Mockup Implementation of a HolidayTagger with sample holiday data from the United States. Doesn't yet follow the pictagger api spec. Requires underscore.js

HolidayTagger

function holidayTagger(date) {
    var dateYear = date.getFullYear();
    var dateMonth = date.getMonth();
    var dateDay = date.getDate();
    var getEasterDate = _.memoize(function (year) {
        var Y = year;
        var C = Math.floor(Y / 100);
        var N = Y - 19 * Math.floor(Y / 19);
        var K = Math.floor((C - 17) / 25);
        var I = C - Math.floor(C / 4) - Math.floor((C - K) / 3) + 19 * N + 15;
        I = I - 30 * Math.floor((I / 30));
        I = I - Math.floor(I / 28) * (1 - Math.floor(I / 28) * Math.floor(29 / (I + 1)) * Math.floor((21 - N) / 11));
        var J = Y + Math.floor(Y / 4) + I + 2 - C + Math.floor(C / 4);
        J = J - 7 * Math.floor(J / 7);
        var L = I - J;
        var M = 3 + Math.floor((L + 40) / 44);
        var D = L + 28 - 31 * Math.floor(M / 4);
        return new Date(Y, M - 1, D);
    });
    //month indicies are zero-based in JS: 0 = January ... 11 = December
    var holidaysUS = [{
        name: 'all saints',
        day: 1,
        month: 10,
        category: 'christian'
    }, {
        name: 'all souls',
        day: 2,
        month: 10,
        category: 'christian'
    }, {
        name: 'christmas eve',
        day: 24,
        month: 11,
        category: 'christian'
    }, {
        name: 'christmas day',
        day: 25,
        month: 11,
        category: 'christian'
    }, {
        name: 'epiphany',
        day: 6,
        month: 1,
        category: 'christian'
    }, {
        name: 'shrove tuesday',
        daysFromEaster: -47,
        category: 'christian'
    }, {
        name: 'ash wednesday',
        daysFromEaster: -46,
        category: 'christian'
    }, {
        name: 'holy thursday',
        daysFromEaster: -3,
        category: 'christian'
    }, {
        name: 'good friday',
        daysFromEaster: -2,
        category: 'christian'
    }, {
        name: 'easter vigil',
        daysFromEaster: -1,
        category: 'christian'
    }, {
        name: 'easter',
        daysFromEaster: 0,
        category: 'christian'
    }, {
        name: 'easter monday',
        daysFromEaster: 1,
        category: 'christian'
    }, {
        name: 'pentecost',
        daysFromEaster: 50,
        category: 'christian'
    }, {
        name: 'corpus christi',
        daysFromEaster: 60,
        category: 'christian'
    }, {
        name: 'assumption of mary',
        day: 15,
        month: 7,
        category: 'christian'
    }, {
        name: 'immaculate conception',
        day: 8,
        month: 11,
        category: 'christian'
    },
    //saecular holidays
    {
        name: 'new years day',
        day: 1,
        month: 0,
        category: 'federal'
    }, {
        name: "Martin Luther King's day",
        day: 17,
        month: 0,
        category: 'federal'
    }, {
        name: "Washington's Birthday",
        day: 21,
        month: 1,
        category: 'federal'
    }, {
        name: "Independence Day",
        day: 4,
        month: 6,
        category: 'federal'
    }, {
        name: 'labor day',
        weekDayInMonth: ['first', 'monday', 'september'],
        category: 'federal'
    }, {
        name: 'columbus day',
        day: 10,
        month: 9,
        category: 'federal'
    }, {
        name: 'veterans day',
        day: 11,
        month: 10,
        category: 'federal'
    }];
    var easterDate = getEasterDate(dateYear);

    function daysFromEaster(days) {
        return (new Date(dateYear, easterDate.getMonth(), easterDate.getDate() + days))
    }
    var matchedHolidays = _(holidaysUS).map(function (holiday) {
        if (!holiday.daysFromEaster) {
            if (holiday.day === dateDay && holiday.month === dateMonth) {
                return {
                    'name': holiday.name,
                    'category': holiday.category
                }
            }
        } else {
            var holidayDate = daysFromEaster(holiday.daysFromEaster);
            if (holidayDate.getDate() === dateDay && holidayDate.getMonth() === dateMonth) {
                return {
                    'name': holiday.name,
                    'category': holiday.category
                }
            }
        }
    });
    return _.compact(matchedHolidays); //remove falsy values
}