#' Add a node to an existing graph object
#'
#' @description
#'
#' With a graph object of class `dgr_graph`, add a new node to the graph. One
#' can optionally provide node attributes for the created node. There is also
#' the option to create edges to and from existing nodes in the graph. Because
#' new edges can also be created through this function, there is the possibility
#' to set edge attributes for any new graph edges.
#'
#' @inheritParams node_edge_aes_data
#' @inheritParams render_graph
#' @param type An optional character object that acts as a group identifier for
#'   the node to be added.
#' @param label An optional character object that describes the node.
#' @param from An optional vector containing node IDs from which edges will be
#'   directed to the new node.
#' @param to An optional vector containing node IDs to which edges will be
#'   directed from the new node.
#'
#' @return A graph object of class `dgr_graph`.
#'
#' @examples
#' # Create an empty graph and add 2 nodes by using
#' # the `add_node()` function twice
#' graph <-
#'   create_graph() %>%
#'   add_node() %>%
#'   add_node()
#'
#' # Get a count of all nodes
#' # in the graph
#' graph %>% count_nodes()
#'
#' # The nodes added were given
#' # ID values `1` and `2`; obtain
#' # the graph's node IDs
#' graph %>% get_node_ids()
#'
#' # Add a node with a `type`
#' # value defined
#' graph <-
#'   graph %>%
#'   add_node(type = "person")
#'
#' # View the graph's internal
#' # node data frame (ndf)
#' graph %>% get_node_df()
#'
#' @family node creation and removal
#'
#' @export
add_node <- function(
    graph,
    type = NULL,
    label = NULL,
    from = NULL,
    to = NULL,
    node_aes = NULL,
    edge_aes = NULL,
    node_data = NULL,
    edge_data = NULL
) {

  # Get the time of function start
  time_function_start <- Sys.time()

  # Validation: Graph object is valid
  check_graph_valid(graph)

  # Get the node ID for the node to be added
  node <- graph$last_node + 1L

  # Get the number of edges in the graph
  edges_in_graph <- nrow(graph$edges_df)

  # Get the number of edges ever created for
  # this graph
  edges_created <- graph$last_edge

  # If `type` or `label` is NULL, convert to NA
  type <- type %||% NA_character_
  label <- label %||% NA_character_

  # Collect node aesthetic attributes
  if (!is.null(node_aes)) {

    node_aes_tbl <- dplyr::as_tibble(node_aes)

    if (nrow(node_aes_tbl) == 1) {

      node_aes$index__ <- 1

      node_aes_tbl <-
        dplyr::as_tibble(node_aes) %>%
        dplyr::select(-"index__")
    }

    if ("id" %in% colnames(node_aes_tbl)) {
      node_aes_tbl$id <- NULL
    }
  }

  # Collect node data attributes
  if (!is.null(node_data)) {

    node_data_tbl <- dplyr::as_tibble(node_data)

    if (nrow(node_data_tbl) == 1) {

      node_data$index__ <- 1

      node_data_tbl <-
        dplyr::as_tibble(node_data) %>%
        dplyr::select(-"index__")
    }

    if ("id" %in% colnames(node_data_tbl)) {
      node_data_tbl$id <- NULL
    }
  }

  # Modify graph if neither `to` nor `from`
  # values provided
  if (is.null(from) && is.null(to)) {

    new_node <-
      create_node_df(
        n = 1,
        label = as.character(label),
        type = as.character(type))

    new_node[1, 1] <- node

    # Add node aesthetics if available
    if (exists("node_aes_tbl")) {

      new_node <-
        new_node %>%
        dplyr::bind_cols(node_aes_tbl)
    }

    # Add node data if available
    if (exists("node_data_tbl")) {

      new_node <-
        new_node %>%
        dplyr::bind_cols(node_data_tbl)
    }

    combined_nodes <-
      combine_ndfs(graph$nodes_df, new_node)

    edges_in_graph_2 <- nrow(graph$edges_df)

    graph$nodes_df <- combined_nodes
    graph$last_node <- graph$last_node + 1

    # Get the name of the function
    fcn_name <- get_calling_fcn()

    # Update the `graph_log` df with an action
    graph$graph_log <-
      add_action_to_log(
        graph_log = graph$graph_log,
        version_id = nrow(graph$graph_log) + 1L,
        function_used = fcn_name,
        time_modified = time_function_start,
        duration = graph_function_duration(time_function_start),
        nodes = nrow(graph$nodes_df),
        edges = nrow(graph$edges_df),
        d_n = 1)

