//Class Project. EE465 Probabilistic Methods in Computer Systems Modeling [Fall 2004]
//File: slottedAloha.c
//Simulation of the Slotted ALOHA System
//Simulation Created by: Nithin Dinker Kamath
//nkamath@usc.edu
//---
//Files Required: arrivals.dat and transmit.dat

#include "stdio.h"
#include "stdlib.h"
#include "math.h"
#include "time.h"

//Function to the factorial of a number
int factorial(int number)
{
	int i = 1;
	int factorial = 1;
	if(number = 0)
	{
		return (1);
	}
	else
	{
		while (i < number)
		{
			factorial = factorial * number;
		}
		return (factorial);
	}
}

//Function to generate random number between 0 and 0.99999
float randomProbability()
{
	float returnValue;
	returnValue = ((float) rand()/RAND_MAX);
	return(returnValue);
}

//Function which, randomly returns 1 or 0
int packet(float probability)
{
	if (randomProbability() <= probability)
	{
		return(1);
	}
	else 
	{
		return(0);
	}
}

//Function to generate Poission arrivals
int poisson(double alpha, float p)
{
	int i;
	double a[1000];
	double f = -1*alpha;
	float total = 0.0;
	for (i=0;i<1000;i++)
	{
         a[i] = 0;
	}
	for(i=0;i<1000;i++)
	{
         a[i] =(((pow(alpha,i))/factorial((long)i))*exp(f));
         total = total + a[i];
         if (randomProbability() < (float) total)
         {
                 return(i);
				 break;
         } 
	}
}

//Main function
int main(int argc, char *argv[])
{
	int choice;
	int i, j, k;
	int timeSlot;
	int state = 0;
	int arrivals = 0, transmissions = 0;
	int transmissionsAttempted = 0;
	int S = 0 , P = 0, G = 0;
	int slot = 0;

//User Interface
	printf("***** Simulation of the Slotted Aloha System ***** \n");
	printf("Enter 1 to simulate the system by reading form the arrival and transmission data files \n");
	printf("Enter 2 to simulate the system using poission arrivals \n");
	printf("Enter 3 to simulate the system using bernoulli arrivals \n");
	printf("Enter 4 to simulate the system using general arrivals \n");
	printf("Enter 0 to exit \n");
	choice = getchar() - 48;
	printf("Option selected: %i \n", choice);

//Data files
	if (choice == 0)
	{
		printf("\nSimulation Exited \n");
		return (0);
	}
	FILE *arrival;
	FILE *transmission;
	FILE *myLog;
	int buffer;
	int junk;
	arrival = fopen("arrivals.dat", "r");
	transmission = fopen("transmit.dat", "r");
	if (arrival == NULL || transmission == NULL)
	{
		printf("arrival.dat and/or transmit.dat file not found\n");
		return (0);
	}
	myLog = fopen("log.dat", "w");
	if (choice == 1)
	{
		while (state < 100)
		{
			if(feof(arrival) != 0 || feof(arrival) != 0)
			{
				break;
			}
			if (state == 0)
			{
				S = 0;
				P = 0;
				G = 0;
			}
			printf("\n%i ", state);
			fprintf(myLog, "%i ", state);
			arrivals = fgetc(arrival) - 48;
			junk = fgetc(arrival);
			printf(" %i ", arrivals);
			fprintf(myLog, " %i ", arrivals);
			for (j = 0; j < state; j++)
			{
				buffer = fgetc(transmission) - 48;
				transmissionsAttempted = transmissionsAttempted + buffer;
				junk = fgetc(transmission);
			}
			state = state + arrivals;
			for (k = 0; k < arrivals; k++)
			{
				transmissionsAttempted = transmissionsAttempted + 1;
			}
			G = G + transmissionsAttempted;
			if (transmissionsAttempted == 1 && arrivals <= 1)
			{
				state = state - 1;
				P = P + 1;
			}
			printf(" %i ", transmissionsAttempted);
			fprintf(myLog, " %i\n", transmissionsAttempted);
			S = S + 1;
			slot = slot + 1;
			transmissionsAttempted = 0;
		}
		fclose(arrival);
		fclose(transmission);
		if (myLog != NULL)
		{
			printf("\nLog file written \n");
		}
		fclose(myLog);
		printf("\n\nlambda = %f", (float) P/S);
		printf("\ngamma = %f", (float) G/S);
		printf("\nE[N] = %f", (float) state/S);
		printf("\nE[T] = %f", (float) state/P);
		printf("\nE[S] = %f", (float) S/100);
		printf("\n");
	}

