# Tabsets tweaking: find Markdown recommended in
# https://bookdown.org/yihui/rmarkdown-cookbook/html-tabs.html
# and https://bookdown.org/yihui/rmarkdown/html-document.html#tabbed-sections
# i.e. "## Heading {.tabset}" or "## Heading {.tabset .tabset-pills}"
#  no matter the heading level -- the headings one level down are the tabs
# and transform to tabsets HTML a la Bootstrap

tweak_tabsets <- function(html) {
  tabsets <- xml2::xml_find_all(html, ".//div[contains(@class, 'tabset')]")
  purrr::walk(tabsets, tweak_tabset)
  invisible()
}

tweak_tabset <- function(div) {
  # Get tabs and remove them from original HTML
  tabs <- xml2::xml_find_all(div, "div")
  xml2::xml_remove(tabs)

  # Add empty ul for nav and div for content
  nav_class <- if (has_class(div, "tabset-pills")) {
    "nav nav-pills"
  } else {
    "nav nav-tabs"
  }
  fade <- has_class(div, "tabset-fade")

  id <- section_id(div)
  nav <- xml2::xml_add_child(div, "ul", class = nav_class, id = id, role = "tablist")
  content <- xml2::xml_add_child(div, "div", class = "tab-content")

  # Fill the ul for nav and div for content
  purrr::walk(tabs, tablist_item, nav = nav, parent_id = id)
  purrr::walk(tabs, tablist_content, content = content, parent_id = id, fade = fade)

  # if not tabs active, activate the first tab
  if (!any(has_class(xml2::xml_children(content), "active"))) {
    first_tab <- xml2::xml_find_first(nav, ".//li/button")
    tweak_class_prepend(first_tab, "active")
    xml2::xml_attr(first_tab, "aria-selected") <- "true"

    tab_class <- paste("active", if (has_class(div, "tabset-fade")) "show")
    tweak_class_prepend(xml2::xml_child(content), tab_class)
  }
}

# Add an item (tab) to the tablist
tablist_item <- function(tab, nav, parent_id) {
  id <- section_id(tab)
  title <- tablist_title(tab)

  # Activate (if there was "{.active}" in the source Rmd)
  active <- has_class(tab, "active")
  li_class <- paste0("nav-link", if (active) " active")
  li <- xml2::xml_add_child(nav, "li", role = "presentation", class = "nav-item")
  button <- xml2::xml_add_child(li, "button",
    `data-bs-toggle` = "tab",
    `data-bs-target` = paste0("#", id),
    id = paste0(id, "-tab"),
    type = "button",
    role = "tab",
    `aria-controls` = id,
    `aria-selected` = tolower(active),
    class = li_class
  )

  # Preserve html in title by adding from xml_nodeset item by item
  for (title_item in title) {
    xml2::xml_add_child(button, title_item)
  }

  invisible()
}

tablist_title <- function(tab) {
  # remove anchor link from tab heading
  tab_heading_anchor <- xml2::xml_find_first(tab, ".//a[@class = 'anchor']")
  xml2::xml_remove(tab_heading_anchor)

  xml2::xml_contents(xml2::xml_child(tab))
}

# Add content of a tab to a tabset
tablist_content <- function(tab, content, parent_id, fade) {
  id <- section_id(tab)
  # remove the header, the first child
  xml2::xml_remove(xml2::xml_child(tab))

  xml2::xml_attr(tab, "id") <- id

  # Activate (if there was "{.active}" in the source Rmd)
  active <- has_class(tab, "active")
  tab_class <- c(
    if (fade && active) "show",
    if (active) "active",
    if (fade) "fade",
    "tab-pane"
  )
  xml2::xml_attr(tab, "class") <- paste(tab_class, collapse = " ")

  xml2::xml_attr(tab, "role") <- "tabpanel"
  xml2::xml_attr(tab, "aria-labelledby") <- paste0(id, "-tab")

  xml2::xml_add_child(content, tab)

  invisible()
}