defmodule Scopes.Core.Environ do
  @cell_registry __MODULE__.Cells

  alias Scopes.Core
  alias Scopes.Core.Shape

  defmodule State do
    defstruct [cells: %{}, init_seq: []]
  end

  def child_spec(opts) do
    %{id: __MODULE__, 
      start: {__MODULE__, :start_link, opts}}
  end

  def start_link() do
    Registry.start_link(keys: :unique, name: @cell_registry)
  end

  def cells(), do: @cell_registry

  def setup({state, proc}, init_seq, proc_env \\ &proc_env/2) do
    env_scope = {%State{init_seq: init_seq}, proc_env, [], self()}
    env = Core.neuron(env_scope)
    msg = Shape.create([:csys, :zero], data: %{addr: [:csys, :c00, "0-0"]})
    proc = {state, proc, [], env}
    Core.create(msg, proc)
    env
  end

  def proc_env(msg, scope = {state, _proc, _syns, env}) do
    case Shape.head(msg) do
      {:exec, func} -> func.(state)
      [:csys, :created | _rest] -> process_creation(msg, scope)
      _ -> send(env, msg) # forward message to application
    end
  end

  def process_creation(msg, {state, proc, syns, env}) do
    data = Shape.data(msg)
    new = data.new
    addr = data[:addr]
    cells = if addr do
      [dom, cat, item] = addr
      Map.update(state.cells, {dom, cat}, %{item => new}, 
        fn x -> Map.put(x, item, new) end)
    else
      state.cells
    end
    {step, seq} = List.pop_at(state.init_seq, 0)
    state1 = %State{cells: cells, init_seq: seq}
    Core.update({state1, proc, syns, env})
    if step do
      step.(state1)
    end
  end

  # accessing cell registry via state.cells

  def get_cell(state, [dom, cat, item]) do
    get_in(state.cells, [{dom, cat}, item])
  end

  def send_message(state, addr, head, data) do
    cell = get_cell(state, addr)
    Core.send_message(cell, head, data)
  end

  def connect(state, addr, target, op \\ []) do
    send_message(state, addr, ~w(csys connect)a,
      %{target: get_cell(state, target), op: op})
  end

  # delegating tasks to env

  def delegate(env, func) do
    Core.send_message(env, {:exec, func})
  end

  def forward_value(env, addr, value) do
    delegate(env, &send_message(&1, addr, ~w(csys data)a, %{value: value}))
  end
end