#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
void error(const char *msg) { perror(msg); exit(1); } 
void onClient(int);
void clean_children();
int to_c(int);
int from_c(int);

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

  int listenSocketFD, establishedConnectionFD, portNumber;
  struct sockaddr_in serverAddress;

  if (argc < 2) { fprintf(stderr,"USAGE: %s port\n", argv[0]); exit(1); }
  
  // Set up the address struct for this process (the server)
  memset((char *)&serverAddress, '\0', sizeof(serverAddress)); // Clear out the address struct
  portNumber = atoi(argv[1]); 
  serverAddress.sin_family = AF_INET; 
  serverAddress.sin_port = htons(portNumber); 
  serverAddress.sin_addr.s_addr = INADDR_ANY; 

  // Set up the socket
  listenSocketFD = socket(AF_INET, SOCK_STREAM, 0); // Create the socket
  if (listenSocketFD < 0) error("ERROR opening socket");

  // Enable the socket to begin listening
  if (bind(listenSocketFD, (struct sockaddr *)&serverAddress, sizeof(serverAddress)) < 0) 
    error("ERROR on binding");

  listen(listenSocketFD, 5);

  while(1) {
    clean_children();
    onClient(listenSocketFD);
  }

  close(listenSocketFD); 
  return 0;
}

void onClient(int listenSocketFD) {

  // Accept a connection, blocking if one is not available until one connects
  struct sockaddr_in clientAddress;
  socklen_t sizeOfClientInfo = sizeof(clientAddress); 
  int establishedConnectionFD = accept(listenSocketFD, (struct sockaddr *)&clientAddress, &sizeOfClientInfo); 

  if (establishedConnectionFD < 0) error("ERROR on accept");

  int f = fork();

  if(!f) {

    int charsRead;
    char* buffer1 = malloc(sizeof(char) * 70001);
    char* buffer2 = malloc(sizeof(char) * 70001);

    charsRead = recv(establishedConnectionFD, buffer1, 10, 0); 
    // check for proper client
    if(!strncmp(buffer1, "enc_client", 10)) {
      send(establishedConnectionFD, "Goood Client", 12, 0);
    }
    else {
      send(establishedConnectionFD, "Wrong Client", 12, 0);
      close(establishedConnectionFD); 
      exit(0);
    }

    memset(buffer1, '\0', 70001);
    charsRead = recv(establishedConnectionFD, buffer1, 70001, MSG_WAITALL); 
    if (charsRead < 0) error("ERROR reading from socket");
    //printf("%d\n", charsRead);

    memset(buffer2, '\0', 70001);
    charsRead = recv(establishedConnectionFD, buffer2, 70001, MSG_WAITALL); 
    if (charsRead < 0) error("ERROR reading from socket");
    //printf("%d\n", charsRead);

    //printf("SERVER: I received this from the client: \"%s\"\n", buffer1);
    //printf("SERVER: I received this from the client: \"%s\"\n", buffer2);
    //printf("strlen: %ld\n", strlen(buffer1));

    // do enc
    char* cyphertext = malloc(70001);
    memset(cyphertext, '\0', strlen(buffer1)+1);
    for(int i = 0; i < strlen(buffer1); i++) {
      cyphertext[i] = from_c((to_c(buffer1[i]) + to_c(buffer2[i])) % 27);
    }
    //printf("Cyphertext: %s\n", cyphertext);
    
    // Send a Success message back to the client
    charsRead = send(establishedConnectionFD, cyphertext, 70001, 0); 

    if (charsRead < 0) error("ERROR writing to socket");
    close(establishedConnectionFD); 
    exit(0);
  }
}

void clean_children() {

  // Clean up any child process that has not been cleaned
  int pid = 43110;
  while(pid >0) {
    int status;
    pid = waitpid(0, &status, WNOHANG | WUNTRACED );
  }
}

int to_c(int c) {
  int ret;
  if(c == ' ')
    ret = 26;
  else
    ret = c - 'A';

  return ret;
}

int from_c(int c) {

  int ret;

  if(c == 26)
    ret = 32;
  else
    ret = c + 'A';

  return ret;
}