#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <syslog.h>
#include <sys/resource.h>


#ifndef INBUFSIZE
#define INBUFSIZE 4096
#endif

#ifndef OUTBUFSIZE
#define OUTBUFSIZE 4096
#endif

#ifndef LISTEN_QLEN
#define LISTEN_QLEN 32
#endif

#ifndef INIT_SESS_ARR_SIZE
#define INIT_SESS_ARR_SIZE 32
#endif

#ifndef FILENAME_SIZE
#define FILENAME_SIZE 1024
#endif

enum fsm_states {
    header_start,
    waiting_host,
    empty_line,
    writing_header,
    writing_body
};

struct session {
    int fd;
    unsigned long from_ip;
    unsigned short from_port;
    char in_buffer[INBUFSIZE];
    char out_buffer[OUTBUFSIZE];
    int in_buf_used;
    int out_buf_used;
    enum fsm_states state;
    int rs_fd;
    int data_transfer_status;
    char *path;
    int bad_request;
    int not_found;
};

struct server {
    int listen_socket;
    struct session **session_array;
    int session_size;
    char *host;
    char *resource_dir;
};

static void init_session(struct session *new_session, struct sockaddr_in *from,
                         int fd)
{
    new_session->fd = fd;
    new_session->from_ip = ntohl(from->sin_addr.s_addr);
    new_session->from_port = ntohs(from->sin_port);
    new_session->in_buf_used = 0;
    new_session->out_buf_used = 0;
    new_session->state = header_start;
    new_session->rs_fd = -1;
    new_session->data_transfer_status = 0;
    new_session->path = NULL;
    new_session->bad_request = 0;
    new_session->not_found = 0;
}

static int accept_client(struct server *serv)
{
    int fd, i, flags;
    struct sockaddr_in addr;
    struct session *new_session;
    socklen_t len = sizeof(addr);
    fd = accept(serv->listen_socket, (struct sockaddr*) &addr, &len);
    if(fd == -1)
        return 0;
    /* setting non-blocking mode for socket*/
    flags = fcntl(fd, F_GETFL);
    fcntl(fd, F_SETFL, flags | O_NONBLOCK);

    if(fd >= serv->session_size) {
        int newlen = serv->session_size;
        while(fd >= newlen)
            newlen += INIT_SESS_ARR_SIZE;
        serv->session_array =
            realloc(serv->session_array, newlen * sizeof(struct session*));
        for(i = serv->session_size; i < newlen; i++)
            serv->session_array[i] = NULL;
        serv->session_size = newlen;
    }
    new_session = malloc(sizeof(struct session));
    serv->session_array[fd] = new_session;
    init_session(new_session, &addr, fd);
    return 1;
}

static int host_search_condition(const char *line)
{
    return !(strncmp(line, "Host:", strlen("Host:")) &&
            strncmp(line, "host:", strlen("host:")));
}

static int match_hosts(struct server *serv, const char *line, int length)
{
    int i, last_idx;

    if(strlen("host:") > length)
        return 0;
    if(!host_search_condition(line))
        return 0;
    for(i = strlen("host:"); i < length; ++i) {
        if(line[i] == ' ')
            continue;
        break;
    }
    if(i+strlen(serv->host) > length)
        return 0;
    if(strncmp(line+i, serv->host, strlen(serv->host)))
        return 0;
    for(last_idx = i+strlen(serv->host); last_idx < length; ++last_idx) {
        if(line[last_idx] == ' ')
            continue;
        else
            break;
    }
    if(line[last_idx] == '\r'|| line[last_idx] == '\n')
        return 1;
    return 0;
}

static int match_protocols(const char *line, int length)
{
    int i;
    /* skip extract path */
    for(i = 4; i < length && line[i] != ' '; ++i)
    {}
    if(i >= length)
        return 0;
    ++i;
    if(i+strlen("HTTP/1.1") > length)
        return 0;
    if(strncmp(line+i, "HTTP/1.1", strlen("HTTP/1.1")))
        return 0;
    for(i += strlen("HTTP/1.1"); i < length; ++i) {
        if(line[i] == ' ')
            continue;
        if(line[i] == '\r' || line[i] == '\n')
            return 1;
        return 0;
    }
    return 0;
}

