#include "ngx_event.h"
#ifdef __clang__
#pragma clang diagnostic ignored "-Wdangling-else"
#else
#pragma GCC   diagnostic ignored "-Wdangling-else"
#pragma GCC   diagnostic ignored "-Wmultistatement-macros"
#endif

#include "muninn.h"

#include <sys/socket.h>
#include <netinet/in.h>


// Configuration functions
static char *mun_conf_listen(ngx_conf_t *cf, ngx_command_t *cmd, void *conf);
static char *mun_conf_connection_ct(ngx_conf_t *cf, ngx_command_t *c, void *v);

// Connection lifecycle
static void mun_init_connection(ngx_connection_t *c);
static void mun_close_connection(ngx_connection_t *c);
static void mun_handle_conn_readable(ngx_event_t *ev);
static void mun_handle_conn_writeable(ngx_event_t *ev);

// Request lifecycle functions
static ngx_int_t mun_log_request(mun_dns_request *r);

// connection pool flag stored here
static ngx_int_t mun_daemon_dns_connection_pool_ct = MUN_DEFAULT_CONN_POOL_SZ;


// Module definitions
static ngx_command_t ngx_muninn_daemon_commands[] = {
    { ngx_string("dns_listen"),
      NGX_MUNINN_CONF|NGX_DIRECT_CONF|NGX_CONF_1MORE,
      mun_conf_listen,
      0, 0, NULL },

    { ngx_string("dns_connection_pool_count"),
      NGX_MUNINN_CONF|NGX_DIRECT_CONF|NGX_CONF_1MORE,
      mun_conf_connection_ct,
      0, 0, NULL },

    ngx_null_command
};

static ngx_core_module_t ngx_muninn_daemon_module_ctx = {
    ngx_string("muninn_daemon"), NULL, NULL
};

ngx_module_t ngx_muninn_daemon_module = {
    NGX_MODULE_V1,
    &ngx_muninn_daemon_module_ctx,
    ngx_muninn_daemon_commands,
    NGX_MUNINN_MODULE,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NGX_MODULE_V1_PADDING
};

// Muninn request handling state machine
static ngx_int_t (*mun_read_handler_list[])(mun_dns_request *) = {
    mun_log_request, // test req state machine logging handler
    // TODO: request parsing
    // TODO: request logging
    // TODO: request cache lookup
    // TODO: request record(s) fetch
    // TODO: request response generation
    // TODO: error handling phase
};

/* ADJACENCY LIST
 * This matrix defines the entire request processing state machine and changes
 * All numbers in this list should correspond to mun_read_handler_list indexes
 * The entries in this list are linked to their same index in the handler list
 *
 * Entries:
 * { NGX_OK       next handler - intended to indidicate phase is complete
 *   NGX_ERROR    next handler - intended to trap error states
 *   NGX_BUSY     next handler - intended to trap waiting state
 *   NGX_DECLINED next handler } intended to trap service refusal
 *
 * Other handler returns:
 * NGX_DONE:  this return code means a request is ready to be finalized
 *            nothing further will be returned.
 * NGX_AGAIN: this return code causes same function to be called again.
 *            primarily used when more input needed than what is available.
 * NGX_ABORT: this return code causes all further action to stop for request
 *
 * For more information, see how this is used in mun_handle_conn_readable
 */
static ngx_uint_t mun_read_handler_adjacency[][4] = {
    {0, 0, 0, 0}
};


static char *mun_conf_connection_ct(
    ngx_conf_t *cf,
    ngx_command_t *cmd,
    void *conf
) {
    ngx_int_t  argc = cf->args->nelts;
    ngx_str_t *argv = cf->args->elts;
    ngx_int_t  num;

    if (argc < 1) {
        ngx_conf_log_error(NGX_LOG_ERR, cf, 0,
                "dns_connection_pool_count requires at least one argument");
        return NGX_CONF_ERROR;
    }

