% Copyright 2016 Slavonic Computing Initialive
% http://sci.ponomar.net
% 
\ProvidesPackage{cu-calendar}[2016/03/30 v1.0 CU Calendars]

\RequirePackage{intcalc}
\RequirePackage{cu-num}

%
% Tools
%
\def\cu@jdn#1-#2-#3-#4{%
  \expandafter\cu@@jdn
  \expandafter{\the\numexpr \intcalcDiv{14 - #2}{12} \relax}{#1}{#2}{#3}{#4}%
}%
\def\cu@@jdn#1#2#3#4#5{%
  \expandafter\cu@@@jdn
  \expandafter{\the\numexpr #2 + 4800 - #1\relax}{#1}{#2}{#3}{#4}{#5}%
}%
\def\cu@@@jdn#1#2#3#4#5#6{%  y a year month day
  \expandafter\cu@@@@jdn
  \expandafter{\the\numexpr #4 - 3 + 12 * (#2)\relax}{#1}{#2}{#3}{#4}{#5}{#6}%
}%
\def\cu@@@@jdn#1#2#3#4#5#6#7{% m y a year month day
  \expandafter #7%
  \expandafter{\the\numexpr #6 + 
    \intcalcDiv{153 * (#1) + 2}{5} + (365 * (#2)) + \intcalcDiv{#2}{4} - 32083\relax}{#2}%
}%
\def\greg@#1#2{% jdn_julian y
  \expandafter\greg@@
  \expandafter{\the\numexpr #1 - \intcalcDiv{#2}{100}\relax}{#2}%
}%
\def\greg@@#1#2{% jdn_julian y
  \the\numexpr #1 + \intcalcDiv{#2}{400} + 32083 - 32045\relax%
}%
%
\def\cu@jdnFromDateJulian#1{%
  \cu@jdn #1-\@firstoftwo
}%
\def\cu@jdnFromDateGregorian#1{%
  \cu@jdn #1-\greg@
}%
%
\def\cu@calendar#1{%
  \expandafter\cu@@calendar
  \expandafter{\the\numexpr (#1 + 1401) * 4 + 3\relax}%
}%
\def\cu@@calendar#1{% e
  \expandafter\cu@@@calendar
  \expandafter{\the\numexpr 2 + 
    \intcalcMul{5}{\intcalcDiv{\intcalcMod{#1}{1461}}{4}} \relax}{#1}%
}%
\def\cu@@@calendar#1#2{%  h  e
  \expandafter\cu@@@@calendar
  \expandafter{\the\numexpr 1 + \intcalcDiv{\intcalcMod{#1}{153}}{5}\relax}{#1}{#2}%
}%
\def\cu@@@@calendar#1#2#3{%  day h  e
  \expandafter\cu@@@@@calendar
  \expandafter{\the\numexpr 1 + 
    \intcalcMod{\intcalcAdd{\intcalcDiv{#2}{153}}{2}}{12}\relax}{#1}{#2}{#3}%
}%
\def\cu@@@@@calendar#1#2#3#4{% month day h  e
  \the\numexpr 
    \intcalcDiv{#4}{1461} - 4716 + \intcalcDiv{14-#1}{12}\relax -#1-#2%
}%
\def\cu@calendarJulian#1{\cu@calendar{#1}}%
\def\cu@calendarGregorian#1{%
  \expandafter\cu@calendar\expandafter{%
    \the\numexpr #1 +
    \intcalcDiv{\intcalcMul{\intcalcDiv{274277 + 4 * (#1)}{146097}}{3}}{4} - 38
    \relax
}}%
%
\def\cu@julianToGregorian#1{%
  \cu@calendarGregorian{\cu@jdnFromDateJulian{#1}}%
}%
\def\cu@gregorianToJulian#1{%
  \cu@calendarJulian{\cu@jdnFromDateGregorian{#1}}%
}%
\let\cu@julianFromGregorian\cu@gregorianToJulian
\let\cu@gregorianFromJulian\cu@julianToGregorian
%
% User API
%
