mob_dev

defmodule MobDev.SecurityScan.HistoryFormatter do
  @moduledoc """
  Render a single changelog entry for `SECURITY_HISTORY.md`.

  Each entry is one Markdown section with the timestamp as the
  heading, severity counts as the lede, and three lists: New
  since last scan / Resolved / Still present. Designed to be
  appended to the head of `SECURITY_HISTORY.md` so the latest run
  is the first thing a reader sees.
  """

  alias MobDev.SecurityScan.{Diff, Finding, Report}

  @doc """
  Build a single Markdown changelog entry for the given report+diff.
  Returns a string with a trailing blank line so successive entries
  separate cleanly.
  """
  @spec entry(Report.t(), Diff.t(), DateTime.t()) :: String.t()
  def entry(%Report{} = report, %Diff{} = diff, %DateTime{} = now) do
    counts = Report.severity_counts(report)
    duration = Report.duration_ms(report)

    [
      "## #{DateTime.to_iso8601(now)}",
      "",
      "**Project:** `#{report.project_root}`  ",
      "**Duration:** #{duration || "?"}ms  ",
      "**Total findings:** #{Enum.sum(Map.values(counts))} " <>
        "(#{counts.critical} critical, #{counts.high} high, #{counts.medium} medium, " <>
        "#{counts.low} low, #{counts.unknown} unknown)",
      "",
      section_new(diff),
      section_resolved(diff),
      section_still_present(diff, now),
      ""
    ]
    |> Enum.join("\n")
  end

  @doc """
  Append `entry` to the top of `path` (after the file's header, if
  any). Creates the file with a default header if it doesn't exist.
  """
  @spec prepend_to_file(Path.t(), String.t()) :: :ok
  def prepend_to_file(path, entry) do
    File.mkdir_p!(Path.dirname(path))

    existing =
      case File.read(path) do
        {:ok, body} -> strip_header(body)
        {:error, _} -> ""
      end

    contents = header() <> entry <> existing
    File.write!(path, contents)
    :ok
  end

  defp header do
    """
    # Security scan history

    Append-only changelog generated by `mix mob.security_scan.log`.
    Newest entries on top.

    """
  end

  defp strip_header(body) do
    case String.split(body, "\n\n", parts: 2) do
      ["# Security scan history" <> _, rest] -> "\n\n" <> strip_old_intro(rest)
      _ -> body
    end
  end

  # The header is "# Security scan history\n\n<intro>\n\n<first-entry>".
  # After splitting on the first "\n\n" we still have "<intro>\n\n<entries>";
  # drop the intro paragraph if it's the auto-generated one.
  defp strip_old_intro(rest) do
    case String.split(rest, "\n\n", parts: 2) do
      ["Append-only changelog" <> _, entries] -> entries
      _ -> rest
    end
  end

  defp section_new(%Diff{new: []}), do: "### New since last scan _(none)_\n"

  defp section_new(%Diff{new: findings}) do
    sorted = Enum.sort_by(findings, &Finding.sort_key/1)

    "### New since last scan (#{length(findings)})\n\n" <>
      Enum.map_join(sorted, "\n", &("- " <> render_finding(&1))) <> "\n"
  end

  defp section_resolved(%Diff{resolved: []}), do: "### Resolved since last scan _(none)_\n"

  defp section_resolved(%Diff{resolved: entries}) do
    sorted =
      Enum.sort_by(entries, fn entry ->
        {severity_rank(entry.severity), entry.id || ""}
      end)

    "### Resolved since last scan (#{length(entries)}) ✓\n\n" <>
      Enum.map_join(sorted, "\n", &("- " <> render_entry(&1))) <> "\n"
  end

  defp section_still_present(%Diff{still_present: []}, _now),
    do: "### Still present from last scan _(none)_\n"

  defp section_still_present(%Diff{still_present: findings, first_seen: first_seen}, now) do
    sorted = Enum.sort_by(findings, &Finding.sort_key/1)

    "### Still present from last scan (#{length(findings)})\n\n" <>
      Enum.map_join(sorted, "\n", fn f ->
        first = Map.get(first_seen, Finding.dedupe_key(f))
        "- " <> render_finding(f) <> age_suffix(first, now)
      end) <> "\n"
  end

  defp render_finding(%Finding{} = f) do
    sev = f.severity |> Atom.to_string() |> String.upcase()
    pkg = if f.package, do: " `#{f.package}#{ver_suffix(f.version)}`", else: ""
    id = if f.id, do: " #{link_id(f.id, f.url)}", else: ""
    fixed = if f.fixed_in, do: " — fixed in #{f.fixed_in}", else: ""
    title = if f.title, do: " — #{escape_md(f.title)}", else: ""

    "**#{sev}**#{pkg}#{id}#{fixed}#{title}"
  end

  defp render_entry(%{} = e) do
    sev = e.severity |> to_string() |> String.upcase()
    pkg = if e.package, do: " `#{e.package}#{ver_suffix(e.version)}`", else: ""
    id = if e.id, do: " #{link_id(e.id, e.url)}", else: ""
    title = if e.title, do: " — #{escape_md(e.title)}", else: ""

    "**#{sev}**#{pkg}#{id}#{title}"
  end

  defp ver_suffix(nil), do: ""
  defp ver_suffix(""), do: ""
  defp ver_suffix(v), do: "@#{v}"

  defp link_id(id, nil), do: "[#{id}]"
  defp link_id(id, ""), do: "[#{id}]"
  defp link_id(id, url), do: "[`#{id}`](#{url})"

  defp age_suffix(nil, _now), do: ""

  defp age_suffix(%DateTime{} = first, %DateTime{} = now) do
    days = DateTime.diff(now, first, :second) |> div(86_400)

    cond do
      days <= 0 -> ""
      days == 1 -> " _(first seen 1 day ago)_"
      true -> " _(first seen #{days} days ago)_"
    end
  end

  defp age_suffix(_, _), do: ""

  defp severity_rank(:critical), do: 0
  defp severity_rank(:high), do: 1
  defp severity_rank(:medium), do: 2
  defp severity_rank(:low), do: 3
  defp severity_rank(_), do: 4

  defp escape_md(nil), do: nil
  defp escape_md(s) when is_binary(s), do: String.replace(s, "|", "\\|")
end