server.R

server <- function(input, output, session) {
  
  output$housing_plot_error <- renderUI({
    if(input$from_year >= input$to_year){
      tags$span(
        style = "color:red; font-weight:bold",
        paste0('"From Year" (', input$from_year, ') must be before "To Year" (', input$to_year, ')')
      )
    } else {
      NULL
    }
  })
  
  output$housing_plot <- renderPlot({
    
    if(input$from_year >= input$to_year) return(NULL)
    
    material_spinner_show(session, "housing_plot")
    
    Sys.sleep(2.5) # sleep to show spinner example longer 
    
    plot_data <- 
      HPI_AT_metro %>% 
      filter(Area_State == input$Area_State,
             Year >= input$from_year,
             Year <= input$to_year) %>% 
      mutate(
        Housing_Price_Index_Plot =
          round(((Housing_Price_Index / Housing_Price_Index[Year_Quarter_num == min(Year_Quarter_num)])) - 1,2)
      )
    
    plot_out <- 
      ggplot(plot_data, aes(x = Year_Quarter_num,
                            y = Housing_Price_Index_Plot)) +
      geom_line(size = 3, color = "#0000ff") +
      geom_label(data = plot_data[plot_data$Year_Quarter_num == max(plot_data$Year_Quarter_num), ],
                 aes(label = paste0(Housing_Price_Index_Plot * 100, "%")),
                 color = "#0000ff", size = 5) + 
      scale_y_continuous(labels = scales::percent) +
      coord_cartesian(
        ylim = c(
          floor((min(plot_data$Housing_Price_Index_Plot) - .1) / .1) * .1,
          ceiling((max(plot_data$Housing_Price_Index_Plot) + .1) / .1) * .1
        )
      ) + 
      geom_hline(yintercept = 0, linetype = 2) +
      scale_x_continuous(
        breaks = sort(unique(plot_data$Year))
      ) +
      # scale_y_continuous(labels = ) + 
      labs(x = "Year", 
           y = "") +
      theme(text = element_text(size = 15),
            legend.position = "none",
            plot.margin = unit(c(0, 0, 0, -5), "mm"),
            axis.text.x = element_text(angle=60, hjust=1))
    
    material_spinner_hide(session, "housing_plot")
    
    plot_out
  })
}