totalPrice.R

getDiscount <- function(currency.input, date.input)
{ # Computes the percentage of discount to apply based on date and currency
  #
  #Args:
  #   currency.input = character of the currency
  #   date.input = the current date
  #
  # Returns: 
  #   The percentage of discount to apply on the sum of products
  #
  # defining percentages for each case
  discount.date <- 0.5
  discount.eur <- 0.2
  discount.usd <-  0.25
  
  #Dataframe with currencies defined
  name <- c("EUR","USD")
  value <- c(discount.eur,discount.usd)
  currencies <- data.frame(name,value)
  #defining specific date
  date.selected <- as.Date("2020-11-27")
  
  disc.currency <- currencies[currencies$name == currency.input,]
  #evaluating type of discount to apply
  discount <- ifelse(date.selected == date.input, discount.date,
                     ifelse(nrow(disc.currency)>0,disc.currency$value,0))
  
  return(discount)
}

totalPrice <- function(order, currency = "EUR", date = Sys.Date()){
  # Computes the sum of all product's of a order after applying discount based 
  # on the currency and date 
  #
  # Args:
  #   order: Dataframe with products to be calculated 
  #   currency: character variable, indicates currency to be used
  #   date: Current date, used for 
  #
  # Returns: 
  #   The sum of products on order after applying a discount  
  #
  # Error handling NULL input and type validation
  if((is.null(dim(order))) || !is.character(currency)) {
    stop("Order is null or input types invalid")
  }
  total <- 0 
  # Validating if the dataframe is empty
  if(nrow(order)> 0)
  {
    discount <- getDiscount(currency, date)
    tryCatch(
      {
        #Cleaning the dataframe from duplicates, negatives, NA values
        order <- unique(order)
        prices <- order[paste0("price_", currency)]
        prices <- prices[prices>0]
        prices <- prices[!is.na(prices)]
        total <- sum(prices * (1-discount))       
      },
      error = function(e){
        #verifying if the currency selected exist on the dataframe
        stop("The currency is not found!")
      }
    )
  }
  else{
    warning("Order without products!")
  }
  return(total)
}