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reach lib reach smell checks multiple_enum_at.ex
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lib/reach/smell/checks/multiple_enum_at.ex 

defmodule Reach.Smell.Checks.MultipleEnumAt do

  @moduledoc "Detects multiple Enum.at/2 calls on the same variable with literal indices."



  use Reach.Smell.Check



  @min_calls 3



  defp findings(function) do

    function

    |> leaf_bodies()

    |> Enum.flat_map(&find_in_body/1)

  end



  defp find_in_body(body_nodes) do

    enum_at_calls =

      for node <- body_nodes,

          node.type == :call,

          node.meta[:module] == Enum,

          node.meta[:function] == :at,

          not is_nil(node.source_span),

          [%{type: :var, meta: %{name: var}}, %{type: :literal} | _] <- [node.children] do

        {var, node}

      end



    enum_at_calls

    |> Enum.group_by(&elem(&1, 0))

    |> Enum.filter(fn {_var, calls} -> length(calls) >= @min_calls end)

    |> Enum.map(fn {var, calls} ->

      finding(

        :suboptimal,

        "Enum.at/2 called #{length(calls)} times on `#{var}` with literal indices; use pattern matching to destructure in one pass",

        List.first(calls) |> elem(1)

      )

    end)

  end



  defp leaf_bodies(function) do

    function.children

    |> Enum.filter(&(&1.type == :clause))

    |> case do

      [] -> [IR.all_nodes(function)]

      clauses -> Enum.map(clauses, &IR.all_nodes/1)

    end

  end

end