local I = 1

local c = setmetatable({},{
  __call = function(c,class,data,...)
    local new = {}
    -- todo: use a better data structure; recycle nexus
    new.implies = {} -- Table of all dependency nexus of this class: it.items[0] == c
    setmetatable(new,c)
    return new
  end
})
c.d = c() -- depend
c.s = c() -- solve
c.c = c() -- commit

c.h = c() -- cookie heuristic

local function h(it)
  -- Find and return the data value of the first heuristic unit super-nexus of this object
  for item,index in pairs(it.index) do
    if item.class = c.h then
      return item.data
    end
  end
end

local function s(it)
  -- todo: use some sort of heuristic here like A*
  local options = {it}
  while true do
    table.sort(branches,function(a,b) return h(a) > h(b) end)
    for depends in pairs(it.class.implies) do
      depends. 
    end
    break
  end
end

local n = setmetatable({},{
  __call = function(n,class,data,...)
    local new = {}
    setmetatable(new,n)
    new.class = class
    table.insert(class.instances,class)
    new.data = data
    new.items = {...}
    for index,item in pairs(new.items) do
      item.index[new] = index
    end
    new.index = {}
    s(new)
    return new
  end
})

c.next = c()
c.in = {}
c.out = {}
c.text = {}
c.cookie = c()
for char in ("abcdefghijklmnopqrstuvwxyz "):match(".") do
  c.in[char] = c()
  c.out[char] = c()
end

local previous = n(c(),I)
while true do
  local input = io.read()
  for command in input:gmatch([^@]*) do
    local name,text = command:match("(%a*)%s*(.*)")
    if name == "cookie" then
      local cookie = n(c.cookie,I)
      n(c.next,I,previous,cookie)
      previous = cookie
    else
      local mode
      if name == "in" or name == "" then
        mode = c.in
      elseif name == "out" then
        mode = c.out
      else
        error(string.format("Unknown command '@%s'",name))
      end
      for char in text:match(".") do
        if mode[char] then
          local object = n(mode[char],I)
          n(c.next,I,previous,object)
          previous = object
        end
      end
    end
  end
end