#include "openssl/err.h"
#include "openssl/ssl.h"
#include <arpa/inet.h>
#include <errno.h>
#include <netinet/in.h>
#include <resolv.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

#define BACKLOG 3
#define BUF_LEN 1024

int open_server(int port) {
    int serverSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (serverSocket == -1) {
        perror("Cannot create socket");
        return -1;
    }
    if (setsockopt(serverSocket, SOL_SOCKET, SO_REUSEADDR, &(int){1},
                   sizeof(int)) == -1) {
        perror("reuseaddr");
    }
    struct sockaddr_in address;
    memset(&address, 0, sizeof(address));
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = htonl(INADDR_ANY);
    address.sin_port = htons(port);
    if (bind(serverSocket, (struct sockaddr *)&address, sizeof(address)) ==
        -1) {
        perror("Bind failed");
        return -1;
    }

    if (listen(serverSocket, BACKLOG) == -1) {
        perror("In listen");
        return -1;
    }
    return serverSocket;
}

SSL_CTX *init_ssl_ctx(void) {
    const SSL_METHOD *method;
    SSL_CTX *ctx;

    OpenSSL_add_all_algorithms();
    SSL_load_error_strings();
    STACK_OF(SSL_COMP) *s = SSL_COMP_get_compression_methods();
    if (s == NULL) {
        fprintf(stderr, "Cannot list compression methods\n");
    } else if (sk_SSL_COMP_num(s) == 0) {
        fprintf(stderr, "This version of OpenSSL does not have any compression "
                        "methods available, cannot enable TLS compression.\n");
    } else {
        for (int i = 0; i < sk_SSL_COMP_num(s); i++) {
            const SSL_COMP *comp = sk_SSL_COMP_value(s, i);
            const char *name = SSL_COMP_get_name(comp);
            printf("Found compression method: %s\n", name);
        }
    }

    method = TLS_server_method();
    ctx = SSL_CTX_new(method);
    SSL_CTX_set_security_level(ctx, 1);
    SSL_CTX_set_options(ctx, SSL_OP_NO_TLSv1_3);
    SSL_CTX_clear_options(ctx, SSL_OP_NO_COMPRESSION);

    if (ctx == NULL) {
        ERR_print_errors_fp(stderr);
        return NULL;
    }

    SSL_CTX_set_cipher_list(ctx, "ALL:eNULL");
    return ctx;
}

int load_certificates(SSL_CTX *ctx, const char *cert_file,
                      const char *key_file) {
    if (SSL_CTX_load_verify_locations(ctx, cert_file, key_file) != 1) {
        ERR_print_errors_fp(stderr);
        return -1;
    }

    if (SSL_CTX_set_default_verify_paths(ctx) != 1) {
        ERR_print_errors_fp(stderr);
        return -1;
    }

    if (SSL_CTX_use_certificate_file(ctx, cert_file, SSL_FILETYPE_PEM) <= 0) {
        ERR_print_errors_fp(stderr);
        return -1;
    }
    if (SSL_CTX_use_PrivateKey_file(ctx, key_file, SSL_FILETYPE_PEM) <= 0) {
        ERR_print_errors_fp(stderr);
        return -1;
    }
    if (!SSL_CTX_check_private_key(ctx)) {
        fprintf(stderr, "Private key does not match the public certificate\n");
        return -1;
    }
    return 0;
}

int handle_request(SSL *ssl, int fd) {
    char buf[BUF_LEN];
    int bytes;

    char output[] = "HTTP/1.1 200 OK\r\nContent-Length: 13\r\nContent-Type: "
                    "text/plain\r\n\r\nHello World!\n";

    if (SSL_accept(ssl) == -1) {
        const char *cipher = SSL_get_cipher(ssl);
        if (cipher == NULL || strcmp(cipher, "NONE")) {
            char error_message[] =
                "HTTP/1.1 400 Bad Request\r\nContent-Type: "
                "text/plain\r\nContent-Length: 18\r\n\r\nInvalid protocol.\n";
            write(fd, error_message, strlen(error_message));
            return 1;
        }
        ERR_print_errors_fp(stderr);
    } else {
        bytes = SSL_read(ssl, buf, sizeof(buf));
        if (bytes > 0) {
            buf[bytes] = 0;
            SSL_write(ssl, output, strlen(output));
        } else {
            ERR_print_errors_fp(stderr);
        }
    }
    SSL_free(ssl);
    return 0;
}

int main(int argc, char **argv) {
    SSL_CTX *ctx;
    int server;
    int port;
    if (argc < 2) {
        fprintf(stderr, "Usage: %s <port>\n", argv[0]);
        return 1;
    } else {
        port = atoi(argv[1]);
    }
    if (port < 1 || port > 65535) {
        fprintf(stderr, "Invalid port number: %s\n", argv[1]);
        return 1;
    }

    const char cert_file[] = "cert.pem";
    const char key_file[] = "key.pem";

    SSL_library_init();

    ctx = init_ssl_ctx();
    if (ctx == NULL) {
        return 1;
    }
    if (load_certificates(ctx, cert_file, key_file) == -1) {
        return 1;
    }
    server = open_server(port);
    if (server == -1) {
        return 1;
    }
    printf("Listening on https://localhost:%d/\n", port);
    while (1) {
        struct sockaddr_in addr;
        socklen_t len = sizeof(addr);
        SSL *ssl;

        int client = accept(server, (struct sockaddr *)&addr, &len);
        printf("Connection: %s:%d\n", inet_ntoa(addr.sin_addr),
               ntohs(addr.sin_port));
        ssl = SSL_new(ctx);
        SSL_set_fd(ssl, client);
        handle_request(ssl, client);
        close(client);
    }
    close(server);
    SSL_CTX_free(ctx);
    return 0;
}