####################################################################
### Add recession bars to ggplot graphs
####################################################################
geom_recession_bars <- function (date_df_start, date_df_end) {

  recessions_df = read.table(textConnection(
    "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"),
    sep = ',',
    colClasses = c('Date', 'Date'),
    header = TRUE)

   recessions_trim <- subset(recessions_df, peak >= min(date_df_start) &
                              trough <= max(date_df_end))

  if (nrow(recessions_trim) > 0) {
    recession_bars = geom_rect(data = recessions_trim, inherit.aes = F,
                               fill = "darkgray", alpha = 0.25,
                               aes(xmin = peak, xmax = trough, ymin = -Inf, ymax = +Inf))
  } else {
    recession_bars = geom_blank()
  }
}