#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <time.h>
#include <sys/resource.h>

#define READ_BUFFER_SIZE 1024
#define SPLIT_BUFFER_SIZE 100
#define extras " \t\r\a\n"
char *command_esp[100];

char **basic_shell_splitcommand(char *command)
{
	int buff_size = SPLIT_BUFFER_SIZE;
	int pos = 0;
	char **words = malloc(buff_size * sizeof(char*));
	char *word;
	if(!words)
	{
		fprintf(stderr, "basic_shell: Memory allocation error\n");
		exit(EXIT_FAILURE);
	}

	word = strtok(command,extras);
	while(word != NULL)
	{
		words[pos] = word;
		pos++;
		if(pos >=buff_size)
		{
			buff_size+= SPLIT_BUFFER_SIZE;
			words = realloc(words, buff_size* sizeof(char*));
			if(!words)
			{
				fprintf(stderr, "basic_shell: Memory allocation error!\n");
				exit(EXIT_FAILURE);
			}
		}

		word = strtok(NULL, extras);

	}
	words[pos] = NULL;
	return words;


}

char *basic_shell_readcommand()
{
	int buff_size = READ_BUFFER_SIZE;
	char *allocate = malloc(buff_size* sizeof(char));
	int pos = 0;
	if(!allocate)
	{
		fprintf(stderr, "basic_shell: Memory allocation error!\n");
		exit(EXIT_FAILURE);
	}
	int n;
	while(1)
	{
		n = getchar();
		if(n == EOF || n == '\n')
		{
			allocate[pos] = '\0';
			return allocate;
		}

		allocate[pos] = n;
		pos++;

		if(pos >=buff_size)
		{
			buff_size+= READ_BUFFER_SIZE;
			allocate = realloc(allocate, buff_size* sizeof(char));
			if(!allocate)
			{
				fprintf(stderr, "basic_shell: Memory allocation error!\n");
				exit(EXIT_FAILURE);
			}
		}
	}
}

int basic_shell_execute(char **words)
{
	if(strcmp(words[0], "cd") == 0) // executes cd command
	{
		chdir(words[1]);
		return 1;
	}
	else if(strcmp(words[0], "exit") == 0) // executes exit command
	{
		return 0;
	}

	else if(strcmp(words[0], "help") == 0) // executes help command
	{
		printf("basic_shell : v1.0.\nBasic shell commands will work in this shell.\n And also shell builtins like cd, exit, help and echo is valid here.\nTo know more about this commands type man command_name and press enter.\n\n\n");
		return 1;
	}

	struct rusage R;
	struct timeval UserTime, SystemTime;
	struct timeval StartTime, EndTime;
	gettimeofday(&StartTime, NULL);
	int p= 0;
	pid_t pid;
	pid = fork();
	if(pid == 0)
	{
		printf("hello");

		if(execvp(words[0], words)==-1)
			printf("Invalid command!\n");

		exit(EXIT_FAILURE);
	}

	if(pid <0)
		printf("Unexpected error occured!\n");
	if(pid>0)
	{
		wait(&p);
		getrusage(RUSAGE_CHILDREN, &R);
		UserTime = R.ru_utime;
		SystemTime = R.ru_stime;
		gettimeofday(&EndTime, NULL);
		printf("\n\tCPU time consumed by User: %ld ms\n",UserTime.tv_sec*1000+UserTime.tv_usec/1000);
		printf("\tCPU time consumed by System: %ld ms\n",SystemTime.tv_sec*1000+SystemTime.tv_usec/1000);
		printf("\tElapsed wall clock time: %ld ms\n",(EndTime.tv_sec-StartTime.tv_sec)*1000 + (EndTime.tv_usec-StartTime.tv_usec)/1000 );
		printf("\tThe number of times the process was preempted involuntarily: %ld\n",R.ru_nivcsw);
		printf("\tThe number of times the process was preempted voluntarily: %ld\n",R.ru_nvcsw);
		printf("\tNumber of page faults(Hard): %ld\n",R.ru_majflt);
		printf("\tNumber of page faults(Soft): %ld\n",R.ru_minflt);
	}
	return 1;
}

void basic_shell_start(int command_given)
{
	int flag;
	char *command;
	char **words;
	if(command_given)
	{
		words = command_esp;
		flag = basic_shell_execute(words);
		int i = 0;
		while(words[i]!=NULL)
		{
			i++;
		}



		basic_shell_start(0);
	}

	else
	{
		do
		{
			printf("-> ");
			command = basic_shell_readcommand();

			words = basic_shell_splitcommand(command);
			flag = basic_shell_execute(words);
			int i = 0;
			while(words[i]!=NULL)
			{
				i++;
			}


		}while(flag);
	}
}




int main(int argc, char *argv[])
{
	if(argc == 1)
		basic_shell_start(0);
	else
	{
		int i = 0, j = 0;
		for(i = 1; i<argc;i++)
			command_esp[j++] = argv[i];
		basic_shell_start(1);
	}
	return 0;
}