/* Shawn Nematbakhsh
 * login: cs153be
 * lab section: wed. night
 * cs153 as1 - shell          */

#define INPUT_LENGTH 500
#define MAX_ARGS 50

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

// data structure for history record
struct hist_t
{
	char *commands[10];
	int on;
};

// carries out pipe
int init_pipe(char line[INPUT_LENGTH],char **envp);
// checks for redirection
int checks(char line[INPUT_LENGTH],int *oldstream,int *oldfid);
// packs input into args
void pack(char *args[MAX_ARGS],char line[INPUT_LENGTH]);
// executes a command
void run_command(char *args[MAX_ARGS],char **envp);
// initializes the history
void hist_init(struct hist_t *history);
//inserts into history
void hist_update(struct hist_t *history,char *command);
//prints history
void hist_print(struct hist_t *history);
// mallocs the history
void hist_free(struct hist_t *history);
// gets a given command in the history
char *hist_get(struct hist_t *history,int num);

int main(int argc,char **argv,char **envp)
{
	// holds user input
	char line[INPUT_LENGTH];
	// line gets spliced up by strtok so we need another copy for history
	char line2[INPUT_LENGTH];
	// I sprintf to this when searching the path
	char cwd[INPUT_LENGTH];
	// args for the input
	char *args[MAX_ARGS];
	// the history
	struct hist_t history;
	// signals a redirect
	int redir=0;
	// old stdin/stdout fid's
	int oldfid;
	int oldstream;

	// initialize history
	hist_init(&history);

	// repeat until exit
	while(1)
	{	
		// if we just did a reditect then set stdio/in back to normal
		if(redir>0)
		{	
			close(oldstream);
			close(redir);
			dup(oldfid);
			redir=0;
		}
		
		// print prompt, get input
		printf("shell>");
		fgets(line,INPUT_LENGTH-1,stdin);

		// make copy for history later
		strcpy(line2,line);

		// check for a redirect op, and change stdio/in
		redir=checks(line,&oldstream,&oldfid);
		
		// check for invalid redirection
		if(redir==-1)
		{
			printf("Invalid redirection\n");
			continue;
		}

		// check for pipe
		if(strchr(line,'|'))
		{
			if(init_pipe(line,envp))
				hist_update(&history,line2);
			continue;
		}
		
		// divide the input into args
		pack(args,line);	
		
		// blank input case
		if(!args[0]) continue;
			
		// check for history command
		if(args[0][0]=='!')
		{
			// execute previous command
			if(strcmp(args[0],"!!")==0)
			{
				if(!hist_get(&history,history.on))
				{
					printf("Event not found\n");
					continue;
				}
				strcpy(line,hist_get(&history,history.on));
			}
			else
			{
				// one of the last ten commands
				if(!hist_get(&history,atoi(args[0]+1)))
				{
					printf("Event not found\n");
					continue;
				}
				
				strcpy(line,hist_get(&history,atoi(args[0]+1)));
			}

			// we have do all this again if we took a command from
			// the history
			strcpy(line2,line);
			redir=checks(line,&oldstream,&oldfid);
			if(redir==-1)
			{
				printf("Invalid redirection\n");
				continue;
			}
			
			if(strchr(line,'|'))
			{
				if(init_pipe(line,envp));
					hist_update(&history,line2);
				continue;
			}
			pack(args,line);
			
		}
			
		// update the history
		hist_update(&history,line2);
		
		// internal exit
		if(strcmp(args[0],"exit")==0)
		{
			hist_free(&history);
			return 0;
		}

		// internal cd
		else if(strcmp(args[0],"cd")==0)
		{
			if(!args[1])
				chdir(getenv("HOME"));
			else
			{
				if(args[1][0]!='/')
				{
					sprintf(cwd,"%s/%s",getcwd(cwd,INPUT_LENGTH),args[1]);
					if(chdir(cwd)==-1)
						printf("Can't access directory %s\n",cwd);
				}
				else if(chdir(args[1])==-1)
					printf("Can't access directory %s\n",args[1]);
			}
		}
	
		// internal history
		else if(strcmp(args[0],"history")==0)
			hist_print(&history);
		// otherwise run an external command
		else
			run_command(args,envp);
	}
	return 0;
}

// this function carries out a pipe
int init_pipe(char line[INPUT_LENGTH],char **envp)
{
int test;
	char pipeD[INPUT_LENGTH];
	int fileID[2];
	char *args[MAX_ARGS];
	
	// empty pipe case
	if(line[strlen(line)-1]=='|')
	{
		printf("Invalid pipe\n");
		return 0;
	}

