import java.io.*;
class Wait {
  public static void oneSec() {
     try {
       Thread.currentThread().sleep(1000);
       }
     catch (InterruptedException e) {
       e.printStackTrace();
       }
     }  
  public static void manySec(long s) {
     try {
       Thread.currentThread().sleep(s * 1000);
       }
     catch (InterruptedException e) {
       e.printStackTrace();
       }
     }
}

public class List
{
    static StudentRecord initial = null; //for the purpose of starting with the first node
    static String selected; //Currently selected database
    public static void main(String[] args) throws IOException
    {
    	String firstname, lastname, phonenum, input, dbchosen;
    	int grade;
    	int level = 0;
    	boolean crimrecord, filecreated, error;
    	boolean loop = true;
    	File newfile;
        BufferedReader br = new BufferedReader (new InputStreamReader (System.in));
        while (loop)
		{
			input = "";
			error = false;
			//Options are selectdb or createdb
			switch (level) 
			{
			case 0:
				System.out.println ("Available commands: (or quit)");
				System.out.println ("selectdb - Selects an existing database (also prints a list of databases)");
				System.out.println ("createdb - Creates a new database");
				System.out.println ("deletedb - Deletes a database");
				System.out.println ("--------------");
				input = br.readLine();
				
				if (input.equals("selectdb"))
				{
					if (viewdbList()) 
					{
						System.out.println("Enter the name of one of the following available databases:");
				
						dbchosen = br.readLine ();
    					try
    					{
					    	FileInputStream fstream = new FileInputStream (dbchosen);
					    }
					    catch (Exception e)
					    {
					    	error = true;
					    }
						if (!error) 
						{
							selected = dbchosen;
							fileToList(selected);
							viewStudentRecords();
							level++;
						} else {
							System.out.println ("Wrong database chosen");
						}
					} else {
						System.out.println ("No databases exist. Please create one.");
					}
					System.out.println ("--------------");
				} else if (input.equals("createdb")) {
					//create the db here
					System.out.println("Enter new database name:");
					selected = "DB_" + br.readLine();
					newfile = new File(selected);
					filecreated = newfile.createNewFile();
        			if (filecreated) {
            			System.out.println ("Created successfully");
            			level++;
        			} else {
           			 	System.out.println ("Failed: File already exists. Try again.");
        			}
					System.out.println ("--------------");
				} else if (input.equals("quit")) {
					loop = false;	
				} else if (input.equals ("deletedb")) {
					
					if (viewdbList()) 
					{
						System.out.println("Enter the name of one of the following available databases to delete:");
				
						dbchosen = br.readLine ();
    					try
    					{
					    	FileInputStream fstream = new FileInputStream (dbchosen);
					    }
					    catch (Exception e)
					    {
					    	error = true;
					    }
					    if (!error)
					    {
					    	File deletedb = new File(dbchosen);
					    	boolean deletion = deletedb.delete();
					    	if (deletion) { System.out.println ("Deletion success."); } else { System.out.println ("Deletion failed."); }
					    }
					} else {
						System.out.println ("No databases to delete");
					}
				
				} else {
					System.out.println("Erroneous input");
					System.out.println ("--------------");
				}
			break;
			
			case 1:
				System.out.println ("Enter command or type help for a list of available commands");
				System.out.println ("--------------");
				input = br.readLine();
				if (input.equals("enrollStudent"))
				{
					System.out.println ("Enter first name");
					firstname = br.readLine();
					System.out.println ("Enter last name");
					lastname = br.readLine();
					System.out.println ("Enter grade");
					grade = Integer.parseInt(br.readLine());
					System.out.println ("Enter phone number");
					phonenum = br.readLine();
					System.out.println ("Enter criminal record (true/false)");
					if ((br.readLine()).equals("true"))
					{
						crimrecord = true;
					} else {
						crimrecord = false;
					}
					enrollStudent(firstname, lastname, grade, phonenum, crimrecord);
					listToFile(selected);
					System.out.println ("--------------");
					
