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

#define PORT 8080
#define BUFFER_SIZE 1024

int main() {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[BUFFER_SIZE] = {0};

    // 1. Create socket file descriptor
    // AF_INET: IPv4, SOCK_STREAM: TCP
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 2. Attach socket to the port 8080
    // SO_REUSEADDR allows restarting the server immediately after closing
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY; // Listen on all interfaces
    address.sin_port = htons(PORT);

    // Bind
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // 3. Listen for incoming connections
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    printf("TCP Server listening on port %d...\n", PORT);

    // 4. Accept connection
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
        perror("accept");
        exit(EXIT_FAILURE);
    }

    printf("Client connected.\n");

    // 5. Receive data
    int valread = read(new_socket, buffer, BUFFER_SIZE);
    if (valread > 0) {
        printf("Received %d bytes: %s\n", valread, buffer);
        
        // 6. Send response (Echo length or simple ack)
        char response[BUFFER_SIZE];
        snprintf(response, BUFFER_SIZE, "Server received %d bytes", valread);
        send(new_socket, response, strlen(response), 0);
        printf("Response sent to client.\n");
    }

    // 7. Close socket
    close(new_socket);
    close(server_fd);

    return 0;
}