Wheat Farmer

local layerCount = nil

local currentPosition = {
    x = 0;
    y = 0;
    z = 0;
}

local currentDirection = 3

local persisted = false

function readData(name)
    if fs.exists('/data/'..name) then
        local handle = fs.open('/data/'..name, 'r')
        local stuff = handle.readAll()
        handle.close()
        return textutils.unserialize(stuff)
    end

    return
end

function writeData(name, data)
    if not fs.exists('/data') then
        fs.makeDir('/data')
    end

    local handle = fs.open('/data/'..name, 'w')
    handle.write(textutils.serialize(data))
    handle.close()
end

function updatePosition(deltaX, deltaY, deltaZ)
    currentPosition.x = currentPosition.x + deltaX
    currentPosition.y = currentPosition.y + deltaY
    currentPosition.z = currentPosition.z + deltaZ

    writeData('position', currentPosition)
end

function updateDirection(deltaD)
    currentDirection = (currentDirection + deltaD - 1) % 4 + 1

    writeData('direction', currentDirection)
end

function updateLayerCount(layers)
    layerCount = layers

    writeData('layerCount', layerCount)
end

function loadData()
    local savedLayerCount = readData('layerCount')
    local savedPosition = readData('position')
    local savedDirection = readData('direction')

    if (savedLayerCount ~= nil) then
        layerCount = savedLayerCount or layerCount
        currentPosition = savedPosition or currentPosition
        currentDirection = savedDirection or currentDirection

        persisted = true
    end
end

function persist()
    loadData()

    if persisted then
        if currentDirection == 1 then
            turnRight()
        elseif currentDirection == 3 then
            turnLeft()
        elseif currentDirection == 4 then
            turnRight()
            turnRight()
        end

        if currentPosition.x > 0 then
            moveForward(currentPosition.x)
        elseif currentPosition.x < 0 then
            moveBack(-currentPosition.x)
        end

        turnLeft()

        if currentPosition.z > 0 then
            moveForward(currentPosition.z)
        elseif currentPosition.z < 0 then
            moveBack(-currentPosition.z)
        end

        if currentPosition.y > 0 then
            moveDown(currentPosition.y)
        elseif currentPosition.y < 0 then
            moveUp(-currentPosition.y)
        end

        storeItems()
    else
        turnRight()
        turtle.suck(64)
        turtle.suck(16)
        turnLeft()
    end
end

function moveForward(n)
    n = n or 1

    for i = 1, n do
        while not turtle.forward() do
            term.clear()
            print('turtle is stuck, please remove the block in front.')
            sleep(1)
        end
        term.clear()

        local dX = (currentDirection - 3) * ((currentDirection + 1) % 2)
        local dZ = (currentDirection - 2) * (currentDirection % 2)

        updatePosition(dX, 0, dZ)
    end
end

function moveBack(n)
    n = n or 1

    for i = 1, n do
        while not turtle.back() do
            term.clear()
            print('turtle is stuck, please remove the block behind.')
            sleep(1)
        end
        term.clear()

        local dX = -(currentDirection - 3) * ((currentDirection + 1) % 2)
        local dZ = -(currentDirection - 2) * (currentDirection % 2)

        updatePosition(dX, 0, dZ)
    end
end

function moveUp(n)
    n = n or 1

    for i = 1, n do
        while not turtle.up() do
            term.clear()
            print('turtle is stuck, please remove the block above.')
            sleep(1)
        end
        term.clear()

        updatePosition(0, 1, 0)
    end
end

function moveDown(n)
    n = n or 1

    for i = 1, n do
        while not turtle.down() do
            term.clear()
            print('turtle is stuck, please remove the block underneath.')
            sleep(1)
        end
        term.clear()

        updatePosition(0, -1, 0)
    end
end

function turnLeft()
    turtle.turnLeft()
    updateDirection(-1)
end

function turnRight()
    turtle.turnRight()
    updateDirection(1)
end

function refuel(level, overrideMoveCount)
    local moveCount = nil

    if overrideMoveCount~= nil then
        moveCount = overrideMoveCount
    else
        moveCount = 98 + level*6
    end

    fuelCount = math.ceil((moveCount - turtle.getFuelLevel()) / 80)

    if fuelCount <= 0 then
        return
    end

    turnLeft()
    turtle.select(16)

    while fuelCount > 0 do
        turtle.suck(fuelCount)
        fuelCount = fuelCount - turtle.getItemCount(16)
        turtle.refuel()

        if fuelCount ~= 0 then
            term.clear()
            print('missing '..fuelCount..' coal, please put coal in the chest')
            sleep(1)
        else
            term.clear()
            break
        end
    end

    turtle.select(1)
    turnRight()
end

function dropByName(name, dropCallback)
    dropCallback = dropCallback or turtle.drop

    for i = 1, 16 do
        local data = turtle.getItemDetail(i)

        if (data ~= nil) and (data.name == 'minecraft:'..name) then
            turtle.select(i)
            while not dropCallback() do
                term.clear()
                print('chest is full, please empty it.')
            end
        end
    end
end

function storeItems()
    dropByName('wheat', turtle.dropDown)

    turnLeft()
    dropByName('wheat_seeds', turtle.drop)
    turtle.select(1)
    turtle.suck(64)
    turtle.suck(16)

    turnLeft()
end

function selectSeeds()
    for i = 1, 16 do
        local data = turtle.getItemDetail(i)

        if (data ~= nil) and data.name == 'minecraft:wheat_seeds' then
            turtle.select(i)

            return
        end
    end
end

function replantOne()
    local _, data = turtle.inspectDown()

    if (data.state == nil) or (data.state.age == nil) then
        selectSeeds()
        turtle.placeDown()
    elseif data.state.age == 7 then
        turtle.digDown()
        selectSeeds()
        turtle.placeDown()
    end
end

function replantLayer(layer)
    refuel(layer)

    local y = (layer-1) * 3

    moveUp(y)
    moveForward()

    for x = 1, 9 do
        for z = 1, 8 do
            replantOne()
            moveForward()
        end

        replantOne()

        if x ~= 9 then
            if x % 2 == 1 then
                turnRight()
                moveForward()
                turnRight()
            else
                turnLeft()
                moveForward()
                turnLeft()
            end
        end
    end

    turnLeft()
    moveForward(8)
    turnLeft()
    moveForward(9)
    moveDown(y)

    storeItems()
end

function replantAll()
    for i = 1, layerCount do
        replantLayer(i)
    end
end

function waitToGrow()
    repeat
        local _, data = turtle.inspectDown()
        sleep(1)
    until (data.state == nil) or (data.state.age == 7) or (data.state.age == nil)
end

function watchCrops()
    refuel(nil, 2)
    moveForward()
    waitToGrow()
    moveBack()
    turtle.select(1)
end

function main()
    term.clear()

    persist()

    if not persisted then
        print('Enter layer count: ')
        local input = nil

        while true do
            input = tonumber(read())

            if (input == nil) or (math.floor(input) ~= input) then
                print('input should be an integer.')
            else
                updateLayerCount(input)
                term.clear()
                break
            end
        end
    end

    while true do
        watchCrops()
        replantAll()
    end
end

main()