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

char* substr(const char *src, int m, int n);
void pipeFunc(char *command1, char *command2);

int main() 
{
	while (1)
	{
		printf("My Shell\n"); 
		printf(">> ");
		//following is the temporary string that I want to keep my char[] read from breaking the above char[] myString 
		//following breaks based on space character
		char commandStr[100], commandStrFull[100];
		char *temp;
		char *temp2;
		char temp3[100];
		//strcpy(commandStr, "exit");
		fgets(commandStr, 100, stdin);
		//strcpy(commandStr, "ls -l > a.txt");
		strcpy(commandStrFull,commandStr);
		char *filename;
		int flag = 0;
		// exit program if command is exit
		if(strcmp(commandStr, "exit\n")==0)
		{
			exit(-1);
		}

		int redir=0;
		int redirIndex;
		int pipeNum=0;
		int single=0;
		char* redirCheckTwo=NULL;
		char* command2;
		char* command1;
		char* pipeCheck = strchr(commandStr, '|');
		char* redirCheck = strchr(commandStr, '>');
		if(pipeCheck!=NULL)
		{
			pipeNum=1;
			redirCheckTwo = strchr(commandStr, '>');
			command1 = strrchr(commandStr, '|');
			redirIndex = strcspn(commandStr, ">");
		}
		else single=1;
		if (redirCheckTwo!=NULL)
		{
			command1 = strrchr(commandStr, '|');
			redir=1;
		}
		if(redirCheck!=NULL) redir=1;
		//commandStr[strcspn(commandStr, "\n")] = 0;
		// pipe or redirect
		if (pipeNum==1 || redir==1)
		{
			temp = strtok(commandStr," "); //include , inside "" 
			while(temp!=NULL) 
			{ 
				//printf("%s\n",temp);
				if (strcmp(temp,">")==0 && redir==1)
				{
					filename = strtok(NULL, " ");
					//printf("Filename: %s\n", filename);
				}
				if (strcmp(temp,"|")==0 && pipeCheck!=NULL)
				{
					command2 = strtok(NULL," >");
					//puts(strchr(temp, '|'));
					flag=1;
				}
				
				if (pipeNum==1 || redir==1)
				{
					temp = strtok(NULL," "); //include , inside ""
				}
				else temp2 = strtok(NULL," "); //include , inside ""
			}
		}
		// single command is run
		if(single==1 && pipeNum==0 && redir==0){
			commandStr[strcspn(commandStr, "\n")] = 0;
			//strcpy(temp,commandStr);

			//execvp expects the arguments to be provided as char[][] 
			//so please make sure you understand strtok before coming here 
			//we will use strtok() to break the sequence of command and argument in myArgument to convert to char[][] 
			char* myBrokenArgs[10]; //this will hold the values after we tokenize
			//printf("Starting tokenization...\n");
			myBrokenArgs[0] = strtok(commandStr," ");
			int counter = 0; 
			while(myBrokenArgs[counter]!=NULL)
			{
				counter+=1;
				myBrokenArgs[counter] = strtok(NULL," ");
			}
			myBrokenArgs[counter] = NULL;
			//printf("\ttokenization complete....\n\nNow executing using execvp\n"); 
			//printf("Following will be the output of execvp\n");
			//printf("=======================================\n");
			if ((strcmp("ls",myBrokenArgs[0]) ==0) && single==1)
			{
				int id;
				//I will spawn a child that will run my execvp command 
				if((id=fork())==0)
						execvp(myBrokenArgs[0],myBrokenArgs);
				else if(id<0)
						printf("Failed to make child...\n");
				else
				{ 
					//parent shall wait until the child is killed
					wait(0); 
					printf("=======================================\n");
					printf("Completed execution\n"); 
				}
			}
			else if (strcmp("date",myBrokenArgs[0]) ==0)
			{
				int id;
				//I will spawn a child that will run my execvp command 
				if((id=fork())==0)
						execvp(myBrokenArgs[0],myBrokenArgs);
				else if(id<0)
						printf("Failed to make child...\n");
				else
				{ 
					//parent shall wait until the child is killed
					wait(0); 
					printf("=======================================\n");
					printf("Completed execution\n"); 
				}
			}
			else if ((strcmp("ps",myBrokenArgs[0]) ==0))
			{
				int id;
				//I will spawn a child that will run my execvp command 
				if((id=fork())==0)
						execvp(myBrokenArgs[0],myBrokenArgs);
				else if(id<0)
						printf("Failed to make child...\n");
				else
				{ 
					//parent shall wait until the child is killed
					wait(0); 
					printf("=======================================\n");
					printf("Completed execution\n"); 
				}
			}
		}
		// pipe is used
		if (pipeNum==1 && redirCheck==NULL && single==0)
		{
			strcpy(commandStrFull, "ls -lah | wc -l");
			int size = strcspn(commandStrFull, "|");
			int end = strcspn(commandStrFull, "\0");
			int beg = strcspn(commandStrFull, "|");
			char* command2 = substr(commandStrFull, beg+2, end);

