defmodule OeditusCredo.Check.Security.CodeInjection do
  @moduledoc """
  Checks for dynamic evaluation patterns that may lead to code injection.

  MITRE reference: [CWE-94](https://cwe.mitre.org/data/definitions/94.html) --
  Improper Control of Generation of Code ("Code Injection").
  """

  use Credo.Check,
    base_priority: :higher,
    category: :warning,
    explanations: [
      check: """
      Detects potential code injection vulnerabilities ([CWE-94](https://cwe.mitre.org/data/definitions/94.html)).

      Functions like `Code.eval_string/1`, `Code.eval_quoted/1`, and
      `Code.eval_file/1` can execute arbitrary code and should be avoided,
      especially with user-controlled input.

      Bad:

          Code.eval_string(user_input)
          Code.eval_quoted(ast_from_user)
          Code.eval_file(params["file"])

      Good:

          # Use pattern matching, parsers, or safe DSLs instead of eval
          Jason.decode!(json_input)
      """,
      params: [
        exclude_test_files: "Set to true to skip test files (default: false)",
        extra_dangerous_functions: "Additional Code.* function atoms to flag (default: [])"
      ]
    ]

  @default_dangerous_functions [:eval_string, :eval_quoted, :eval_file]

  @doc false
  @impl true
  def run(%SourceFile{} = source_file, params) do
    issue_meta = IssueMeta.for(source_file, params)

    if Params.get(params, :exclude_test_files, __MODULE__) and
         test_file?(source_file.filename) do
      []
    else
      extra = Params.get(params, :extra_dangerous_functions, __MODULE__)
      dangerous = @default_dangerous_functions ++ extra

      source_file
      |> Credo.Code.prewalk(&traverse(&1, &2, {issue_meta, dangerous}))
    end
  end

  @doc false
  @impl true
  def param_defaults, do: [exclude_test_files: false, extra_dangerous_functions: []]

  defp traverse(
         {{:., _, [{:__aliases__, _, [:Code]}, func]}, meta, _args} = ast,
         issues,
         {issue_meta, dangerous}
       )
       when is_atom(func) do
    if func in dangerous do
      {ast, [issue_for(issue_meta, meta[:line], "Code.#{func}") | issues]}
    else
      {ast, issues}
    end
  end

  defp traverse(ast, issues, _ctx), do: {ast, issues}

  defp test_file?(filename) do
    String.ends_with?(filename, "_test.exs") or String.contains?(filename, "/test/")
  end

  defp issue_for(issue_meta, line_no, func_name) do
    format_issue(
      issue_meta,
      message:
        "Potential code injection (CWE-94): #{func_name} can execute arbitrary code. " <>
          "Avoid eval with untrusted input.",
      trigger: func_name,
      line_no: line_no
    )
  end
end