#/usr/bin/env lua

require('strict')

board = {
  {0,0,0,0},
  {0,0,0,0},
  {0,0,0,0},
  {0,0,0,0},
}

function show_board(board)
  local r, c

  print("  UUUU")
  print(" +----+")
  for r=1,4 do
    io.write("L:")
    for c=1,4 do
      if board[r][c] == 0 then
        io.write('.')
      else
        io.write(string.char(string.byte('a') - 1 + board[r][c]))
      end
    end
    print(":R")
  end
  print(" +----+")
  print("  DDDD")
  print()
end

function add_blocks_at_random(number)
  local function add_block_at_random()
    local r = math.random(4)
    local c = math.random(4)

    while board[r][c] ~= 0 do
      r = math.random(4)
      c = math.random(4)
    end

    board[r][c] = 1
  end

  local c

  for c=1,number do
    add_block_at_random()
  end
end

function can_make_a_move()
  local r, c

  -- Game over once a 'z' appears
  for r=1,4 do
    for c=1,4 do
      if board[r][c] == 26 then
        return false
      end
    end
  end

  -- Are there any free spaces?
  for r=1,4 do
    for c=1,4 do
      if board[r][c] == 0 then
        return true
      end
    end
  end

  -- Could non empty spaces be merged?
  for r=1,3 do
    for c=1,3 do
      if board[r][c] ~= 0 then
        if board[r][c] == board[r][c+1] or board[r][c] == board[r+1][c] then
          return true
        end
      end
    end
  end

  for c=1,3 do
    if board[4][c] ~= 0 then
      if board[4][c] == board[4][c+1] then
        return true
      end
    end
  end

  -- Well that would be a no then
  return false
end

function get_user_move()
  local here, waiting_for_input

  waiting_for_input = true

  while waiting_for_input do
    waiting_for_input = false

    print("Enter a direction to move: U, D, L or R")
    here = io.read()

    if here == 'U' or here == 'u' then
      here = 'u'
    elseif here == 'D' or here == 'd' then
      here = 'd'
    elseif here == 'L' or here == 'l' then
      here = 'l'
    elseif here == 'R' or here == 'r' then
      here = 'r'
    else
      waiting_for_input = true
      print("That was not a valid instruction")
    end
  end

  return here
end

function move_board(here)
  local function check(r, c, dr, dc)
    local moved = 0

    if board[r][c] == 0 then
      if board[r+dr][c+dc] ~= 0 then
        board[r][c] = board[r+dr][c+dc]
        board[r+dr][c+dc] = 0
        moved = moved + 1
      end
    elseif board[r][c] == board[r+dr][c+dc] then
      board[r][c] = board[r][c] + 1
      board[r+dr][c+dc] = 0
      moved = moved + 1
    end

    return moved
  end

  local function find(row_from,row_to,row_step,column_from,column_to,column_step,row_offset,column_offset)
    local r, c

    local x = 0

    for r=row_from,row_to,row_step do
      for c=column_from,column_to,column_step do
        x = x + check(r, c, row_offset, column_offset)
      end
    end

    return x > 0
  end

  if here == 'l' then
    return find(1,4,1,1,3,1,0,1) and here or 'x'
  elseif here == 'r' then
    return find(1,4,1,4,2,-1,0,-1) and here or 'x'
  elseif here == 'u' then
    return find(1,3,1,1,4,1,1,0) and here or 'x'
  else
    return find(4,2,-1,1,4,1,-1,0) and here or 'x'
  end
end

function add_new_block(here)
  local function pick_one(t)
    local x = math.random(#t)
    return t[x]
  end

  local function add_to_column(c)
    local r
    local v = {}

    for r=1,4 do
      if board[r][c] == 0 then
        v[#v+1] = r
      end
    end

    board[pick_one(v)][c] = 1
  end

  local function add_to_row(r)
    local c
    local v = {}

    for c=1,4 do
      if board[r][c] == 0 then
        v[#v+1] = c
      end
    end

    board[r][pick_one(v)] = 1
  end

  if here == 'l' then
    add_to_column(4)
  elseif here == 'r' then
    add_to_column(1)
  elseif here == 'u' then
    add_to_row(4)
  else
    add_to_row(1)
  end
end

function score_game(board)
  -- Better scoring values required
  local scores = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26}

  local r, c
  local score = 0
  local max = 0

  for r=1,4 do
    for c=1,4 do
      score = score + scores[board[r][c]]
      if max < board[r][c] then
        max = board[r][c]
      end
    end
  end

  print("Final score was " .. score .. " The highest letter was '" .. string.char(string.byte('a') + max - 1) .. "'")
end

math.randomseed( os.time() )
add_blocks_at_random(2)

while can_make_a_move() do
  show_board(board)
  here = get_user_move()
  if move_board(here) == 'x' then
    print("Unable to move in that directions (" .. here .. ")")
  else
    add_new_block(here)
  end
end

show_board(board)
score_game(board)