Organiser

local WHEREIS_CHANNEL = 420

local CHEST_BLOCK = "ironchest:BlockIronChest"

local activities = {
    COLLECT = 1, -- suck up the contents of the chest, then DROP
    DROP = 2, -- drop left, then drop right, then forward until the invetory is empty or movement is blocked
    RETURN = 3, -- go back to the chest until movement is blocked
}

local directions = {
    HOME_AWAY = 0,
    CHEST_RIGHT = 1,
    HOME_TOWARD = 2,
    CHEST_LEFT = 3
}

-- fix the modem bug
if not peripheral.find("modem") then
    -- first find an empty slot
    for i = 1, 16 do
        if turtle.getItemCount(i) == 0 then
            turtle.select(i)
            break
        elseif i == 16 then
            turtle.select(i)
            turtle.drop()
        end
    end
    turtle.equipLeft()
    turtle.equipLeft()
    turtle.equipRight()
    turtle.equipRight()
end

local state
local function loadState()
    local h = fs.open("organiser.state", "r")
    if h then
        state = textutils.unserialise(h.readAll())
        h.close()
    else
        state = {
            activity = activities.COLLECT,
            direction = directions.HOME_AWAY,
            startFuel = turtle.getFuelLevel()
        }
    end
end

local function saveState()
    local h = fs.open("organiser.state", "w")
    if h then
        h.write(textutils.serialise(state))
        h.close()
    end
end

local function turnTo(direction)
    local difference = direction - state.direction
    if math.abs(difference) >= 3 then
        difference = (difference - 2 * (difference / math.abs(difference))) * -1
    end
    if difference > 0 then
        for i = 1, difference do
            turtle.turnLeft()
            state.direction = (state.direction + 1) % 4
            saveState()
        end
    elseif difference < 0 then
        for i = 1, math.abs(difference) do
            turtle.turnRight()
            state.direction = (state.direction - 1) % 4
            saveState()
        end
    end
end

local function setActivity(activity)
    if not activity then error('act') end
    state.activity = activity
    saveState()
end

local funcs = {}

local function activity(activity)
    setActivity(activity)
    return funcs[activity]()
end

funcs[activities.COLLECT] = function()
    print("Collecting the melon...")
    turnTo(directions.HOME_TOWARD)
    local okay = turtle.suck()
    if not okay then
        print("Nothing to collect...")
        -- there is nothing to collect, wait 10 seconds and try again
        sleep(10)
        return activity(activities.COLLECT)
    end
    while turtle.suck() do end
    return activity(activities.DROP)
end

local function drop() -- return false if the chest is full, return true if the turtle is empty
    for i = 1, 16 do
        local okay, err = turtle.drop()
        if not okay then
            if err == "No space for items" then
                return false
            else
                return true
            end
        end
    end
    return true
end

funcs[activities.DROP] = function()
    print("Dropping the melon in chests")
    while true do
        turnTo(directions.CHEST_RIGHT)
        if drop() then
            break
        end
        turnTo(directions.CHEST_LEFT)
        if drop() then
            break
        end
        turnTo(directions.HOME_AWAY)
        if not turtle.forward() then
            break
        end
    end
    return activity(activities.RETURN)
end

funcs[activities.RETURN] = function()
    print("Heading toward chest")
    turnTo(directions.HOME_TOWARD)
    while turtle.forward() do end
    return activity(activities.COLLECT)
end

-- depart from the idle chest location
function resume()
    print("Resuming...")
    loadState()
    activity(state.activity)
end

parallel.waitForAll(function()
    resume()
    while true do
        sleep(delay)
        print("Starting fresh...")
        state.startFuel = turtle.getFuelLevel()
        state.isChestRight = false
        saveState()
        activity(activities.COLLECT)
    end
end, function()
    local modem = peripheral.find("modem")
    modem.open(WHEREIS_CHANNEL)
    while true do
        local event, side, channel, replyChannel, message = os.pullEvent("modem_message")
        if channel == WHEREIS_CHANNEL and message == "WHEREIS" then
            modem.transmit(replyChannel, channel, {os.getComputerID(), os.getComputerLabel(), gps.locate()})
        end
    end
end)