#' Test and/or coerce fill behavior
#'
#' Filling layouts in bslib are built on the foundation of fillable containers
#' and fill items (fill carriers are both fillable and fill). This is why most
#' bslib components (e.g., [card()], [card_body()], [layout_sidebar()]) possess
#' both `fillable` and `fill` arguments (to control their fill behavior).
#' However, sometimes it's useful to add, remove, and/or test fillable/fill
#' properties on arbitrary [htmltools::tag()], which these functions are
#' designed to do.
#'
#' @references The [Filling Layouts](https://rstudio.github.io/bslib/articles/filling.html)
#'   article on the bslib website introduces the concept of fillable containers
#'   and fill items.
#'
#' @seealso These functions provide a convenient interface to the underlying
#'   [htmltools::bindFillRole()] function.
#'
#' @details
#' Although `as_fill()`, `as_fillable()`, and `as_fill_carrier()` can work with
#' non-tag objects that have a [htmltools::as.tags] method (e.g., htmlwidgets),
#' they return the "tagified" version of that object.
#'
#' @examplesIf rlang::is_interactive()
#' library(shiny)
#' shinyApp(
#'   page_fillable(
#'     # without `as_fill_carrier()`, the plot won't fill the page because
#'     # `uiOutput()` is neither a fillable container nor a fill item by default.
#'     as_fill_carrier(uiOutput("ui"))
#'   ),
#'   function(input, output) {
#'     output$ui <- renderUI({
#'       div(
#'         class = "bg-info text-white",
#'         as_fill_item(),
#'         "A fill item"
#'       )
#'     })
#'   }
#' )
#'
#' @return
#'   * For `as_fill()`, `as_fillable()`, and `as_fill_carrier()`: the _tagified_
#'     version `x`, with relevant tags modified to possess the relevant fill
#'     properties.
#'   * For `is_fill()`, `is_fillable()`, and `is_fill_carrier()`: a logical vector,
#'     with length matching the number of top-level tags that possess the relevant
#'     fill properties.
#'
#' @param x An [htmltools::tag()].
#' @param ... Currently ignored.
#' @param min_height,max_height Any valid [CSS unit][htmltools::validateCssUnit]
#'   (e.g., `150`).
#' @param gap Any valid [CSS unit][htmltools::validateCssUnit].
#' @param class A character vector of class names to add to the tag.
#' @param style A character vector of CSS properties to add to the tag.
#' @param css_selector A character string containing a CSS selector for
#'   targeting particular (inner) tag(s) of interest. For more details on what
#'   selector(s) are supported, see [htmltools::tagAppendAttributes()].
#'
#' @export
as_fill_carrier <- function(
  x,
  ...,
  min_height = NULL,
  max_height = NULL,
  gap = NULL,
  class = NULL,
  style = NULL,
  css_selector = NULL
) {
  rlang::check_dots_empty()

  attrs <- fillable_attributes(
    min_height = min_height,
    max_height = max_height,
    gap = gap,
    class = class,
    style = style
  )

  if (rlang::is_missing(x)) {
    warn_css_selector_null(css_selector)
    attrs <- c(
      attrs,
      list(class = "html-fill-item html-fill-container", fill_dependency())
    )
    return(rlang::splice(attrs))
  }

  x <- bindFillRole(
    x,
    item = TRUE,
    container = TRUE,
    .cssSelector = css_selector
  )
  tagAppendAttributes(x, .cssSelector = css_selector, !!!attrs)
}

