-- Heimdall116, University of Michigan, August 2014
    -- Stole several local functions from dan200's ComputerCraft 1.58 package.
    local tArgs = { ... }
    if #tArgs ~= 1 then
        print( "Usage: dome <radius>" )
        return
    end

    -- Read in the radius
    local radius = tonumber( tArgs[1] )
    if radius < 1 then
        print( "Radius must be positive" )
        return
    end

    -- To be implemented later
    local depth = 0
    local collected = 0
    local facing = 1
    local xRel = 0
    local yRel = 0

    local function collect()
        collected = collected + 1
        if math.fmod(collected, 25) == 0 then
            print( "Mined "..collected.." items." )
        end
    end

    local function tryDig()
        while turtle.detect() do
            if turtle.dig() then
                collect()
                sleep(0.5)
            else
                return false
            end
        end
        return true
    end

    local function tryDigUp()
        while turtle.detectUp() do
            if turtle.digUp() then
                collect()
                sleep(0.5)
            else
                return false
            end
        end
        return true
    end

    local function tryDigDown()
        while turtle.detectDown() do
            if turtle.digDown() then
                collect()
                sleep(0.5)
            else
                return false
            end
        end
        return true
    end

    local function refuel()
        local fuelLevel = turtle.getFuelLevel()
        if fuelLevel == "unlimited" or fuelLevel > 0 then
            return
        end

        local function tryRefuel()
            for n=1,16 do
                if turtle.getItemCount(n) > 0 then
                    turtle.select(n)
                    if turtle.refuel(1) then
                        turtle.select(1)
                        return true
                    end
                end
            end
            turtle.select(1)
            return false
        end

        if not tryRefuel() then
            print( "Add more fuel to continue." )
            while not tryRefuel() do
                sleep(1)
            end
            print( "Resuming Tunnel." )
        end
    end

    local function tryUp()
        refuel()
        while not turtle.up() do
            if turtle.detectUp() then
                if not tryDigUp() then
                    return false
                end
            elseif turtle.attackUp() then
                collect()
            else
                sleep( 0.5 )
            end
        end
        return true
    end

    local function tryDown()
        refuel()
        while not turtle.down() do
            if turtle.detectDown() then
                if not tryDigDown() then
                    return false
                end
            elseif turtle.attackDown() then
                collect()
            else
                sleep( 0.5 )
            end
        end
        return true
    end

    local function tryForward()
        refuel()
        while not turtle.forward() do
            if turtle.detect() then
                if not tryDig() then
                    return false
                end
            elseif turtle.attack() then
                collect()
            else
                sleep( 0.5 )
            end
        end
        return true
    end

    local function round(q)
        if q == 0 then return 0 end
        b = math.abs(q)
        if q < 0 then a = -1 else a = 1 end

        if b-math.floor(b) < .5 then
            return math.floor(b) * a
        else
            return math.ceil(b) * a
        end
    end

    local function face(f)
        while f ~= facing do
            turtle.turnRight()
            if facing == 4 then
                facing = 1
            else
                facing = facing + 1
            end
        end
    end

    local function face1(n)
    -- Re-orient the turtle WRT original facing: 1=forward; 2=right; 3=back; 4=left
        if n-facing == 0 then return
        elseif n-facing > 0 and n-facing < 3 then
            while n-facing ~= 0 do
                turtle.turnRight()
                facing = facing + 1
                if facing == 5 then facing = 1 end
            end
        else
            turtle.turnLeft()
            facing = facing - 1
            if facing == 0 then facing = 4 end
        end
    end

    local function goTo(x2,y2)
        local dx = round(x2-xRel)
        local dy = round(y2-yRel)

        if dx == 0 then
            -- don't bother turning
        elseif dx > 0 then
            face(1)
        else
            face(3)
        end

        for n = 1,math.abs(dx) do
            tryDig()
            tryForward()
        end

        if dy == 0 then
            -- don't turn
        elseif dy > 0 then
            face(4)
        else
            face(2)
        end

        for n = 1,math.abs(dy) do
            tryDig()
            turtle.forward()
        end

        xRel = xRel + dx
        yRel = yRel + dy
    end

    print( "Building dome..." )

    for h=1,radius do
        -- r is the "local" radius for height "h"
        local r = round(radius * math.cos((h-1)/radius * math.pi/2))
        print('r='..r)
        tryDigUp()
        turtle.up()

        -- Plot circle in increments of angle theta
        local theta = math.atan(1/r)

        for c = 0,(2*math.pi / theta) do
            xNew = r - round(r*math.cos(c*theta))
            yNew = round(r*math.sin(c*theta))
            goTo(xNew,yNew)
            turtle.placeDown()
        end
    end

print( "Work complete..." )