import java.awt.*;
import java.applet.*;
import java.util.*;
import java.awt.Graphics;
import java.awt.event.*;

public class GraphApplet extends Applet implements Runnable, MouseListener {
 private int delay=20;

 private int nWindowWidth=500;//平滑窗口大小
 private int alpha=6;//控制顯示的參數

 private double beta=1.9;//控制斜率的參數
 private double hold=10.0;//斜率閾值
 private int nMax=40;//閾值，超過此閾值，開始修改斜率
 private int nMin=-40;
 private int bUp=0;//控制上升還是下降0正常1上升2下降

 Thread thread;

 private int[] nPosXY;//存放坐標信息的數組,數組下標為x值，相應單元存的為y值
 private int nOffset=0;//偏移量

 boolean bPause=false;//暫停標志
 boolean bFirst=true;//第一次顯示

 private Image offImg;//聲明備用屏幕類型
 private Graphics offG;//聲明備用屏幕繪圖類型

 static Random rand = new Random();

 private int[] nRand = new int[nWindowWidth];//用于存放產生的隨即數，以及平滑處理

 public void init()
 {
  setBackground(Color.black);

  addMouseListener(this);
  try
  {
   offImg=createImage(getSize().width,getSize().height);//創建備用屏幕
   offG=offImg.getGraphics();//獲取備用屏幕繪圖環境
  }
  catch(Exception e)
  {
   offG=null;
   showStatus("備用屏幕初始化失敗！");
  }
  //初始化坐標數組
  nPosXY=new int[getSize().width];
  for(int x=0;x<nPosXY.length;x++)
  {
   nPosXY[x]=(int)f(x);
  }
  //初始化隨機數數組
  for(int i=0;i<nRand.length;i++)
   nRand[i]=rand.nextInt()%(alpha*getSize().height);
  //初始化閾值為屏幕坐標
  nMax=getSize().height/2-nMax;
  nMin=getSize().height/2-nMin;
 }

 public void start()
 {
  thread=new Thread(this);//啟動線程
  thread.start();
  nOffset=nPosXY.length;
 }

 public void stop()
 {
  thread=null;//停止線程
  nPosXY=null;
  nRand=null;
  removeMouseListener(this);//刪除鼠標監聽
 }

 public void run()
 {
  Thread current=Thread.currentThread();
  while(thread==current)//如果thread是當前線程的話
  {
   try
   {
    Thread.currentThread().sleep(delay);
   }
   catch(InterruptedException e)
   {   }
   repaint();//調用update方法,update方法再調用paint()方法
   if(!bPause)//如果是暫停標志是false
   {
    if(nOffset>=nPosXY.length)
    {
     for(int i=0;i<nPosXY.length-1;i++)
     {
      nPosXY[i]=nPosXY[i+1];
     }
     nPosXY[nPosXY.length-1]=(int)f(nOffset);
     nOffset++;
    }
   }
  }
 }

 double smooth()
 {//平滑處理函數
  int sum=0;
  for(int i=0;i<nRand.length-1;i++)
   nRand[i]=nRand[i+1];
  if(bUp==0)
   sum=rand.nextInt()%(alpha*getSize().height);
  else if(bUp==1)
   sum=(rand.nextInt()+(int)hold)%(alpha*getSize().height);
  else if(bUp==2)
   sum=(rand.nextInt()-(int)hold)%(alpha*getSize().height);
  nRand[nRand.length-1]=sum;
  for(int i=0;i<nRand.length-1;i++)
   sum+=nRand[i];
  sum/=nWindowWidth;
  return -sum+getSize().height/2;
    }

 double f(double x)
 {
  double temp=0.0;
  temp=smooth();
  hold(temp);
  if(temp<=0||temp>=getSize().height)
   bPause=true;
  return temp;
 }

 void hold(double x)
 {//斜率控制
  if(x==nMax&&bUp==0)
   for(int i=0;i<nRand.length;i++)
   {
    nRand[i]+=hold;
    bUp=1;
   }
  else if(x==nMin&&bUp==0)
   for(int i=0;i<nRand.length;i++)
   {
    nRand[i]-=hold;
    bUp=2;
   }
  else if(bUp==1)
   for(int i=0;i<nRand.length;i++)
    nRand[i]+=hold;
  else if(bUp==2)
   for(int i=0;i<nRand.length;i++)
    nRand[i]-=hold;
//  hold*=beta;
//  hold*=1.2;
/*  for(int i=0;i<nPosXY.length;i++)
  {
   if(nPosXY[i]==nMax)
   {
    x=i;
    y=nPosXY[i];
    bUp=true;
    break;
   }
  }
  for(int i=0;i<nPosXY.length;i++)
  {
   if(nPosXY[i]==nMin)
   {
    if(i<x)
    {
     x=i;
     y=nPosXY[i];
     bUp=false;
    }
    break;
   }
  }
  while(x<nPosXY.length&&bUp)
  {
   x++;
   nPosXY[x]=nPosXY[x-1]-(int)hold;
  }
  while(x<nPosXY.length&&!bUp)
  {
   x++;
   nPosXY[x]=nPosXY[x-1]+(int)hold;
  }*/
// return bUp;
 }

    public void paint(Graphics g) 
 {
//  hold();//控制斜率
  if(bFirst)
  {
   offG.clearRect(0,0,getSize().width,getSize().height);
   offG.setColor(Color.red);
   offG.drawLine(0,nMax-10,getSize().width,nMax-10);
   offG.drawLine(0,nMin+10,getSize().width,nMin+10);
   offG.setColor(Color.green);
   for(int i=0;i<getSize().width-1;i++)
   {
    offG.drawLine(i,nPosXY[i],i+1,nPosXY[i+1]);
    if(offG!=null)
     g.drawImage(offImg,0,0,this);
   }
   bFirst=false;
  }
  else
  {
   g.clearRect(0,0,getSize().width,getSize().height);
   offG.setColor(Color.red);
   offG.drawLine(0,nMax-10,getSize().width,nMax-10);
   offG.drawLine(0,nMin+10,getSize().width,nMin+10);
   g.setColor(Color.green);
   for(int i=0;i<getSize().width-1;i++)
    g.drawLine(i,nPosXY[i],i+1,nPosXY[i+1]);
  }
    }

 public void update(Graphics g)
 {//重畫
  if(offG!=null)
  {
   paint(offG);//將備用屏幕上的圖像畫到當前屏幕
   g.drawImage(offImg,0,0,this);
  }
  else
   paint(g);
 }

 public void mouseEntered(MouseEvent e)
 {//鼠標監聽
  bPause=true;//設置暫停
 }

 public void mouseExited(MouseEvent e)
 {
  bPause=false;//取消暫停
 }

 public void mouseReleased(MouseEvent e)
 {
 }

 public void mousePressed(MouseEvent e)
 {
 }

 public void mouseClicked(MouseEvent e)
 {
 }

 public String getAppletInfo() {
  return "測試繪圖";
 }
}