/**
 * Calendar Script
 * Creates a calendar widget which can be used to select the date more easily than using just a text box
 * http://www.openjs.com/scripts/ui/calendar/
 *
 * Example:
 * <input type="text" name="date" id="date" />
 * <script type="text/javascript">
 *              calendar.set("date");
 * </script>
 */
calendar = {
        month_names: ["January","February","March","April","May","June","July","Augest","September","October","November","December"],
        weekdays: ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"],
        month_days: [31,28,31,30,31,30,31,31,30,31,30,31],
        //Get today's date - year, month, day and date
        today : new Date(),
        opt : {},
        data: [],

        //Functions
        /// Used to create HTML in a optimized way.
        wrt:function(txt) {
                this.data.push(txt);
        },

        /* Inspired by http://www.quirksmode.org/dom/getstyles.html */
        getStyle: function(ele, property){
                if (ele.currentStyle) {
                        var alt_property_name = property.replace(/\-(\w)/g,function(m,c){return c.toUpperCase();});//background-color becomes backgroundColor
                        var value = ele.currentStyle[property]||ele.currentStyle[alt_property_name];

                } else if (window.getComputedStyle) {
                        property = property.replace(/([A-Z])/g,"-$1").toLowerCase();//backgroundColor becomes background-color

                        var value = document.defaultView.getComputedStyle(ele,null).getPropertyValue(property);
                }

                //Some properties are special cases
                if(property == "opacity" && ele.filter) value = (parseFloat( ele.filter.match(/opacity\=([^)]*)/)[1] ) / 100);
                else if(property == "width" && isNaN(value)) value = ele.clientWidth || ele.offsetWidth;
                else if(property == "height" && isNaN(value)) value = ele.clientHeight || ele.offsetHeight;
                return value;
        },
        getPosition:function(ele) {
                var x = 0;
                var y = 0;
                while (ele) {
                        x += ele.offsetLeft;
                        y += ele.offsetTop;
                        ele = ele.offsetParent;
                }
                if (navigator.userAgent.indexOf("Mac") != -1 && typeof document.body.leftMargin != "undefined") {
                        x += document.body.leftMargin;
                        offsetTop += document.body.topMargin;
                }

                var xy = new Array(x,y);
                return xy;
        },
        /// Called when the user clicks on a date in the calendar.
        selectDate:function(year,month,day) {
                var ths = _calendar_active_instance;
                document.getElementById(ths.opt["input"]).value = month + "-" + day + "-" + year; // Date format is :HARDCODE:
                ths.hideCalendar();
        },
        /// Creates a calendar with the date given in the argument as the selected date.
        makeCalendar:function(year, month, day) {
                year = parseInt(year);
                month= parseInt(month);
                day      = parseInt(day);

                //Display the table
                var next_month = month+1;
                var next_month_year = year;
                if(next_month>=12) {
                        next_month = 0;
                        next_month_year++;
                }

                var previous_month = month-1;
                var previous_month_year = year;
                if(previous_month< 0) {
                        previous_month = 11;
                        previous_month_year--;
                }

                this.wrt("<table>");
                this.wrt("<tr><th><a href='javascript:calendar.makeCalendar("+(previous_month_year)+","+(previous_month)+");' title='"+this.month_names[previous_month]+" "+(previous_month_year)+"'>&lt;</a></th>");
                this.wrt("<th colspan='5' class='calendar-title'><select name='calendar-month' class='calendar-month' onChange='calendar.makeCalendar("+year+",this.value);'>");
                for(var i in this.month_names) {
                        this.wrt("<option value='"+i+"'");
                        if(i == month) this.wrt(" selected='selected'");
                        this.wrt(">"+this.month_names[i]+"</option>");
                }
                this.wrt("</select>");
                this.wrt("<select name='calendar-year' class='calendar-year' onChange='calendar.makeCalendar(this.value, "+month+");'>");
                var current_year = this.today.getYear();
                if(current_year < 1900) current_year += 1900;

                for(var i=current_year-70; i<current_year+10; i++) {
                        this.wrt("<option value='"+i+"'")
                        if(i == year) this.wrt(" selected='selected'");
                        this.wrt(">"+i+"</option>");
                }
                this.wrt("</select></th>");
                this.wrt("<th><a href='javascript:calendar.makeCalendar("+(next_month_year)+","+(next_month)+");' title='"+this.month_names[next_month]+" "+(next_month_year)+"'>&gt;</a></th></tr>");
                this.wrt("<tr class='header'>");
                for(var weekday=0; weekday<7; weekday++) this.wrt("<td>"+this.weekdays[weekday]+"</td>");
                this.wrt("</tr>");