				} else if (input.equals("expellStudent")) {
					System.out.println ("Enter first name");
					firstname = br.readLine();
					System.out.println ("Enter last name");
					lastname = br.readLine();
					expellStudent(firstname, lastname);
					listToFile(selected);
					System.out.println ("--------------");
				} else if (input.equals("enterGrade")) { 
					System.out.println ("Enter first name");
					firstname = br.readLine();
					System.out.println ("Enter last name");
					lastname = br.readLine();
					System.out.println ("Enter grade");
					grade = Integer.parseInt(br.readLine());
					enterGrade(firstname, lastname, grade);
					listToFile(selected);
					System.out.println ("--------------");
				} else if (input.equals("classAverage")) { 
					System.out.println ("Class average is: " + classAverage());
					System.out.println ("--------------");
				} else if (input.equals("sortByName")) { 
				sortByName();
				viewStudentRecords();
				System.out.println ("--------------");
				} else if (input.equals("sortByGrade")) { 
				sortByGrade();
				viewStudentRecords();
				sortByName();
				System.out.println ("--------------");
				} else if (input.equals("viewdb")) { 
				viewStudentRecords();
				System.out.println ("--------------");
				} else if (input.equals("back")) { 
				level = 0;
				initial = null;
				System.out.println ("--------------");
				} else if (input.equals("quit")) {
					loop = false;
				} else if (input.equals("help")) {
					System.out.println ("Available commands: (case-sensitive)");
					System.out.println ("enrollStudent - Enrolls a new student");
					System.out.println ("expellStudent - Expells a student");
					System.out.println ("enterGrade - Enters a new grade for a student");
					System.out.println ("classAverage - Prints the class grade average");
					System.out.println ("sortByName - Sorts the database by name");
					System.out.println ("sortByGrade - Sorts the database by grade");
					System.out.println ("viewdb - views the database");
					System.out.println ("back - Goes back to previous selection screen");
					System.out.println ("--------------");
				} else {
									
					System.out.println("Erroneous input");
					System.out.println ("--------------");
				}
				
			}
		}
	}
    
  public static void viewStudentRecords()
    {
    StudentRecord currentpos = initial;
    System.out.println("Last name         First name        Grade Phone Number   Criminal Record");
    while (currentpos != null)
    {
        System.out.println (currentpos.returnFormattedString ());
        currentpos = currentpos.nextStudentRecord ();
    }
    }
    
  public static void sortByGrade ()
  {
  	StudentRecord currentpos;
  	StudentRecord templink;
  	StudentRecord secondpos;
  	StudentRecord lastpos;
  	StudentRecord previouslink;
  	StudentRecord currentpostemp;
  	boolean sort = true;
  	boolean breakit;
  	int debugcount = 0;
  	//Sort it now (alter the link list)
  	
  	while (sort)
  	{
  		sort = false;
  		//Sorting the first one
  		if (initial.returnGrade() < initial.nextStudentRecord().returnGrade()) 
  		{
  			
  			templink = initial.nextStudentRecord();
  			initial.nextLink(templink.nextStudentRecord());
  			templink.nextLink(initial);
  			initial = templink;	
  				
  		}
  		previouslink = initial;
  		currentpos = initial.nextStudentRecord();
  		breakit = false;
  		while (!breakit)
  		{
  			
  			
  			currentpostemp = currentpos;
  			secondpos = currentpos.nextStudentRecord();
 			if (secondpos != null)
 			{
 			
 			if (secondpos.nextStudentRecord() != null) 
  			{
  				lastpos = secondpos.nextStudentRecord();
  			} else {
  				lastpos = null;
  				breakit = true;
  			}
  			} else {
  				break;
  				//Have to do this to catch NULL POINTER EXCEPTION
  			}
  			if (currentpos.returnGrade() < secondpos.returnGrade()) 
  			{	
  				previouslink.nextLink(secondpos);
 				secondpos.nextLink(currentpos);
  				currentpos.nextLink(lastpos);
  				sort = true;
  				previouslink = currentpostemp;
				currentpos = currentpostemp.nextStudentRecord();

  			} else {
  				previouslink = currentpos;
  				currentpos = currentpostemp.nextStudentRecord(); 				
  			 				
  			}
  			
  			  	
  				
  		} 

  	}
  }
  	
  public static void sortByName ()
  {
  	StudentRecord currentpos;
  	StudentRecord templink;
  	StudentRecord secondpos;
  	StudentRecord lastpos;
  	StudentRecord previouslink;
  	StudentRecord currentpostemp;
  	boolean sort = true;
  	boolean breakit;
  	int debugcount = 0;
  	//Sort it now (alter the link list)
  	
  	while (sort)
  	{
  		sort = false;
  		//Sorting the first one
  		if ((initial.returnlName()).compareTo (initial.nextStudentRecord().returnlName ()) > 0) 
  		{
  			
  			templink = initial.nextStudentRecord();
  			initial.nextLink(templink.nextStudentRecord());
  			templink.nextLink(initial);
  			initial = templink;	
  				
