/* bhttp - shitty HTTP/1.0 server
 *
 * Written by phoebos (https://bvnf.space/) in 2022.
 * This file is in the public domain.
 *
 * Whatever you do, don't use this!
 */

#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <netdb.h>
#include <unistd.h>

enum OP { GET, HEAD, UNKNOWN };

struct header {
    enum OP op;
    char *path;
    off_t size;
};

struct header *
parse_header(char *b, size_t n) {
    char *pathend;
    char *space = memchr(b, ' ', n);
    struct header *myhdr = malloc(sizeof(struct header));
    if (myhdr == NULL) {
        perror("malloc");
        exit(1);
    }
    if (space == NULL) {
        free(myhdr);
        return NULL;
    }
    if (strncmp(b, "GET", space - b) == 0) {
        myhdr->op = GET;
    } else if (strncmp(b, "HEAD", space - b) == 0) {
        myhdr->op = HEAD;
    } else
        myhdr->op = UNKNOWN;
    if (space[1] != '/') {
        free(myhdr);
        return NULL;
    }

    pathend = memchr(space + 1, ' ', n - ((space + 1) - b));
    if (pathend == NULL)
        return NULL;
    *pathend = '\0';
    myhdr->path = malloc(pathend-space+1);
    if (myhdr->path == NULL) {
        perror("malloc");
        exit(1);
    }
    if (snprintf(myhdr->path, pathend-space+1, ".%s", space+1) < 0) {
        perror("snprintf");
        exit(1);
    }
    fprintf(stderr, "request \"%s\"\n", myhdr->path+1);
    return myhdr;
}

void
status_reply(int code, int fd) {
    if (code < 100 || code > 999) return;
    if (code < 400) return;
#define REASON_MAXLEN 21
#define REPLY_MAXLEN (17+REASON_MAXLEN)
    char *reason = NULL;
    switch (code) {
        break; case 400: reason = "Bad Request";
        break; case 401: reason = "Unauthorized";
        break; case 403: reason = "Forbidden";
        break; case 404: reason = "Not Found";
        break; case 500: reason = "Internal Server Error";
        break; case 501: reason = "Not Implemented";
        break; case 502: reason = "Bad Gateway";
        break; case 503: reason = "Service Unavailable";
        break; default:  reason = "Internal Server Error";
    }
    char reply[REPLY_MAXLEN] = {'\0'};
    int n = snprintf(reply, REPLY_MAXLEN, "HTTP/1.0 %0.3d %s\r\n\r\n", code, reason);
    if (n < 0) {
        perror("snprintf");
        return;
    }
    if (send(fd, reply, n, 0) != n) {
        perror("send");
        return;
    }
    return;
}

void
file_reply(int fd, struct header *h) {
    if (access(h->path, R_OK) != 0) {
        status_reply(404, fd);
        return;
    }
    struct stat sb;
redo_stat:
    if (stat(h->path, &sb) != 0) {
        status_reply(404, fd);
        return;
    }
    if (S_ISDIR(sb.st_mode)) {
        char *newpath = malloc(strlen(h->path) + 12);
        if (newpath == NULL || snprintf(newpath, strlen(h->path) + 12, "%s/index.html", h->path) < 0) {
            perror("strcat(dir,\"/index.html\")");
            status_reply(500, fd);
            return;
        }
        free(h->path);
        h->path = newpath;
        goto redo_stat;
    }
    int file = open(h->path, O_RDONLY);
    if (file == -1) {
        status_reply(404, fd);
        return;
    }

    char *replyheader = 
        "HTTP/1.0 200 OK\r\n"
        "Content-Length: %d\r\n"
        /*"Content-Type: text/plain\r\n"*/
        "Server: bhttp/0.1\r\n"
        "\r\n";
    int rn = snprintf(NULL, 0, replyheader, sb.st_size);
    if (rn < 0) {
        perror("snprintf");
        exit(1);
    }
    char *reply = malloc(rn+1); /* +1 for the end null */
    if (reply == NULL) {
        perror("malloc");
        exit(1);
    }
    snprintf(reply, rn+1, replyheader, sb.st_size);
    if (send(fd, reply, rn, 0) != rn) {
        perror("send");
        return;
    }

    if (h->op != GET)
        return; /* HEAD ends here. */

    char *buf = malloc(sb.st_size);
    if (buf == NULL) {
        perror("malloc");
        exit(1);
    }

