defmodule Mix.Tasks.Ptc.UpdateSpecChecksums do
  @moduledoc """
  Regenerates the spec checksums file for drift detection.

  Reads the current PTC-Lisp specification and generates hashes for each section,
  storing them in `priv/spec/checksums.ex`.

  ## Usage

      mix ptc.update_spec_checksums

  ## Output

  Updates `priv/spec/checksums.ex` with current section hashes.
  """

  use Mix.Task

  @shortdoc "Regenerate spec section checksums"

  alias PtcRunner.Lisp.SpecValidator

  @checksums_path "priv/spec/checksums.ex"

  @impl Mix.Task
  def run(_args) do
    case SpecValidator.section_hashes() do
      {:ok, hashes} ->
        case write_checksums(hashes) do
          :ok ->
            Mix.shell().info("")
            Mix.shell().info("✓ Updated #{@checksums_path}")
            Mix.shell().info("  #{map_size(hashes)} sections")
            Mix.shell().info("")

          {:error, reason} ->
            Mix.shell().error("Error: #{reason}")
            System.halt(1)
        end

      {:error, reason} ->
        Mix.shell().error("Error: #{reason}")
        System.halt(1)
    end
  end

  defp write_checksums(hashes) do
    content = format_checksums(hashes)

    case File.write(@checksums_path, content) do
      :ok -> :ok
      {:error, reason} -> {:error, "Could not write checksums file: #{reason}"}
    end
  end

  defp format_checksums(hashes) do
    header =
      "# Section hashes for spec drift detection\n# Generated by: mix ptc.update_spec_checksums\n\n%{\n"

    entries =
      hashes
      |> Enum.sort()
      |> Enum.map_join(fn {section, hash} ->
        "  \"#{section}\" => \"#{hash}\",\n"
      end)

    footer = "}\n"
    header <> entries <> footer
  end
end