local tArgs = { ... }
if #tArgs ~= 1 then
    print( "Usage: excavate <diameter>" )
    return
end

-- Mine in a quarry pattern until we hit something we can't dig
local size = tonumber( tArgs[1] )
if size < 1 then
    print( "Excavate diameter must be positive" )
    return
end

local depth = 0
local collected = 0

local xPos,zPos = 0,0
local xDir,zDir = 0,1

local function dropUseless()
    local x = turtle.getItemCount(1);
    if (x > 1) then
        turtle.drop(x-1);
    end
end

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

    for n=1,9 do
        if turtle.getItemCount(n) == 0 then
            return true
        end
    end

    dropUseless();

    print( "No empty slots left." )
    return false
end

local function tryForwards()
    while not turtle.forward() do
        if turtle.dig() then
            if not collect() then
                return false
            end
        else
            -- give sand a chance to fall
            sleep(0.8)
            if turtle.dig() then
                if not collect() then
                    return false
                end
            else
                return false
            end
        end
    end
    xPos = xPos + xDir
    zPos = zPos + zDir
    return true
end

local function tryDown()
    if not turtle.down() then
        if turtle.digDown() then
            if not collect() then
                return false
            end
        end
        if not turtle.down() then
            return false
        end
    end
    depth = depth + 1
    if math.fmod( depth, 10 ) == 0 then
        print( "Descended "..depth.." metres." )
    end
    return true
end

local function turnLeft()
    turtle.turnLeft()
    xDir, zDir = -zDir, xDir
end

local function turnRight()
    turtle.turnRight()
    xDir, zDir = zDir, -xDir
end

print( "Excavating..." )

local reseal = false
if turtle.digDown() then
    reseal = true
end

local alternate = 0
local done = false
while not done do
    for n=1,size do
        for m=1,size-1 do
            if not tryForwards() then
                done = true
                break
            end
        end
        if done then
            break
        end
        if n<size then
            if math.fmod(n + alternate,2) == 0 then
                turnLeft()
                if not tryForwards() then
                    done = true
                    break
                end
                turnLeft()
            else
                turnRight()
                if not tryForwards() then
                    done = true
                    break
                end
                turnRight()
            end
        end
    end
    if done then
        break
    end

    if size > 1 then
        if math.fmod(size,2) == 0 then
            turnRight()
        else
            if alternate == 0 then
                turnLeft()
            else
                turnRight()
            end
            alternate = 1 - alternate
        end
    end

    if not tryDown() then
        done = true
        break
    end
end

print( "Returning to surface..." )

-- Return to where we started
while depth > 0 do
    if turtle.up() then
        depth = depth - 1
    elseif turtle.digUp() then
        collect()
    else
        sleep( 0.5 )
    end
end

if xPos > 0 then
    while xDir ~= -1 do
        turnLeft()
    end
    while xPos > 0 do
        if turtle.forward() then
            xPos = xPos - 1
        elseif turtle.dig() then
            collect()
        else
            sleep( 0.5 )
        end
    end
end

if zPos > 0 then
    while zDir ~= -1 do
        turnLeft()
    end
    while zPos > 0 do
        if turtle.forward() then
            zPos = zPos - 1
        elseif turtle.dig() then
            collected = collected + 1
        else
            sleep( 0.5 )
        end
    end
end
while zDir ~= 1 do
    turnLeft()
end

-- Seal the hole
if reseal then
    turtle.placeDown()
end