/**
 * @file net_ipv4_arp_probe.c
 * @author Ambroz Bizjak <ambrop7@gmail.com>
 * 
 * @section LICENSE
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the author nor the
 *    names of its contributors may be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * 
 * @section DESCRIPTION
 * 
 * ARP probing module.
 * 
 * Synopsis:
 *   net.ipv4.arp_probe(string ifname, string addr)
 * 
 * Description:
 *   Monitors local presence of an IPv4 host on a network interface.
 *   On initialization, may take some time to determine whether
 *   the host is present or not, then goes to UP state. When it
 *   determines that presence has changed, toggles itself DOWN then
 *   UP to expose the new determination.
 * 
 * Variables:
 *   exists - "true" if the host exists, "false" if not
 */

#include <stdlib.h>

#include <misc/ipaddr.h>
#include <arpprobe/BArpProbe.h>
#include <ncd/NCDModule.h>
#include <ncd/extra/value_utils.h>

#include <generated/blog_channel_ncd_net_ipv4_arp_probe.h>

#define ModuleLog(i, ...) NCDModuleInst_Backend_Log((i), BLOG_CURRENT_CHANNEL, __VA_ARGS__)

#define STATE_UNKNOWN 1
#define STATE_EXIST 2
#define STATE_NOEXIST 3

struct instance {
    NCDModuleInst *i;
    BArpProbe arpprobe;
    int state;
};

static void instance_free (struct instance *o, int is_error);

static void arpprobe_handler (struct instance *o, int event)
{
    switch (event) {
        case BARPPROBE_EVENT_EXIST: {
            ASSERT(o->state == STATE_UNKNOWN || o->state == STATE_NOEXIST)
            
            ModuleLog(o->i, BLOG_INFO, "exist");
            
            if (o->state == STATE_NOEXIST) {
                // signal down
                NCDModuleInst_Backend_Down(o->i);
            }
            
            // signal up
            NCDModuleInst_Backend_Up(o->i);
            
            // set state exist
            o->state = STATE_EXIST;
        } break;
        
        case BARPPROBE_EVENT_NOEXIST: {
            ASSERT(o->state == STATE_UNKNOWN || o->state == STATE_EXIST)
            
            ModuleLog(o->i, BLOG_INFO, "noexist");
            
            if (o->state == STATE_EXIST) {
                // signal down
                NCDModuleInst_Backend_Down(o->i);
            }
            
            // signal up
            NCDModuleInst_Backend_Up(o->i);
            
            // set state noexist
            o->state = STATE_NOEXIST;
        } break;
        
        case BARPPROBE_EVENT_ERROR: {
            ModuleLog(o->i, BLOG_ERROR, "error");
            
            // die
            instance_free(o, 1);
            return;
        } break;
        
        default: ASSERT(0);
    }
}

static void func_new (void *vo, NCDModuleInst *i, const struct NCDModuleInst_new_params *params)
{
    struct instance *o = vo;
    o->i = i;
    
    // read arguments
    NCDValRef arg_ifname;
    NCDValRef arg_addr;
    if (!NCDVal_ListRead(params->args, 2, &arg_ifname, &arg_addr)) {
        ModuleLog(o->i, BLOG_ERROR, "wrong arity");
        goto fail0;
    }
    if (!NCDVal_IsStringNoNulls(arg_ifname) || !NCDVal_IsString(arg_addr)) {
        ModuleLog(o->i, BLOG_ERROR, "wrong type");
        goto fail0;
    }
    
    // parse address
    uint32_t addr;
    if (!ipaddr_parse_ipv4_addr_bin(NCDVal_StringData(arg_addr), NCDVal_StringLength(arg_addr), &addr)) {
        ModuleLog(o->i, BLOG_ERROR, "wrong address");
        goto fail0;
    }
    
    // null terminate ifname
    NCDValNullTermString ifname_nts;
    if (!NCDVal_StringNullTerminate(arg_ifname, &ifname_nts)) {
        ModuleLog(i, BLOG_ERROR, "NCDVal_StringNullTerminate failed");
        goto fail0;
    }
    
    // init arpprobe
    int res = BArpProbe_Init(&o->arpprobe, ifname_nts.data, addr, i->params->iparams->reactor, o, (BArpProbe_handler)arpprobe_handler);
    NCDValNullTermString_Free(&ifname_nts);
    if (!res) {
        ModuleLog(o->i, BLOG_ERROR, "BArpProbe_Init failed");
        goto fail0;
    }
    
    // set state unknown
    o->state = STATE_UNKNOWN;
    return;
    
fail0:
    NCDModuleInst_Backend_DeadError(i);
}

static void instance_free (struct instance *o, int is_error)
{
    // free arpprobe
    BArpProbe_Free(&o->arpprobe);
    
    if (is_error) {
        NCDModuleInst_Backend_DeadError(o->i);
    } else {
        NCDModuleInst_Backend_Dead(o->i);
    }
}

static void func_die (void *vo)
{
    struct instance *o = vo;
    
    instance_free(o, 0);
}

static int func_getvar (void *vo, const char *name, NCDValMem *mem, NCDValRef *out)
{
    struct instance *o = vo;
    ASSERT(o->state == STATE_EXIST || o->state == STATE_NOEXIST)
    
    if (!strcmp(name, "exists")) {
        *out = ncd_make_boolean(mem, o->state == STATE_EXIST, o->i->params->iparams->string_index);
        return 1;
    }
    
    return 0;
}

static struct NCDModule modules[] = {
    {
        .type = "net.ipv4.arp_probe",
        .func_new2 = func_new,
        .func_die = func_die,
        .func_getvar = func_getvar,
        .alloc_size = sizeof(struct instance)
    }, {
        .type = NULL
    }
};

const struct NCDModuleGroup ncdmodule_net_ipv4_arp_probe = {
    .modules = modules
};