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

//Database limits and grading configuration
define MAX_STUDENTS 100
define MAX_GRADES 10
define PASSING_GRADE 60

//Represents a student and their recorded grades
struct Student {
	int id;
	char name[64];
	int age;
	int grades[MAX_GRADES];
	int grade_count;
};

//Student database and ID counter
struct Student students[MAX_STUDENTS];
int student_count = 0;
int next_id = 1;

//Prints a separator line
void print_line() {
	printf("----------------------------------------\n");
}

//Displays the program header
void print_header() {
	printf("\n");
	print_line();
	printf("       MODULON STUDENT MANAGER\n");
	print_line();
	printf("Students: %d / %d\n", student_count, MAX_STUDENTS);
	print_line();
}

//Finds a student by ID and returns its array index
int find_student(int id) {
	for (var i = 0; i < student_count; i++) {
		if (students[i].id == id) {
			return i;
		}
	}
	return -1;
}

//Calculates the average grade for a student
float calculate_average(int index) {
	if (students[index].grade_count == 0) {
		return 0.0;
	}
	var total = 0;
	for (var i = 0; i < students[index].grade_count; i++) {
		total += students[index].grades[i];
	}
	return (float)total / students[index].grade_count;
}

//Converts a numerical average into a letter grade
char get_letter_grade(float average) {
	if (average >= 90) return 'A';
	if (average >= 80) return 'B';
	if (average >= 70) return 'C';
	if (average >= 60) return 'D';
	return 'F';
}

//Creates a new student record
void add_student() {
	if (student_count >= MAX_STUDENTS) {
		printf("Student database is full.\n");
		return;
	}
	var index = student_count;
	printf("\nADD STUDENT\n");
	print_line();

	//Copy the name before another input call can reuse its buffer
	var name = input("Student name: ");
	strncpy(students[index].name, name, 63);
	students[index].name[63] = '\0';
	var age = input("Student age: ");

	//Initialize the remaining student information
	students[index].id = next_id;
	students[index].age = atoi(age);
	students[index].grade_count = 0;
	student_count++;
	next_id++;
	printf("\nStudent successfully added.\n");
	printf("Assigned ID: %d\n", students[index].id);
}

//Displays all registered students
void list_students() {
	printf("\nSTUDENT DIRECTORY\n");
	print_line();
	if (student_count == 0) {
		printf("No students registered.\n");
		return;
	}
	printf("%-5s %-20s %-5s %-8s\n", "ID", "NAME", "AGE", "AVERAGE");
	print_line();
	for (var i = 0; i < student_count; i++) {
		var average = calculate_average(i);
		printf("%-5d %-20s %-5d %6.2f\n",
		       students[i].id, students[i].name,
		       students[i].age, average);
	}
	print_line();
	printf("Total: %d students\n", student_count);
}

//Adds a numerical grade to an existing student
void add_grade() {
	printf("\nADD GRADE\n");
	print_line();
	var id = atoi(input("Student ID: "));
	var index = find_student(id);
	if (index == -1) {
		printf("Student not found.\n");
		return;
	}
	if (students[index].grade_count >= MAX_GRADES) {
		printf("Maximum grades reached.\n");
		return;
	}
	printf("Student: %s\n", students[index].name);
	var grade = atoi(input("Grade (0-100): "));
	if (grade < 0 || grade > 100) {
		printf("Invalid grade.\n");
		return;
	}
	var position = students[index].grade_count;
	students[index].grades[position] = grade;
	students[index].grade_count++;
	printf("Grade added successfully.\n");
	printf("New average: %.2f\n", calculate_average(index));
}

//Displays detailed information about one student
void show_student() {
	printf("\nSTUDENT INFORMATION\n");
	print_line();
	var id = atoi(input("Student ID: "));
	var index = find_student(id);
	if (index == -1) {
		printf("Student not found.\n");
		return;
	}
	var average = calculate_average(index);
	printf("ID:      %d\n", students[index].id);
	printf("Name:    %s\n", students[index].name);
	printf("Age:     %d\n", students[index].age);
	printf("Grades:  %d\n", students[index].grade_count);
	print_line();
	for (var i = 0; i < students[index].grade_count; i++) {
		printf("Grade %d: %d\n", i + 1, students[index].grades[i]);
	}
	print_line();
	printf("Average: %.2f\n", average);
	printf("Letter:  %c\n", get_letter_grade(average));
	if (students[index].grade_count == 0) {
		printf("Status:  NO GRADES\n");
	} else if (average >= PASSING_GRADE) {
		printf("Status:  PASSING\n");
	} else {
		printf("Status:  FAILING\n");
	}
}