\let\cuAsJulian\cu@julianFromGregorian
\let\cuAsGregorian\cu@gregorianFromJulian
%
\def\cuDateJulian#1{%
  \expandafter\cu@formatDate\number\cu@julianFromGregorian{#1}\relax
}%
\def\cuTodayJulian{%
  \cu@julianFromGregorian{\year -\month -\day}%
}%
\def\cuToday{%
  \year -\month -\day
}%
\def\cuDate#1{%
  \expandafter\cu@formatDate\number #1\relax
}%
%
\def\cuMonthName#1{%
  \ifcase#1\or%
    і҆аннꙋа́рїа\or
    феврꙋа́рїа\or
    ма́рта\or
    а҆прі́ллїа\or
    ма́їа\or
    і҆ꙋ́нїа\or
    і҆ꙋ́лїа\or
    а҆́ѵгꙋста\or
    септе́мврїа\or
    ѻ҆ктѡ́врїа\or
    ное́мврїа\or
    деке́мврїа\fi
}%
%
\def\cuDayName#1{%
  \ifcase#1 недѣ́лѧ\or%
    понедѣ́льникъ\or
    вто́рникъ\or
    среда̀\or
    четверто́къ\or
    пѧто́къ\or
    сꙋббѡ́та\fi
}%
%
\def\cuDayNameAccusative#1{%
  \ifcase#1 недѣ́лю\or%
    понедѣ́льникъ\or
    вто́рникъ\or
    сре́дꙋ\or
    четверто́къ\or
    пѧто́къ\or
    сꙋббѡ́тꙋ\fi
}%
%
\def\cuDefineDateFormat#1#2{%
	\expandafter\def\csname cs@dateformat@#1\endcsname{#2}%
}%
\def\cuUseDateFormat#1{%
	\expandafter\let\expandafter\cu@current@dateformat\csname cs@dateformat@#1\endcsname
}%
\def\cu@@formatDate#1-#2-#3\relax{%
	\edef\cu@JDN{\cu@jdnFromDateGregorian{#1-#2-#3}}%
	\edef\cu@JDN@March@First{\cu@jdnFromDateJulian{#1-3-1}}%
	\edef\cuYEAR{\number #1}%
	\edef\cuYEARAM{\the\numexpr #1 + 5508\ifnum\cu@JDN<\cu@JDN@March@First\else + 1\fi}% 
	\edef\cuMONTH{\number #2}%
	\edef\cuDAY{\number #3}%
	\edef\cuDOW{\intcalcMod{1+\cu@JDN}{7}}%
	\edef\cuINDICTION{\intcalcAdd{15}{\intcalcMod{#1 - 312}{-15}}}%
	\edef\cuDISPLAYDATE{\cu@current@dateformat}%
}%
\def\cu@@formatDateJulian#1-#2-#3\relax{%
	\edef\cu@JDN{\cu@jdnFromDateJulian{#1-#2-#3}}%
	\edef\cu@JDN@March@First{\cu@jdnFromDateJulian{#1-3-1}}%
	\edef\cuYEAR{\number #1}%
	\edef\cuYEARAM{\the\numexpr #1 + 5508\ifnum\cu@JDN<\cu@JDN@March@First\else + 1\fi}% 
	\edef\cuMONTH{\number #2}%
	\edef\cuDAY{\number #3}%
	\edef\cuDOW{\intcalcMod{1+\cu@JDN}{7}}%
	\edef\cuINDICTION{\intcalcAdd{15}{\intcalcMod{#1 - 312}{-15}}}%
	\edef\cuDISPLAYDATE{\cu@current@dateformat}%
}%
\protected\def\cu@formatDate#1-#2-#3\relax{%
	\bgroup
	\cu@@formatDate#1-#2-#3\relax
	\cuDISPLAYDATE
	\egroup
}%
%
\protected\def\cu@formatDateJulian#1-#2-#3\relax{%
	\bgroup
	\cu@@formatDateJulian#1-#2-#3\relax
	\cuDISPLAYDATE
	\egroup
}%
\cuDefineDateFormat{default}{%
	\cuNum{\cuDAY}~\cuMonthName{\cuMONTH},~лѣ́та~\cuNum{\cuYEAR}%
}%
\cuUseDateFormat{default}%
%