fix: A1-12 functional client-side search with real PagefindUI and fragment index

lib/bds/generation/pagefind.ex

@@ -7,10 +7,25 @@ defmodule BDS.Generation.Pagefind do
   @typedoc "A (relative_path, content) generated file tuple."
   @type generated_file :: {String.t(), String.t()}
 
+  @assets_dir Application.app_dir(:bds, "priv/preview_assets/assets")
+  @ui_js_path Path.join(@assets_dir, "pagefind-ui.js")
+  @ui_css_path Path.join(@assets_dir, "pagefind-ui.css")
+
+  @external_resource @ui_js_path
+  @external_resource @ui_css_path
+
+  @ui_js File.read!(@ui_js_path)
+  @ui_css File.read!(@ui_css_path)
+
   @doc """
   Build the per-language Pagefind index outputs (`pagefind/index.json`,
   `pagefind/pagefind-ui.js`, `pagefind/pagefind-ui.css`) for every blog
   language declared on the plan.
+
+  The fragment index records one entry per indexable page, where indexable
+  means the page carries a `data-pagefind-body` region. Each entry stores the
+  page URL, its title, and the body text scoped to that region — mirroring
+  Pagefind's behaviour of ignoring content outside `data-pagefind-body`.
   """
   @spec build_outputs(map(), [html_output()]) :: [generated_file()]
   def build_outputs(plan, html_outputs) do
@@ -31,8 +46,8 @@ defmodule BDS.Generation.Pagefind do
       [
         {Path.join(prefix ++ ["index.json"]),
          Jason.encode!(%{"language" => language, "pages" => pages})},
-        {Path.join(prefix ++ ["pagefind-ui.js"]), ui_js(language)},
-        {Path.join(prefix ++ ["pagefind-ui.css"]), ui_css()}
+        {Path.join(prefix ++ ["pagefind-ui.js"]), @ui_js},
+        {Path.join(prefix ++ ["pagefind-ui.css"]), @ui_css}
       ]
     end)
   end
@@ -43,11 +58,14 @@ defmodule BDS.Generation.Pagefind do
       String.ends_with?(relative_path, ".html") and
         language_match?(relative_path, route_language, other_prefixes)
     end)
-    |> Enum.map(fn {relative_path, content} ->
-      %{
-        "url" => "/" <> relative_path,
-        "text" => text(content)
-      }
+    |> Enum.flat_map(fn {relative_path, content} ->
+      case body_text(content) do
+        nil ->
+          []
+
+        text ->
+          [%{"url" => "/" <> relative_path, "title" => title(content), "text" => text}]
+      end
     end)
   end
 
@@ -60,19 +78,94 @@ defmodule BDS.Generation.Pagefind do
   defp language_match?(relative_path, route_language, _other_prefixes),
     do: String.starts_with?(relative_path, route_language <> "/")
 
-  defp text(content) do
-    content
+  # Extract the indexable body text scoped to the data-pagefind-body element.
+  # Returns nil when the page is not marked, so unmarked pages are excluded
+  # from the index entirely (matching Pagefind semantics).
+  defp body_text(content) do
+    case Regex.run(~r/<([a-zA-Z0-9]+)[^>]*\bdata-pagefind-body\b[^>]*>/, content,
+           return: :index
+         ) do
+      [{open_start, open_len}, {tag_start, tag_len}] ->
+        tag = binary_part(content, tag_start, tag_len)
+        region = scoped_region(content, tag, open_start + open_len)
+        plain_text(region)
+
+      _no_match ->
+        nil
+    end
+  end
+
+  # Capture the inner HTML of the marked element by balancing same-tag
+  # open/close pairs from the opening tag onward.
+  defp scoped_region(content, tag, body_start) do
+    rest = binary_part(content, body_start, byte_size(content) - body_start)
+    open_re = Regex.compile!("<#{tag}\\b", "i")
+    close_re = Regex.compile!("</#{tag}\\s*>", "i")
+
+    events =
+      (Regex.scan(open_re, rest, return: :index) ++ Regex.scan(close_re, rest, return: :index))
+      |> Enum.map(fn [{pos, _len}] -> pos end)
+      |> Enum.map(fn pos -> {pos, event_kind(rest, pos, tag)} end)
+      |> Enum.sort_by(&elem(&1, 0))
+
+    close_at = balanced_close(events, 0)
+
+    case close_at do
+      nil -> rest
+      pos -> binary_part(rest, 0, pos)
+    end
+  end
+
+  defp event_kind(rest, pos, tag) do
+    if String.starts_with?(binary_part(rest, pos, min(2 + byte_size(tag), byte_size(rest) - pos)), "</") do
+      :close
+    else
+      :open
+    end
+  end
+
+  defp balanced_close([], _depth), do: nil
+
+  defp balanced_close([{pos, :close} | _rest], 0), do: pos
+
+  defp balanced_close([{_pos, :close} | rest], depth),
+    do: balanced_close(rest, depth - 1)
+
+  defp balanced_close([{_pos, :open} | rest], depth),
+    do: balanced_close(rest, depth + 1)
+
+  defp title(content) do
+    tag_text(content, ~r/<title[^>]*>(.*?)<\/title>/si) ||
+      tag_text(content, ~r/<h1[^>]*>(.*?)<\/h1>/si) ||
+      ""
+  end
+
+  defp tag_text(content, regex) do
+    case Regex.run(regex, content) do
+      [_full, raw] -> raw |> plain_text() |> nil_if_blank()
+      _no_match -> nil
+    end
+  end
+
+  defp nil_if_blank(""), do: nil
+  defp nil_if_blank(value), do: value
+
+  defp plain_text(html) do
+    html
     |> String.replace(~r/<[^>]+>/, " ")
+    |> decode_entities()
     |> String.replace(~r/\s+/u, " ")
     |> String.trim()
   end
 
-  defp ui_js(language) do
-    "window.bDSPagefind = { language: #{Jason.encode!(language)} };\n"
-  end
-
-  defp ui_css do
-    ".pagefind-ui{display:block;}\n"
+  defp decode_entities(text) do
+    text
+    |> String.replace("&amp;", "&")
+    |> String.replace("&lt;", "<")
+    |> String.replace("&gt;", ">")
+    |> String.replace("&quot;", "\"")
+    |> String.replace("&#39;", "'")
+    |> String.replace("&nbsp;", " ")
   end
 
   defp route_language(main_language, language) when main_language == language, do: nil