/*
 * This source code is only for illustration purpose for project1.
 * It may not contain complete functions for codes required.
 * If you find any bug, please email me, thanks!
 *
 * Author: Ning Yan
 * Data: 11/4/2013
 */

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

#define REC_FILE "students.csv"
#define SIZE 100

/* definition of student structure */
typedef struct {
  int ID;
  char name[20];
  int age;
  char dept[10];
  int grade;
}Student;

/* student records as global static variable, local variable is also fine
   global variables automatically initialized to 0*/
static Student records[SIZE];

/* print program main menu  */
void print_menu();

/* print record table header */
void print_record_header();

/* print a student record */
void print_student_record(Student* s);
void print_all_student_records();

/* functions comments omitted */
void add_student();

void modify_student();

void delete_student();

void list_student_dept();

void average_grade();


int main() {

  FILE * rec_file;

  
  /* load records from csv */  
  if(rec_file = fopen(REC_FILE, "r")) {
	int i=0;
	while(fscanf(rec_file, "%d, %[^,], %d, %[^,], %d\n", // can also use fgets and strtok
				 &records[i].ID,                         // needs to check file format
				 records[i].name,
				 &records[i].age,
				 records[i].dept,
				 &records[i].grade) != EOF) {
	  i++;
	}
	fclose(rec_file);
	printf("Existing record file loaded!\n");	
  } else {
	printf("No record file exists!\n");
  }
  print_all_student_records();
  
  /* process user input until exit */
  int c;
  print_menu();
  // getchar() is OK, but have to ignore LINEFEED char '\n'   
  scanf("%d", &c);
  while( c != 6) {
	printf("You choose %d\n", c);
	switch (c) {
	case 1: add_student(); break;
	case 2: modify_student(); break;
	case 3: delete_student(); break;
	case 4: list_student_dept(); break;
	case 5: average_grade(); break;
	default: printf("Invalid choice! Enter again...\n"); 
	}
	printf("\n");
	print_menu();
	scanf("%d", &c);
  }

  
  /* save record into csv */
  if(rec_file = fopen(REC_FILE, "w")) {
	int i=0;
	for ( ; i<SIZE; i++) {
	  if (records[i].ID!=0) {
		fprintf(rec_file, "%d, %s, %d, %s, %d\n",
				records[i].ID,
				records[i].name,
				records[i].age,
				records[i].dept,
				records[i].grade);
	  }
	}
	fclose(rec_file);
	printf("Records saved.\n");	
  } else {
	printf("Cannot save records.\n");		
  }

  printf("Bye!\n");
  
  return 1;
}


void print_menu() {
  printf("\n");  
  printf("---------Menu------------"); 	  printf("\n");
  printf("1. add a student");	  	  printf("\n");
  printf("2. modify a student");	  printf("\n");
  printf("3. delete a student");	  printf("\n");
  printf("4. list department students");     	  printf("\n");
  printf("5. average grade");     	  printf("\n");
  printf("6. save and exit");     	  printf("\n");
  printf("-------------------------"); 	  printf("\n");  printf("\n");
  printf("Please enter your choice...");     	  printf("\n");
}

void print_record_header() {
  printf("ID\tname\t\tage\tdepartment\tgrade\n");
}

void print_student_record(Student* s) {
  printf("%d\t%s\t%d\t%s\t\t%d\n", s->ID, s->name, s->age, s->dept, s->grade);
}

void print_all_student_records() {
  print_record_header();
  int i;
  for (i=0; i<SIZE; i++) {
	if(records[i].ID!=0)
	  print_student_record(&records[i]);
  }
}


void add_student() {
  int pos=-1, i;
  char firstname[10], lastname[10];
  char* space = " ";
  for (i=0; i<SIZE; i++) {
	if(records[i].ID==0) {
	  pos = i;
	  break;
	}
  }
  if (pos==-1) {
	printf("Records full!\n");
	return;
  }
  // may check duplicate ID
  printf("Enter new student ID: \n"); scanf("%d", &records[pos].ID);
  printf("Enter new student name: \n"); scanf("%9s %9s", firstname, lastname);
  strncpy(records[pos].name, firstname, 10); // TODO: add space
  strncat(records[pos].name, space, 1);  
  strncat(records[pos].name, lastname, 10);
  printf("Enter new student age: \n"); scanf("%d", &records[pos].age);
  printf("Enter new student department: \n"); scanf("%9s", records[pos].dept);
  printf("Enter new student grade: \n"); scanf("%d", &records[pos].grade);
}

void modify_student() {
  // omitted, similar to add_student()
}

void delete_student() {
  int ID, del_flag=0, i;  
  print_all_student_records();
  printf("Enter student ID you want to delete...\n");
  scanf("%d", &ID);
  for (i=0; i<SIZE; i++) {
	if(records[i].ID==ID) {
	  records[i].ID = 0; // set to 0 indicates delete
	  del_flag = 1;
	  printf("Student ID %d deleted.\n", ID);
	}
  }
  if(del_flag==0)
	printf("Student ID %d not found!\n", ID);
}

void list_student_dept() {
  char dept[10];
  printf("which department are you looking for?\n");
  scanf("%9s", dept);
  int i, flag;
  flag = 0;
  print_record_header();
  for(i=0; i<SIZE; i++) {
	if(!strcmp(records[i].dept, dept)) {
	  print_student_record(&records[i]);
	  flag = 1;
	}
  }
  if (flag==0) printf("Empty set!\n");
}

void average_grade() {
  float total = 0.0, average;
  int i;
  int count;
  for (i=0, count=0; i<SIZE; i++) {
	if (records[i].ID!=0) {
	  total += records[i].grade;
	  count ++;
	}
  }
  average = total / count;
  printf("Average grade is %.2f.\n", average);
}