defmodule CPSolver.Examples.GraphColoring do
  alias CPSolver.Constraint.NotEqual
  alias CPSolver.IntVariable

  def solve(instance) when is_binary(instance) do
    instance
    |> parse_instance()
    |> solve()
  end

  def solve(data) do
    color_vars = Enum.map(1..data.vertices, fn _idx -> IntVariable.new(1..data.max_color) end)

    edge_color_constraints =
      Enum.map(data.edges, fn [v1, v2] ->
        {NotEqual, Enum.at(color_vars, v1), Enum.at(color_vars, v2)}
      end)

    model = %{
      variables: color_vars,
      constraints: edge_color_constraints
    }

    CPSolver.solve(model)
    |> tap(fn _ -> Process.sleep(1000) end)
  end

  defp parse_instance(instance) do
    [header | edge_lines] = File.read!(instance) |> String.split("\n", trim: true)
    [v, _e, max_color] = header |> String.split(" ", trim: true) |> Enum.map(&String.to_integer/1)

    edges =
      Enum.map(edge_lines, fn e -> String.split(e, " ") |> Enum.map(&String.to_integer/1) end)

    %{vertices: v, edges: edges, max_color: max_color}
  end
end