TreeMiner

x, y, z, f = 0, 0, 0, 0
local breaks = 0
local returning = false
local template = {"log", "leaves"}

function checkFuel(flag)
  if not flag then
    local fuel = turtle.getFuelLevel()
    local distance = math.abs(x) + math.abs(y) + math.abs(z)
    if fuel-1 <= distance then
      home()
      error("Alert: Fuel level critical. Returning to home point...")
    end
  end
end

function forward(num)
  num = num or 1
  for i = 1, num do
    if turtle.forward() then
      if f == 0 then
        x = x + 1
      elseif f == 1 then
        z = z + 1
      elseif f == 2 then
        x = x - 1
      elseif f == 3 then
        z = z - 1
      end
      checkFuel(returning)
    else
      return false
    end
  end
  return true
end

function back(num)
  num = num or 1
  for i = 1, num do
    if turtle.back() then
      if f == 0 then
        x = x - 1
      elseif f == 1 then
        z = z - 1
      elseif f == 2 then
        x = x + 1
      elseif f == 3 then
        z = z + 1
      end
      checkFuel(returning)
    else
      return false
    end
  end
  return true
end

function up(num)
  num = num or 1
  for i = 1, num do
    if turtle.up() then
      y = y + 1
      checkFuel(returning)
    else
      return false
    end
  end
  return true
end

function down(num)
  num = num or 1
  for i = 1, num do
    if turtle.down() then
      y = y - 1
      checkFuel(returning)
    else
      return false
    end
  end
  return true
end

function left(num)
  num = num or 1
  for i = 1, num do
    turtle.turnLeft()
    f = (f+3)%4
  end
end

function right(num)
  num = num or 1
  for i = 1, num do
    turtle.turnRight()
    f = (f+1)%4
  end
end

function home()
  returning = true
  while y ~= 0 do
    if y < 0 then
      turtle.digUp()
      up()
    elseif y > 0 then
      turtle.digDown()
      down()
    end
  end
  if z > 0 then
    while f ~= 3 do
      left()
    end
  elseif z < 0 then
    while f ~= 1 do
      left()
    end
  end
  while z ~= 0 do
    forward()
  end
  if x > 0 then
    while f ~= 2 do
      left()
    end
  elseif x < 0 then
    while f ~= 0 do
      left()
    end
  end
  while x ~= 0 do
    forward()
  end
end

function log(data)
  local h = fs.open("log", "w")
  if type(data) == "string" then
    h.writeLine(data)
  elseif type(data) == "table" then
    for i = 1, #data do
      h.writeLine(data[i])
    end
  end
  h.close()
end

function surface()
  while down() do
  end
end

function bottom()
  turtle.digDown()
  while down() do
    turtle.digDown()
  end
end

function scan(tStr)
  local s,d = turtle.inspect()
  if s then
    for i = 1, #tStr do
      if string.find(d.name, tStr[i]) then
        return true
      end
    end
    return false
  end
  return false
end
function scanUp(tStr)
  local s,d = turtle.inspectUp()
  if s then
    for i = 1, #tStr do
      if string.find(d.name, tStr[i]) then
        return true
      end
    end
    return false
  end
  return false
end
function scanDown(tStr)
  local s,d = turtle.inspectDown()
  if s then
    for i = 1, #tStr do
      if string.find(d.name, tStr[i]) then
        return true
      end
    end
    return false
  end
  return false
end

function mineVein(tStr)
  breaks = breaks + 1
  if breaks == 200 then
    home()
    error("reached block limit")
  end
  if scan(tStr) then
    turtle.dig()
    forward()
    mineVein(tStr)
    back()
  end
  left()
  if scan(tStr) then
    turtle.dig()
    forward()
    mineVein(tStr)
    back()
  end
  right(2)
  if scan(tStr) then
    turtle.dig()
    forward()
    mineVein(tStr)
    back()
  end
  left()
  if scanUp(tStr) then
    turtle.digUp()
    up()
    mineVein(tStr)
    down()
  end
  if scanDown(tStr) then
    turtle.digDown()
    down()
    mineVein(tStr)
    up()
  end
end

function drillDown(num)
  for i = 1, num do
    turtle.digDown()
    if not down() then
      break
    end
  end
end

function stripMine(length, strips)
  for i = 1, strips do
    for i = 1, length do
      turtle.dig()
      forward()
      mineVein(template)
    end
    left((i%2)*2+1)
    for i = 1, 3 do
      turtle.dig()
      forward()
      mineVein(template)
    end
    left((i%2)*2+1)
  end
end

function coast(num)
  for i = 1, num do
    while not forward() do
      turtle.digUp()
      up()
    end
    surface()
    mineVein(template)
  end
end


------------------------Actual Program------------------------
mineVein(template)