var nowdate = new Date();
//var date_y = nowdate.getFullYear(); // 年
//var date_m  = nowdate.getMonth() + 1; // 月
var firstDate = 200800;
var endDate;
var prevDate;
var nextDate;

function Init(){
	var date_m_str = date_m;
	var date_y_str = date_y;

	endDate = nowdate.getMonth() + 1;
	if(endDate < 10)endDate = "0" + endDate;
	if(date_m_str < 10)date_m_str = "0" + date_m_str;
//	endDate = String(date_y_str) + String(date_m_str);
	endDate = String(nowdate.getFullYear()) + String(endDate);
	endDate = parseInt(endDate,10) +1;

	if(document.getElementById("backYm_"+date_y+date_m_str)){
		document.getElementById("backYm_"+date_y+date_m_str).style.display = "block";
	}else{
		date_m  = nowdate.getMonth(); // 月
		if(date_m < 1){
			date_m = 12; // 月
			date_y_str -= 1;
		}
		date_m_str = date_m;
		if(date_m_str < 10)date_m_str = "0" + date_m_str;
		if(document.getElementById("backYm_"+date_y_str+date_m_str)){
			document.getElementById("backYm_"+date_y_str+date_m_str).style.display = "block";
		}
	}
	document.getElementById("back_n_tit").innerHTML = date_y_str + "年";
	document.getElementById("backNum_title").innerHTML = date_m_str + "月";

	//次月表示
	Display_Next();

	//前月表示
	Display_Prev();
}

function Display_Prev(){
	var ChkDate;
	var mm = parseInt(date_m,10) -1;
	var yy = parseInt(date_y,10);
	if(mm < 1){
		mm = 12; // 月
		yy -= 1;
	}
	if(mm < 10)mm = "0" + mm;

	ChkDate = String(yy)+String(mm);

	document.getElementById("prev_month").style.display = "none";
	while(firstDate < ChkDate){
		if(document.getElementById("backYm_"+ChkDate)){
			document.getElementById("prev_month").style.display = "block";
			prevDate = ChkDate;
			break;
		}else{
			mm = parseInt(mm,10) -1;
			if(mm < 1){
				mm = 12; // 月
				yy -= 1;
			}
			if(mm < 10)mm = "0" + mm;
			ChkDate = String(yy)+String(mm);
		}
	}
}

function Display_Next(){
	var ChkDate;
	var mm = parseInt(date_m,10) +1;
	var yy = parseInt(date_y,10);
	if(mm > 12){
		mm = 1; // 月
		yy += 1;
	}
	if(mm < 10)mm = "0" + mm;

	ChkDate = String(yy)+String(mm);

	document.getElementById("next_month").style.display = "none";
	while(endDate > ChkDate){
		if(document.getElementById("backYm_"+ChkDate)){
			document.getElementById("next_month").style.display = "block";
			nextDate = ChkDate;
			break;
		}else{
			mm = parseInt(mm,10) +1;
			if(mm > 12){
				mm = 1; // 月
				yy += 1;
			}
			if(mm < 10)mm = "0" + mm;
			ChkDate = String(yy)+String(mm);
		}
	}
}

function Ch_BN_Prev(){
	var date_m_str = parseInt(date_m,10);
	var date_y_str = parseInt(date_y,10);

	if(date_m_str < 10)date_m_str = "0" + date_m_str;

	//現在の表示を非表示
	if(document.getElementById("backYm_"+date_y+date_m_str)){
		document.getElementById("backYm_"+date_y+date_m_str).style.display = "none";
	}

	date_y = parseInt(prevDate.substring(0,4),10);
	date_m = parseInt(prevDate.substring(4,6),10);

	date_m_str = parseInt(date_m,10);
	date_y_str = parseInt(date_y,10);
	if(date_m_str < 10)date_m_str = "0" + date_m_str;
	if(document.getElementById("backYm_"+date_y+date_m_str)){
		document.getElementById("backYm_"+date_y+date_m_str).style.display = "block";
		document.getElementById("back_n_tit").innerHTML = date_y_str + "年";
		document.getElementById("backNum_title").innerHTML = date_m_str + "月";
	}

	Display_Next();	//次月表示
	Display_Prev();	//前月表示
}

function Ch_BN_Next(){
	var date_m_str = parseInt(date_m,10);
	var date_y_str = parseInt(date_y,10);

	if(date_m_str < 10)date_m_str = "0" + date_m_str;

	//現在の表示を非表示
	if(document.getElementById("backYm_"+date_y+date_m_str)){
		document.getElementById("backYm_"+date_y+date_m_str).style.display = "none";
	}

	date_y = parseInt(nextDate.substring(0,4),10);
	date_m = parseInt(nextDate.substring(4,6),10);

	date_m_str = parseInt(date_m,10);
	date_y_str = parseInt(date_y,10);
	if(date_m_str < 10)date_m_str = "0" + date_m_str;
	if(document.getElementById("backYm_"+date_y+date_m_str)){
		document.getElementById("backYm_"+date_y+date_m_str).style.display = "block";
		document.getElementById("back_n_tit").innerHTML = date_y_str + "年";
		document.getElementById("backNum_title").innerHTML = date_m_str + "月";
	}

	Display_Next();	//次月表示
	Display_Prev();	//前月表示
}