//Poission Arrivals
	else if (choice == 2)
	{
		state = 0;
		int slot;
		float arrivalProbability = 0, transmissionProbability = 0;
		double alpha = 1.15;
		float p = 0.03;
		while (state < 100)
		{
			transmissionProbability = randomProbability();
			if (state == 0)
			{
				S = 0;
				P = 0;
				G = 0;
			}
			printf("\n%i ", state);
			arrivals = poisson(alpha, p);
			printf(" %i ", arrivals);
			for (j = 0; j < state; j++)
			{
				transmissionsAttempted = transmissionsAttempted + packet(transmissionProbability);
			}
			state = state + arrivals;
			for (k = 0; k < arrivals; k++)
			{
				transmissionsAttempted = transmissionsAttempted + 1;
			}
			if (transmissionsAttempted == 1 && arrivals <= 1)
			{
				state = state - 1;
				P = P +1;
			}
			S = S + 1;
			printf(" %i ", transmissionsAttempted);
			transmissionsAttempted = 0;
		}
		printf("\n\nlambda = %f", (float) P/S);
		printf("\ngamma = %f", (float) G/S);
		printf("\nE[N] = %f", (float) state/S);
		printf("\nE[T] = %f", (float) state/P);
		printf("\nE[S] = %f", (float) S/100);
		printf("\n");
	}

//Bernouilli Arrivals
	else if (choice == 3)
	{
		state = 2;
		float arrivalProbability = 0, transmissionProbability = 0;
		printf("\nEnter the initial state \n");
		scanf("%d", &state);
		getchar();
		if (state == 0)
		{
			printf("\nThis simulation will enter infinite loop. Simulation Exited\n");
			return (0);
		}
		while (state < 100)
		{
			arrivalProbability = randomProbability();
			transmissionProbability = randomProbability();
			if (state == 0)
			{
				S = 0;
				P = 0;
				G = 0;
			}
			printf("\n%i ", state);
			arrivals = packet(arrivalProbability);
			printf(" %i ", arrivals);
			for (j = 0; j < state; j++)
			{
				transmissionsAttempted = transmissionsAttempted + packet(transmissionProbability);
			}
			state = state + arrivals;
			for (k = 0; k < arrivals; k++)
			{
				transmissionsAttempted = transmissionsAttempted + 1;
			}
			if (transmissionsAttempted == 1 && arrivals <= 1)
			{
				state = state - 1;
				P++;
			}
			printf(" %i ", transmissionsAttempted);
			S = S + 1;
			slot = slot + 1;
			transmissionsAttempted = 0;
		}
		fclose(arrival);
		fclose(transmission);
		printf("\n\nlambda = %f", (float) P/S);
		printf("\ngamma = %f", (float) G/S);
		printf("\nE[N] = %f", (float) state/S);
		printf("\nE[T] = %f", (float) state/P);
		printf("\nE[S] = %f", (float) S/100);
		printf("\n");
	}

//General arrivals
	else if (choice == 4)
	{
		state = 0;
		float arrivalProbability = 0, transmissionProbability = 0;
		printf("\nEnter the initial state \n");
		scanf("%d", &state);
		getchar();
		for (i = 0; i < 100; i++)
		{
			arrivalProbability = (float) (1/pow(2, i));
			printf("Probability : %f", arrivalProbability);
			transmissionProbability = 0.4;
			if (state == 0)
			{
				S = 0;
				P = 0;
				G = 0;
			}
			printf("\n%i ", state);
			arrivals = packet(arrivalProbability);
			printf(" %i ", arrivals);
			for (j = 0; j < state; j++)
			{
				transmissionsAttempted = transmissionsAttempted + packet(transmissionProbability);
			}
			state = state + arrivals;
			for (k = 0; k < arrivals; k++)
			{
				transmissionsAttempted = transmissionsAttempted + 1;
			}
			if (transmissionsAttempted == 1 && arrivals <= 1)
			{
				state = state - 1;
				P = P + 1;
			}
			printf(" %i ", transmissionsAttempted);
			S = S + 1;
			slot = slot + 1;
			transmissionsAttempted = 0;
		}
		printf("\n\nlambda = %f", (float) P/S);
		printf("\ngamma = %f", (float) G/S);
		printf("\nE[N] = %f", (float) state/S);
		printf("\nE[T] = %f", (float) state/P);
		printf("\nE[S] = %f", (float) S/100);
		printf("\n");
	}
	else
	{
		printf("Wrong choice: Simulation Exited \n");
	}
	return 0;
}