    # Write graph backup if the option is set
    if (graph$graph_info$write_backups) {
      save_graph_as_rds(graph = graph)
    }

    return(graph)
  }

  # Modify graph if only `from` values provided
  if (!is.null(from) && is.null(to)) {

    from_nodes_available <-
      all(from %in% get_node_ids(graph))

    if (!from_nodes_available) {

      cli::cli_abort(c(
        "The nodes from which edges should be applied to the new node are not available."
      ))
    }

    # from_nodes_available

    new_node <-
      create_node_df(
        n = 1,
        label = as.character(label),
        type = as.character(type)
      )

    new_node[1, 1] <- node

    # Add node aesthetics if available
    if (exists("node_aes_tbl")) {
      new_node <-
        new_node %>%
        dplyr::bind_cols(node_aes_tbl)
    }

    # Add node data if available
    if (exists("node_data_tbl")) {
      new_node <-
        new_node %>%
        dplyr::bind_cols(node_data_tbl)
    }

    # Combine the new nodes with those in the graph
    combined_nodes <-
      combine_ndfs(graph$nodes_df, new_node)

    # Collect edge aesthetic attributes
    if (!is.null(edge_aes)) {

      edge_aes_tbl <- dplyr::as_tibble(edge_aes)

      if (nrow(edge_aes_tbl) < length(from)) {
        edge_aes$index__ <- seq_along(from)

        edge_aes_tbl <-
          dplyr::as_tibble(edge_aes) %>%
          dplyr::select(-"index__")
      }

      if ("id" %in% colnames(edge_aes_tbl)) {
        edge_aes_tbl$id <- NULL
      }
    }

    # Collect edge data attributes
    if (!is.null(edge_data)) {
      edge_data_tbl <- dplyr::as_tibble(edge_data)

      if (nrow(edge_data_tbl) < length(from)) {
        edge_data$index__ <- seq_along(from)

        edge_data_tbl <-
          dplyr::as_tibble(edge_data) %>%
          dplyr::select(-"index__")
      }

      if ("id" %in% colnames(edge_data_tbl)) {
        edge_data_tbl$id <- NULL
      }
    }

    new_edges <-
      create_edge_df(
        from = from,
        to = rep(node, length(from))
      )

    new_edges$id <-
      new_edges$id + edges_created

    # Add edge aesthetics if available
    if (exists("edge_aes_tbl")) {
      new_edges <-
        new_edges %>%
        dplyr::bind_cols(edge_aes_tbl)
    }

    # Add edge data if available
    if (exists("edge_data_tbl")) {
      new_edges <-
        new_edges %>%
        dplyr::bind_cols(edge_data_tbl)
    }

    # Use `bind_rows()` to add the
    # new edges
    combined_edges <-
      dplyr::bind_rows(
        graph$edges_df,
        new_edges
      )

    edges_in_graph_2 <- nrow(combined_edges)
    edges_added <- edges_in_graph_2 - edges_in_graph

    # Create a revised graph
    graph$nodes_df <- combined_nodes
    graph$edges_df <- combined_edges
    graph$last_node <- graph$last_node + 1
    graph$last_edge <- graph$last_edge + edges_added

    # Get the name of the function
    fcn_name <- get_calling_fcn()

    # Update the `graph_log` df with an action
    graph$graph_log <-
      add_action_to_log(
        graph_log = graph$graph_log,
        version_id = nrow(graph$graph_log) + 1L,
        function_used = fcn_name,
        time_modified = time_function_start,
        duration = graph_function_duration(time_function_start),
        nodes = nrow(graph$nodes_df),
        edges = nrow(graph$edges_df),
        d_n = 1,
        d_e = length(from)
      )

