owid      = read.csv(paths$owid, stringsAsFactors = F)
owid$Date = as.Date(owid$Date, format = "%b %d, %Y")
colnames(owid)[4:5] = c("Tests", "Cases")

sel = c("AUT", "AUS", "DEU", "USA", "GBR", "FRA", "ESP", "ISL", "BRA",
        "BRA", "LVA", "NLD", "BEL", "ISL")

owid = owid[owid$Code %in% sel, ]

codes = unique(owid$Code)
owid2 = NULL
for(i in 1:length(codes)){
  sub = owid[owid$Code == codes[i], ]
  sub = sub[sub$Cases >= 100, ]
  idx_na = which(!is.na(sub$Tests))

  if(length(idx_na) > 4){

    sub       = sub[idx_na[1]:tail(idx_na, 1), ]
    sub$Tests = approx(sub$Date, sub$Tests, n = nrow(sub))$y
    owid2     = rbind(owid2, sub)
  }
}
rownames(owid2) = NULL


codes  = unique(owid2$Code)
slopes = as.data.frame(matrix(nrow = length(codes), ncol = 2))
colnames(slopes) = c("Cases", "Tests")
par(mfrow = c(3, 4))
for(i in 1:length(codes)){
  sub = owid2[owid2$Code == codes[i], ]
  sub = sub[1:20,]
  sub$idx = 1:nrow(sub)
  slopes[i, 1] = coef(lm(log(Cases)~idx, sub[1:20,]))[2]
  slopes[i, 2] = coef(lm(log(Tests)~idx, sub[1:20,]))[2]

  par(bg = "Black", fg = "White")

  plot(sub$Date, sub$Tests,
       col.lab  = "White",
       col.axis = "White",
       col.main = "White",
       ylim = c(1, max(sub$Tests, na.rm = T)),
       xlab = "",
       ylab = "# per day",
       type = "b",
       col  = "Light Blue",
       log  = "y",
       main = sub$Entity[1])
  lines(sub$Date, sub$Cases, type = "b", col = "Red")

  abline(h   = axTicks(2),
         v   = axTicks.Date(1, trak$date),
         lty = 3,
         col = "Light Grey")
  legend("bottomright",
         legend = c(paste0("Tests (", round(slopes[i, 2], 2), ")"),
                    paste0("Cases (", round(slopes[i, 1], 2), ")")),
         bty = "n",
         col = c("Light Blue", "Red"),
         lwd = 2)

}

slopes = log(2)/slopes

hist(slopes$Cases,
     col.lab  = "White",
     col.axis = "White",
     col.main = "White",
     col  = rgb(1, 0, 0, 0.75),
     xlab = "log(2)/slope",
     xaxs = "i",
     yaxs = "i",
     main = "Cases",
     breaks = seq(0, 16, by = 1))
hist(slopes$Tests, add = T,
     col.lab  = "White",
     col.axis = "White",
     col.main = "White",
     col  = rgb(0, 0, 1, 0.5),
     xlab = "log(2)/Tests",
     xaxs = "i",
     yaxs = "i",
     main = "Tests",
     breaks = seq(0, 16, by = 1))

  legend("topright", legend = c("Tests", "Cases"),
         bty = "n",
         col = c("Blue", "Red"),
         lwd = 2)



  plot(slopes$Tests, slopes$Cases,
       col.lab  = "White",
       col.axis = "White",
       col.main = "White",
       xlab = "log(2)/slope(Tests)",
       ylab = "log(2)/slope(Cases)",
       type = "p",
       col  = "Red",
       main = "Tests vs Cases")
  abline(h   = axTicks(2),
         v   = axTicks(1),
         lty = 3,
         col = "Light Grey")

  m = round(median(slopes$Cases/slopes$Tests, na.rm = T), 2)
  lines(slopes$Tests, m*slopes$Tests, col = "Red")

  legend("topleft", legend = paste0(m, "*log(2)/slope(Tests)"),
         bty = "n",
         col = c("Red"),
         lwd = 2)