#include <sys/inotify.h>
#include <sys/syscall.h>

// Use this if syscalls not defined
#ifndef __NR_inotify_init
#include <sys/inotify-syscalls.h>
#endif // __NR_inotify_init


#include <stdio.h>
#include <unistd.h>
#include <map>
#include <string>

using namespace std;

typedef map<string, int> StrIntMap;
typedef pair<string, int> StrIntPair;

typedef map<int, string> IntStrMap;
typedef pair<int, string> IntStrPair;

StrIntMap pathsToWds;
IntStrMap wdsToPaths;

int fd;

int AddWatch(const string &path)
{
    int wd = inotify_add_watch( fd, (char*)(path.c_str()), IN_CREATE | IN_DELETE | IN_MODIFY );
    pathsToWds.insert(StrIntPair(path, wd));
    wdsToPaths.insert(IntStrPair(wd, path));
    printf("Adds %s as wd %d. Has %d watches\n", path.c_str(), wd, pathsToWds.size());
    return wd;
}

void RemoveWatch(const string &path)
{
    int wd = pathsToWds[path];
    pathsToWds.erase(path);
    wdsToPaths.erase(wd);
    printf("Removes %s as wd %d. Has %d watches\n", path.c_str(), wd, pathsToWds.size());
    
    if( inotify_rm_watch(fd, wd) != -1)
    {
        throw string("No no no...");
    }
}


void RemoveWatch(int wd)
{
    RemoveWatch(wdsToPaths[wd]);
}


int main( ) 
{
  
    try
    {
    
    int EVENT_SIZE =  sizeof (struct inotify_event) ;
    int EVENT_BUF_LEN =  ( 1024 * ( EVENT_SIZE + 16 ) );
    int length, i = 0;
    char buffer[EVENT_BUF_LEN];

    /*creating the INOTIFY instance*/
    fd = inotify_init();

    /*checking for error*/
    if ( fd < 0 ) {
    //    perror( "inotify_init" );
    }

    /*adding the “/tmp” directory into watch list. Here, the suggestion is to validate the existence of the directory before adding into monitoring list.*/
    string bd = "/tmp";
    AddWatch(bd);



    while(1) {
        length = 0; 
        i = 0;
        length = read( fd, buffer, EVENT_BUF_LEN ); 
        /*checking for error*/
        if ( length < 0 ) {
            perror( "read" );
        }  

        /*actually read return the list of change events happens. Here, read the change event one by one and process it accordingly.*/
        while ( i < length ) {     
      
            struct inotify_event *event = ( struct inotify_event * ) &buffer[ i ];     
            
            if ( event->len ) {

                string parentdir;
                parentdir = wdsToPaths[event->wd];

                if ( event->mask & IN_CREATE ) {
                    if ( event->mask & IN_ISDIR ) {
                        printf( "New directory %s created in %s.\n", event->name, parentdir.c_str());
                        
                        AddWatch(parentdir+"/"+event->name);
                    }
                    else {
                        printf( "New file %s created in %s.\n", event->name, parentdir.c_str());
                    }
                }
                else if ( event->mask & IN_DELETE ) {
                    if ( event->mask & IN_ISDIR ) {
                        printf( "Directory %s deleted in %s.\n", event->name, parentdir.c_str() );
                        RemoveWatch(parentdir+"/"+event->name);
                    }
                    else {
                        printf( "File %s deleted in %s.\n", event->name, parentdir.c_str());
                    }
                }
                else if ( event->mask & IN_MODIFY)
                {
                    if ( event->mask & IN_ISDIR ) {
                        printf( "Directory %s modified in %s.\n", event->name, parentdir.c_str());
                    }
                    else {
                        printf( "File %s modified in %s.\n", event->name, parentdir.c_str());
                    }
                }
            }
            i += EVENT_SIZE + event->len;
        }
    }
    /*removing the “/tmp” directory from the watch list.*/
    

    /*closing the INOTIFY instance*/
    close( fd );
    }
    catch(string s)
    {
        printf("Caught: %s\n", s.c_str());
    }
}