    if ((num = ngx_atoi(argv[1].data, argv[1].len)) == NGX_ERROR) {
        ngx_conf_log_error(NGX_LOG_ERR, cf, 0,
                "invalid integer passed to dns_connection_pool_count");
        return NGX_CONF_ERROR;
    }

    if (num < 1) {
        ngx_conf_log_error(NGX_LOG_ERR, cf, 0,
                "dns_connection_pool_count must be set to at least 1");
        return NGX_CONF_ERROR;
    }

    mun_daemon_dns_connection_pool_ct = num;
    return NGX_CONF_OK;
}

static char *mun_conf_listen(ngx_conf_t *cf, ngx_command_t *cmd, void *in) {
    ngx_url_t        *u;
    ngx_int_t         argc;
    ngx_str_t        *argv;
    ngx_listening_t  *listening;

    argc = cf->args->nelts;
    argv = cf->args->elts;

    if (argc < 1) {
        ngx_conf_log_error(NGX_LOG_ERR, cf, 0,
                "dns_listen needs at least one argument");
        return NGX_CONF_ERROR;
    }

    if (!(u = ngx_pcalloc(cf->pool, sizeof(ngx_url_t)))) return NGX_CONF_ERROR;

    u->url = argv[1];
    u->listen = 1;
    u->default_port = 53;
    if (ngx_parse_url(cf->pool, u) != NGX_OK) {
        if (u->err) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                    "%s in \"%V\" of the \"dns_listen\" directive",
                    u->err, &u->url);
        }

        return NGX_CONF_ERROR;
    }

    listening = ngx_create_listening(cf, (struct sockaddr *) &u->sockaddr,
            u->socklen);
    if (!listening) return NGX_CONF_ERROR;

    listening->addr_ntop = 1;
    listening->pool_size = mun_daemon_dns_connection_pool_ct;
    listening->handler = mun_init_connection;
    listening->logp = cf->log;
    listening->log.data = &listening->addr_text;
    listening->log.handler = ngx_accept_log_error;
    listening->sndbuf = 1;
    listening->rcvbuf = 1;
    listening->backlog = mun_daemon_dns_connection_pool_ct * 2;
    listening->protocol = IPPROTO_UDP;
    listening->type = SOCK_DGRAM;

    // listener added to cycle at creation
    ngx_conf_log_error(NGX_LOG_NOTICE, cf, 0, "muninn DNS server enabled");

    return NGX_CONF_OK;
}

static void mun_init_connection(ngx_connection_t *c) {
    mun_dns_request *r;
    if (!(r = ngx_pcalloc(c->pool, sizeof(mun_dns_request)))) {
        mun_close_connection(c);
        return;
    }

    ngx_log_error(NGX_LOG_NOTICE, c->log, 0, "muninn: new request accepted");

    c->data = r;
    c->log->connection = c->number;
    c->log_error = NGX_ERROR_INFO;

    c->read->handler = mun_handle_conn_readable;
    c->write->handler = mun_handle_conn_writeable;

    if (c->read->ready) {
        ngx_post_event(c->read, &ngx_posted_events);

    } else {
        if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
            mun_close_connection(c);
            return;
        }
    }
}

static void mun_close_connection(ngx_connection_t *c) {
    c->destroyed = 1;
    ngx_close_connection(c);
    ngx_destroy_pool(c->pool);
}

static void mun_handle_conn_readable(ngx_event_t *ev) {
    ngx_connection_t *c;
    mun_dns_request  *r;
    ngx_chain_t      *cur;
    ngx_int_t         ret, idx, space, filled;

    c = ev->data;
    r = c->data;
    ret = 0;
    filled = 0;

    if (r && r->finalized) {
        ngx_log_error(NGX_LOG_ERR, c->log, 0,
                "muninn: read called for finalized request");
        return;
    }

    if (ev->timedout) {
        // TODO: handle timedout according to DNS proto
        mun_close_connection(c);
        return;
    }

    if (!r->in) {
        if (!(r->in = ngx_alloc_chain_link(c->pool))) {
            ret = NGX_ERROR;
            goto content;
        }

        if (!(r->in->buf = ngx_create_temp_buf(c->pool,
                                               MUN_DNS_LEGACY_UDP_SZ))) {
            ret = NGX_ERROR;
            goto content;
        }

        cur = r->in;
        cur->buf->last_buf = 1;
        cur->next = NULL;
        space = MUN_DNS_LEGACY_UDP_SZ;

