local RNN = {}

function RNN.rnn(input_size, rnn_size, n)
  
  -- there are n+1 inputs (hiddens on each layer and x)
  local inputs = {}
  table.insert(inputs, nn.Identity()()) -- x
  for L = 1,n do
    table.insert(inputs, nn.Identity()()) -- prev_h[L]
  end

  local x, input_size_L
  local outputs = {}
  for L = 1,n do
    
    local prev_h = inputs[L+1]
    if L == 1 then x = inputs[1] else x = outputs[L-1] end
    if L == 1 then input_size_L = input_size else input_size_L = rnn_size end

    -- RNN tick
    local i2h = nn.Linear(input_size_L, rnn_size)(x)
    local h2h = nn.Linear(rnn_size, rnn_size)(prev_h)
    local next_h = nn.Tanh()(nn.CAddTable(){i2h, h2h})

    table.insert(outputs, next_h)
  end

  return nn.gModule(inputs, outputs)
end

return RNN