/*
 * Project 3 - Shared memory and semaphores.
 * Dr. Silaghi's Operating System Concepts.
 * main.c - Main entry point for the client application.
 * By: Michael Rywalt - 2569
 */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "main.h"

/**************
 * InitScreen *
 **************
 *
 * Function: InitScreen
 *
 * Purpose: Print welcome message to user when application begins.
 *
 * Parameters: None.
 *
 * Returns: Nothing.
 */
void InitScreen()
{
	printf("Welcome to the cilent application.\n");
	printf("r - read current counter value.\nw - write a new value to counter.\nq - quit.\n");
}

/*******************
 * IsDaemonRunning *
 *******************
 *
 * Function: IsDaemonRunning
 *
 * Purpose: To check if the daemon is running. It must be running
 *          for the client to run.
 *
 * Parameters: None.
 *
 * Returns: TRUE if running, FALSE if not.
 */
int IsDaemonRunning()
{
	int iDaemonsLockFile;

	/* Set up a lockfile so no other instances of this daemon run at once. */
	iDaemonsLockFile = open(LOCKFILE, O_RDWR | O_CREAT, 0640);

	/* Validate lockfile. */
	if(iDaemonsLockFile < 0)
	{
		perror(" [IsDaemonRunning] ");
		exit(EXIT_ERROR);
	}

	if(lockf(iDaemonsLockFile, F_TLOCK, 0) < 0)
	{
		return 1;
	}
	
	return 0;
}

/********
 * main *
 ********
 *
 * Function: main
 *
 * Purpose: Main entry point.
 *
 * Parameters: None for this program. 
 *
 * Returns: EXIT_OK on success, 
 *          EXIT_ERROR on error.
 */
int main()
{
	/* The integer that comes from the shared memory segment. */
	int *pInteger	= NULL;
	int  iValue	= 0;
	char cUserEntry = 0;
	char szValue[256];

	/* Check if daemon is running first... */
	if(!IsDaemonRunning())
	{
		printf("Daemon doesn't appear to be running. Try starting it first.\n");
		exit(EXIT_ERROR);
	}

	/* Use existing semaphores from daemon. */
	InitSemaphore();

	/* Use shared memory that daemon set up. */
	pInteger = InitSharedMemory();

	/* Prompt user with basic instructions before starting. */
	InitScreen();

	/* Main loop. */
	do
	{
		printf("> ");

		/* The daemon must be running and must exit after we do. */
		if(!IsDaemonRunning())
		{
			printf("Daemon has disappeared. Aborting.\n");
			exit(EXIT_ERROR);
		}

		switch(cUserEntry)
		{
		case 'w':
			fflush(stdin);
			printf("Enter new value [or -1 to cancel action]: ");
			scanf("%s", szValue);
			iValue = atoi(szValue);
			
			if(iValue != -1)
			{
				if(SEMAPHORE(&WaitMutex) == 0)
				{
					*pInteger = iValue;
				}
				SEMAPHORE(&SignalMutex);
			}
			else
			{
				printf("Cancelled.\n");
			}
		case 'r':
			if(SEMAPHORE(&WaitMutex) == 0)
			{
				printf("Counter value: %i\n", *pInteger);
			}
			SEMAPHORE(&SignalMutex);
			break;
		default:
			break;
		}

	}while((cUserEntry = getchar()) != 'q');

	printf("Quitting...\n");

	/* Exit. */
	return 0;
}