defmodule Liquex.Expression do
  @moduledoc false

  alias Liquex.Argument
  alias Liquex.Context

  @spec eval(maybe_improper_list | {:field, any} | {:literal, any}, Context.t()) :: any
  def eval([left: left, op: op, right: right], %Context{} = context) do
    do_eval({
      left |> Argument.eval(context),
      op,
      right |> Argument.eval(context)
    })
  end

  def eval({type, _} = argument, context) when type in [:field, :literal],
    do: [argument] |> Argument.eval(context) |> do_eval()

  def eval(expressions, context) when is_list(expressions) do
    expressions
    |> Enum.chunk_every(2)
    |> Enum.reverse()
    |> Enum.reduce(nil, fn
      [exp, :and], acc ->
        eval(exp, context) and acc

      [exp, :or], acc ->
        eval(exp, context) or acc

      [exp], nil ->
        eval(exp, context)
    end)
  end

  defp do_eval({left, :<=, nil}) when is_number(left), do: false
  defp do_eval({left, :<, nil}) when is_number(left), do: false
  defp do_eval({nil, :>=, right}) when is_number(right), do: false
  defp do_eval({nil, :>, right}) when is_number(right), do: false
  defp do_eval({nil, :contains, _right}), do: false
  defp do_eval({_, :contains, nil}), do: false
  defp do_eval({left, :contains, right}) when is_list(left), do: right in left

  defp do_eval({left, :contains, right}) when is_binary(left) and is_binary(right),
    do: String.contains?(left, right)

  defp do_eval({left, op, right}), do: apply(Kernel, op, [left, right])

  # Truthy values
  defp do_eval(nil), do: false
  defp do_eval(false), do: false
  defp do_eval(_), do: true
end