// Shell Example Fall 2005
//
#include <iostream>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <string>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <dirent.h>
using namespace std;

// Shell variables
class Environment {
public:
   string SHELL;              // fully qualified shell executable
   string HOME;               // home directory
   string PWD;                // working directory
   string PATH;               // shell path

   string Prompt() const {    // construct shell for "pregnant prompt"
      return PWD + ">> ";
   }

   char** getENV() const {    // create argv-style listing of shell variables
      char** envp = new char*[5];
      string SH = string("SHELL=") + SHELL;
      envp[0] = new char[7 + SHELL.length()];
      strcpy(envp[0], SH.c_str());
      // ... 
      return envp;
   }
};

Environment Environ;  // cheesy global environment... not good practice

const unsigned int PATHLIMIT = 100;
const unsigned int MAXARGS   =  10;
const char pathSeparator = '/';

void initShell();
char** getPath(unsigned int& Length);
bool serviceEntry(string userEntry, char** pathList, unsigned int pathLength);
bool validCommand(const string& Command, char** pathList, unsigned int pathLength,
                  string& fullyQualifiedCommand);
void cdHandler( istringstream& User );
string updatePWD(string Suffix);

int main(int argc, char** argv) {

	initShell();
	
	char** pathList = NULL;
	unsigned int pathLength = 0;
	pathList = getPath(pathLength);

    string userEntry;
	cout << Environ.Prompt();
	getline(cin, userEntry, '\n');
    while ( serviceEntry(userEntry, pathList, pathLength) ) {
	   cout << Environ.Prompt();
	   getline(cin, userEntry, '\n');
    }
   	
   return 0;
}

void initShell() {
	
   char* value = getenv("HOME");
   Environ.HOME = string(value);
   // ...
}

bool serviceEntry(string userEntry, char** pathList, unsigned int pathLength) {
	
	string Command;
	istringstream User(userEntry);
	User >> Command;
	if ( Command == "quit" ) {       // internal command "quit"
		return false;
	}
	else if ( Command == "cd" ) {    // internal command "cd"
		cdHandler( User );
	}
    // ...
	else {                           // external program invocation
		string fullyQualified;
		// check for existence/executability of specified program (and get its fully-qualified name)
		if ( !validCommand(Command, pathList, pathLength, fullyQualified) ) {
			cout << "McShell could not find the command: " << fullyQualified << endl;
		   return true;
	    }
		char* argv[MAXARGS];
		unsigned int argc = 0;
		
		argv[argc] = new char[Command.length() + 1];
		strcpy(argv[argc], Command.c_str());
		argc++;
		
		// Grab command-line parameters here
		string Arg;
		User >> Arg;
		while ( User ) {
           // ...
           User >> Arg;
	    }
        argv[argc] = NULL;
	   
        // ...	      
		int childPID = -1;
		if ( (childPID = fork()) == 0 ) {
 		      
		   char** envp = Environ.getENV();
		   execve(fullyQualified.c_str(), argv, envp);
		   exit(0);
	   }
	   // ...
	}
	return true;
}


char** getPath(unsigned int& Length) {
	
	char** pathList = NULL;
	Length = 0;
	   
   //parse out path components into argc-like structure
		   
	return pathList;
}

void cdHandler( istringstream& User ) {
	
	string newDirectory;
	User >> newDirectory;
	if ( newDirectory.length() == 0 ) {
		cout << Environ.PWD << endl;
	}
	else if ( newDirectory == "./" || newDirectory == "." ) {   // no change
		return;
	}
	else {
	   string newPWD = updatePWD( newDirectory );
	   Environ.PWD = newPWD;
	   setenv("PWD", newPWD.c_str(), true);
	}
}


string updatePWD(string Suffix) {

   // reset PWD, compressing if needed (e.g., for "cd ..")
}