    # Write graph backup if the option is set
    if (graph$graph_info$write_backups) {
      save_graph_as_rds(graph = graph)
    }

    return(graph)
  }

  # Modify graph if only `to` values provided
  if (is.null(from) && !is.null(to)) {
    to_nodes_available <-
      all(to %in% get_node_ids(graph))

    if (!to_nodes_available) {
      cli::cli_abort(
        "The nodes to which edges should be applied from the new node are not available.")
    }

    # Assume to_nodes is available.
    new_node <-
      create_node_df(
        n = 1,
        label = as.character(label),
        type = as.character(type))

    new_node[1, 1] <- node

    # Add node aesthetics if available
    if (exists("node_aes_tbl")) {

      new_node <-
        new_node %>%
        dplyr::bind_cols(node_aes_tbl)
    }

    # Add node data if available
    if (exists("node_data_tbl")) {

      new_node <-
        new_node %>%
        dplyr::bind_cols(node_data_tbl)
    }

    combined_nodes <-
      combine_ndfs(graph$nodes_df, new_node)

    # Collect edge aesthetic attributes
    if (!is.null(edge_aes)) {

      edge_aes_tbl <- dplyr::as_tibble(edge_aes)

      if (nrow(edge_aes_tbl) < length(from)) {
        edge_aes$index__ <- seq_along(from)

        edge_aes_tbl <-
          dplyr::as_tibble(edge_aes) %>%
          dplyr::select(-"index__")
      }

      if ("id" %in% colnames(edge_aes_tbl)) {
        edge_aes_tbl$id <- NULL
      }
    }

    # Collect edge data attributes
    if (!is.null(edge_data)) {

      edge_data_tbl <- dplyr::as_tibble(edge_data)

      if (nrow(edge_data_tbl) < length(from)) {
        edge_data$index__ <- seq_along(from)

        edge_data_tbl <-
          dplyr::as_tibble(edge_data) %>%
          dplyr::select(-"index__")
      }

      if ("id" %in% colnames(edge_data_tbl)) {
        edge_data_tbl$id <- NULL
      }
    }

    new_edges <-
      create_edge_df(
        from = rep(node, length(to)),
        to = to)

    new_edges$id <-
      new_edges$id + edges_created

    # Add edge aesthetics if available
    if (exists("edge_aes_tbl")) {

      new_edges <-
        new_edges %>%
        dplyr::bind_cols(edge_aes_tbl)
    }

    # Add edge data if available
    if (exists("edge_data_tbl")) {
      new_edges <-
        new_edges %>%
        dplyr::bind_cols(edge_data_tbl)
    }

    # Use `bind_rows()` to add the
    # new edges
    combined_edges <-
      dplyr::bind_rows(
        graph$edges_df,
        new_edges)

    edges_in_graph_2 <- nrow(combined_edges)
    edges_added <- edges_in_graph_2 - edges_in_graph

    # Create a revised graph
    graph$nodes_df <- combined_nodes
    graph$edges_df <- combined_edges
    graph$last_node <- graph$last_node + 1
    graph$last_edge <- graph$last_edge + edges_added

    # Get the name of the function
    fcn_name <- get_calling_fcn()

    # Update the `graph_log` df with an action
    graph$graph_log <-
      add_action_to_log(
        graph_log = graph$graph_log,
        version_id = nrow(graph$graph_log) + 1L,
        function_used = fcn_name,
        time_modified = time_function_start,
        duration = graph_function_duration(time_function_start),
        nodes = nrow(graph$nodes_df),
        edges = nrow(graph$edges_df),
        d_n = 1,
        d_e = length(to))

    # Write graph backup if the option is set
    if (graph$graph_info$write_backups) {
      save_graph_as_rds(graph = graph)
    }

    return(graph)
  }

  # Modify graph if both `to` and `from` values provided
  if (!is.null(from) && !is.null(to)) {

    from_nodes_available <-
      all(from %in% get_node_ids(graph))

    to_nodes_available <-
      all(to %in% get_node_ids(graph))

    if (!from_nodes_available) {

      cli::cli_abort(
        "The nodes from which edges should be applied to the new node are not available.")
    }

    if (!to_nodes_available) {

      cli::cli_abort(
        "The nodes to which edges should be applied from the new node are not available."
      )
    }

