module Eth::Abi::Function

def decode(interfaces, data)
  data = Util.remove_hex_prefix(data)
  selector = Util.prefix_hex(data[0, 8])
  payload = Util.prefix_hex(data[8..] || "")
  selector_to_interfaces = Hash[interfaces.map { |i| [selector(i), i] }]
  if (interface = selector_to_interfaces[selector])
    inputs = interface.fetch("inputs", [])
    types = inputs.map { |i| type(i) }
    args = Abi.decode(types, payload)
    kwargs = {}
    inputs.each_with_index do |input, i|
      name = input.fetch("name", "")
      kwargs[name.to_sym] = args[i] unless name.empty?
    end
    CallDescription.new(interface, selector, args, kwargs)
  end
end

def selector(interface)
  sig = signature(interface)
  Util.prefix_hex(Util.bin_to_hex(Util.keccak256(sig))[0, 8])
end

def signature(interface)
  name = interface.fetch("name")
  inputs = interface.fetch("inputs", [])
  types = inputs.map { |i| type(i) }
  "#{name}(#{types.join(",")})"
end

def type(input)
  if input["type"] == "tuple"
    "(#{input["components"].map { |c| type(c) }.join(",")})"
  elsif input["type"] == "enum"
    "uint8"
  else
    input["type"]
  end
end