defmodule Solid.Tag.Assign do
  import NimbleParsec
  alias Solid.Parser.{BaseTag, Literal, Variable, Argument}

  @behaviour Solid.Tag

  @impl true
  def spec(_parser) do
    space = Literal.whitespace(min: 0)

    ignore(BaseTag.opening_tag())
    |> ignore(string("assign"))
    |> ignore(space)
    |> concat(Variable.field())
    |> ignore(space)
    |> ignore(string("="))
    |> ignore(space)
    |> tag(Argument.argument(), :argument)
    |> optional(tag(repeat(Argument.filter()), :filters))
    |> ignore(BaseTag.closing_tag())
  end

  @impl true
  def render(
        [field: [field_name], argument: argument, filters: filters],
        context,
        options
      ) do
    {:ok, new_value, context} =
      Solid.Argument.get(argument, context, [{:filters, filters} | options])

    context = %{context | vars: Map.put(context.vars, field_name, new_value)}

    {[], context}
  end
end