			end = strcspn(commandStrFull, "|");
			char* command1 = substr(commandStrFull, 0, end-1);

			char* command1Args[10]; //this will hold the values after we tokenize
			//printf("Starting tokenization...\n");
			command1Args[0] = strtok(command1," ");
			int counter = 0; 
			while(command1Args[counter]!=NULL)
			{
				counter+=1;
				command1Args[counter] = strtok(NULL,"\0");
			}
			command1Args[counter] = NULL;

			char* command2Args[10]; //this will hold the values after we tokenize
			//printf("Starting tokenization...\n");
			command2Args[0] = strtok(command2," ");
			counter = 0;
			while(command2Args[counter]!=NULL)
			{
				counter+=1;
				command2Args[counter] = strtok(NULL," ");
			}
			command2Args[counter] = NULL;

			int fds[2];
			pipe(fds);
			// Child 1 will duplicate downstream into stdin
			if(fork() == 0)
			{
				dup2(fds[0], 0); // normally 0 is for stdin
						// will now read to fds[0]
						// end of pipe 
				close(fds[1]);   // close other end of pipe
				execlp(command2Args[0] ,command2Args[0], command2Args, 0);
				//execlp("wc", "wc", "-l", 0); // Note the first argument is the command
								// After it are the arguments including
								// original command
			}
			// Child2 duplicates upstream into stdout
			else if (fork() == 0)
			{
				dup2(fds[1], 1); // normally 1 is for stdout
						// will now write to fds[1] 
						// end of pipe
				close(fds[0]);   // close other end of pipe
				execlp(command1Args[0],command1Args[0], command1Args, 0);
			}
			// Parent
			else
			{
				close(fds[0]);
				close(fds[1]);
				wait(0);
				wait(0);
			}
		}
		if (pipeNum==0 && redir==1)
		{
			int end = strcspn(commandStrFull, ">");
			int beg = strcspn(commandStrFull, "|");
			char* command1 = substr(commandStrFull, 0, end-1);
			char* myBrokenArgs[10]; //this will hold the values after we tokenize
			printf("Starting tokenization...\n");
			myBrokenArgs[0] = strtok(command1," ");
			int counter = 0; 
			while(myBrokenArgs[counter]!=NULL)
			{
				counter+=1;
				myBrokenArgs[counter] = strtok(NULL," ");
			}
			myBrokenArgs[counter] = NULL;

			int myDescriptor = open(filename,O_CREAT|O_RDWR|O_TRUNC,0644); 
			int id; 
			//creating a child that redirects the stdout to test.txt 
			// you can use similar functionality for '>' operator 
			if((id=fork())==0) 
			{ 
				//lets call dup2 so that out stdout (second argument) is now copied to (points to) test.txt (first argument) 
				// what this essentially means is that anything that you send to stdout will be sent to myDescriptor 
				dup2(myDescriptor,1); //1 is stdout, 0 is stdin and 2 is stderr 
				execvp(myBrokenArgs[0],myBrokenArgs);
				close(myDescriptor); 
				exit(0);
			}else 
				wait(0); 
			printf("Completed execution.\n");
		}
	}	 
		return 0;
	
}

void pipeFunc(char *command1, char *command2)
{
	
}

char* substr(const char *src, int m, int n)
{
    // get the length of the destination string
    int len = n - m;
 
    // allocate (len + 1) chars for destination (+1 for extra null character)
    char *dest = (char*)malloc(sizeof(char) * (len + 1));
 
    // start with m'th char and copy `len` chars into the destination
    strncpy(dest, (src + m), len);
 
    // return the destination string
    return dest;
}