static char* extract_path(const char *line, int length)
{
    int i;
    char *path;

    for(i = 4; i < length && line[i] != ' '; ++i)
    {}
    if(i >= length)
        return NULL;

    length = i-4+1 ;
    path = malloc(length);
    memcpy(path, line+4, length-1);
    path[length-1] = '\0';
    return path;
}

static int command_processing(struct server *serv, struct session *cur_session,
                           const char *line, int length)
{
    switch(cur_session->state) {
    case header_start:
        if(length > strlen("GET") && !strncmp(line, "GET", strlen("GET"))) {
            cur_session->path = extract_path(line, length);
            if(cur_session->path == NULL)
                return 0;
            if(!match_protocols(line, length))
                return 0;
            cur_session->state = waiting_host;
            return 1;
        }
    case waiting_host:
        if(!match_hosts(serv, line, length))
            return 0;
        cur_session->state = empty_line;
        return 1;
    case empty_line:
        if(line == NULL) {
            cur_session->data_transfer_status = 1;
            cur_session->state = writing_header;
            return 1;
        }
    default:
        return 0;
    }
}

/*
 * 0 - close current session
 * 1 - continue
 */
static int read_in_session(struct server *serv, struct session *cur_session)
{
    int read_res, i, end_idx, bufp = cur_session->in_buf_used;
    char *line = NULL;
    end_idx = -1;

    read_res = read(cur_session->fd, cur_session->in_buffer + bufp, 
			INBUFSIZE - cur_session->in_buf_used);
    if(read_res <= 0)
        return 0;

    cur_session->in_buf_used += read_res;

    do {
        for(i = 0; i < cur_session->in_buf_used; ++i) {
            if(cur_session->in_buffer[i] == '\n') {
                end_idx = i;
                break;
            }
        }
        if(end_idx == -1) {
            if(cur_session->in_buf_used >= INBUFSIZE)
                return 0;
            return 1;
        }
        if(cur_session->state != empty_line) {
            line = malloc(end_idx+1);
            memcpy(line, cur_session->in_buffer, end_idx+1);
        }
        cur_session->in_buf_used -= end_idx+1;
        memmove(cur_session->in_buffer, cur_session->in_buffer+end_idx+1,
                cur_session->in_buf_used);

        /* skip the remaining data in the header */
        if(cur_session->state == empty_line &&
                strncmp(cur_session->in_buffer, "\r\n", 2))
            continue;
        else if(cur_session->state == empty_line &&
                !strncmp(cur_session->in_buffer, "\r\n", 2))
            cur_session->in_buf_used = 0;

        if(!command_processing(serv, cur_session, line, end_idx)) {
            cur_session->bad_request = 1;
            cur_session->data_transfer_status = 1;
            cur_session->state = writing_header;
        }
        if(line) {
            free(line);
            line = NULL;
        }
        if(cur_session->bad_request)
            return 1;
    } while(cur_session->in_buf_used);
    return 1;
}

static void print_header(struct session *cur_session, char *status)
{
    write(cur_session->fd, status, strlen(status));
}

static int is_index_page(char *path)
{
    int i;
    for(i = strlen(path)-1; i >= 0 && path[i] != '/'; --i) {
        if(path[i] == '.')
            return 0;
    }
    return 1;
}

static void remove_slash(char *root)
{
    int last_idx = strlen(root);
    --last_idx;
    if(root[last_idx] == '/')
        root[last_idx] = '\0';
}

static int open_file(char *root, struct session *cur_session)
{
    int i, j;
    int add_index_page = 0;
    char *given_path = cur_session->path;
    char *str_index_page = "index.html";
    char new_path[FILENAME_SIZE];

    remove_slash(root);
    strncpy(new_path, root, strlen(root));
    add_index_page = is_index_page(given_path) ? 1 : 0;
    for(i = strlen(root), j = 0; i < FILENAME_SIZE &&
                                            j < strlen(given_path); ++i, ++j)
        new_path[i] = given_path[j];
    if(add_index_page) {
        for(j = 0; i < FILENAME_SIZE && j < strlen(str_index_page); ++i, ++j)
            new_path[i] = str_index_page[j];
    }
    if(i < FILENAME_SIZE)
        new_path[i] = '\0';
    cur_session->rs_fd = open(new_path, O_RDONLY);
    if(cur_session->rs_fd == -1)
        return 0;
    else return 1;
}

