import Base: @get!
import DataFlow: Constant, postwalk, value, inputs, constant
import TensorFlow: RawTensor

# TODO: implement Julia's type promotion rules

cvalue(x) = x
cvalue(c::Constant) = c.value
cvalue(v::Vertex) = cvalue(value(v))

graph(x::Tensor) = x
graph(x::Number) = TensorFlow.constant(Float32(x))

graph(::typeof(*), args...) = *(args...)
graph(::typeof(.*), args...) = .*(args...)
graph(::typeof(.-), args...) = -(args...)
graph(::typeof(+), args...) = +(args...)
graph(::typeof(softmax), x) = nn.softmax(x)
graph(::typeof(relu), x) = nn.relu(x)
graph(::typeof(tanh), x) = tanh(x)
graph(::typeof(σ), x) = nn.sigmoid(x)

# reshape hack due to https://github.com/malmaud/TensorFlow.jl/issues/79
batchsize(x::Tensor) = reduce_sum(slice(TensorFlow.shape(x), [0], [1]))
graph(::typeof(flatten), x) = reshape(x, pack([batchsize(x), Int32(-1)]))
graph(r::Reshape, x) = reshape(x, pack([batchsize(x), map(Int32, r.dims)...]))

graph(::Input, x) = x

graph(p::MaxPool, x) =
  nn.max_pool(x, [1, p.size..., 1], [1, p.stride..., 1], "VALID")

graph(::DataFlow.Group, xs...) = (xs...,)

graph(params::Associative, c::Conv2D, x) =
  nn.conv2d(x, graph(params, c.filter), [1,c.stride...,1], "VALID")

graph(op::Op, xs...) = op.f(xs...)
Flux.shape(op::Op, d...) = op.shape(d...)

graph{T<:AArray}(params::Associative, p::Flux.Param{T}) =
  @get!(params, p, Variable(p.x))

function graph(params::Associative, v::IVertex, args...)
  # TODO: check number of arguments
  v = spliceinputs(v, map(constant, args)...) |> detuple
  postwalk(v) do v
    vertex(graph(params, cvalue(v), cvalue.(inputs(v))...))
  end |> value
end

function graph(params::Associative, model, args...)
  g = Flux.graph(model)
  g == nothing && return graph(model, args...)
  DataFlow.iscyclic(g) && error("This model has a cycle; try unrolling it first.")
  graph(params, g, args...)
end

function tograph(model, args...)
  params = Dict{Flux.Param,Tensor}()
  g = graph(params, model, args...)
  return params, g
end

TensorFlow.Tensor(m::Flux.Model, args...) = graph(Dict(), m, args...)

RawTensor(data::Union{Batch,Seq}) = RawTensor(rawbatch(data))

function makesession(model, n)
  sess = Session(Graph())
  inputs = [placeholder(Float32) for _ = 1:n]
  params, output = tograph(model, inputs...)
  run(sess, initialize_all_variables())
  sess, params, inputs, output
end

function storeparams!(sess, params)
  for (p, t) in params
    p.x = run(sess, t)
  end
end