/**
*  A menu-driven program for elementary database management
*  @author: Bibek Subedi
*  @language: C
*  This program uses file handling in Binary mode
*/

/// List of library functions
#include <stdio.h> ///for input output functions like printf, scanf
#include <stdlib.h>
#include <conio.h>
#include <windows.h> ///for windows related functions (not important)
#include <string.h>  ///string operations

/** List of Global Variable */
COORD coord = {0,0}; /// top-left corner of window

/**
    function : gotoxy
    @param input: x and y coordinates
    @param output: moves the cursor in specified position of console
*/
void gotoxy(int x,int y){
    coord.X = x; coord.Y = y;
    SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE),coord);
}

/** Main function started */

int main(){
    FILE *fp, *ft; /// file pointers
    char another, choice;

    /** structure that represent a employee */
    struct emp{
        char name[40]; ///name of employee
        int age; /// age of employee
        float bs; /// basic salary of employee
    };

    struct emp e; /// structure variable creation

    char empname[40]; /// string to store name of the employee

    long int recsize; /// size of each record of employee

    /** open the file in binary read and write mode
    * if the file EMP.DAT already exists then it open that file in read write mode
    * if the file doesn't exit it simply create a new copy
    */
    fp = fopen("EMP.DAT","rb+");
    if(fp == NULL){
        fp = fopen("EMP.DAT","wb+");
        if(fp == NULL){
            printf("Connot open file");
            exit(1);
        }
    }

    /// sizeo of each record i.e. size of structure variable e
    recsize = sizeof(e);

    /// infinite loop continues untile the break statement encounter
    while(1){
        system("cls"); ///clear the console window
        gotoxy(30,10); /// move the cursor to postion 30, 10 from top-left corner
        printf("1. Add Record"); /// option for add record
        gotoxy(30,12);
        printf("2. List Records"); /// option for showing existing record
        gotoxy(30,14);
        printf("3. Modify Records"); /// option for editing record
        gotoxy(30,16);
        printf("4. Delete Records"); /// option for deleting record
        gotoxy(30,18);
        printf("5. Exit"); /// exit from the program
        gotoxy(30,20);
        printf("Your Choice: "); /// enter the choice 1, 2, 3, 4, 5
        fflush(stdin); /// flush the input buffer
        choice  = getche(); /// get the input from keyboard
        switch(choice){
            case '1':  /// if user press 1
                system("cls");
                fseek(fp,0,SEEK_END); /// search the file and move cursor to end of the file
                                        /// here 0 indicates moving 0 distance from the end of the file

                another = 'y';
                while(another == 'y'){ /// if user want to add another record
                    printf("\nEnter name: ");
                    scanf("%s",e.name);
                    printf("\nEnter age: ");
                    scanf("%d", &e.age);
                    printf("\nEnter basic salary: ");
                    scanf("%f", &e.bs);

                    fwrite(&e,recsize,1,fp); /// write the record in the file

                    printf("\nAdd another record(y/n) ");
                    fflush(stdin);
                    another = getche();
                }
                break;
            case '2':
                system("cls");
                rewind(fp); ///this moves file cursor to start of the file
                while(fread(&e,recsize,1,fp)==1){ /// read the file and fetch the record one record per fetch
                    printf("\n%s %d %.2f",e.name,e.age,e.bs); /// print the name, age and basic salary
                }
                getch();
                break;

            case '3':  /// if user press 3 then do editing existing record
                system("cls");
                another = 'y';
                while(another == 'y'){
                    printf("Enter the employee name to modify: ");
                    scanf("%s", empname);
                    rewind(fp);
                    while(fread(&e,recsize,1,fp)==1){ /// fetch all record from file
                        if(strcmp(e.name,empname) == 0){ ///if entered name matches with that in file
                            printf("\nEnter new name,age and bs: ");
                            scanf("%s%d%f",e.name,&e.age,&e.bs);
                            fseek(fp,-recsize,SEEK_CUR); /// move the cursor 1 step back from current position
                            fwrite(&e,recsize,1,fp); /// override the record
                            break;
                        }
                    }
                    printf("\nModify another record(y/n)");
                    fflush(stdin);
                    another = getche();
                }
                break;
            case '4':
                system("cls");
                another = 'y';
                while(another == 'y'){
                    printf("\nEnter name of employee to delete: ");
                    scanf("%s",empname);
                    ft = fopen("Temp.dat","wb");  /// create a intermediate file for temporary storage
                    rewind(fp); /// move record to starting of file
                    while(fread(&e,recsize,1,fp) == 1){ /// read all records from file
                        if(strcmp(e.name,empname) != 0){ /// if the entered record match
                            fwrite(&e,recsize,1,ft); /// move all records except the one that is to be deleted to temp file
                        }
                    }
                    fclose(fp);
                    fclose(ft);
                    remove("EMP.DAT"); /// remove the orginal file
                    rename("Temp.dat","EMP.DAT"); /// rename the temp file to original file name
                    fp = fopen("EMP.DAT", "rb+");
                    printf("Delete another record(y/n)");
                    fflush(stdin);
                    another = getche();
                }
                break;
            case '5':
                fclose(fp);  /// close the file
                exit(0); /// exit from the program
        }
    }
    return 0;
}