geom_recession_bars prototype

####################################################################
### Add NBER recession bars to ggplot graphs
####################################################################

geom_recession_bars <- function(date_start, date_end, fill = "darkseagreen4") {

   date_start <- as.Date(date_start, origin = "1970-01-01")
   date_end   <- as.Date(date_end,   origin = "1970-01-01")

   recessions_tibble <-
     tribble(
       ~peak,        ~trough,
       "1857-06-01", "1858-12-01",
       "1860-10-01", "1861-06-01",
       "1865-04-01", "1867-12-01",
       "1869-06-01", "1870-12-01",
       "1873-10-01", "1879-03-01",
       "1882-03-01", "1885-05-01",
       "1887-03-01", "1888-04-01",
       "1890-07-01", "1891-05-01",
       "1893-01-01", "1894-06-01",
       "1895-12-01", "1897-06-01",
       "1899-06-01", "1900-12-01",
       "1902-09-01", "1904-08-01",
       "1907-05-01", "1908-06-01",
       "1910-01-01", "1912-01-01",
       "1913-01-01", "1914-12-01",
       "1918-08-01", "1919-03-01",
       "1920-01-01", "1921-07-01",
       "1923-05-01", "1924-07-01",
       "1926-10-01", "1927-11-01",
       "1929-08-01", "1933-03-01",
       "1937-05-01", "1938-06-01",
       "1945-02-01", "1945-10-01",
       "1948-11-01", "1949-10-01",
       "1953-07-01", "1954-05-01",
       "1957-08-01", "1958-04-01",
       "1960-04-01", "1961-02-01",
       "1969-12-01", "1970-11-01",
       "1973-11-01", "1975-03-01",
       "1980-01-01", "1980-07-01",
       "1981-07-01", "1982-11-01",
       "1990-07-01", "1991-03-01",
       "2001-03-01", "2001-11-01",
       "2007-12-01", "2009-06-01",
       "2020-02-01", "2020-04-01"
     ) %>%
     mutate(peak   = as.Date(peak),
            trough = as.Date(trough))

   recessions_trim <- recessions_tibble %>%
                      filter(peak   >= min(date_start) &
                             trough <= max(date_end))

  if (nrow(recessions_trim) > 0) {

    recession_bars <- geom_rect(data       = recessions_trim,
                               inherit.aes = F,
                               fill        = fill,
                               alpha       = 0.25,
                               aes(xmin = as.Date(peak,   origin = "1970-01-01"),
                                   xmax = as.Date(trough, origin = "1970-01-01"),
                                   ymin = -Inf, ymax = +Inf))
  } else {
        recession_bars <- geom_blank()
  }
}