	// create pipe and divide input in two
	pipe(fileID);
	strcpy(pipeD,strchr(line,'|')+1);
	*(strchr(line,'|'))='\0';
	test=dup(1);		
	// redirect output of left command
	if(fork()==0)
	{
		close(fileID[0]);
		close(1);
		
		printf("foo\n");
		dup(fileID[1]);
		close(fileID[1]);
		pack(args,line);
		
		run_command(args,envp);
				
		exit(0);
	}
	
	// ...to the input of right command
	if(fork()==0)
	{
		close(fileID[1]);
		close(0);
		dup(fileID[0]);
		close(fileID[0]);
		pack(args,pipeD);
				
		run_command(args,envp);
				
		exit(0);
	}
	close(fileID[0]);
	close(fileID[1]);
	wait(NULL);
	return 1;
}

// this function checks for a redirect op
int checks(char line[INPUT_LENGTH],int *oldstream,int *oldfid)
{
	char *tok;
	int redir;
	
	// append
	if(strstr(line,">>"))
	{
		// seperate op from redirected file
		tok=strtok(strstr(line,">>")+2," \t\n");
		*(strstr(line,">>"))='\0';
			
		if(tok)
		{
			// change streams
			*oldfid=dup(1);
			redir=open(tok,O_WRONLY | O_CREAT | O_APPEND,S_IWRITE | S_IREAD);
			close(1);
			*oldstream=1;
			dup(redir);
			return redir;
		}
	}

	// output redirect
	else if(strstr(line,">"))
	{
		tok=strtok(strstr(line,">")+1," \t\n");
		*(strstr(line,">"))='\0';
		if(tok)
		{
			
			*oldfid=dup(1);
			redir=open(tok,O_WRONLY | O_CREAT | O_TRUNC,S_IWRITE | S_IREAD);
			*oldstream=1;
			close(1);
			dup(redir);
			return redir;
		}
	}

	// input redirect
	else if(strstr(line,"<"))
	{
		tok=strtok(strstr(line,"<")+1," \t\n");
		*(strstr(line,"<"))='\0';
		if(tok)
		{
			// case where file doesn't exist
			if(access(tok,R_OK)) return -1;
			*oldfid=dup(0);
			redir=open(tok,O_RDONLY);
			*oldstream=0;
			close(0);
			dup(redir);
			return redir;
		}
	}
	else
		return 0;
	return -1;
}

// seperates a line into args
void pack(char *args[MAX_ARGS],char line[INPUT_LENGTH])
{
	int on=0;
	
	args[on++]=strtok(line," \t\n");
	if(!args[0]) return;	
	
	while((args[on++]=strtok(NULL," \t\n")));
}

// carries out execution of a command
void run_command(char *args[MAX_ARGS],char **envp)
{
	
	char bigPath[INPUT_LENGTH];
	char path[INPUT_LENGTH];
	char *dir;
	
	if(fork()) 
		// parent
		wait(NULL);			
	else 
	{
		// chile
		if(*args[0]=='.' || *args[0] =='/')
		{
			if(!access(args[0],X_OK))
				execve(args[0],args,envp);
			fprintf(stderr,"%s: No such file or directory\n",args[0]);
		}
		else
		{	
			// search path for executable
			strcpy(bigPath,getenv("PATH"));
			dir=strtok(bigPath,":");
			while(dir)
			{
				sprintf(path,"%s/%s",dir,args[0]);
				if(!access(path,X_OK))
				{
					
					execve(path,args,envp);
					
				}
				dir=strtok(NULL,":");
			}
			fprintf(stderr,"%s: command not found\n",args[0]);
		}
		exit(0);
	}
}

// initialize the history
void hist_init(struct hist_t *history)
{
	int i;
	for(i=0;i<10;++i)
		history->commands[i]=NULL;
	history->on=0;
}

// add an item to the history
void hist_update(struct hist_t *history,char *command)
{
	if(history->commands[history->on%10]) free(history->commands[history->on%10]);
	history->commands[history->on%10]=malloc(strlen(command)+1);
	strcpy(history->commands[history->on%10],command);
	history->on++;
}

// prints out teh history
void hist_print(struct hist_t *history)
{
	int i;
	for(i=0;i<10;++i)
		if(history->on-10+i > -1)
			printf("%5d  %s",history->on-9+i,history->commands[(history->on-10+i)%10]);

}

// frees up memory once we are done
void hist_free(struct hist_t *history)
{
	int i;
	for(i=0;i<10;++i)
		if(history->commands[i])
			free(history->commands[i]);
}

// gets an iten from teh history
char *hist_get(struct hist_t *history,int num)
{
	if(num < 1 || num > history->on || num < history->on - 10)
		return NULL;
	return history->commands[(num-1)%10];
}