/* 
 * vendorInfo.c
 *
 * Program that 
 *
 *
 *    Created by Win (Thanawin Pattanaphol), 28th August 2024
 */

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

#define MAX_VENDORS 20
#define MAX_FILENAME_LENGTH 4096

/* STRUCTURES */
struct vendor
{
	char vendor_name[20];
	char merchandise[15];
	int inventory_count;
	int item_price_baht;	
} vendors[MAX_VENDORS];

struct search_r
{
	int status;
	int item_id;
};

struct purchase_r
{
	int status;
	char vendor_name[20];
	int price_owe_baht; 
}; 

/* FUNCTION DECLARATION */
int read_input(char str[], size_t n);
char *strnlower(char *s, size_t n);
int validate_data(struct vendor vendors[MAX_VENDORS]);

struct search_r search
(
	char query[], 
	struct vendor vendors[MAX_VENDORS], 
	int total_vendors
);
		   
struct purchase_r purchase
(
	int item_id, 
	int amount, 
	struct vendor vendors[MAX_VENDORS]
);

int main() 
{
	char file_name[MAX_FILENAME_LENGTH];
	printf("Enter name of input file: ");
	read_input(file_name, MAX_FILENAME_LENGTH);
	
	FILE *fp;
	if ((fp = fopen(file_name, "r")) == NULL) 
	{
		printf("%s cannot be opened.\n", file_name);
		exit(EXIT_FAILURE);
	}

	// calculate file size
	fseek(fp, 0, SEEK_END);
	unsigned long file_size = ftell(fp);
	fseek(fp, 0, SEEK_SET);

	// read file to buffer
	char *file_buffer = (char *) malloc(file_size);
	int index = 0;

	while ((fgets(file_buffer, 50, fp) != NULL) && (index <= MAX_VENDORS))
	{
		/* TO-DO: VALIDATE FILE DATA */
		char *token = strtok(file_buffer, " ");
		strncpy(vendors[index].vendor_name, token, strlen(token) + 1); 
		
		token = strtok(NULL, " ");
		/* TO-DO: VALIDATE MERCHANDISE BY PUTTING EVERYTHING AS LOWERCASE */
		strncpy(vendors[index].merchandise, token, strlen(token) + 1); 
				
		token = strtok(NULL, " ");
		vendors[index].inventory_count = atoi(token);
				
		token = strtok(NULL, " ");
		vendors[index].item_price_baht = atoi(token);
				
		index++;	
	}

	int total_vendors = index - 1;
	printf("\n>>> Read %d vendors from file %s\n", total_vendors, file_name);

	// print out each vendor's info
	for (int i = 0; i <= total_vendors; i++) 
	{
		char vendor_info[200];
		sprintf(vendor_info, "%s sells %s for %d each",
			vendors[i].vendor_name, 
			vendors[i].merchandise, 
			vendors[i].item_price_baht
		);
		
		char vendor_stock[50];
		sprintf(vendor_stock, "Inventory %d items",
			vendors[i].inventory_count
		);
	
		printf("%-50s %s\n", vendor_info, vendor_stock);		
	}
	
	while (1) 
	{
		char user_query[100];
		printf("What do you want to buy? (DONE to end) ");
		read_input(user_query, 100);

		if ((strcmp(user_query, "DONE") == 0)) 
		{
			break;
		}

		// convert string to lowercase - each character one by one
		int user_query_length = strlen(user_query);	
		strnlower(user_query, user_query_length);
		
		struct search_r item = search(user_query, vendors, total_vendors);
		if(item.status == 0)
		{
			char input[10];
			read_input(input, 10);

			if(atoi(input) < 0) 
			{
				int item_amount = atoi(input);
				struct purchase_r response = purchase(item.item_id, item_amount, vendors);

				if (response.status == 0)
				{
					printf("You owe %s a total of %d baht.\n",
						response.vendor_name,
						response.price_owe_baht
					);
				}
			}
			else 
			{
				printf("You must enter a positive whole number for the number of items");		
			}

		}
		else
		{
			printf("No vendor in this market sells %s\n", user_query);
		}
	}
		
	fclose(fp);
	free(file_buffer);
	return 0;
};

/*
	read_input: Custom read input function
	str = string itself
	n = max amount of characters that the function is able to read into buffer

	reads one character at a time into buffer and adds a null terminator when finish reading
*/
int read_input(char str[], size_t n) 
{
	int ch, i = 0;

	while ((ch = getchar()) != '\n') 
	{
		if (i < (int)n) 
		{
			str[i++] = ch;
		}
	}

	str[i] = '\0';
	return i;
};

/* 
	strnlower: Convert string to lowercase

	Parameters:
		- s: String
		- n: Length of string
	
*/
char *strnlower(char *s, size_t n)
{
	for (int i = 0; i < (int) n; i++)
	{
		s[i] = tolower(s[i]);
	};
}

/* 
	Search function

	Parameters:
		- query: search query
		- vendors: the vendor table
		- total_vendors: the amount of vendors

	Return values:
		- i: Item Number
		- 0: No results found
*/

/* TO-DO IMPLEMENT RESPONSE STRUCT */
struct search_r search(char query[], struct vendor vendors[MAX_VENDORS], int total_vendors)
{
	int i; 
	for (i = 0; i < total_vendors; i++)
	{
		if (strcmp(query, vendors[i].merchandise) == 0)
		{
			struct search_r response;
			response.status = 0;
			response.item_id = i;
			
			return (response);
			break;
		};
	};

	if (i == total_vendors)
	{
		struct search_r response;
		response.status = 1;
		response.item_id = 0;
		return (response);
	}
};

/* 
	Purchase function

	Parameters:
		- item_id: The item id that the user is purchasing
		- amount: How many items that the user is purchasing
		- vendors: vendor table

	Return values:
		- 
*/
struct purchase_r purchase(int item_id, int amount, struct vendor vendors[MAX_VENDORS])
{
	if(amount <= vendors[item_id].inventory_count)
	{
		// Decrease vendor inventory
		vendors[item_id].inventory_count = vendors[item_id].inventory_count - amount;

		struct purchase_r response;

		response.status = 0;
		strcpy(response.vendor_name, vendors[item_id].vendor_name);
		response.price_owe_baht = vendors[item_id].item_price_baht * amount;
		
		return (response);
	}
	else
	{
		struct purchase_r response; 
		response.status = 1;
		
		return response;
	} 
};