    # If both to_nodes and from_nodes are available, continue.
      new_node <-
        create_node_df(
          n = 1,
          label = as.character(label),
          type = as.character(type))

      new_node[1, 1] <- node

      # Add node aesthetics if available
      if (exists("node_aes_tbl")) {
        new_node <-
          new_node %>%
          dplyr::bind_cols(node_aes_tbl)
      }

      # Add node data if available
      if (exists("node_data_tbl")) {

        new_node <-
          new_node %>%
          dplyr::bind_cols(node_data_tbl)
      }

      # Combine the new nodes with those in the graph
      combined_nodes <-
        combine_ndfs(graph$nodes_df, new_node)

      new_edges <-
        combine_edfs(
          create_edge_df(
            from = rep(node, length(to)),
            to = to),
          create_edge_df(
            from = from,
            to = rep(node, length(from))))

      new_edges$id <-
        new_edges$id + edges_created

      # Collect edge aesthetic attributes
      if (!is.null(edge_aes)) {

        edge_aes_tbl <- dplyr::as_tibble(edge_aes)

        if (nrow(edge_aes_tbl) < (length(from) + length(to))) {
          edge_aes$index__ <- seq_len(length(from) + length(to))

          edge_aes_tbl <-
            dplyr::as_tibble(edge_aes) %>%
            dplyr::select(-"index__")
        }

        if ("id" %in% colnames(edge_aes_tbl)) {
          edge_aes_tbl$id <- NULL
        }
      }

      # Collect edge data attributes
      if (!is.null(edge_data)) {

        edge_data_tbl <- dplyr::as_tibble(edge_data)

        if (nrow(edge_data_tbl) < (length(from) + length(to))) {

          edge_data$index__ <- seq_len(length(from) + length(to))

          edge_data_tbl <-
            dplyr::as_tibble(edge_data) %>%
            dplyr::select(-"index__")
        }

        if ("id" %in% colnames(edge_data_tbl)) {
          edge_data_tbl$id <- NULL
        }
      }

      # Add edge aesthetics if available
      if (exists("edge_aes_tbl")) {

        new_edges <-
          new_edges %>%
          dplyr::bind_cols(edge_aes_tbl)
      }

      # Add edge data if available
      if (exists("edge_data_tbl")) {

        new_edges <-
          new_edges %>%
          dplyr::bind_cols(edge_data_tbl)
      }

      # Use `bind_rows()` to add the
      # new edges
      combined_edges <-
        dplyr::bind_rows(
          graph$edges_df,
          new_edges)

      edges_in_graph_2 <- nrow(combined_edges)
      edges_added <- edges_in_graph_2 - edges_in_graph

      # Create a revised graph and return that graph
      graph$nodes_df <- combined_nodes
      graph$edges_df <- combined_edges
      graph$last_node <- graph$last_node + 1
      graph$last_edge <- graph$last_edge + edges_added

      # Get the name of the function
      fcn_name <- get_calling_fcn()

      # Update the `graph_log` df with an action
      graph$graph_log <-
        add_action_to_log(
          graph_log = graph$graph_log,
          version_id = nrow(graph$graph_log) + 1L,
          function_used = fcn_name,
          time_modified = time_function_start,
          duration = graph_function_duration(time_function_start),
          nodes = nrow(graph$nodes_df),
          edges = nrow(graph$edges_df),
          d_n = 1,
          d_e = length(from) + length(to))

      # Perform graph actions, if any are available
      if (nrow(graph$graph_actions) > 0) {
        graph <-
          trigger_graph_actions(graph)
      }

      # Write graph backup if the option is set
      if (graph$graph_info$write_backups) {
        save_graph_as_rds(graph = graph)
      }

      return(graph)
  }
}