  		}
  		previouslink = initial;
  		currentpos = initial.nextStudentRecord();
  		breakit = false;
  		while (!breakit)
  		{
  			
  			
  			currentpostemp = currentpos;
  			secondpos = currentpos.nextStudentRecord();
 			if (secondpos != null)
 			{
 			
 			if (secondpos.nextStudentRecord() != null) 
  			{
  				lastpos = secondpos.nextStudentRecord();
  			} else {
  				lastpos = null;
  				breakit = true;
  			}
  			} else {
  				break;
  				//Have to do this to catch NULL POINTER EXCEPTION
  			}
  			if (currentpos.returnlName().compareTo(secondpos.returnlName()) > 0) 
  			{	
  				previouslink.nextLink(secondpos);
 				secondpos.nextLink(currentpos);
  				currentpos.nextLink(lastpos);
  				sort = true;
  				previouslink = currentpostemp;
				currentpos = currentpostemp.nextStudentRecord();

  			} else {
  				previouslink = currentpos;
  				currentpos = currentpostemp.nextStudentRecord(); 				
  			 				
  			}
  			
  			  	
  				
  		} 

  	}
  }	
      
  public static void enrollStudent(String firstname, String lastname, int grade, String phonenumber, boolean criminalrecord)
  {
    StudentRecord newStudentRecord = new StudentRecord(firstname, lastname, grade, phonenumber, criminalrecord);  
    if (initial != null) 
    {
    	if (lastname.compareTo (initial.returnlName ()) < 0)
		{
		newStudentRecord.nextLink(initial);
		initial = newStudentRecord;
		} else {
		StudentRecord searchResult = searchByName(firstname, lastname);
		newStudentRecord.nextLink (searchResult.nextStudentRecord());
		searchResult.nextLink (newStudentRecord);
		}

    } else {
    	
        initial = newStudentRecord;
    	newStudentRecord.nextLink(null);	
    }
    
  }
  
  //Expells the student
  //The searchByName cannot be used (as there is no link to the previous node)
  public static void expellStudent(String firstname, String lastname)
  {
  	if (initial != null)
  	{
  		if (((initial.returnlName()).equals(lastname)) && ((initial.returnfName()).equals(firstname)))
  		{
  			//First check if the first user in the list is a match
  			initial = initial.nextStudentRecord();		
  		} else {
  			StudentRecord currentpos = initial;
  			boolean foundpos = false;
  			//Checks for two records ahead so that it's possible to expel the last student in the list
  			//without having a null pointer exception
  			while ((currentpos.nextStudentRecord()).nextStudentRecord() != null && !foundpos) 
  			{
  				if (lastname.compareTo ((currentpos.nextStudentRecord ()).returnlName ()) > 0)
  				{
  					currentpos = currentpos.nextStudentRecord();
  				} else {
  					foundpos = true;
  				}
  			}
  			currentpos.nextLink(currentpos.nextStudentRecord().nextStudentRecord());
  		}
  		
  		
  		
  	} else {
  		
  		System.out.println ("No students to expell");
  		
  	}
  	
  	
  }
  
  public static int classAverage()
  {
  	StudentRecord currentpos = initial;
  	int gradeTotal = 0;
  	int numStudents = 0;
  	while (currentpos.nextStudentRecord() != null) 
  	{	
  		gradeTotal = gradeTotal + currentpos.returnGrade();
  		numStudents++;
  		currentpos = currentpos.nextStudentRecord();
  	}
  	return gradeTotal / numStudents;
  }
 
  //Enters a new grade for a student (no output)
  public static void enterGrade(String firstname, String lastname, int newgrade)
  {
  	if (initial != null)
  	{
  		if (((initial.returnlName()).equals(lastname)) && ((initial.returnfName()).equals(firstname))) 
  		{
  			initial.assignGrade(newgrade);
  		} else {
  			StudentRecord searchResult = searchByName(firstname, lastname);
  			searchResult.nextStudentRecord().assignGrade(newgrade);
  		}
  	} else {
  		
  		System.out.println ("Error: No entries exist in database");
  	}
  	
  	
  	
  	
  }
   
   //Performs a search for the name (outputs the search result)
  private static StudentRecord searchByName(String firstname, String lastname)
   {
   boolean foundpos = false; 
	StudentRecord current = initial;
			if (lastname.compareTo (current.returnlName ()) < 0)
			{
				foundpos = true;
								
			}
   
            while (((current.nextStudentRecord ()) != null) && !foundpos) //Start the search
            {

				
                if (lastname.compareTo ((current.nextStudentRecord ()).returnlName ()) > 0) //Compare the entry and the existing    
                {
                 current = current.nextStudentRecord (); //Advance to the next one
                } else { 
                foundpos = true; //or indicate the position is found
                }
                