static void change_out_buffer(char *out_buffer, int *out_buf_used,
                              int writed_size)
{
    memmove(out_buffer, out_buffer+writed_size, (*out_buffer)-writed_size);
    *out_buf_used -= writed_size;
}

static void write_error_page(struct session *cur_session)
{
    int read_result;

    read_result = read(cur_session->rs_fd, cur_session->out_buffer,
                       OUTBUFSIZE);
    write(cur_session->fd, cur_session->out_buffer, read_result);
}

static int file_open_condition(struct session *cur_session)
{
    return !cur_session->bad_request  && !cur_session->not_found &&
            cur_session->rs_fd == -1;
}

static char* get_page_error_path(struct server *serv, char *page)
{
    char *new_path;

    new_path = malloc(strlen(serv->resource_dir) + strlen(page));
    strcpy(new_path, serv->resource_dir);
    strcat(new_path, page);
    return new_path;
}

static int write_in_session(struct server *serv, struct session *cur_session)
{
    int read_result, write_result, open_result;
    char *page_error_path = NULL;

    if(file_open_condition(cur_session)) {
        open_result = open_file(serv->resource_dir, cur_session);
        if(!open_result) {
            cur_session->state = writing_header;
            cur_session->not_found = 1;
        }
    }
    switch(cur_session->state) {
    case writing_header:
        if(cur_session->bad_request)
            print_header(cur_session, "HTTP/1.1 400 Bad Request\n\n");
        else if(cur_session->not_found)
            print_header(cur_session, "HTTP/1.1 404 Not Found\n\n");
        else
            print_header(cur_session, "HTTP/1.1 200 OK\n\n");
        cur_session->state = writing_body;
        return 1;
    case writing_body:
        /* ---------- error page write ---------- */
        if(cur_session->bad_request)
            page_error_path = get_page_error_path(serv, "/400.html");
        else if(cur_session->not_found)
            page_error_path = get_page_error_path(serv, "/404.html");

        if(cur_session->bad_request || cur_session->not_found) {
            cur_session->rs_fd = open(page_error_path, O_RDONLY);
            if(cur_session->rs_fd == -1)
                syslog(LOG_ERR, "can't find error page");
            free(page_error_path);
            write_error_page(cur_session);
            return 0;
        }
        /* ---------- normal page write ---------- */

        /* if buffer doesn't contain any data*/
        if(!cur_session->out_buf_used) {
            read_result = read(cur_session->rs_fd, cur_session->out_buffer,
                               OUTBUFSIZE);
            /* end of file */
            if(!read_result) {
                if(cur_session->rs_fd != -1)
                    close(cur_session->rs_fd);
                cur_session->rs_fd = -1;
                cur_session->data_transfer_status = 0;
                cur_session->state = header_start;
                return 0;
            }
            cur_session->out_buf_used += read_result;
        }
        write_result = write(cur_session->fd, cur_session->out_buffer,
                             cur_session->out_buf_used);

        /* writed remaining some of data */
        if(write_result < cur_session->out_buf_used)
            change_out_buffer(cur_session->out_buffer,
                              &cur_session->out_buf_used,
                              write_result);
        /* writed all data from out_buffer */
        else
            cur_session->out_buf_used = 0;
        return 1;
    default:
        return 0;
    }
}

static void close_session(struct server *serv, int fd)
{
    if(fd != -1)
        close(fd);
    serv->session_array[fd]->fd = -1;
    if(serv->session_array[fd]->path)
        free(serv->session_array[fd]->path);
    if(serv->session_array[fd]->rs_fd != -1)
        close(serv->session_array[fd]->rs_fd);
    serv->session_array[fd] = NULL;
}

static int reading_condition(struct session *cur_session)
{
    return cur_session && !cur_session->data_transfer_status;
}

