defmodule Scopes.CSys.Program do
  import Scopes.CSys, only: [
    neuron: 1, update_neuron: 1, synapse: 3, 
    syns: 1, env: 1
  ]
  alias Scopes.Core.Actor

  defmodule State do
    defstruct [:value, :stage, :prog]
  end

  def prepare(prog, value \\ []) do
    state = %State{value: value, stage: :initial, prog: prog}
    {state, get_proc(state)}
  end

  def get_proc(stages, stage) do
    stages[stage] || stages[:default]
  end

  def get_proc(state) do
    get_proc(elem(state.prog, 0), state.stage)
  end


  # basic program

  def basic_prog() do
    default = &basic_active/2
    stages = %{
      default: default,
      initial: &basic_initial/2,
      active: default,
      retired: default
    }
    transitions = %{
      restart: :initial,
      retire: :retired,
      next:  [initial: :active, active: :retired]
    }
    {stages, transitions}
  end

  def prepare_basic(value \\ []) do
    prepare(basic_prog(), value)
  end

  # basic processors
  
  def basic_initial(msg, scope) do
    basic(msg, scope)
  end

  def basic_active(msg, scope) do
    basic(msg, scope)
  end

  def basic(msg = {head, _info}, scope) do
    case head do
      [:csys, :create, :pred | _rest] -> create_pred(scope)
      [:csys, :create, :succ | _rest] -> create_succ(scope)
      #[:csys, :next | _rest] -> next(scope, meta)
      #[:csys, :data | rest] -> process_data(rest, Shape.data(msg), scope)
      #[:csys, action | rest] -> transition(action, scope)
      _ -> forward(msg, scope) || notify(msg, scope)
    end
  end

  def basic(msg, scope) do
    forward(msg, scope) || notify(msg, scope)
  end

# processor steps, helper functions

  def notify(msg, scope) do
    Actor.send(env(scope), msg)
  end

  def forward(msg, scope) do
    Enum.reduce(syns(scope), false, fn s, _acc -> s.(msg); true end)
  end

  def restart({state, _proc, syns, env}) do
    nstate = %{state | stage: :initial}
    {nstate, get_proc(nstate), syns, env}
  end

# step functions

# create_... steps
# todo: provide parameters for initial state, proc / stage, op,
#       depending on state and stage (proc) of self, as well as message, env, ...

  def create_pred(scope = {state, proc, _syns, env}) do
    syn = synapse(self(), &Function.identity/1, 0)
    new = neuron(restart({state, proc, [syn], env}))
    notify({:created, new}, scope)
    update_neuron(restart(scope))
  end

  def create_succ (scope = {state, proc, syns, env}) do
    new = neuron(restart({state, proc, [], env}))
    notify({:created, new}, scope)
    syn = synapse(new, &Function.identity/1, 0)
    update_neuron(restart({state, proc, [syn | syns], env}))
  end
end