            }
			return current;
    }
        
  public static boolean viewdbList () throws IOException
{
    //Lists the List .txt files in the List folder and their respective ids
    //List files start with "DB" and have no extention
    String userdir = System.getProperty ("user.dir");
    boolean condition = false;
    File f = new File (userdir);
    String[] files = f.list ();
    for (int i = 0 ; i < files.length ; i++)
    {

    File f2 = new File (userdir, files [i]);
    if (!f2.isDirectory () && f2.exists ())
    {
        if (f2.isFile ())
        {
        //Check if it starts with "DB"
        if ((f2.getName ().charAt (0) == 68) && (f2.getName ().charAt (1) == 66))
        {
            System.out.println (f2.getName ());
            condition = true;
        }
        }
    }
    }
    return condition;
   
}

  public static void fileToList(String dbname)
  {
  	try
	{
       FileInputStream fstream = new FileInputStream(dbname);

	   DataInputStream lines = new DataInputStream(fstream);
	   
       while (lines.available() !=0)
		{
			//Now seperate lines
			String[] parsed = parseLine(lines.readLine());
			boolean crimrecord = false;
			if (parsed[4].equals("true")) {
				crimrecord = true;
			}
			enrollStudent(parsed[0], parsed[1], Integer.parseInt(parsed[2]), parsed[3], crimrecord);
		}

		lines.close();
	} 
                catch (Exception e)
	{
		System.err.println("File error");
	}


  	
  }
  public static void listToFile(String dbname)
  {
   	try
    {
       FileOutputStream database = new FileOutputStream(selected);
       PrintStream p = new PrintStream(database);
	   StudentRecord currentpos = initial;
       while (currentpos != null) 
       {
       	p.println ("^" + currentpos.returnfName() + "^" + currentpos.returnlName() + "^" + currentpos.returnGrade() + "^" + currentpos.returnPhoneNum() + "^" + currentpos.returnCrimRecord() + "^");
       	
       	currentpos = currentpos.nextStudentRecord ();
       }	
       

       p.close();
    }
       catch (Exception e)
       {

       		
       		System.out.println ("Error writing to file");
       }
  }
 
  private static String[] parseLine(String line)
  {
	String curstring = "";
	int inputcount = 0;
	String[] rarray = new String[5];

  	for (int i = 0; i < line.length(); i++)
  	{
  		//System.out.println("Current character: " + i);
  		if (line.charAt(i) == 94)
  		{
  			//To prevent the addition of a ^ to the first return
  			if (i == 0) { i++; } 			
  			
  			//System.out.println("Character is a ^");
  			if (curstring.equals(""))
  			{
  				//System.out.println("Curstring = " + curstring);
  				curstring = String.valueOf(line.charAt(i));
  				//System.out.println("Now Curstring = " + curstring);
  			} else {
  				//System.out.println("Curstring to return = " + curstring);
  				rarray[inputcount] = curstring;
  				inputcount++;
  				curstring = "";
  			}
  			
  		} else {
  			
  			curstring = curstring + String.valueOf(line.charAt(i));
  		}
  		
  	}
  	
  	return rarray;
  	
  }
  
  
}
class StudentRecord
{
    String fName, lName, phoneNum;
    int grade;
    boolean crimRecord;
    StudentRecord next;
    public StudentRecord (String fname1, String lName1, int grade1, String phoneNum1, boolean crimRecord1)
    {
        fName = fname1;
        lName = lName1;
        grade = grade1;
        phoneNum = phoneNum1;
        crimRecord = crimRecord1;
    }
    public StudentRecord nextStudentRecord()
    {
        return next;
    }
    public String returnlName()
    {
        return lName;
    }
    public String returnfName()
    {
        return fName;
    }
    public void nextLink (StudentRecord newLink)
    {
        next = newLink;
    }
    public int returnGrade ()
    {
        return grade;
    }
    public String returnPhoneNum()
    {
    	return phoneNum;
    }
    public boolean returnCrimRecord()
    {
    	return crimRecord;
    }
    public void assignGrade (int newGrade)
    {
        grade = newGrade;
    }
    public String returnFormattedString ()
    {
        return (lName + generateSpaces(18 - lName.length()) + fName + generateSpaces(18 - fName.length()) + grade + generateSpaces(6 - String.valueOf(grade).length()) + phoneNum + generateSpaces(15 - phoneNum.length()) + crimRecord);      
    }
    private String generateSpaces(int numspaces) 
    {
        String spaces = "";
        for (int i = 0; i < numspaces; i++) 
        {
            spaces = spaces + " ";  
        }
        return spaces;
    }


}