HierarchiesAndCareers:

#' Create line of with eigenvector centrality for nodes over time
#'
#' @param .eigen.centr.over.years a df that contains nodes and their centrality in a given year
#' @param .filename
#'
#' @return a line chart as ggplot object.
#' Eigenvector centrality was converted to NA if there was no exhibition before or after a given year.
#' Consequently, the line chart only shows centrality of an exhibition place during exhibition activity.
#' Moreover,
#' @export
#'
#' @examples
#' g <- create_example_graph()
#' centr.over.years <- compute_eigen_centr_period(g, 1995, 2002)
#'
#' plot_eigen_centr_over_years(centr.over.years)
plot_ecoy <- function(.eigen.centr.over.years, .filename = NULL){


  plot <- ggplot(.eigen.centr.over.years) +

    # create basic line chart
    geom_line(aes(x = yr_centr_computed, y = eigen_centr, group = name_exhplace),
              color = alpha("grey", 0.8)) +

    # add color for top nodes according to eigenvector centrality from complete graph
    geom_line(aes(x = yr_centr_computed, y = eigen_centr, color = name_exhplace),
              data = .eigen.centr.over.years %>%
                filter(eigen_centr >= 0.95) %>%
                distinct(name) %>%
                left_join(.eigen.centr.over.years, by = "name")) +

    # customize layout
    theme_minimal() +
    labs(x = "Year", y = "Eigenvector Centrality", color = "Exhibition Venue") +

    # remove left and right margin from plot
    scale_x_continuous(expand = c(0,0), breaks = seq(1905, 2015, 10)) +

    # highlighted exhibition venues should be displayed in columns
    guides(color = guide_legend(ncol = 2, byrow = T)) +

    theme(
      # reduce text size
      legend.text = element_text(size = 8.5),
      # replace legend from right to bottom
      legend.position = "bottom",
      # reduce vertical and add horizontal spacing
      legend.key.height = unit(0.7, 'lines'),
      legend.key.width = unit(1.5, 'lines'),
      # exclude varible name
      legend.title = element_blank()
      )

  # save plot to drive
  if(!is.null(.filename)){
    ggsave(.filename, plot,
           width = 7, height = 5)
  }

  return(plot)

}