    // TODO: handle r/w errors and partial r/ws
    ssize_t n = read(file, buf, sb.st_size);
    if (n == -1) {
        perror("read");
        free(buf);
        exit(0);
    }
    write(fd, buf, (size_t)n);
    free(buf);
}

void
handle_conn(int fd) { /* called in child */
    char buf[0x100] = {'\0'};
    ssize_t n;
    struct header *h = NULL;
retry:
    n = recv(fd, buf, 0x100, 0);
    if (n == 0)
        // we've been shutdown
        return;
    if (n == -1) {
        if (errno == EAGAIN || errno == EWOULDBLOCK)
            goto retry;
        perror("recv");
        return;
    }
    h = parse_header(buf, (size_t)n);
    if (h == NULL || h->path == NULL) {
        status_reply(400, fd);
        return;
    }
    if (h->op == GET || h->op == HEAD)
        file_reply(fd, h);
    free(h->path);
    free(h);
    return;
}

void
usage(char *argv0) {
    fprintf(stderr, "usage: %s [-p port] dir\n", argv0);
}

int
start_listening(char *argv0, int port) {
    int sfd = -1;
    struct addrinfo hints = {0}, *result, *rp;
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;
    hints.ai_protocol = 0;

    /* TODO: how long can a servname be? Do a n = snprintf(NULL, 0, ...) first
     * to get the required size?
     */
    char port_string[10] = {'\0'};
    snprintf(port_string, 10, "%d", port);

    int s = getaddrinfo(NULL, port_string, &hints, &result);
    if (s != 0) {
        fprintf(stderr, "%s: getaddrinfo: %s\n", argv0, gai_strerror(s));
        return -1;
    }

    for (rp = result; rp != NULL; rp = rp->ai_next) {
        sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
        if (sfd == -1)
            continue;

        if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0)
            break;

        if (close(sfd) == -1) {
            perror("close");
            freeaddrinfo(result);
            return -1;
        }
    }

    freeaddrinfo(result);

    if (rp == NULL) {
        fprintf(stderr, "%s: localhost:%s: connection refused\n", argv0, port_string);
        return -1;
    }

    /* can have up to SOMAXCONN backlogged. */
    if (listen(sfd, 10) == -1) {
        fprintf(stderr, "%s: listen: %s\n", argv0, strerror(errno));
        close(sfd);
        return -1;
    }

    return sfd;
}

int
accept_one(int sfd) {
    int newfd;
    struct sockaddr their_addr;
    socklen_t addr_size = sizeof their_addr;
    newfd = accept(sfd, &their_addr, &addr_size);
    if (newfd == -1) {
        perror("accept");
        return -1;
    }
    // note: don't want to be DoS'd; unrestricted forking isn't a great idea.
    switch (fork()) {
        case -1:
            return -1;
        case 0:
            close(sfd);
            handle_conn(newfd);
            shutdown(newfd, SHUT_RDWR);
            close(newfd);
            exit(0);
            break;
        default:
            return 0;
    }
}

int
loop(int sfd) {
    int pollret;
    struct pollfd fds[1];
    fds[0].fd = sfd;
    fds[0].events = POLLIN;

    while (1) {
        fds[0].revents = 0;
        pollret = poll(fds, 1, -1);
        if (pollret < 0) {
            if (errno == EAGAIN)
                continue;
            perror("poll");
            return 1;
        }
        if (fds[0].revents) {
            accept_one(sfd);
        }
    }
    return 0;
}

int
main(int argc, char **argv) {
    int c, port, ret, sfd;
    char *path;
    ret = 0;
    port = 80;

    while ((c = getopt(argc, argv, "p:")) != -1) {
        switch(c) {
            case 'p':
                port = atoi(optarg);
                if (port <= 0) {
                    fprintf(stderr, "bad port number '%s'\n", optarg);
                    return 1;
                }
                break;
            case '?':
                usage(argv[0]);
                return 1;
        }
    }
    if (argc - optind != 1) {
        usage(argv[0]);
        return 1;
    }

    path = argv[optind];
    if (chdir(path) == -1) {
        fprintf(stderr, "couldn't chdir(%s): %s\n", path, strerror(errno));
        return 1;
    }

    sfd = start_listening(argv[0], port);
    if (sfd == -1) {
        return 1;
    }
    fprintf(stderr, "bound to port %d\n", port);

    if (loop(sfd) != 0)
        ret = 1;

    close(sfd);
    return ret;
}