function modrefuel()
    for i  = 1, 16 do
        turtle.select(i)
        if turtle.refuel(0) then
            print("Slot "..i.." is valid fuel.")
            turtle.refuel()
        end
    end
    turtle.select(1)
end

function digLine(length)
  local backCheck = false
  local forwardCheck = false
  for i = 2, length do
    while (forwardCheck == false) do
      turtle.dig()
      forwardCheck = turtle.forward()
    end
    forwardCheck = false
  end
  for i = 2, length do
    while (backCheck == false) do
      backCheck = turtle.back()
    end
    backCheck = false
  end
end

function digSquare(height, width)
  local upCheck = false
  local downCheck = false
  if width > 1 then
    digLine(width)
  end
  for i = 1, height do
    while (upCheck == false) do
      turtle.digUp()
      upCheck = turtle.up()
    end
    upCheck = false
    if width > 1 then
      digLine(width)
    end
  end
  for i = 1, height do
    while (downCheck == false) do
      turtle.digDown()
      downCheck = turtle.down()
    end
    downCheck = false
end

function mine(depth, height, width, chestX, chestY, chestZ)
  local backCheck = false
  local downCheck = false
  local forwardCheck = false
  local upCheck = false
  for i = 1, depth do
    print("Digging forward!")
    turtle.dig()
    while (forwardCheck == false) do
        turtle.dig()
        forwardCheck = turtle.forward()
    end
    forwardCheck = false
    turtle.turnRight()
    for i = 1, width do
      turtle.dig()
      while (forwardCheck == false) do
        turtle.dig()
        forwardCheck = turtle.forward()
      end
      forwardCheck = false
    end
    for i = 1, width do
      while (backCheck == false) do
        backCheck = turtle.back()
      end
      backCheck = false
    end
    turtle.turnLeft()
    for i = 1, height do
      print("Digging up!")
      turtle.digUp()
      while (upCheck == false) do
        turtle.digUp()
        upCheck = turtle.up()
      end
      upCheck = false
      print("Turning right!")
      turtle.turnRight()
      for i = 1, width do
        print("Digging wide, right!")
        turtle.dig()
        while (forwardCheck == false) do
            turtle.dig()
            forwardCheck = turtle.forward()
        end
        forwardCheck = false
      end
      for i = 1, width do
        print("Heading back!")
        while (backCheck == false) do
            backCheck = turtle.back()
        end
        backCheck = false
      end
      print("Turning left!")
      turtle.turnLeft()
    end
    for i = 1, height do
      print("Heading down!")
      while (downCheck == false) do
        turtle.digDown()
        downCheck = turtle.down()
      end
      downCheck = false
    end
    print("Checking for fuel...")
    modrefuel()
    print("Checking inventory full...")
    fullCheck(chestX, chestY, chestZ)
  end
end

function dropOff(chestX, chestY, chestZ)
    local chestCheck = false

    print("Inventory full, dropping off!")
    local turtleX, turtleY, turtleZ = gps.locate()
    if (turtleX == nil) or (turtleY == nil) or (turtleZ == nil) then
        print("GPS not functioning or out of range")
    end
    print("I am at (" ..turtleX.. ", " ..turtleY.. ", " ..turtleZ.. ")")
    shell.run("goto", chestX, chestZ, chestY)
    for i = 1, 16 do
        turtle.select(i)
        while (chestCheck == false) do
            chestCheck = turtle.dropDown()
            if (chestCheck == false) then
                print("Chest is full!")
                sleep(10)
            end
        end
        chestCheck = false
    end
    turtle.select(1)
    shell.run("goto", turtleX, turtleZ, turtleY)
end

function fullCheck(chestX, chestY, chestZ)
    if turtle.getItemCount(16) > 0 then
        dropOff(chestX, chestY, chestZ)
    end
end

local chestCheck
local chestX
local chestY
local chestZ
local turtleX
local turtleY
local turtleZ
local digDepth
local digHeight
local digWidth

--print("Input chest coordinates\n")
--print("X: ")
--chestX = io.read()
--print("\nZ: ")
--chestZ = io.read()
--print("\nY: ")
--chestY = io.read()
--print(chestX, chestY, chestZ)
--print("Input digging dimensions\n")
--print("Depth: ")
--digDepth = io.read()
--print("\nHeight: ")
--digHeight = io.read()
--print("\nWidth: ")
--digWidth = io.read()
--print(digDepth, digHeight, digWidth)
--print("Running mining protocol")
digSquare(4, 2)