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DIRECTIONS = {"north", "east", "south", "west"}
NORTH, EAST, SOUTH, WEST, UP, DOWN = 1, 2, 3, 4, 5, 6
DELTA = {vector.new(0, 0, -1), vector.new(1, 0, 0), vector.new(0, 0, 1), vector.new(-1, 0, 0), vector.new(0, 1, 0), vector.new(0, -1, 0)}

BLOCKS_TO_MINE = {
  ["minecraft:diamond_ore"]=true,
  ["minecraft:coal_ore"]=true,
}

BLOCKS_PER_CHUNK = 16
MAX_LOADED_CHUNKS_PER_DIRECTION = 20
FUEL_PER_COAL = 80
FUEL_SAFETY_MARGIN = 1 * FUEL_PER_COAL

local start_pos = vector.new()  -- FILL IN BEFORE START
local current_direction = NORTH -- FILL IN BEFORE START
local current_pos = start_pos


function info()
  print("-------------------------")
  print("XYZ:", current_pos.x, "/", current_pos.y, "/", current_pos.z)
  print("Facing: "..DIRECTIONS[current_direction])
  print("Fuel Level: "..turtle.getFuelLevel())
  print("-------------------------")
end

function calculate_rotation(dir, amount)
  local d = dir - 1
  d = (d + amount) % 4
  return d + 1
end

function rotate_right(amount)
  local amount = amount or 1

  for i=1, amount do
    turtle.turnRight()
  end

  current_direction = calculate_rotation(current_direction, amount)
end

function rotate_left(amount)
  local amount = amount or 1

  for i=1, amount do
    turtle.turnLeft()
  end

  current_direction = calculate_rotation(current_direction, -amount)
end

function face(direction)
  if current_direction == direction then
    return
  elseif calculate_rotation(current_direction, 1) == direction then
    rotate_right()
  elseif calculate_rotation(current_direction, -1) == direction then
    rotate_left()
  else
    rotate_right(2)
  end
end

function move_forward(amount, dig)
  local amount = amount or 1
  local dig = dig or false

  for i=1, amount do
    while turtle.detect() do
      if dig then
        turtle.dig()
      else
        print("Stepbro I'm Stuck! (in front)")
      end
    end

    turtle.forward()
    current_pos = current_pos + DELTA[current_direction]
    info()
  end
end

function move_backward(amount, dig)
  rotate_right(2)
  move_forward(amount, dig)
  rotate_left(2)
end

function move_right(amount, dig)
  rotate_right()
  move_forward(amount, dig)
  rotate_left()
end

function move_left(amount, dig)
  rotate_left()
  move_forward(amount, dig)
  rotate_right()
end

function move_up(amount, dig)
  local amount = amount or 1
  local dig = dig or false

  for i=1, amount do
    while turtle.detectUp() do
      if dig then
        turtle.digUp()
      else
        print("Stepbro I'm Stuck! (above)")
      end
    end

    turtle.up()
    current_pos = current_pos + DELTA[UP]
    info()
  end
end

function move_down(amount, dig)
  local amount = amount or 1
  local dig = dig or 1

  for i=1, amount do
    while turtle.detectDown() do
      if dig then
        turtle.digDown()
      else
        print("Stepbro I'm Stuck! (below)")
      end
    end

    turtle.down()
    current_pos = current_pos + DELTA[DOWN]
    info()
  end
end

function manhattan_distance(pos1, pos2)
  return math.abs(pos1.x - pos2.x) + math.abs(pos1.y - pos2.y) + math.abs(pos1.z - pos2.z)
end

function get_available_fuel()
  local available_fuel = turtle.getFuelLevel()

  for i=1, 16 do
    local item = turtle.getItemDetail(i)

    if item and item.name == "minecraft:coal" then
      available_fuel = available_fuel + item.count * FUEL_PER_COAL
    end
  end

  return available_fuel
end

function has_ore_in_vicinity()
  blocks = {}

  table.insert(blocks, select(2, turtle.inspectDown()).name)
  table.insert(blocks, select(2, turtle.inspectUp()).name)

  table.insert(blocks, select(2, turtle.inspect()).name)
  rotate_left()
  table.insert(blocks, select(2, turtle.inspect()).name)
  rotate_right(2)
  table.insert(blocks, select(2, turtle.inspect()).name)
  rotate_left()

  for _, block in ipairs(blocks) do
    if BLOCKS_TO_MINE[block] ~= nil then
      return true
    end
  end

  return false
end

function mine_vein(depth, visited)
  local visited = visited or {}
  if depth == 0 then return end

  local local_start_dir = current_direction

  -- Forward/Backward/Left/Right
  for i=0, 3 do
    local new_dir = calculate_rotation(local_start_dir, i)
    local block = (current_pos + DELTA[new_dir]):tostring()

    if visited[block] == nil then
      visited[block] = true

      face(new_dir)

      local not_air, block_data = turtle.inspect()
      if not_air and BLOCKS_TO_MINE[block_data.name] ~= nil then
        move_forward(1, true)
        mine_vein(depth - 1, visited)
        face(calculate_rotation(new_dir, 2))
        move_forward(1, true)
      end
    end
  end

  -- Up/Down
  local block = (current_pos + DELTA[UP]):tostring()
  if visited[block] == nil then
    visited[block] = true

    local not_air, block_data = turtle.inspectUp()
    if not_air and BLOCKS_TO_MINE[block_data.name] ~= nil then
      move_up(1, true)
      mine_vein(depth - 1, visited)
      move_down(1, true)
    end
  end

  local block = (current_pos + DELTA[DOWN]):tostring()
  if visited[block] == nil then
    visited[block] = true

    local not_air, block_data = turtle.inspectDown()
    if not_air and BLOCKS_TO_MINE[block_data.name] ~= nil then
      move_down(1, true)
      mine_vein(depth - 1, visited)
      move_up(1, true)
    end
  end

  face(local_start_dir)
end

function go_down(level)
  move_down(level, true)
end

function go_up()
  while current_pos.y ~= start_pos.y do
    move_up(1, true)
  end
end

function go_back_to_mine_start()
  rotate_right(2)

  while current_pos.x ~= start_pos.x and current_pos.z ~= start_pos.z do
    move_forward(1, true)
  end
end

function should_return_home()
  local distance = manhattan_distance(current_pos, start_pos)
  local available_fuel = get_available_fuel()

  if available_fuel - FUEL_SAFETY_MARGIN <= distance then
    return true
  end

  return false
end

function strip_mine(distance)
  distance = distance or BLOCKS_PER_CHUNK * MAX_LOADED_CHUNKS_PER_DIRECTION
  local distance_mined = 0

  while distance_mined < distance and not should_return_home() do
    if has_ore_in_vicinity() then
      mine_vein(99)
    end

    move_forward(1, true)
    distance_mined = distance_mined + 1
  end
end

function main()
  go_down()
  strip_mine()
  go_back_to_mine_start()
  go_up()
end