#' Minimum detectable or WO for alternative hypothesis for given power (no ties)
#'
#' @param N a numeric vector of sample size values (two arms combined).
#' @param power the given power. The default is 0.5 corresponding to the minimum detectable win odds. A numeric vector of length 1.
#' @param SD assumed standard deviation of the win proportion. By default uses the conservative SD. A numeric vector of length 1.
#' @param k proportion of active group in the overall sample size. Default is 0.5 (balanced randomization). A numeric vector of length 1.
#' @param alpha the significance level for the 2-sided test. Default is 0.05. A numeric vector of length 1.
#' @param WOnull the win odds value of the null hypothesis (default is 1). A numeric vector of length 1.
#' @param digits precision to use for reporting calculated win odds.
#'
#' @return a data frame containing the calculated WO with input values.
#' @export
#' @md
#' @seealso [hce::powerWO()], [hce::sizeWO()]  for WO power and sample size calculation.
#' @references Gasparyan SB et al. (2021) "Power and sample size calculation for the win odds test: application to an ordinal endpoint in COVID-19 trials." Journal of Biopharmaceutical Statistics 31.6: 765-787. <doi:10.1080/10543406.2021.1968893>
#' @examples
#' minWO(N = 100, digits = 5)
#' minWO(N = 1200, power = 0.9)
#' minWO(N = 1200, power = 0.9, k = 0.75)
minWO <- function(N, power = 0.5, SD = NULL, k = 0.5, alpha = 0.05, WOnull = 1, digits = 2){
  digits <- digits[1]
  power <- power[1]
  SD <- SD[1]
  alpha <- alpha[1]
  WOnull <- WOnull[1]
  WPnull <- WOnull/(WOnull + 1)
  k <- k[1]
  if(k < 0 | k > 1) stop("k should be between 0 and 1.")
  VAR <- 1/(12*k*(1 - k))
  if(is.null(SD)) SD <- sqrt(VAR)
  SE <- SD/base::sqrt(N)
  C <- stats::qnorm(1 - alpha/2)

  WP <- WPnull + SE*(C - stats::qnorm(1 - power))
  WO <- WP/(1 - WP)
  d <- base::data.frame(WO = base::round(WO, digits), WP = WP, SampleSize = N, power = power, WPnull = WPnull, WOnull = WOnull, alpha = alpha, SD = SD, k = k)
  l <- base::list(result = d, value = WO, input = N, input_name = "Sample Size", value_name = "Win Odds")
  attr(d, "res") <- l
  base::class(d) <- c("hce_results")
  d
}