/****
 * CS 518 : Assignment 4
 * Submitted By: Debzani Deb
 * programmed on Red  Hat linux 9 kernel version 2.4.20-8  
 ***/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/dir.h>
#include <sys/param.h>


/* Structure to hold user typed commands */ 
typedef struct command_struct{
  char name[100];     /* Command's maximum length */
  int argc;           /* Number of arguments */
  char args[10][30];  /* Argument array, Each aurgemnet can be 30 character long */
}command;

command cmd;


/**
 * Parse the command line and break it down
 * to appropriate command structure
 * Acknowledge : M. Muztaba Fuad for this function
 **/
command parse_command(char *line){
  command result;
  char temp[30],temp1[256];
  int i=0,j=0,args=-1;
  
  strcpy(temp1,line);

  /* Tokenize the line */
  for(i=0;i<strlen(temp1);i++){
    if ((temp1[i]==' ') || (temp1[i]=='\n')|| (temp1[i]=='\t')){
      temp[j]='\0';
      j=0;
      /* First token in the line must be the */
      /* name of the command to be executed  */
      if (args==-1){ 
	strcpy(result.name,temp);
	args=0;
      }
      else /* Rest are just aurguments to the command */
	strcpy(result.args[args++],temp);	
    }else
      temp[j++]=temp1[i];
  }

  result.argc=args; /* How many aurguments */
  return result;
}

/**
 * Determines if 'file_name' is inside 'path_name'
 **/
int is_in_path(char *path_name, char *file_name){ 
  int count,i,result=-1;
  struct direct **files;
  
  count = scandir(path_name, &files, NULL, NULL);
 
  /* If no files found */
  if (count <= 0)
    result=-1;
  
  for (i=0;i<count;++i)
    if (strcmp(files[i]->d_name,file_name)==0){
      result=0;
      break;
    }
      
  return result;
}

/**
 * Determines if string 'line' starts with string 'with'
 **/
int starts_with(char *line, char *with){
  size_t len=(size_t) strlen(with);

  if(strncmp(line,with,len)==0)
    return 0; /* Yes, 'line' starts 'with' */
  else
    return -1; /* Nope!! */
}

/**
 * Determine if string 'line' ends with character 'with'
 **/
int ends_with(char *line, char with){

  if (line[strlen(line)-1]==with)
    return 0; /* Yes, 'line' ends 'with' */
  else
    return -1; /* Nope!! */
		 
}

/**
 * Main program
 **/
int main (int argc, char *argv[]){
  char *path_val,t[100],*prompt;
  int done=1,found_command=0,path_item=0,i=0,j=0,status;
  char command_line[251],path[MAXPATHLEN],paths[256][256],cmd_to_exe[256];
    
  /* Find the host name, The following three lines are commented */
  /* is commented to run in esus  */
  //  prompt=strtok(getenv("HOSTNAME"),".");
  
  /* Form the shell prompt*/
  // if (prompt==NULL)
  //  strcpy(prompt, "[TEST]>");

  /* Find the value of environment variable 'PATH' */
  strcpy(path,getenv("PATH"));
  
  /* To look for a command, the program should       */
  /* look at the current folder and all the          */
  /* folders listed in the PATH environment variable */
  
  path_val=getenv("PWD");  /* Find path to the current folder */ 
  strcpy(paths[path_item++],path_val); /* copy the path to current folder in paths*/
  
  /* Parse each path from 'PATH' and copy that to paths*/
  path_val=strtok(path,": ");
  while(path_val!=NULL){
    strcpy(paths[path_item++],path_val);
    path_val=strtok(NULL,": ");
  }
  
  /* Run as long as user don't type the 'done' */
  while(done){
      printf("[Test]>");

    /* Read the command and parse it */
    fgets(command_line,251,stdin);
   
    if (!strcmp(command_line, "done\n"))
      exit(0);
     
    cmd = parse_command(command_line);

    /* If the path name user gave is not absolute */
    /* then construct the absolute path from relative path names */
    if ((starts_with(cmd.name,"/")==0) ||(starts_with(cmd.name,"./")==0)||
	(starts_with(cmd.name,"../")==0)) found_command = 1;
    else {
      for(i=0;i<path_item;i++){      /* For each path in paths */
	strcpy(t,paths[i]);
	
	/* Find if the command apperas in that path */
	if(is_in_path(paths[i],cmd.name)==0){ 
	  found_command =1;           /* command found in the path*/ 
	  if (ends_with(paths[i],'/')==0) 
	    strcat(t,cmd.name);       /* If the path is declared as /usr/bin/ */
	  else{
	    strcat(t,"/");            /* If the path is declared as /usr/bin */
	    strcat(t,cmd.name);
	  } 
	  strcpy(cmd.name,t);
	  break;
	} // If (is_in_path()
	else
	  found_command = 0;           /* command not found in the path*/
      }  // for
    } // else

    /* Prepare the aurguments in the format    */
    /* compatible for the system call 'execvp' */
    char *argv[cmd.argc+2]; 
    j=0;
    argv[j]=malloc(strlen(cmd.name));
    strcpy(argv[j++],cmd.name);

    for(i=0;i<cmd.argc;i++){
      argv[j]=malloc(strlen(cmd.args[i]));
      strcpy(argv[j],cmd.args[i]);
      j++;
    }
    argv[j]=malloc(5);
    argv[j]=NULL;
   
       if (found_command == 1){
      if(fork()==0)
	execvp(cmd.name,argv); /* Execute the command */
      else
	wait(status);  /* Wait until finish */    
     }
     else 
     printf("Command not found\n");
  }
  return 0;
}