
#' A `RoxyTopic` is an ordered collection of unique rd_sections
#'
#' @description
#' A `RoxyTopic` object corresponds to a generated `.Rd` file.
#'
#' @param type Section type, a character scalar.
#' @param overwrite Whether to overwrite an existing section. If `FALSE`
#' then the two sections will be merged.
#'
#' @keywords internal

RoxyTopic <- R6::R6Class("RoxyTopic", public = list(

  #' @field sections Named list of sections. Each item must be an
  #' [rd_section()] object.
  sections = list(),

  #' @field filename Path to the `.Rd` file to generate.
  filename = "",

  #' @description Format the `.Rd` file. It considers the sections in
  #' particular order, even though Rd tools will reorder them again.
  #'
  #' @param ... Passed to the `format()` methods of the [rd_section()]
  #' objects, the sections.
  #' @return Character string.

  format = function(...) {
    # This has to happen here to get a better order when combining topics
    order <- c("backref", "docType", "encoding", "name", "alias", "title",
      "format", "source", "usage", "param", "value", "description",
      "details", "minidesc", "field", "slot", "rcmethods", "note",
      "section", "examples", "references", "seealso", "author",
      "concept", "keyword", "rawRd")
    sections <- move_names_to_front(self$sections, order)

    formatted <- lapply(sections, format, ...)
    paste0(
      made_by("%"),
      paste0(unlist(formatted), collapse = "\n")
    )
  },

  #' @description Check if an `.Rd` file is valid
  #' @return Logical flag, `TRUE` for valid `.Rd` files

  is_valid = function() {
    # Needs both title and name sections to generate valid Rd
    all(self$has_section(c("title", "name")))
  },

  #' @description Check if an `.Rd` file has a certain section.
  #' @return Logical flag.

  has_section = function(type) {
    type %in% names(self$sections)
  },

  #' @description Query a section.
  #' @return The [rd_section] object representing the section, or `NULL`
  #' if the topic has no such section.

  get_section = function(type) {
    self$sections[[type]]
  },

  #' @description Query the value of a section. This is the value of
  #' the [rd_section] object.
  #' @return Value.

  get_value = function(type) {
    self$get_section(type)$value
  },

  #' @description Get the Rd code of a section.
  #' @return Character vector, one element per line.

  get_rd = function(type) {
    format(self$get_section(type))
  },

  #' @description Get the value of the `name` section. This is the name
  #' of the Rd topic.
  #' @return Character scalar.

  get_name = function() {
    self$get_value("name")
  },

  #' @description Query the topics this topic inherits `type` from.
  #' @return A character vector of topic names.

  inherits_from = function(type) {
    if (!self$has_section("inherit")) {
      return(character())
    }

    inherit <- self$get_value("inherit")

    inherits_field <- map_lgl(inherit$fields, function(x) type %in% x)
    sources <- inherit$source[inherits_field]

    if ("NULL" %in% sources)
      return(character())

    sources
  },

  #' @description Query the topics this topic inherits sections from.
  #' @return A character vector of topic names.

  inherits_section_from = function() {
    if (!self$has_section("inherit_section")) {
      return(character())
    }

    self$get_value("inherit_section")$source
  },

  #' @description Add one or more sections to the topic.
  #' @param x Section(s) to add. It may be
  #' another `RoxyTopic` object, all of its sections will be added;
  #' or an [rd_section] object;
  #' or a list of [rd_section] objects to add.

  add = function(x, overwrite = FALSE) {
    if (inherits(x, "RoxyTopic")) {
      self$add(x$sections, overwrite = overwrite)
    } else if (inherits(x, "rd_section")) {
      self$add_section(x, overwrite = overwrite)
    } else if (is.list(x)) {
      for (section in x) {
        self$add_section(section, overwrite = overwrite)
      }
    } else if (is.null(x)) {
      # skip
    } else {
      stop("Don't know how to add object of type ", class(x)[1])
    }
    invisible()
  },

  #' @description Add a section.
  #' @details
  #' Ensures that each type of name (as given by its name), only appears
  #' once in `self$sections`. This method if for internal use only.
  #' @param section [rd_section] object to add.

  add_section = function(section, overwrite = FALSE) {
    if (is.null(section)) return()
    type <- section$type
    if (self$has_section(type) && !overwrite) {
      section <- merge(self$get_section(type), section)
    }

    self$sections[[type]] <- section
    invisible()
  }
))

move_names_to_front <- function(x, to_front) {
  nms <- names(x)
  x[union(intersect(to_front, nms), nms)]
}
