE = { num_potatoes = 0 }

function DISPENSE_STATE:enter(args)
    if (args == 0 or not args) then 
        sm_switch_states(STATES['idle'], nil)
        return
    end

    DISPENSE_STATE.num_potatoes = args
end

function DISPENSE_STATE:execute()
    while (DISPENSE_STATE.num_potatoes > 0) do
        local num_thrown = DISPENSE_STATE:grab_and_throw(DISPENSE_STATE.num_potatoes)
        DISPENSE_STATE.num_potatoes = DISPENSE_STATE.num_potatoes - num_thrown
    end

    sm_switch_states(STATES['idle'], nil)
    return
end

function DISPENSE_STATE:grab_and_throw(num_to_grab)
    turtle.turnRight()
    turtle.turnRight()

    for i = 1, math.floor(num_to_grab/64), 1 do
        success = turtle.suck(64)
        if not success then break end
    end

    turtle.suck(num_to_grab%64)

    -- Check how many potatoes we're actually going to throw
    local num_thrown = 0

    for i = 1, NUM_SLOTS, 1 do
        x = turtle.getItemCount(i)
        num_thrown = num_thrown + x
    end

    turtle.turnLeft()
    turtle.turnLeft()
    empty_inventory()

    return num_thrown
end

function DISPENSE_STATE:exit()
    -- Make sure inventory is empty
    empty_inventory()
end

-- Main thread

STATES['idle'] = IDLE_STATE
STATES['exchange'] = EXCHANGE_STATE
STATES['dispense'] = DISPENSE_STATE

sm_switch_states(STATES['idle'], nil)

while (true) do
    CURRENT_STATE:execute()
end