new 'go' utility

--   Block actions combinators v1 (go)
--
-- f b u d l r   -- Move forward, backward, up, down, turn left, turn right
-- F B U D         -- same moves, but move until block detected
-- m M   --  mine block, mine blocks while block present (usefull for gravel mining)
-- [commands lastcommand]   --  loop while lastcommand returns success
-- commandNUMBER   -- loop command NUMBER times
-- [commands]NUMBER -- loop commands list NUMBER times
-- >DIGIT   --   place block from DIGIT slot. When DIGIT == 0, place first available
-- ^DIGIT   --   place block up
-- _DIGIT   --   place block down

local tArgs = { ... }
if #tArgs ~= 1 then
  print("Usage: go <list of commands>")
  return
end

-- Enables mob detection capabilities of CAPS move forward for noncaps forward
local function mdForward()
  if turtle.detect() == false then
    turtle.forward()
    return true
  else
    return false
  end
end

-- CAPS-letter commands evaluator, move-only
-- Remove code duplication by encapsulating common pattern in function
local function mdMove(command, detector)
  while detector() == false do
        command()
  end
end

-- CAPS-letter commands evaluator, dig-only
-- Remove code duplication by encapsulating common pattern in function
local function mdDig(command, detector)
  while detector() do
        command()
        sleep(0.4)
  end
end

-- Evaluate prefix commands
local function runPrefixCmd(ch, digCmd, detectCmd, placeCmd)
  local chCode = string.byte(ch, 1) - 48
  if false then
  elseif ch == 'm' then return true, digCmd()
  elseif ch == 'M' then mdDig(digCmd, detectCmd); return true, false -- todo: better result return
  elseif ch == '0' then return true, placeCmd()
  elseif chCode > 0 and chCode < 10 then
        turtle.select(chCode)
        res = placeCmd()
        return true, res
  end
  return false, false
end

-- Lua specific array length
local function lngth(lst)
  if lst == nil then return 0 else return #lst end
end

local function parseNumber(st)
  _, _, num, rest = string.find(st, "^(%d+)(.*)$")
  return num, lngth(st) - lngth(rest)
end

local function parseLoop(st)
  _, _, loop, rest = string.find(st, "^(%b[])(.*)$")
  if loop ~= nil and loop ~= '' then
        return loop:sub(2,-2), lngth(st) - lngth(rest)
  elseif st:sub(1,1) == '[' then return nil, 1
  else return nil, 0
  end
end

function go(command)
  local i = 1
  local prevCommand = ''
  local result = false

  while i <= #command do
        local ch = command:sub(i, i)
        local nextCh = i == #command and '' or command:sub(i+1, i+1)

        local number, nLen = parseNumber(command:sub(i))
        local loop, lLen   = parseLoop(command:sub(i))

        -- if we found number, repeat last command number times
        if number ~= nil then
          number = tonumber(number)
          while number > 1 do
                go(prevCommand)
                number = number - 1
          end
          i = i + nLen - 1
        -- if we found loop, parse possible number and evaluate expression
        elseif loop ~= nil then
          local number, nLen = parseNumber(command:sub(i + lLen))
          if number ~= nil then
                number = tonumber(number)
                while number > 0 do
                  go(loop)
                  number = number - 1
                end
                i = i + nLen
          else
                while go(loop) do end
          end
          i = i + lLen - 1

        elseif ch == 'f' then result = mdForward()
        elseif ch == 'b' then result = turtle.back()
        elseif ch == 'u' then result = turtle.up()
        elseif ch == 'd' then result = turtle.down()

        elseif ch == 'F' then mdMove(mdForward, turtle.detect)
        elseif ch == 'B' then go("aFa") -- this is not primitive
        elseif ch == 'U' then mdMove(turtle.up, turtle.detectUp)
        elseif ch == 'D' then mdMove(turtle.down, turtle.detectDown)

        elseif ch == 'l' then turtle.turnLeft()
        elseif ch == 'r' then turtle.turnRight()
        elseif ch == 'a' then go("ll")

        elseif ch == 'm' then result = turtle.dig()
        elseif ch == 'M' then mdDig(turtle.dig, turtle.detect)

        elseif ch == '>' then
          local result1,result2 = runPrefixCmd(nextCh, turtle.dig, turtle.detect, turtle.place)
          if result1 then
                i = i + 1 -- todo: better prefix parsing
          end
          result = result2
        elseif ch == '^' then
          local result1,result2 = runPrefixCmd(nextCh, turtle.digUp, turtle.detectUp, turtle.placeUp)
          if result1 then
                i = i + 1
          end
          result = result2
        elseif ch == '_' then
          local result1,result2 = runPrefixCmd(nextCh, turtle.digDown, turtle.detectDown, turtle.placeDown)
          if result1 then
                i = i + 1
          end
          result = result2
        end

        prevCommand = ch
        i = i + 1
  end
  return result
end

go(tArgs[1])