sphere

-- v. 1.0 : Build a sphere with radius r

local tArgs = {...}
if #tArgs < 1 then
    print("Usage : sphere <radius> \n        sphere <radius> <wallSlotId>")
end

local radius = tonumber(tArgs[1])
local slot = 0
if #tArgs > 1 then
    slot = tonumber(tArgs[2])
end

local FRONT = 0
local LEFT = 1
local BACK = 2
local RIGHT = 3

local x = 0
local y = 0
local z = -radius
local direction = 0

-- Fuel methods

local function checkFuel()
    local minFuelLevel = math.abs(x) + math.abs(y) + math.abs(z)

    if turtle.getFuelLevel() <= minFuelLevel then
        refuel()
    end

    if turtle.getFuelLevel() <= minFuelLevel then
        waitForFuel()
    end
end

local function waitForFuel()
    print("Waiting for fuel")

    while refuel() == false do
        os.sleep(1)
    end
end

local function refuel()
    local fueled = false
    for i=1,16 do
        if i ~= slot then
            turtle.select(i)
            fueled = fueled or turtle.refuel()
        end
    end
    return fueled
end

-- Inventory methods

local function checkItems()
    if slot ~= 0 and turtle.getItemCount(slot) < 5 then

        for i=1,16 do
            if i ~= slot then
                turtle.select(i)
                if turtle.compareTo(slot) then
                    turtle.transferTo(slot)
                end
            end
        end

        local wallItemMessageShown = false
        while turtle.getItemCount(slot) < 5 do
            os.sleep(1)
            if wallItemMessageShown == false then
                print("Waiting for more wall items")
                wallItemMessageShown = true
            end
        end
    end

    while true do
        local messageShown = false

        for i=1,16 do
            if i ~= slot then
                if turtle.getItemSpace(i) > 5 then
                    return
                end
            end
        end

        if messageShown == false then
            print("Please empty some items")
            messageShown = true
        end

        os.sleep(1)
    end
end

-- Move method

local function setDirection(targetDirection)
    local testDirection = direction
    local moveCountLeft = 0

    while testDirection ~= targetDirection do
        testDirection = testDirection + 1
        if testDirection > 3 then
            testDirection = 0
        end
        moveCountLeft = moveCountLeft + 1
    end

    testDirection = direction
    local moveCountRight = 0
    while testDirection ~= targetDirection do
        testDirection = testDirection - 1
        if testDirection < 0 then
            testDirection = 3
        end
        moveCountRight = moveCountRight + 1
    end

    if moveCountLeft < moveCountRight then
        for i=1,moveCountLeft do
            turtle.turnLeft()
        end
    else
        for i=1,moveCountRight do
            turtle.turnRight()
        end
    end

    direction = targetDirection
end

local function moveUp()
    checkFuel()
    checkItems()

    turtle.digUp()
    turtle.up()
end

local function moveDown()
    checkFuel()
    checkItems()

    turtle.digDown()
    turtle.down()
end

local function moveForward()
    checkFuel()
    checkItems()

    while turtle.forward() == false do
        turtle.dig()
        os.sleep(1)
    end
end

local function goto(targetX,targetY,targetZ)
    local currentX = x
    local currentY = y
    local currentZ = z



    if currentZ > targetZ then
        while currentZ > targetZ do
            moveDown()
            currentZ = currentZ - 1
        end
    else
        while currentZ < targetZ do
            moveUp()
            currentZ = currentZ + 1
        end
    end

    local doXFirst = math.abs(x) > math.abs(y)
    for i=1,2 do
        if (doXFirst and i == 1) or i == 2 then
            if currentX > targetX then
                setDirection(RIGHT)
                while currentX > targetX do
                    moveForward()
                    currentX = currentX - 1
                end
            else
                setDirection(LEFT)
                while currentX < targetX do
                    moveForward()
                    currentX = currentX + 1
                end
            end
        end

        if (doXFirst and i == 2) or i == 1 then
            if currentY > targetY then
                setDirection(BACK)
                while currentY > targetY do
                    moveForward()
                    currentY = currentY - 1
                end
            else
                setDirection(FRONT)
                while currentY < targetY do
                    moveForward()
                    currentY = currentY + 1
                end
            end
        end
    end

    x = targetX
    y = targetY
    z = targetZ
end

-- Drawing methods

local function testIsInShape(targetX,targetY,targetZ)
    local localRadius = radius - math.abs(targetZ)
    local targetRadius = math.abs(targetX) + math.abs(targetY)

    return targetRadius <= localRadius
end

local function checkWall()
    if slot ~= 0 then
        turtle.select(slot)

        if testIsInShape(x, y + 1, z) == false then
            setDirection(FRONT)
            if turtle.compare(slot) == false then
                turtle.dig()
                turtle.place()
            end
        end

        if testIsInShape(x + 1, y, z) == false then
            setDirection(LEFT)
            if turtle.compare(slot) == false then
                turtle.dig()
                turtle.place()
            end
        end

        if testIsInShape(x, y - 1, z) == false then
            setDirection(BACK)
            if turtle.compare(slot) == false then
                turtle.dig()
                turtle.place()
            end
        end

        if testIsInShape(x - 1, y, z) == false then
            setDirection(RIGHT)
            if turtle.compare(slot) == false then
                turtle.dig()
                turtle.place()
            end
        end
    end
end

-- Render
for i=-radius,radius do
    goto(0,0,i)
    for j=-radius,radius do
        for k=-radius,radius do
            local yValue = k
            if j % 2 == 0 then
                yValue = -k
            end

            if testIsInShape(j,yValue,i) then
                goto(j,yValue,i)
                checkWall()
            end
        end
    end
end