#############################
 #       EVALUATION         #
 ############################
 
 #' Condition evaluation functions
 #'

 #' This function is used to support joinBy and/or groupBy function parameter.

 #'

 #' @param default concatenation of string identifying a name of metadata 
 #' attribute to be evaluated. 
 #' It defines a DEFAULT evaluation of the input values. 

 #' DEFAULT evaluation: the two attributes match if both end with value.
 #' 

 #' @param full concatenation of string identifying a name of metadata 
 #' attribute to be evaluated.

 #' It defines a FULL (FULLNAME) evaluation of the input values.

 #' FULL evaluation: two attributes match if they both end with value and,

 #' if they have further prefixes, the two prefix sequences are identical.
 #' 

 #' @param exact concatenation of string identifying a name of metadata 
 #' attribute to be evaluated.

 #' It defines a EXACT evaluation of the input values.

 #' EXACT evaluation: only attributes exactly as value match; 

 #' no further prefixes are allowed. 

 #' 

 #' @return list of 2-D array containing method of evaluation and metadata 
 #' attribute name

 #' 
 #' 

 #' @name Evaluation-Function

 #' @aliases condition_evaluation

 #' @rdname condition_eval_func
 #' @export

 conds <- function(default = c(""), full = c(""), exact = c("")) {

   df <- .condition("DEF",default)
   fn <- .condition("FULL",full)
   ex <- .condition("EXACT",exact)
   list("condition" = list("def" = df, "full" = fn, "exact" = ex))

 }
 

 .condition <- function(cond, array) {

   array = array[!array %in% ""]
   array = array[!duplicated(array)]
   

   if(!length(array)) {

     join_condition_matrix <- NULL

   } else {

     join_condition_matrix <- t(vapply(array, function(x) {
       new_value = c(cond, x)
       matrix <- matrix(new_value)
     },character(2)))
   }
   join_condition_matrix

 }