//Removes a student from the database
void remove_student() {
	printf("\nREMOVE STUDENT\n");
	print_line();
	var id = atoi(input("Student ID: "));
	var index = find_student(id);
	if (index == -1) {
		printf("Student not found.\n");
		return;
	}
	printf("Removing: %s\n", students[index].name);
	for (var i = index; i < student_count - 1; i++) {
		students[i] = students[i + 1];
	}
	student_count--;
	printf("Student removed successfully.\n");
}

//Searches student names for a matching substring
void search_students() {
	printf("\nSEARCH STUDENTS\n");
	print_line();
	var query = input("Search name: ");
	var found = 0;
	for (var i = 0; i < student_count; i++) {
		if (strstr(students[i].name, query) != NULL) {
			printf("[%d] %s\n", students[i].id, students[i].name);
			found++;
		}
	}
	if (found == 0) {
		printf("No matching students.\n");
	} else {
		printf("\n%d result(s) found.\n", found);
	}
}

//Sorts students alphabetically using bubble sort
void sort_students() {
	for (var i = 0; i < student_count - 1; i++) {
		for (var j = 0; j < student_count - i - 1; j++) {
			if (strcmp(students[j].name, students[j + 1].name) > 0) {
				var temp = students[j];
				students[j] = students[j + 1];
				students[j + 1] = temp;
			}
		}
	}
	printf("Students sorted alphabetically.\n");
}

//Calculates statistics for the student database
void show_statistics() {
	printf("\nDATABASE STATISTICS\n");
	print_line();
	if (student_count == 0) {
		printf("No statistics available.\n");
		return;
	}
	var total_average = 0.0;
	var highest = 0.0;
	var lowest = 101.0;
	var passing = 0;
	var failing = 0;
	var graded = 0;
	for (var i = 0; i < student_count; i++) {
		if (students[i].grade_count == 0) {
			continue;
		}
		var average = calculate_average(i);
		total_average += average;
		graded++;
		if (average > highest) highest = average;
		if (average < lowest) lowest = average;
		if (average >= PASSING_GRADE) {
			passing++;
		} else {
			failing++;
		}
	}
	printf("Total students: %d\n", student_count);
	printf("Graded students: %d\n", graded);
	if (graded == 0) {
		printf("No grades recorded.\n");
		return;
	}
	printf("Class average:   %.2f\n", total_average / graded);
	printf("Highest average: %.2f\n", highest);
	printf("Lowest average:  %.2f\n", lowest);
	printf("Passing: %d\n", passing);
	printf("Failing: %d\n", failing);
}

//Displays the available menu commands
void print_menu() {
	printf("\nMAIN MENU\n");
	print_line();
	printf("1. Add student\n");
	printf("2. List students\n");
	printf("3. Add grade\n");
	printf("4. View student\n");
	printf("5. Remove student\n");
	printf("6. Search students\n");
	printf("7. Sort students\n");
	printf("8. Statistics\n");
	printf("0. Exit\n");
	print_line();
}

//Program entry point
int main() {
	//Initialize globals explicitly for JIT execution
	student_count = 0;
	next_id = 1;
	var running = 1;
	print_header();
	while (running) {
		print_menu();
		var choice = atoi(input("Selection: "));
		if (choice == 1) {
			add_student();
		} else if (choice == 2) {
			list_students();
		} else if (choice == 3) {
			add_grade();
		} else if (choice == 4) {
			show_student();
		} else if (choice == 5) {
			remove_student();
		} else if (choice == 6) {
			search_students();
		} else if (choice == 7) {
			sort_students();
		} else if (choice == 8) {
			show_statistics();
		} else if (choice == 0) {
			printf("Goodbye!\n");
			running = 0;
		} else {
			printf("Invalid selection.\n");
		}
	}
	return 0;
}