excavator

-- Digs a rectangular hole down to bedrock, or where water meets lava
-- creating a blocking layer of cobblestone. Dimensions are specified directly
-- below. Width starts at current block and extends rightward. Length starts
-- at the current block and extends forward.
length = 2
width = 2

x = 0
y = 0
z = 0
workx = 0
worky = 0
workz = 0
orientation = 0

function moveForward()
    -- Moves forward keeping track of location
    turtle.forward()
    if (orientation == 0) then
        z = z + 1
    elseif (orientation == 1) then
        x = x + 1
    elseif (orientation == 2) then
        z = z - 1
    elseif (orientation == 3) then
        x = x - 1
    else
        print("Error, invalid orientation.")
    end
end

function goDown()
    -- Moves down keeping track of location
    turtle.down()
    y = y - 1
end

function goUp()
    -- Moves up keeping track of location
    turtle.up()
    y = y + 1
end

function turnRight()
    -- Turns turtle to the right keeping track of location
    turtle.turnRight()
    orientation = (orientation + 1) % 4
end

function turnLeft()
    -- Turns turtle to the left keeping track of location
    turtle.turnLeft()
    orientation = orientation - 1
    if (orientation == -1) then
        orientation = 3
    end
end

function safeUp()
    if (not turtle.detectUp()) then
        goUp()
        return true
    end
    return false
end

function safeDown()
    if (not turtle.detectDown()) then
        goDown()
        return true
    end
    return false
end

function tryDown()
    turtle.digDown()
    return safeDown()
end

function progressUp()
    while not safeUp() do
        turtle.digUp()
    end
end

function progressDown()
    while not safeDown() do
        turtle.digDown()
    end
end

function safeForward()
    if (not turtle.detect()) then
        moveForward()
        return true
    end
    return false
end

function progressForward()
    while not safeForward() do
        turtle.dig()
    end
end

function comebackDirection()
    if (orientation == 0) then
        while z < 0 do
            progressForward()
        end
    elseif (orientation == 1) then
        while x < 0 do
            progressForward()
        end
    elseif (orientation == 2) then
        while (z > 0) do
            progressForward()
        end
    else
        while (x > 0) do
            progressForward()
        end
    end
end

function goToHeightZero()
    while (y < 0) do
        progressUp()
    end
    while (y > 0) do
        progressDown()
    end
end

function comeBack()
    workx = x
    worky = y
    workz = z
    for i=1, 4 do
        comebackDirection()
        turnLeft()
    end
    goToHeightZero()
end

function comeback()
    comeBack()
end

function backToWork()
    x = -workx
    y = -worky
    z = -workz
    for i=1, 4 do
        comebackDirection()
        turnRight()
    end
    goToHeightZero()
    x = workx
    y = worky
    z = workz
end

function unload()
    for i=1, 16 do
        turtle.select(i)
        turtle.drop(64)
    end
end

function dropOff()
    comeBack()
    turnRight()
    turnRight()
    unload()
    turnRight()
    turnRight()
    backToWork()
end

function unloadAndBackToStart()
    comeback()
    turnRight()
    turnRight()
    unload()
    turnRight()
    turnRight()
end

function goToDigCoreLocation(xlocation, zlocation)
    -- Go to digging location on x z grid
    for zmoveCounter=1, zlocation do
        progressForward()
    end
    turnRight()
    for xmoveCounter=1, xlocation do
        progressForward()
    end
    turnLeft()
end

function digCore()
    while (tryDown()) do
    end
end

function digCoreAtAndBackToStart(xlocation, zlocation)
    goToDigCoreLocation(xlocation, zlocation)
    digCore()
    unloadAndBackToStart()
end

function runJob()
    adjustedWidth = width - 1
    adjustedLength = length - 1
    for currentX=0, adjustedWidth do
        for currentZ=0, adjustedLength do
            digCoreAtAndBackToStart(currentX, currentZ)
        end
    end
end

runJob()