static int writing_condition(struct session *cur_session)
{
    return cur_session && cur_session->data_transfer_status;
}

int main_loop(struct server *serv)
{
    int i, maxfd, select_result, accept_result, read_result, write_result;
    fd_set readfds, writefds;

    for(;;) {
        FD_ZERO(&readfds);
        FD_ZERO(&writefds);
        FD_SET(serv->listen_socket, &readfds);
        maxfd = serv->listen_socket;
        for(i = 0; i < serv->session_size; ++i) {
            if(reading_condition(serv->session_array[i])) {
                FD_SET(i, &readfds);
                if(i > maxfd)
                    maxfd = i;
            }
            if(writing_condition(serv->session_array[i])) {
                FD_SET(i, &writefds);
                if(i > maxfd)
                    maxfd = i;
            }
        }

        select_result = select(maxfd + 1, &readfds, &writefds, NULL, NULL);
        if(!select_result) {
            syslog(LOG_ERR, "select error");
            return 3;
        }

        if(FD_ISSET(serv->listen_socket, &readfds)) {
            accept_result = accept_client(serv);
            if(!accept_result) {
                syslog(LOG_ERR, "accept error");
                return 4;
            }
        }

        for(i = 0; i < serv->session_size; ++i) {
            if(serv->session_array[i] && FD_ISSET(i, &readfds)) {
                read_result = read_in_session(serv, serv->session_array[i]);
                /* normal connection closure (by user or full of in_buffer) */
                if(!read_result)
                    close_session(serv, serv->session_array[i]->fd);
            }
            if(serv->session_array[i] && FD_ISSET(i, &writefds)) {
                write_result = write_in_session(serv, serv->session_array[i]);;
                /*
                 * Closing the connection if all data is written or
                 * error 400 or 404 occurs
                 */
                if(!write_result)
                    close_session(serv, serv->session_array[i]->fd);
            }
        }
    }
}

/*
 * 0 - error
 * 1 - success
 */
static int init_server(struct server *serv, int port, char *host,
                       char *resource_dir)
{
    int opt, i;
    struct sockaddr_in addr;

    serv->host = host;
    serv->resource_dir = resource_dir;

    serv->listen_socket = socket(AF_INET, SOCK_STREAM, 0);
    if(serv->listen_socket == -1)
        return 0;

    opt = 1;
    setsockopt(serv->listen_socket, SOL_SOCKET, SO_REUSEADDR, &opt,
               sizeof(opt));

    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    addr.sin_port = htons(port);

    if(bind(serv->listen_socket, (struct sockaddr*) &addr, sizeof(addr)) == -1)
        return 0;

    serv->session_array = malloc(sizeof(serv->session_array) *
                                INIT_SESS_ARR_SIZE);
    serv->session_size = INIT_SESS_ARR_SIZE;
    for(i = 0; i < INIT_SESS_ARR_SIZE; i++)
        serv->session_array[i] = NULL;

    listen(serv->listen_socket, LISTEN_QLEN);
    return 1;
}

static void demonization()
{
    int pid;

    close(0);
    close(1);
    close(2);
    open("/dev/null", O_RDONLY);
    open("/dev/null", O_WRONLY);
    open("/dev/null", O_WRONLY);
    chdir("/");
    pid = fork();
    if(pid)
        exit(0);
    setsid();
    pid = fork();
    if(pid)
        exit(0);
}

int main(int argc, char **argv)
{
    unsigned short port;
    struct server serv;

    if(argc != 4) {
        fprintf(stderr,
                "Usage: <port> <host> <full_path/to/host_files\n");
        return 1;
    }
    demonization();
    struct rlimit core_limits;
    core_limits.rlim_cur = core_limits.rlim_max = RLIM_INFINITY;
    setrlimit(RLIMIT_CORE, &core_limits);
    openlog("http server", 0, LOG_USER);
    syslog(LOG_INFO, "daemon started");
    port = strtol(argv[1], NULL, 10);

    if(!init_server(&serv, port, argv[2], argv[3])) {
        syslog(LOG_ERR, "server initialization error");
        return 2;
    }
    return main_loop(&serv);
    syslog(LOG_INFO, "server terminated");
    closelog();
}