stripmine.lua

local x = 0
local y = 0
local z = 0
local dir = "north"

function sortFuel()
    local data = turtle.getItemDetail(16)
    if data ~= nil then
        if data.name ~= "minecraft:coal" then
            turtle.select(16)
            sleep(0.25)
            turtle.drop()
            sleep(0.25)
            turtle.select(1)
            sleep(0.25)
        end
    end
    for i = 1,15 do
        data = turtle.getItemDetail(i)
        if data ~= nil then
            if data.name == "minecraft:coal" then
                turtle.select(i)
                turtle.transferTo(16)
                return
            end
        end
    end
end

function saveHere()
    local file = fs.open("here","w")
    file.writeLine(tostring(x).."\n"..tostring(y).."\n"..tostring(z).."\n"..dir)
    file.close()
    print("x:"..tostring(x)..", y:"..tostring(y)..", z:"..tostring(z))
end

function right()
    if dir == "north" then
        dir = "east"
    elseif dir == "east" then
        dir = "south"
    elseif dir == "south" then
        dir = "west"
    else
        dir = "north"
    end
    turtle.turnRight()
    saveHere()
end

function left()
    if dir == "north" then
        dir = "west"
    elseif dir == "west" then
        dir = "south"
    elseif dir == "south" then
        dir = "east"
    else
        dir = "north"
    end
    turtle.turnLeft()
    saveHere()
end

function forward()
    if turtle.getFuelLevel() < 500 then
        sortFuel()
        turtle.select(16)
        sleep(0.25)
        while turtle.getItemCount(16) > 2 and turtle.getFuelLevel() < 1000 do
            if turtle.getItemCount(16) > 2 then
                turtle.refuel(1)
            end
        end
        sleep(0.25)
    end
    if dir == "north" then
        z = z - 1
    elseif dir == "south" then
        z = z + 1
    elseif dir == "east" then
        x = x + 1
    else
        x = x - 1
    end
    if turtle.detect() then
        if string.find(block(),"turtle") then
            if math.random(1,2) == 2 then
                down()
                forward()
                up()
                return
            else
                up()
                forward()
                down()
                return
            end
        else
           repeat
               dig()
               sleep(0.5)
           until not turtle.detect()
        end
   end
   repeat
       dig()
   until turtle.forward()
   saveHere()
end

function back()
    if dir == "north" then
        z = z + 1
    elseif dir == "south" then
        z = z - 1
    elseif dir == "east" then
        x = x - 1
    else
        x = x + 1
    end
    repeat
    until turtle.back()
    saveHere()
end

function down()
    local tries = 250
    repeat
        digDown()
        tries = tries-1
    until turtle.down() or tries < 0
    if not (tries < 0) then
        y = y - 1
    end
    saveHere()
end

function up()
    repeat
        digUp()
    until turtle.up()
    y = y+1
    saveHere()
end

if fs.exists("here") then
    local file = fs.open("here","r")
    x = tonumber(file.readLine())
    y = tonumber(file.readLine())
    z = tonumber(file.readLine())
    dir = file.readLine()
    file.close()
else
    local file = fs.open("here","w")
    file.writeLine("0\n0\n0\nnorth")
    file.close()
end

function block(o)
    local d,data = turtle.inspect()
    if o ~= nil then
        if o == "up" then
            d,data = turtle.inspectUp()
        else
            d,data = turtle.inspectDown()
        end
    end
    if not d then
        return "air"
    else
        return data.name
    end
end

function dig()

    while string.find(block(),"turtle")
        sleep(0.5)
    end
    turtle.dig()
end

function digUp()
    repeat
    sleep(0.5)
    until not string.find(block("up"),"turtle")
    turtle.digUp()
end

function digDown()
    repeat
    sleep(0.5)
    until not string.find(block("down"),"turtle")
    turtle.digDown()
end

function vien()
    if string.find(block(),"ore") then
        dig()
        forward()
        vien()
        back()
    end
    right()
    if string.find(block(),"ore") then
        dig()
        forward()
        vien()
        back()
    end
    right()
    right()
    if string.find(block(),"ore") then
        dig()
        forward()
        vien()
        back()
    end
    right()
    if string.find(block("up"),"ore") then
        digUp()
        up()
        vien()
        down()
    end

    if string.find(block("down"),"ore") then
        digDown()
        down()
        vien()
        up()
    end
end

function goHome()
    if x ~= 0 or y ~= 0 or z ~= 0 or dir ~= "north" then
        if x > 0 then
            if dir ~= "west" then
                repeat
                    right()
                until dir == "west"
            end
            forward()
        elseif x < 0 then
            if dir ~= "east" then
                repeat
                    right()
                until dir == "east"
            end
            forward()
        elseif z > 0 then
            if dir ~= "north" then
                repeat
                    right()
                until dir == "north"
            end
            forward()
        elseif z < 0 then
            if dir ~= "south" then
                repeat
                    right()
                until dir == "south"
            end
        elseif y > 0 then
            down()
        elseif y < 0 then
            up()
        elseif dir ~= north then
            right()
        end
        goHome()
    else
        print("home!")
    end
end

function dump()
    for i = 1,15 do
        turtle.select(i)
        sleep(0.25)
        turtle.drop()
    end
    turtle.select(1)
end

function shouldGoHome()
    local dist = math.abs(x)+math.abs(y)+math.abs(z)
    if (dist*2) > turtle.getFuelLevel() or dist > 150 then
        return true
    end
    for i = 1,15 do
        if turtle.getItemCount(i) == 0 then
            return false
        end
    end
    return true
end

goHome()
right()
right()

while turtle.getFuelLevel() > 100 do
    turtle.dig()
    forward()
    left()
    if turtle.detect() then
        while not shouldGoHome() do
            dig()
            forward()
            vien()
        end
        goHome()
        dump()
        right()
        right()
    else
        right()
        dig()
        forward()
        right()
        if turtle.detect() then
            while not shouldGoHome() do
                dig()
                forward()
                vien()
            end
            goHome()
            dump()
            right()
            right()
        else
            left()
        end
    end
end

print("no fuel!")