compareSlotMax = 1   -- all slots up to this one are used for comparing, order the blocks in decreasing probability

xRelPos = 0 -- "positive = forward"
yRelPos = 0 -- "positive = right"
zRelPos = 0 -- "positive = upwards"

facing = {
    x = 1,
    y = 0
}

holeCounter = {
    line = 0,
    hole = 0
}

function printPos()
    print("At (", xRelPos, ", ", yRelPos, ") facing (", facing.x, ", ", facing.y, ")")
end

-- helper functions for movement
function forward()
    if turtle.forward() then
        xRelPos = xRelPos + facing.x
        yRelPos = yRelPos + facing.y
    else
        if not turtle.dig() then
            turtle.attack()
        end
    end
end

function upwards()
    if turtle.up() then
        zRelPos = zRelPos + 1
        return true
    end
    return false
end

function downwards()
    if turtle.down() then
        zRelPos = zRelPos - 1
        return true
    end
    return false

function turnRight()
    turtle.turnRight()
    if facing.x == 1 and facing.y == 0 then -- facing forward
        facing.x = 0
        facing.y = 1
    elseif facing.x == 0 and facing.y == 1 then -- facing right
        facing.x = -1
        facing.y = 0
    elseif facing.x == -1 and facing.y == 0 then -- facing backward
        facing.x = 0
        facing.y = -1
    elseif facing.x == 0 and facing.y == -1 then -- facing left
        facing.x = 1
        facing.y = 0
    else 
        print("turnRight: This should never happen")
    end
end

function turnLeft()
    turtle.turnLeft()
    if facing.x == 1 and facing.y == 0 then -- facing forward
        facing.x = 0
        facing.y = -1
    elseif facing.x == 0 and facing.y == 1 then -- facing right
        facing.x = 1
        facing.y = 0
    elseif facing.x == -1 and facing.y == 0 then -- facing backward
        facing.x = 0
        facing.y = 1
    elseif facing.x == 0 and facing.y == -1 then -- facing left
        facing.x = -1
        facing.y = 0
    else 
        print("turnLeft: This should never happen")
    end
end

function faceTo(x, y)
    if (x == facing.x) and (y == facing.y) then
        return
    end
    if (x == 1 and facing.x == -1) or (x == -1 and facing.x == 1) or (y == 1 and facing.y == -1) or (y == -1 and facing.y == 1) then
        turnRight()
        turnRight()
    elseif (facing.y == -1 and x == 1) or (facing.y == 1 and x == -1) or (facing.x == 1 and y == 1) or (facing.x == -1 and y == -1) then
        turnRight()
    elseif (facing.y == -1 and x == -1) or (facing.y == 1 and x == 1) or (facing.x == 1 and y == -1) or (facing.x == -1 and y == 1) then
        turnLeft()
    else
        print("faceTo: This should never happen")
    end
end

function moveTo(x, y)
    if (yRelPos > y) then
        faceTo(0, -1)
        while yRelPos > y do
            forward()
        end
    elseif (yRelPos < y) then
        faceTo(0, 1)
        while yRelPos < y do
            forward()
        end
    end

    if (xRelPos > x) then
        faceTo(-1, 0)
        while xRelPos > x do
            forward()
        end
    elseif (xRelPos < x) then
        faceTo(1, 0)
        while xRelPos < x do
            forward()
        end
    end
end

function blockIsWorth()

    for i = 1, compareSlotMax do
        turtle.select(i)
        if turtle.compare() then
            return false
        end
    end

    return true
end

function checkForItems(z)

    dir = math.fmod(z, 2)

    -- alternatingly check relative facing (left, forward, right) and (right, forward, left) blocks, so at the end we can face backwards when going up and check without turning at all
    -- -> two turns per mined level
    if (dir == 0) then
        faceTo(0, -1)   -- just to be safe, but this should never really do anything except for the first level
        if blockIsWorth() then
            turtle.dig()
        end
        turnRight()
        if blockIsWorth() then
            turtle.dig()
        end
        turnRight()
        if blockIsWorth() then
            turtle.dig()
        end
    else
        faceTo(0, 1)
        if blockIsWorth() then
            turtle.dig()
        end
        turnLeft()
        if blockIsWorth() then
            turtle.dig()
        end
        turnLeft()
        if blockIsWorth() then
            turtle.dig()
        end
    end
end

-- Digs straight down right where it is, taking resources with it
function digHole()
    z = 0

    -- go down
    turtle.digDown()
    while downwards() do
        z = z + 1
        checkForItems(z)
        turtle.digDown()
    end

    -- go back up
    -- look at the remaining direction (-1, 0) and check blocks
    faceTo(-1, 0)
    while zRelPos < 0 do
        if blockIsWorth() then
            turtle.dig()
        end
        upwards()
    end
end

function returnItems()
    -- chest coordinates are -1, 0, so go to 0, 0 facing "backwards"
    moveTo(0, 0)

    faceTo(-1, 0)

    -- already facing right direction, put items
    for slot = compareSlotMax + 1, 16 do
        turtle.select(slot)
        turtle.drop()
    end
end

function moveToNext()
    xPos = 1
    yPos = 1

    -- find out where the next hole should be
    for i = 1, holeCounter.line do
        if math.fmod(i, 2) == 0 then
            xPos = xPos + 2
            yPos = 1
        else
            xPos = xPos + 3
            yPos = 0
        end
    end
    
    for i = 1, holeCounter.hole do
        xPos = xPos - 1
        yPos = yPos + 2
    end

    moveTo(xPos, yPos)

    -- update holeCounter
    -- if the xPos we calculated is 1 that means we need to start the next line
    if xPos == 0 then
        holeCounter.line = holeCounter.line + 1
        holeCounter.hole = 0
    else
        holeCounter.hole = holeCounter.hole + 1
    end

end

print("Starting...")

-- startup
while not xRelPos == 1 do
    forward()
end

while true do
    print("Digging Hole (", holeCounter.line, ", ", holeCounter.hole, ")")
    moveToNext()
    digHole()
    returnItems()
end