    } else {
        for (cur = r->in; cur && !cur->buf->last_buf; cur = cur->next) {}
        if (!cur) {
            ngx_log_error(NGX_LOG_ERR, r->conn->log, 0,
                    "muninn: failed to find next buffer to read into");
        }
        space = cur->buf->end - cur->buf->last;
    }

    if (!r->read_cur) {
        r->read_cur = r->in;
    }

    while (1) {
        filled = c->recv(c, cur->buf->last, space);
        if (c->read->error || c->read->eof) {
            ngx_log_error(NGX_LOG_ERR, c->log, ngx_errno,
                    "muninn: recv() failed");
            ret = NGX_ERROR;
            goto content;
        }

        if (filled == space) {
            cur->buf->last_buf = 0;
            if (!(cur = (cur->next = ngx_alloc_chain_link(c->pool))) ||
                !(cur->buf = ngx_create_temp_buf(c->pool,
                                                 MUN_DNS_LEGACY_UDP_SZ)) ||
                !(space = MUN_DNS_LEGACY_UDP_SZ)) break;

            cur->next = NULL;
            cur->buf->last_buf = 1;
            continue;
        }

        break;
    }


content:
    if (!ret) ret = mun_read_handler_list[r->read_state](r);
    idx = mun_read_handler_adjacency[r->read_state][0 - ret];
    r->read_state = idx;

    switch (ret) {
    // Abort case: immediately cease all action on this request.
    case NGX_ABORT:
        mun_close_connection(c);
        return;

    // These cases mark the end of one phase of request processing.
    case NGX_ERROR:
    case NGX_BUSY:
    case NGX_DECLINED:
    case NGX_OK:
        // may still be more data to process in next phase
        ngx_post_event(ev, &ngx_posted_events);
        break;

    // This request is fully finished being processed. Time to write response.
    case NGX_DONE:
        r->finalized = 1;
        if (ngx_handle_write_event(c->write, 0) != NGX_OK) {
            mun_close_connection(c);
        }

        if (c->write->ready) ngx_post_event(c->write, &ngx_posted_events);
        /* fallthrough */

    // Need more data for current phase.
    case NGX_AGAIN:
        if (ngx_handle_read_event(ev, 0) != NGX_OK) {
            mun_close_connection(c);
        }
        break;
    }

}

static void mun_handle_conn_writeable(ngx_event_t *ev) {
    ngx_chain_t      *tmp;
    ngx_connection_t *c;
    mun_dns_request  *r;

    c = ev->data;
    r = c->data;
    tmp = r->out;

    /* this event posted for one of two reasons:
     * 1. mun_handle_request_read has reached end of request processing
     * 2. socket newly available after incomplete write
     */

    // write wouldnt work here anyways. event will retrigger when ready
    if (!ev->ready) return;

    if (!r->out) {
        ngx_log_debug(NGX_LOG_ALERT, r->conn->log, 0,
                      "muninn: request processed but no output");
        return;
    }

    r->out = c->send_chain(c, tmp, MUN_DNS_LEGACY_UDP_SZ);
    for (/* tmp */; tmp != r->out; tmp = tmp->next) {
        if (tmp->buf->pos == tmp->buf->last) ngx_free_chain(c->pool, tmp);
    }

    // request lifecycle complete condition
    if (!r->out) return mun_close_connection(c);

    // event will retrigger when write possible
    if (!ev->ready) return;

    // more can be written but we want to yield to other events on task loop
    ngx_post_event(ev, &ngx_posted_events);
}


static ngx_int_t mun_log_request(mun_dns_request *r) {
    ngx_log_error(NGX_LOG_INFO, r->conn->log, 0,
                  "muninn: request state machine entered");

    return NGX_DONE;
}