                //Get the first day of this month
                var first_day = new Date(year,month,1);
                var start_day = first_day.getDay();

                var d = 1;
                var flag = 0;

                //Leap year support
                if(year % 4 == 0) this.month_days[1] = 29;
                else this.month_days[1] = 28;

                var days_in_this_month = this.month_days[month];

                //Create the calender
                for(var i=0;i<=5;i++) {
                        if(w >= days_in_this_month) break;
                        this.wrt("<tr>");
                        for(var j=0;j<7;j++) {
                                if(d > days_in_this_month) flag=0; //If the days has overshooted the number of days in this month, stop writing
                                else if(j >= start_day && !flag) flag=1;//If the first day of this month has come, start the date writing

                                if(flag) {
                                        var w = d, mon = month+1;
                                        if(w < 10)      w       = "0" + w;
                                        if(mon < 10)mon = "0" + mon;

                                        //Is it today?
                                        var class_name = '';
                                        var yea = this.today.getYear();
                                        if(yea < 1900) yea += 1900;

                                        if(yea == year && this.today.getMonth() == month && this.today.getDate() == d) class_name = " today";
                                        if(day == d) class_name += " selected";

                                        class_name += " " + this.weekdays[j].toLowerCase();

                                        this.wrt("<td class='days"+class_name+"'><a href='javascript:calendar.selectDate(\""+year+"\",\""+mon+"\",\""+w+"\")'>"+w+"</a></td>");
                                        d++;
                                } else {
                                        this.wrt("<td class='days'>&nbsp;</td>");
                                }
                        }
                        this.wrt("</tr>");
                }
                this.wrt("</table>");
                this.wrt("<input type='button' value='Cancel' class='calendar-cancel' onclick='calendar.hideCalendar();' />");

                document.getElementById(this.opt['calendar']).innerHTML = this.data.join("");
                this.data = [];
        },

        /// Display the calendar - if a date exists in the input box, that will be selected in the calendar.
        showCalendar: function() {
                var input = document.getElementById(this.opt['input']);

                //Position the div in the correct location...
                var div = document.getElementById(this.opt['calendar']);
                var xy = this.getPosition(input);
                var width = parseInt(this.getStyle(input,'width'));
                div.style.left=(xy[0]+width+10)+"px";
                div.style.top=xy[1]+"px";

                // Show the calendar with the date in the input as the selected date
                var existing_date = new Date();
                var date_in_input = input.value;
                if(date_in_input) {
                        var selected_date = false;
                        var date_parts = date_in_input.split("-");
                        if(date_parts.length == 3) {
                                date_parts[0]--; //Month starts with 0
                                selected_date = new Date(date_parts[2], date_parts[0], date_parts[1]);
                        }
                        if(selected_date && !isNaN(selected_date.getYear())) { //Valid date.
                                existing_date = selected_date;
                        }
                }

                var the_year = existing_date.getYear();
                if(the_year < 1900) the_year += 1900;
                this.makeCalendar(the_year, existing_date.getMonth(), existing_date.getDate());
                document.getElementById(this.opt['calendar']).style.display = "block";
                _calendar_active_instance = this;
        },

        /// Hides the currently show calendar.
        hideCalendar: function(instance) {
                var active_calendar_id = "";
                if(instance) active_calendar_id = instance.opt['calendar'];
                else active_calendar_id = _calendar_active_instance.opt['calendar'];

                if(active_calendar_id) document.getElementById(active_calendar_id).style.display = "none";
                _calendar_active_instance = {};
        },

        /// Setup a text input box to be a calendar box.
        set: function(input_id) {
                var input = document.getElementById(input_id);
                if(!input) return; //If the input field is not there, exit.

                if(!this.opt['calendar']) this.init();

                var ths = this;
                input.onclick=function(){
                        ths.opt['input'] = this.id;
                        ths.showCalendar();
                };
        },

        /// Will be called once when the first input is set.
        init: function() {
                if(!this.opt['calendar'] || !document.getElementById(this.opt['calendar'])) {
                        var div = document.createElement('div');
                        if(!this.opt['calendar']) this.opt['calendar'] = 'calender_div_'+ Math.round(Math.random() * 100);

                        div.setAttribute('id',this.opt['calendar']);
                        div.className="calendar-box";

                        document.getElementsByTagName("body")[0].insertBefore(div,document.getElementsByTagName("body")[0].firstChild);
                }
        }
}