import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Date;
import java.util.GregorianCalendar;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;


public class CalenderTrain extends JFrame implements ActionListener {
	
	//年份
	private JLabel YearLabel = new JLabel("年份:");
	private JComboBox YearBox = new JComboBox();
	
	//月份
	private JLabel MonthLabel = new JLabel("月份:");
	private JComboBox MonthBox = new JComboBox();
	
	//檢視
	JButton button_ok = new JButton("檢視");
	
	//今天
	JButton button_today = new JButton("今天");
	
	//今天的日期,年份,月份
	private Date now_date = new Date();
	private int now_year = now_date.getYear() + 1900;
	private int now_month = now_date.getMonth();
	private boolean todayFlag = false;   //是否顯示今天的日期
	
	//用一行來顯示日期
	private JButton[] button_day = new JButton[42];
	private final String[] week = {"日", "一", "二", "三", "四", "五", "六"};
	private JButton[] button_week = new JButton[7];
	
	//使用者選擇年份和月份
	private String year_int = null;
	private int month_int;
	
	
	public CalenderTrain(){
		super();
		setTitle("日曆");
		init();
		setLocation(500, 300);
		setResizable(false);
		pack();
	}
	

	//----->初始化日曆
	private void init() {
		Font font = new Font("Dialog", Font.BOLD, 14);
		YearLabel.setFont(font);
		MonthLabel.setFont(font);
		button_ok.setFont(font);
		button_today.setFont(font);
		
		//當前年份前10年和未來20年時間區間
		for(int i = now_year - 10; i <= now_year + 20; i++){
			YearBox.addItem(i + "");
		}
		YearBox.setSelectedIndex(10);
		
		//12個月的月份區間
		for(int i = 1; i < 13; i++){
			MonthBox.addItem(i + "");
		}
		MonthBox.setSelectedIndex(now_month);
		
		//年份,月份,檢視,今天
		JPanel panel_ym = new JPanel();
		panel_ym.add(YearLabel);
		panel_ym.add(YearBox);
		panel_ym.add(MonthLabel);
		panel_ym.add(MonthBox);
		panel_ym.add(button_ok);
		panel_ym.add(button_today);
		button_ok.addActionListener(this);
		button_today.addActionListener(this);
		
		//星期 "日", "一", "二", "三", "四", "五", "六"
		JPanel panel_day = new JPanel();
		panel_day.setLayout(new GridLayout(7, 7, 3, 3));
		for(int i = 0; i < 7; i++){
			button_week[i] = new JButton(week[i]);
			button_week[i].setForeground(Color.black);
			panel_day.add(button_week[i]);
		}
		button_week[0].setForeground(Color.red);
		button_week[6].setForeground(Color.red);
		
		//1,2,3..30等日
		for(int i = 0; i < 42; i++){
			button_day[i] = new JButton(" ");
			panel_day.add(button_day[i]);
		}
		printDay();
		
		//
		JPanel panel_main = new JPanel();
		panel_main.setLayout(new BorderLayout());
		panel_main.add(panel_ym, BorderLayout.NORTH);
		panel_main.add(panel_day, BorderLayout.SOUTH);
		
		getContentPane().add(panel_main);
	}

	//----->顯示當前年月的日期
	private void printDay(){
		clearBtns();
		
		if(todayFlag){
			year_int = now_year + "";
			month_int = now_month;
		}else{
			year_int = YearBox.getSelectedItem().toString();
			month_int = MonthBox.getSelectedIndex();
		}
		
		int year_sel = Integer.parseInt(year_int) - 1900;
		
		/**Date建構函式
		 *@param   year    the year minus 1900.
	     *@param   month   the month between 0-11.
	     *@param   date    the day of the month between 1-31.
		 */
		Date firstDay = new Date(year_sel, month_int, 1);
		GregorianCalendar cal = new GregorianCalendar();
		cal.setTime(firstDay);
		
		//
		int days = 0; //本月有多少天
		int day_week = firstDay.getDay();  //星期幾
		if(month_int == 0 || month_int == 2 || month_int == 4 || month_int == 6 || month_int == 7 || month_int == 9 || month_int == 11 ){
			days = 31;
		}else if(month_int == 3 || month_int == 5|| month_int == 8 || month_int == 10 ){
			days = 30;
		}else{
			if(cal.isLeapYear(year_sel)){
				days = 29;
			}else{
				days = 28;
			}
		}
		
		//根據選定月份第一天是星期幾來確定按鈕的繪製位置 day_week就是我們繪製的起始位置。
		int count = 1;
		
		for(int i = day_week; i < day_week + days; count++, i++){
			if(i % 7 == 0 || i == 6 || i == 13 || i == 20 || i == 27 || i == 34 || i == 41){  //6+31 = 37
				if(i == day_week + now_date.getDate() - 1){
					button_day[i].setForeground(Color.blue);
					button_day[i].setText(count + "");
				}else{
					button_day[i].setForeground(Color.red);
					button_day[i].setText(count + "");
				}
			}else{
				if(i == day_week + now_date.getDate() - 1){
					button_day[i].setForeground(Color.blue);
					button_day[i].setText(count + "");
				}else{
					button_day[i].setForeground(Color.black);
					button_day[i].setText(count + "");
				}
			}
		}
		
		//
		if(day_week == 0){
			for(int i = days; i < 42; i++){
				button_day[i].setText("");
			}
		}else{
			//第一天不是週日,則將第一天前面的按鈕置空
			for(int i = 0; i < day_week; i++){
				button_day[i].setText("");
			}
			//最後一天後面的按鈕置空
			for(int i = day_week + days; i < 42; i++){
				button_day[i].setText("");
			}
		}
	}

	private void clearBtns(){
		for(int i = 0; i < 42; i++){
			button_day[i].setText("");
		}
	}
	
	//----->按鈕監聽函式
	public void actionPerformed(ActionEvent e) {
		if(e.getSource() == button_ok){
			todayFlag = false;
			printDay();
		}else if(e.getSource() == button_today){
			todayFlag = true;
			YearBox.setSelectedIndex(10);
			MonthBox.setSelectedIndex(now_month);
			printDay();
		}	
	}
	
	
	//----->主函式
	public static void main(String[] args){
		CalenderTrain ct = new CalenderTrain();
		ct.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		ct.setVisible(true);
	}	
}