#' @rdname as_fill_carrier
#' @export
as_fillable_container <- function(
  x,
  ...,
  min_height = NULL,
  max_height = NULL,
  gap = NULL,
  class = NULL,
  style = NULL,
  css_selector = NULL
) {
  rlang::check_dots_empty()

  attrs <- fillable_attributes(
    min_height = min_height,
    max_height = max_height,
    gap = gap,
    class = class,
    style = style
  )

  if (rlang::is_missing(x)) {
    warn_css_selector_null(css_selector)
    attrs <- c(attrs, list(class = "html-fill-container", fill_dependency()))
    return(rlang::splice(attrs))
  }

  x <- bindFillRole(x, container = TRUE, .cssSelector = css_selector)

  tagAppendAttributes(x, .cssSelector = css_selector, !!!attrs)
}

#' @rdname as_fill_carrier
#' @export
as_fill_item <- function(
  x,
  ...,
  min_height = NULL,
  max_height = NULL,
  class = NULL,
  style = NULL,
  css_selector = NULL
) {
  rlang::check_dots_empty()

  attrs <- fillable_attributes(
    min_height = min_height,
    max_height = max_height,
    class = class,
    style = style
  )

  if (rlang::is_missing(x)) {
    warn_css_selector_null(css_selector)
    attrs <- c(attrs, list(class = "html-fill-item", fill_dependency()))
    return(rlang::splice(attrs))
  }

  x <- bindFillRole(x, item = TRUE, .cssSelector = css_selector)

  tagAppendAttributes(x, .cssSelector = css_selector, !!!attrs)
}

fill_dependency <- local({
  fill_dep <- NULL

  function() {
    if (!is.null(fill_dep)) return(fill_dep)
    fill_dep <<- htmltools::findDependencies(
      htmltools::bindFillRole(htmltools::tags$div(), container = TRUE)
    )[[1]]
    fill_dep
  }
})

fillable_attributes <- function(
  min_height = NULL,
  max_height = NULL,
  gap = NULL,
  class = NULL,
  style = NULL
) {
  list(
    style = css(
      min_height = validateCssUnit(min_height),
      max_height = validateCssUnit(max_height),
      gap = validateCssUnit(gap)
    ),
    class = class,
    style = style
  )
}

warn_css_selector_null <- function(x) {
  if (is.null(x)) return()

  rlang::warn(
    "Ignoring non-NULL `css_selector` because an input tag `x` was not provided.",
    call = rlang::caller_env()
  )
}

#' @rdname as_fill_carrier
#' @export
remove_all_fill <- function(x) {
  # NOTE: this doesn't remove the `htmltools-fill` dependency from `x`
  bindFillRole(
    x,
    item = FALSE,
    container = FALSE,
    overwrite = TRUE
  )
}

#' @rdname as_fill_carrier
#' @export
is_fill_carrier <- function(x) {
  classes <- paste0("html-fill-", c("container", "item"))
  renders_to_tag_class(x, classes)
}

#' @rdname as_fill_carrier
#' @export
is_fillable_container <- function(x) {
  UseMethod("is_fillable_container")
}

#' @export
is_fillable_container.htmlwidget <- function(x) {
  # won't actually work until (htmltools#334) gets fixed
  renders_to_tag_class(x, "html-fill-container", ".html-widget")
}

#' @export
is_fillable_container.default <- function(x) {
  renders_to_tag_class(x, "html-fill-container")
}

#' @rdname as_fill_carrier
#' @export
is_fill_item <- function(x) {
  UseMethod("is_fill_item")
}

#' @export
is_fill_item.htmlwidget <- function(x) {
  # won't actually work until (htmltools#334) gets fixed
  renders_to_tag_class(x, "html-fill-item", ".html-widget")
}

#' @export
is_fill_item.default <- function(x) {
  renders_to_tag_class(x, "html-fill-item")
}

renders_to_tag_class <- function(x, class, selector = NULL) {
  x <- try(as.tags(x), silent = TRUE)
  if (inherits(x, "try-error")) {
    return(FALSE)
  }
  xq <- tagQuery(x)
  if (length(selector)) {
    xq <- xq$find(selector)
  }
  vapply(
    xq$selectedTags(),
    function(y) tagQuery(y)$hasClass(class),
    logical(1),
    USE.NAMES = FALSE
  )
}

is_tag <- function(x) {
  inherits(x, "shiny.tag")
}