Add format-aware monograph reader selection and dual-format indexing

[Copilot]

Monographs with both public EPUB and PDF featured representatives always resolved to EPUB, with no user-facing way to select format. This change adds a format-selection flow (reader_format) to reader/ToC behavior and updates indexing to include accessibility metadata and ToCs from both ebook formats.

• Reader format selection + visibility gating

  • Added reader_ebook_id_for_format(format_param) while preserving existing reader_ebook_id EPUB-preferred behavior.
  • Added both_ebook_formats_public? to detect when EPUB+PDF reps both exist and are publicly visible.
  • Sanitized and threaded @reader_format (epub|pdf only) in MonographCatalogController.
  • Updated reader_links_display visibility checks to evaluate the selected ebook format, not implicit EPUB.

• Catalog UI updates

  • Added a Choose Format dropdown (left of Read Book) when both ebook formats are public and reader UI is shown.
  • Dropdown links set reader_format on the monograph catalog URL.
  • Updated Read Book link target to resolve via selected format while preserving princess_de_cleves routing behavior.
  • Added monograph_catalog.index.choose_format locale string.

• ToC format-awareness

  • Updated _index_epub_toc to select EPUB/PDF presenter based on @reader_format.
  • Updated ToC entry links to route into the selected ebook.
  • Kept fallback behavior to default reader ebook when needed.

• Indexer: include both formats

  • maybe_index_accessibility_metadata now indexes both EPUB and PDF metadata when present and writes multivalued reader_ebook_format_sim.
  • table_of_contents now aggregates titles from both EPUB and PDF ToCs and de-duplicates for table_of_contents_tesim.

• Spec updates

  • Added/updated presenter specs for reader_ebook_id_for_format and both_ebook_formats_public?.
  • Added controller specs for reader_format sanitization and format-aware reader visibility behavior.
  • Updated indexer specs to assert dual-format accessibility indexing and combined ToC indexing.
  • Updated view specs for choose-format rendering and format-aware read-link behavior.

def reader_ebook_id_for_format(format_param = nil)
  epub_id_val = nil
  pdf_id_val = nil

  featured_representatives.each do |fr|
    epub_id_val = fr.file_set_id if fr.kind == 'epub'
    pdf_id_val = fr.file_set_id if fr.kind == 'pdf_ebook'
  end

  if format_param == 'pdf' && pdf_id_val.present?
    pdf_id_val
  else
    epub_id_val || pdf_id_val
  end
end

Original prompt

Overview

When a Monograph has both an EPUB and a PDF FeaturedRepresentative (each with a public FileSet), users should be able to choose which format to read. Currently the system always silently prefers the EPUB. This PR introduces:

1. A "Choose Format" dropdown button — shown to the left of "Read Book" when both EPUB and PDF are available and public.
2. A ?reader_format=pdf URL parameter — selecting PDF from the dropdown appends this param to the reader URL, and all presenter / ToC logic respects it.
3. Indexing both formats' accessibility metadata in MonographIndexer#maybe_index_accessibility_metadata.
4. Indexing both ebooks' ToCs in MonographIndexer#table_of_contents (the table_of_contents_tesim field is multivalued and is only used for Monograph discovery at the Press level).

---

Detailed Changes

1. New presenter method: both_ebook_formats_public?

Add to app/presenters/concerns/featured_representatives/monograph_presenter.rb:

# Returns true when both an EPUB and a PDF ebook FeaturedRepresentative exist
# AND the corresponding FileSets are both publicly visible.
# Used to decide whether to show the "Choose Format" dropdown.
def both_ebook_formats_public?
  return false unless epub? && pdf_ebook?
  epub_doc = featured_representative_docs.find { |doc| doc.id == epub_id }
  pdf_doc  = featured_representative_docs.find { |doc| doc.id == pdf_ebook_id }
  epub_doc&.fetch('visibility_ssi', nil) == 'open' &&
    pdf_doc&.fetch('visibility_ssi', nil) == 'open'
end

2. Update reader_ebook_id to respect ?reader_format=pdf

The presenter currently has no knowledge of the request. Pass the optional format preference into reader_ebook_id (or add a separate preferred_reader_ebook_id(format: nil) helper). The cleanest approach that avoids threading request through the presenter is to add a new method and keep the original for backwards compatibility:

def reader_ebook_id_for_format(format_param = nil)
  epub_id_val = nil
  pdf_id_val  = nil
  featured_representatives.each do |fr|
    epub_id_val = fr.file_set_id if fr.kind == 'epub'
    pdf_id_val  = fr.file_set_id if fr.kind == 'pdf_ebook'
  end
  if format_param == 'pdf' && pdf_id_val.present?
    pdf_id_val
  else
    epub_id_val || pdf_id_val
  end
end

3. Thread reader_format param through MonographCatalogController

In monograph_auth_for (and reader_links_display), expose @reader_format = params[:reader_format] and set it on the instance. Pass it to view helpers where needed.

Update reader_links_display to use reader_ebook_id_for_format(@reader_format) when checking visibility:

def reader_links_display
  return :not_shown if @monograph_presenter.tombstone? || @monograph_presenter.subdomain == 'ee' || !@monograph_presenter.reader_ebook?

  return :linked if valid_share_link?

  # Use the format-aware ebook ID for visibility check
  ebook_id = @monograph_presenter.reader_ebook_id_for_format(@reader_format)
  ebook_doc = @monograph_presenter.featured_representative_docs.find { |doc| doc.id == ebook_id }
  return :not_shown unless ebook_doc&.fetch('visibility_ssi', nil) == 'open'

  if @monograph_presenter.access_level(@actor_product_ids, @allow_read_product_ids).show? &&
     @monograph_presenter.access_level(@actor_product_ids, @allow_read_product_ids).level == :restricted
    :not_linked
  else
    :linked
  end
end

4. Update _read_download_buy.html.erb — add "Choose Format" dropdown

Insert the new dropdown before the Read Book button (i.e. it appears to the left of it). Show it only when @monograph_presenter.both_ebook_formats_public? and the reader is shown (not tombstoned, not ee press, etc.).

<%# Choose Format dropdown — only shown when both EPUB and PDF are public %>
<% if @monograph_presenter.both_ebook_formats_public? && @reader_links_display != :not_shown %>
  <div class="btn-group btn-group-lg" id="monograph-choose-format-group">
    <button type="button"
            id="monograph-choose-format-btn"
            aria-haspopup="true"
            class="btn btn-default dropdown-toggle"
            data-toggle="dropdown"
            aria-expanded="false">
      <%= t('monograph_catalog.index.choose_format', default: 'Choose Format') %>
      <span class="caret"></span>
    </button>
    <ul class="dropdown-menu" role="menu">
      <li role="menuitem">
        <a href="<%= monograph_catalog_path(@monograph_presenter.id, reader_format: 'epub') %>"
           data-turbolinks="false">EPUB</a>
      </li>
      <li role="menuitem">
        <a href="<%= monograph_catalog_path(@monograph_presenter.id, reader_format: 'pdf') %>"
           data-turbolinks="false">PDF</a>
      </li>
    </ul>
  </div>
<% end %>

5. Update the Read Book button href to carry reader_format through to the reader

The Read Book button currently links directly to epub_path(@monograph_presenter.reader_ebook). When `@reader_format ==...

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