#
# Compute the day of a date
# http://fr.wikipedia.org/wiki/Détermination_du_jour
#
# Olivier Corby - Wimmics, Inria, I3S - 2015
#
prefix cal: <http://ns.inria.fr/sparql-extension/calendar#>
select 

(cal:jour(now()) as ?fr)

where  { }

@public {
function xt:day(?d)  { cal:day(?d)}

function xt:jour(?d) { cal:jour(?d) }

function cal:day(?d)  { cal:en(cal:find(?d))}

function cal:jour(?d) { cal:fr(cal:find(?d)) }

function cal:div(?a, ?b) { xsd:integer(floor(?a / ?b))}

function cal:mod(?a, ?b) { xsd:integer(?a - (?b * cal:div(?a, ?b)))}

function cal:bisextile(?y) {
    ((cal:mod(?y, 4) = 0) &&
      ((cal:mod(?y, 100) != 0) || (cal:mod(?y, 400) = 0)))
}
      
function cal:ab(?y) { cal:div(?y, 100)}
function cal:cd(?y) { cal:mod(?y, 100)}
function cal:k(?y)  { cal:div(cal:cd(?y), 4)}
function cal:q(?y)  { cal:div(cal:ab(?y), 4)}

function cal:monthday(?m, ?y) {
  if (?m <= 2,
    if (cal:bisextile(?y),
      if (?m = 1, 3, 6),
      if (?m = 1, 4, 0)),
  if (?m in (3, 11), 0,
    if (?m in (6), 1,
      if (?m in (9, 12), 2,
	if (?m in (4, 7), 3,
	  if (?m in (10), 4,
	    if (?m in (5), 5, 6)))))))
}
	    
function cal:get(?y, ?m, ?d) {
  let (?n = cal:k(?y) + cal:q(?y) + cal:cd(?y) +
        cal:monthday(?m, ?y) + ?d + 2 + 5 * cal:ab(?y))
    {
      cal:mod(?n, 7)
    }
}
    
function cal:find(?d) {
  cal:get(year(?d), month(?d), day(?d))
}
  
function cal:en(?n) {
  if (?n = 0, "Sunday",
  if (?n = 1, "Monday",
  if (?n = 2, "Tuesday",
  if (?n = 3, "Wednesday",
  if (?n = 4, "Thursday",
  if (?n = 5, "Friday",
  if (?n = 6, "Saturday", "Unknown")))))))
}
  
function cal:fr(?n) {
  if (?n = 0, "Dimanche",
  if (?n = 1, "Lundi",
  if (?n = 2, "Mardi",
  if (?n = 3, "Mercredi",
  if (?n = 4, "Jeudi",
  if (?n = 5, "Vendredi",
  if (?n = 6, "Samedi", "Inconnu")))))))
}

function cal:num(?day) {
    if (?day in( "Lundi", "Monday"), 1,
    if (?day in( "Mardi", "Tuesday"), 2,
    if (?day in( "Mercredi", "Wednesday"), 3,
    if (?day in( "Jeudi", "Thursday"), 4,
    if (?day in( "Vendredi", "Friday"), 5,
    if (?day in( "Samedi", "Saturday"), 6,
    if (?day in( "Dimanche", "Sunday"), 7, 0)))))))
}

function cal:days(?y, ?m) {
    let (?list = 
	xt:list(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31)){ 
        if (?m != 2, xt:get(?list, ?m - 1),
            if (cal:bisextile(?y), 29, 28))
    }
}


}