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


#include <stdbool.h>
#define BUF_SIZE 2
#define minus "-1"
#define enter "\n"


// gets 4 elements, filename ,in1, in2,out
int main(int argc, char* argv[])
{

    int input1_fd,input2_fd, output_fd,curfile = 2 , enOrMinus=0;
    char buffer[BUF_SIZE];
    bool flag = true ,eof1 = true, eof2 = true ,lflag = true;

            /* Number of bytes returned by read() and write() */
    /* Character buffer */
    /* Are src and dest file name arguments missing */

    if(argc != 4)
    {
        printf ("arguments missing");
        return 1;
    }

    /* Input and output file
    /*Create input file descriptor*/
    input1_fd = open (argv[1],O_RDONLY);
    if (input1_fd == -1)
    {
      perror("open");
      return 1;
    }
    input2_fd = open (argv[2],O_RDONLY);
    if (input2_fd == -1)
    {
      perror("open");
      return 2;
    }



    /*Create output file descriptor*/

    output_fd = open (argv[3],O_WRONLY | O_CREAT,0644);
    if (output_fd == -1)
    {
      perror("open");
      return 3;
    }



    while(flag)         // while we still have tx1 and tx2
    {
        switch (curfile)            //checks what file we are in
        {
            case 1 :
            {
                //printf("curfile is = %d\n",curfile);
                read(input1_fd, buffer,1); // reads 1 char to buffer
                if(strcmp(buffer,enter) == 0) // checks if enter
                enOrMinus=1;
                if(strcmp(buffer,minus) == 0) // checks if enter
                enOrMinus=2;

                switch(enOrMinus)           //  checks if enter
                    {
                                        case 1 :

                                                    if(eof2)            // enter and tx2 not empty
                                                        {
                                                            curfile = 2;
                                                            lflag = false;
                                                            write(output_fd,buffer,1); // writes enter to output
                                                        }
                                        break; // break enter


                                        case 2 :            // end of for file 1
                                        {
                                                eof1 = false;
                                                if(eof2)        //checks stile have file 2
                                                {
                                                    curfile = 2;
                                                    lflag = false;
                                                }

                                        break; // break minus
                                    }
                    }// end switch(buffer)
                }// end case 1
                break; // break case 1
            case 2 :
            {
            //  printf("%d\n",curfile);
                read(input1_fd, buffer,1); // reads 1 char to buffer
                if(strcmp(buffer,enter) == 0) // checks if enter
                enOrMinus=1;
                if(strcmp(buffer,minus) == 0) // checks if enter
                enOrMinus=2;
                switch(enOrMinus)           //  checks if enter
                    {
                                        case 1 :

                                                    if(eof1)            // enter and tx1 not empty
                                                        {
                                                            curfile = 1;
                                                            lflag = false;
                                                            write(output_fd,buffer,1); // writes enter to output
                                                        }
                                        break; // end enter


                                        case 2 :            // end of for file 2
                                        {
                                                eof2 = false;
                                                if(eof1)        //checks stile have file 1
                                                {
                                                    curfile = 1;
                                                    lflag = false;
                                                }
                                        }
                                        break; // end minus
                            }// end switch(buffer)
                    } // end case2

            break; // end case 2

        }// end switch(curfile)

        // chesks if a letter
        if((strcmp(buffer,enter) !=0 && ( strcmp(buffer,minus) !=0)))
        {
            write(output_fd,buffer,1); // writes enter to output
        }

        if (eof1 == false && eof2 == false)
            {
                flag=false;
                printf("output file generated succssesfuly");
                close(input1_fd);
                close(input2_fd);
                close(output_fd);
            }
        } // end while loop
}// end main