#include <iostream>
#include <fstream>
#include <string>
using namespace std;

const int FILENAME = 21;

class inventory
{
public:
	string item;
	int quantity,
		day,
		month,
		year;
	double wholesale,
		   retail;
};

inventory add_rec();
int menu();
void display_rec(inventory add_rec, char filename[FILENAME]);
void single_rec(char filename[FILENAME], int record_num);
int search_rec(inventory add_rec, char filename[FILENAME]);
long byte_num(int);
int num_elements(char filename[FILENAME]);

int menu()
{
	int num;

	system("cls");
	cout << "Select a number for the choices below: " << endl;
	cout << "--------------------------------------" << endl;
	cout << "1. Add a record..." << endl;
	cout << "2. Display all records contents..." << endl;
	cout << "3. Display a single records contents..." << endl;
	cout << "4. Change any records contents..." << endl;
	cout << "5. End program." << endl <<endl;
	cout << "Choice: ";
	cin >> num;

	return num;
}

inventory add_rec()
{
	inventory record;
	char yesno;

	do
	{
		cout << endl;
		cout << "Enter a description of the item: ";
		cin >> record.item;
		cout << "Enter the quantity on hand: ";
		do{cin >> record.quantity;}while(record.quantity <= 0);
		cout << "Enter the wholesale cost: ";
		do{cin >> record.wholesale;}while(record.wholesale <= 0);
		cout << "Enter the retail cost: ";
		do{cin >> record.retail;}while(record.retail <= 0);
		cout << "Enter the data added to the inventory (XX XX XXXX) : ";
		do{cin >> record.month;
		if(record.month < 1 || record.month > 12)
			cout << "Invalid month!\t";}while(record.month <= 0 || record.month > 12);
		do{cin >> record.day;
		if(record.day < 1 || record.day > 31)
			cout << "Invalid day!\t";}while(record.day <= 0 || record.day > 31);
		do{cin >> record.year;
		if(record.year < 1960 || record.year > 2020)
			cout << "Invalid year!\t";}while(record.year <= 1960 || record.year > 2020);
		cout << "Would you like to enter another record? (y or n) ";
		cin >> yesno;
	}while(yesno == 'y' || yesno == 'Y');
	
	return record;
}

void display_rec(inventory record, char filename[FILENAME])
{
	fstream dataFile;
	//char ch;

	dataFile.open(filename, ios::in | ios::binary);
	dataFile.read(reinterpret_cast<char *>(&record), sizeof(record));
	do
	{
		cout << "Item description  : " << record.item << endl;
		cout << "Quantity on hand  : " << record.quantity << endl;
		cout << "Wholesale cost    : " << record.wholesale << endl;
		cout << "Retail cost       : " << record.retail << endl;
		cout << "Date added        : "
			 << record.day << "/" << record.month << "/" << record.year
			 << endl << endl;
		//cout << "Press any key for next record." << endl << endl;
		//cin.get(ch);
		dataFile.read(reinterpret_cast<char *>(&record), sizeof(record));
	}while(!dataFile.eof());
	dataFile.close();
}

int search_rec(char filename[FILENAME], char value[81])
{
	inventory record;
	fstream dataFile;
	int index = 0;
	int position = -1;
	bool found = false;
	int num_elements = 0; 
	
	num_elements = num_elements(filename);
	dataFile.open(filename, ios::in | ios::binary);
		while((index < num_elements) && !found)
		{	
			dataFile.seekg(byte_num(index), ios::beg);
			dataFile.read(reinterpret_cast<char *>(&record),sizeof(record));
			if(strcmp(record.item,value) == 0)
			{	found = true;
				position = index;
			}
			index++;
		}
	dataFile.close();
	return position;
}

void single_rec(char filename[FILENAME], int record_num)
{
	inventory record;
	fstream dataFile;
	
	dataFile.open(filename, ios::in | ios::binary);
	dataFile.seekg(byte_num(record_num), ios::beg);
	dataFile.read(reinterpret_cast<char *>(&record), sizeof(record));

	cout << "Item description  : " << record.item << endl;
	cout << "Quantity on hand  : " << record.quantity << endl;
	cout << "Wholesale cost    : " << record.wholesale << endl;
	cout << "Retail cost       : " << record.retail << endl;
	cout << "Date added        : "
		 << record.day << "/" << record.month << "/" << record.year
		 << endl << endl;
	dataFile.close();

	return;
}

long byte_num(int record_num)
{
	return sizeof(inventory) * record_num;
}

int num_elements(char filename[FILENAME])
{
	inventory record;
	fstream dataFile;
	int num_elements = 0;

	dataFile.open(filename, ios::in | ios::binary);
	while(!dataFile.eof())
	{
		dataFile.read(reinterpret_cast<char *>(&record),sizeof(record));
	    num_elements++;
	}
	dataFile.close();

	return num_elements;
}

int main()
{
	inventory record;
	fstream dataFile;
	char filename[FILENAME] = "record.txt";
	int num,
		position;
	char target[81];
	
	do
	{
		num = menu();
		switch(num)
		{
			case 1: cin.ignore();
					dataFile.open(filename, ios::app | ios::out | ios::binary);
					record = add_rec();
					dataFile.write(reinterpret_cast<char *>(&record),sizeof(record));
					dataFile.close();
					break;
			case 2: display_rec(record, filename);
					system("pause");
					break;
			case 3:	cout << "Enter the item's description to view: ";
					cin >> target;
					position = 0;
					position = search_rec(filename, target);
					if(position == -1)
						{cout << "Invalid record..." << endl;}
					else 
						single_rec(filename, position);
					break;
			case 4:	cout << "Enter the item's description to change: ";
					cin >> target;
					position = 0;
                    if(position == -1)
						{cout << "Invalid record..." << endl;}
					else 
						dataFile.open(filename, ios::in | ios::out | ios::binary);
						record = add_rec();
						dataFile.seekp(position * sizeof(record), ios::beg);
						dataFile.write(reinterpret_cast<char *>(&record), sizeof(record));
						dataFile.close();
					break;
			default:
					cout << "Please enter a valid choice." << endl << endl;
					break;
		}
	}while(num != 5);
				
    return 0;
}