local Error = require('Module:Error')

local this = {};



this.calendars = {};



function this.registerCalendar(moduleName, ...)

    moduleName = require(moduleName); --debug only: not lazily

    this.calendars#(this.calendars)] = moduleName; --indexed by number, module loaded lazily

    for i = 1, arg.n do    

        this.calendarsargi]] = moduleName; -- indexed by code, module loaded lazily

    end;

end;



this.registerCalendar("Module:Sandbox/DixonD/Datetime/Gregorian", "Gregorian", "g"); --first position is the default

this.registerCalendar("Module:Sandbox/DixonD/Datetime/Julian",    "Julian",    "j");

-- more calendars may be added later in new modules pluggable here into this factory...



function this.selectCalendar(index)

    if index == nil then

        index = 0; -- use the default calendar (Gregorian as set above)

    end;



    local calendar = this.calendarsindex];

    if calendar == nil then

        return index; -- fast path: assume that index is a calendar object (not indexed) already loaded

    end;



    if type(calendar) == "string" then -- calendar is a string (i.e. a module name)

        local moduleName = calendar;

        calendar = require(moduleName); -- effective loading of calendar object

        if calendar == nil then

            return tostring(Error.error{"Calendar module name ''" .. moduleName .. "'' is either missing or cannot be loaded!"});

        end;

        -- replace the moduleName given ad value of any calendar key by the newly loaded calendar object

        for k, v in pairs(this.calendars) do

            if v == moduleName then

                this.calendarsk = calendar;

            end;

        end;

    end; -- else assume calendar is a valid calendar object



    return calendar;

end;



-- main functions

function this.julianDay(year, month, day, hour, minute, second, calendar)

    calendar = this.selectCalendar(calendar);

    if calendar == nil then

        return tostring(Error.error{"Calendar ''" .. calendar .. "'' is either missing or unknown!"});

    end;



    return calendar.julianDay(year, month, day, hour, minute, second);

end;



function this.dateOfJulianDay(julianDay, calendar)

    calendar = this.selectCalendar(calendar);

    if calendar == nil then

        return tostring(Error.error{"Calendar ''" .. calendar .. "'' is either missing or unknown!"});

    end;



    return calendar.dateOfJulianDay(julianDay);

end;



function this.yearOfJulianDay(julianDay, calendar)

    calendar = this.selectCalendar(calendar);

    if calendar == nil then

        return tostring(Error.error{"Calendar ''" .. calendar .. "'' is either missing or unknown!"});

    end;



    return calendar.yearOfJulianDay(julianDay);

end;

 

function this.monthOfJulianDay(julianDay, calendar)   

    calendar = this.selectCalendar(calendar);

    if calendar == nil then

        return tostring(Error.error{"Calendar ''" .. calendar .. "'' is either missing or unknown!"});

    end;



    return calendar.monthOfJulianDay(julianDay);

end;

 

function this.dayOfJulianDay(julianDay, calendar)   

    calendar = this.selectCalendar(calendar);

    if calendar == nil then

        return tostring(Error.error{"Calendar ''" .. calendar .. "'' is either missing or unknown!"});

    end;



    return calendar.dayOfJulianDay(julianDay);

end;

 

function this.weekdayOfJulianDay(julianDay, calendar)   

    calendar = this.selectCalendar(calendar);

    if calendar == nil then

        return tostring(Error.error{"Calendar ''" .. calendar .. "'' is either missing or unknown!"});

    end;



    return calendar.weekdayOfJulianDay(julianDay);

end;

 

function this.hourOfJulianDay(julianDay, calendar)   

    calendar = this.selectCalendar(calendar);

    if calendar == nil then

        return tostring(Error.error{"Calendar ''" .. calendar .. "'' is either missing or unknown!"});

    end;



    return calendar.hourOfJulianDay(julianDay);

end;

 

function this.minuteOfJulianDay(julianDay, calendar)   

    calendar = this.selectCalendar(calendar);

    if calendar == nil then

        return tostring(Error.error{"Calendar ''" .. calendar .. "'' is either missing or unknown!"});

    end;



    return calendar.minuteOfJulianDay(julianDay);

end;

 

function this.secondOfJulianDay(julianDay, calendar)   

    calendar = this.selectCalendar(calendar);

    if calendar == nil then

        return tostring(Error.error{"Calendar ''" .. calendar .. "'' is either missing or unknown!"});

    end;



    return calendar.secondOfJulianDay(julianDay);

end;



return this;