data_navbar <- function(pkg = ".", depth = 0L) {
  pkg <- as_pkgdown(pkg)

  # Take structure as is from meta
  navbar <- purrr::pluck(pkg, "meta", "navbar")
  structure <- navbar$structure %||% navbar_structure()

  # Merge components from meta
  components <- navbar_components(pkg)
  components_meta <- navbar$components %||% list()
  components[names(components_meta)] <- components_meta
  components <- purrr::compact(components)

  # Any unplaced components go to the right of the left navbar
  right_comp <- intersect(structure$right, names(components))
  left_comp <- intersect(structure$left, names(components))
  extra_comp <- setdiff(names(components), c(left_comp, right_comp))

  # Backward compatiblity
  left <- navbar$left %||% components[c(left_comp, extra_comp)]
  right <- navbar$right %||% components[right_comp]

  list(
    type = navbar$type %||% "default",
    left = render_navbar_links(left, depth = depth),
    right = render_navbar_links(right, depth = depth)
  )
}

render_navbar_links <- function(x, depth = 0L) {
  stopifnot(is.integer(depth), depth >= 0L)

  tweak <- function(x) {
    if (!is.null(x$menu)) {
      x$menu <- lapply(x$menu, tweak)
      x
    } else if (!is.null(x$href) && !grepl("://", x$href, fixed = TRUE)) {
      x$href <- paste0(up_path(depth), x$href)
      x
    } else {
      x
    }
  }

  if (depth != 0L) {
    x <- lapply(x, tweak)
  }
  rmarkdown::navbar_links_html(x)
}

# Default navbar ----------------------------------------------------------

navbar_structure <- function() {
  print_yaml(list(
    left = c("home", "intro", "reference", "articles", "tutorials", "news"),
    right = "github"
  ))
}

navbar_components <- function(pkg = ".") {
  pkg <- as_pkgdown(pkg)

  menu <- list()
  menu$home <- menu_icon("home", "index.html")
  menu$reference <- menu_link("Reference", "reference/index.html")
  menu$tutorials <- menu("Tutorials",
    menu_links(pkg$tutorials$title, pkg$tutorials$file_out)
  )

  vignettes <- pkg$vignettes
  pkg_intro <- vignettes$name == pkg$package
  if (any(pkg_intro)) {
    intro <- vignettes[pkg_intro, , drop = FALSE]
    vignettes <- vignettes[!pkg_intro, , drop = FALSE]

    menu$intro <- menu_link("Get started", intro$file_out)
  }
  menu$articles <-  menu("Articles", menu_links(vignettes$title, vignettes$file_out))
  menu$news <- navbar_news(pkg)

  if (!is.null(pkg$github_url)) {
    menu$github <- menu_icon("github", pkg$github_url, style = "fab")
  }

  print_yaml(menu)
}


# Menu helpers -------------------------------------------------------------

menu <- function(text, children) {
  if (length(children) == 0)
    return()
  list(text = text, menu = children)
}
menu_link <- function(text, href) {
  list(text = text, href = href)
}
menu_links <- function(text, href) {
  purrr::map2(text, href, ~ list(text = .x, href = .y))
}
menu_icon <- function(icon, href, style = "fas") {
  list(icon = paste0(style, " fa-", icon, " fa-lg"), href = href)
}
menu_text <- function(text) {
  list(text = text)
}
menu_spacer <- function() {
   menu_text("---------")
}