#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

#define N_PROCESS 2
#define MAXLINE 80
#define MAXDIGITNUM 16


void charArray_reverse(char* b, int count) {
    char tmp;
    int i;
    for ( i = 0; i <= count/2 - 1; i++ ) {
        tmp = b[i];
        b[i] = b[count - i -1];
        b[count - i -1] =  tmp;
    }
}

int int_to_charArray(int a, char* b, int b_len) {
    int i =  a % 10;
    int count = 0;
    
//    printf("a is %d\n", a);
    
    for ( ; a != 0 && count < b_len; a /= 10 ) {
        i = a % 10;
        b[count++] = '0' + i;
    }
    
//    printf("count is %d\n", count);
    
    if ( count >= b_len && a != 0 )
        return -1;
    
    charArray_reverse(b, count);
    return count;
}


int main()
{
    pid_t pid[N_PROCESS];
    int i;
    int status;
    
    int fd[2];
    char line[MAXLINE];
    char line1[MAXLINE];
    char charArray[MAXDIGITNUM];
    
    if ( pipe(fd) < 0 ) {
        perror("pipe fail");
        exit(0);
    }
    
    // have not check whether fork() is successful
    
    /* create child process */
    for (i = 0; i < N_PROCESS; i++) {
        if ((pid[i] = fork()) == 0) {
            printf("in child %d\n", getpid());
            break;    /* 让子进程退出 */
        }
    }
    
//    printf("\n\nI am sleeping for 2 seconds...\n\n");
//    sleep(2);
    
    if ( pid[0] > 0 && pid[1] > 0 ) {
        printf("in parent\n");
        sleep(4);
        exit(50);
    }
    
    if ( pid[0] == 0 ) {
        printf("for child 0, pid[1] is %d\n", pid[1]);
        
        sleep(2);
        
        int n = read(fd[0], line, MAXLINE);
//        printf("Hi pid1, I get your pid now, thank you!\n");
        write(STDOUT_FILENO, line, n);
        
        write(fd[1], "Hi pid1, I get your pid now, thank you!\n", 40);
        exit(0);
    }
    
    if ( pid[1] == 0 ) {
        printf("for child 1, pid[0] is %d\n", pid[0]);
        
        int child1Pid = getpid();
        
        write(fd[1], "Hi, pid0, I know you don't know my pid, so I will tell you that. My pid is: ", 66);
        int charArrayLen = int_to_charArray(child1Pid, charArray, MAXDIGITNUM);
//        printf("char array len is %d\n", charArrayLen);
        if ( charArrayLen == -1 ) {
            write(fd[1], "pid id to large", 4);
        } else {
            write(fd[1], charArray, charArrayLen);
            write(fd[1], "\n", 1);
            
            sleep(4);
            
            int n = read(fd[0], line1, MAXLINE);
            //        printf("Hi pid1, I get your pid now, thank you!\n");
            write(STDOUT_FILENO, line1, n);
        }
        exit(1);
    }
    
    return 0;
}