#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>

struct TokenizedQuerry {
    int left;
    char operand;
    int right;
};

void handle_arguments(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s PORT\n", argv[0]);
        exit(EXIT_FAILURE);
    }
}

struct TokenizedQuerry tokenize(const char *querry) {
    struct TokenizedQuerry tokenized_querry;
    // printf("QUERRY: %s\n", querry);
    char left[50], *operand_ptr, right[50];
    char valid_operands[4] = {'+', '-', '/', '*'};
    for (int i = 0; i < sizeof(valid_operands); ++i) {
        operand_ptr = strchr(querry, valid_operands[i]);
        if (operand_ptr != NULL) break;
    }
    if (operand_ptr == NULL) {
        fprintf(stderr, "Wrong operand!\n");
        exit(EXIT_FAILURE);
    }
    int left_length = operand_ptr - querry;

    strncpy(left, querry, left_length);
    strcpy(right, querry + left_length + 1);
    // printf("Tokenized: %s %c %s\n", left, *operand_ptr, right);
    tokenized_querry.left = strtol(left, NULL, 10);
    tokenized_querry.operand = *operand_ptr;
    tokenized_querry.right = strtol(right, NULL, 10);

    return tokenized_querry;
}

int calculate_TokenizedQuerry(struct TokenizedQuerry expression) {
    switch (expression.operand) {
        case '+':
            return expression.left + expression.right;
        case '-':
            return expression.left - expression.right;
        case '*':
            return expression.left * expression.right;
        case '/':
            return expression.left / expression.right;
    }

    return 0;
}

void run_server(int port) {
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) {
        fprintf(stderr, "socket: ");
        exit(EXIT_FAILURE);
    }

    struct sockaddr_in serv_addr, client_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));
    memset(&client_addr, 0, sizeof(client_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(port);
    serv_addr.sin_addr.s_addr = INADDR_ANY;

    int rv = bind(sockfd, (const struct sockaddr *)&serv_addr, sizeof(serv_addr));
    if (rv < 0) {
        fprintf(stderr, "bind: ");
        exit(EXIT_FAILURE);
    }

    size_t buffer_size = 100;
    char buffer[buffer_size];
    memset(&buffer, 0, buffer_size);
    socklen_t client_addr_len;
    struct TokenizedQuerry tokenized_querry;

    while (1) {
        rv = recvfrom(sockfd, buffer, buffer_size, 0, (struct sockaddr *)&client_addr, &client_addr_len);
        tokenized_querry = tokenize(buffer);
        int result = calculate_TokenizedQuerry(tokenized_querry);
        memset(&buffer, 0, buffer_size);
        snprintf(buffer, buffer_size, "%d", result);
        rv = sendto(sockfd, buffer, sizeof(buffer), 0, (const struct sockaddr *)&client_addr, sizeof(client_addr));
        memset(&buffer, 0, sizeof(buffer));
    }


}

int main(int argc, char *argv[]) {
    handle_arguments(argc, argv);
    run_server(strtol(argv[1], NULL, 10));
    return 0;
}