#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <error.h>

//extern int errno;

struct std_info
{
	int no;
	char name[30];
	struct std_info *next;
};

struct std_info *head=NULL,*current=NULL;
int student_num=0;
int edit_flag=0;

int write(void)
{
	struct std_info *p;

	FILE *fp;

	if(head==NULL) {
		printf("\nNo data. Please load data.\n");
		return;
	}
	
	fp=fopen("test.txt","w");
	if(!fp) {
		printf("Error in writing file \n");
		return -1;
	}


	p=head;
	while(p) {
		fprintf(fp,"%d,%s\n",p->no,p->name);
		p=p->next;
	}
	fclose(fp);
}

int add_student(struct std_info *st)
{
	struct std_info *new_std;
	new_std = (struct std_info *)malloc(sizeof(struct std_info));
	if(new_std != NULL) {
		  new_std->no = st->no;
		  strcpy(new_std->name,st->name);
		  new_std->next = NULL;
		  if(head==NULL) {
			head=new_std;
			current=new_std;
		  }
		  else {
			current->next = new_std;
			current=new_std;
		  }
		  return 0;
	}
	else {
		printf("\nError in memory alloc\n");
		return -1;
	}
}

int append(void)
{
 struct std_info student_info;

 char key;
 int num=0;

 do {
	printf("please input student number:");
	scanf("%d",&student_info.no);
	printf("name:");
	scanf("%s",student_info.name);

	printf("No.\tName\n");
	printf("\n%d\t%s\n",student_info.no,student_info.name);
	add_student(&student_info);
	num++;
	
	do {
		printf("Do you need input again?[y/n]");
		key=getchar();
	} while(key!='n' && key!='N' && key!='y' && key!='Y');

  }  while(key=='y'|| key=='Y');
	printf("\n");
	return(num);
}


int load(void)
{
	FILE *fp;
	int flen,fpn1,num=0;
	struct std_info student;

	fp=fopen("test.txt","r");
	if(!fp) {
		printf("Error in loading file : \n");
		return -1;
	}

	fseek(fp,0,2);
	flen=ftell(fp);
	fseek(fp,0,0);

	while(!feof(fp))
	 {	fscanf(fp,"%d,%s",&student.no,student.name);
		num++;
		fpn1=ftell(fp);

		if(add_student(&student)!=0)
		 {	num=-1;
			break;
		 }

		if((flen-fpn1)<2)
			break;

	 }

	fclose(fp);
	printf("\nThere are %d students\n",num);
	return(num);
}

void display(void)
{
	struct std_info *p;

	if(head==NULL) {
		printf("\nNo data. Please load data.\n");
		return;
	}

	printf("\nNo.\tName\n");
	p=head;
	while(p) {
		printf("%d\t%s\n",p->no,p->name);
		p=p->next;
	}
}

void modify(void)
{
	printf("You can finish this function by yourself\n");
}

void search(void)
{

 int w;
 struct std_info *l;
 if(head==NULL)
    {
     printf("\nNo data.Please load data.\n");
     return;
    }
 l=head;
 printf("Please input the student number:");
 scanf("%d",&w);
 while(l)
 {
  if(w==l->no)
  break;

  l=l->next;

 }
 printf("%d %s\n",l->no,l->name);

}

void del_all()
{
	struct std_info *p,*next;

	p=head;

	while(p) {
		next=p->next;
		free(p);
		p=next;
	}
	printf("All data be deleted.\n");
	head=NULL;
	current=NULL;

}

void help(void)
{
	char *cmdstr="\nl: load\t\t\td: display\n"
		     "w: write\t\ts: search\n"
		     "a: append\t\tm: modify\n"	
		     "e: empty\t\tq: quit\n";

	printf("%s",cmdstr);

}

void print_prompt(void)
{

	printf("Input command(? for help):");
}

int menu(void)
{
	int kin;

	kin=getchar();
	printf("\n");
	return(kin);

}

int main(void)
{
	int key,ctl=1;

	while(ctl) {
		print_prompt();
		key=menu();

		switch(key) {
			case 'l':
				student_num=load();
				break;
			case 'e':
				del_all();
				student_num=0;
				edit_flag=1;
				break;
			case 'd':
				display();
				break;
			case 'q':
				ctl=0;
				break;
			case '?':
				help();
				break;
			case 'w':
				write();
				break;
			case 's':
				search();
				break;
			case 'a':
				student_num += append();
				edit_flag=1;
				break;
			case 'm':
				modify();
				break;
	
		}
	}

	printf("\nbye!\n");
	return(0);
}