/*
 *
 * Copyright 2015, Google Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * 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.
 *     * Neither the name of Google Inc. 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 COPYRIGHT
 * OWNER OR CONTRIBUTORS 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.
 *
 */

#include "src/core/client_config/resolvers/dns_resolver.h"

#include <string.h>

#include <grpc/support/alloc.h>
#include <grpc/support/host_port.h>
#include <grpc/support/string_util.h>

#include "src/core/client_config/lb_policy_registry.h"
#include "src/core/client_config/subchannel_factory_decorators/add_channel_arg.h"
#include "src/core/iomgr/resolve_address.h"
#include "src/core/support/string.h"

typedef struct
{
  /** base class: must be first */
  grpc_resolver base;
  /** refcount */
  gpr_refcount refs;
  /** name to resolve */
  char *name;
  /** default port to use */
  char *default_port;
  /** subchannel factory */
  grpc_subchannel_factory *subchannel_factory;
  /** load balancing policy name */
  char *lb_policy_name;

  /** mutex guarding the rest of the state */
  gpr_mu mu;
  /** are we currently resolving? */
  int resolving;
  /** which version of resolved_config have we published? */
  int published_version;
  /** which version of resolved_config is current? */
  int resolved_version;
  /** pending next completion, or NULL */
  grpc_closure *next_completion;
  /** target config address for next completion */
  grpc_client_config **target_config;
  /** current (fully resolved) config */
  grpc_client_config *resolved_config;
} dns_resolver;

static void dns_destroy (grpc_exec_ctx * exec_ctx, grpc_resolver * r);

static void dns_start_resolving_locked (dns_resolver * r);
static void dns_maybe_finish_next_locked (grpc_exec_ctx * exec_ctx, dns_resolver * r);

static void dns_shutdown (grpc_exec_ctx * exec_ctx, grpc_resolver * r);
static void dns_channel_saw_error (grpc_exec_ctx * exec_ctx, grpc_resolver * r, struct sockaddr *failing_address, int failing_address_len);
static void dns_next (grpc_exec_ctx * exec_ctx, grpc_resolver * r, grpc_client_config ** target_config, grpc_closure * on_complete);

static const grpc_resolver_vtable dns_resolver_vtable = {
  dns_destroy, dns_shutdown, dns_channel_saw_error, dns_next
};

static void
dns_shutdown (grpc_exec_ctx * exec_ctx, grpc_resolver * resolver)
{
  dns_resolver *r = (dns_resolver *) resolver;
  gpr_mu_lock (&r->mu);
  if (r->next_completion != NULL)
    {
      *r->target_config = NULL;
      grpc_exec_ctx_enqueue (exec_ctx, r->next_completion, 1);
      r->next_completion = NULL;
    }
  gpr_mu_unlock (&r->mu);
}

static void
dns_channel_saw_error (grpc_exec_ctx * exec_ctx, grpc_resolver * resolver, struct sockaddr *sa, int len)
{
  dns_resolver *r = (dns_resolver *) resolver;
  gpr_mu_lock (&r->mu);
  if (!r->resolving)
    {
      dns_start_resolving_locked (r);
    }
  gpr_mu_unlock (&r->mu);
}

static void
dns_next (grpc_exec_ctx * exec_ctx, grpc_resolver * resolver, grpc_client_config ** target_config, grpc_closure * on_complete)
{
  dns_resolver *r = (dns_resolver *) resolver;
  gpr_mu_lock (&r->mu);
  GPR_ASSERT (!r->next_completion);
  r->next_completion = on_complete;
  r->target_config = target_config;
  if (r->resolved_version == 0 && !r->resolving)
    {
      dns_start_resolving_locked (r);
    }
  else
    {
      dns_maybe_finish_next_locked (exec_ctx, r);
    }
  gpr_mu_unlock (&r->mu);
}

static void
dns_on_resolved (grpc_exec_ctx * exec_ctx, void *arg, grpc_resolved_addresses * addresses)
{
  dns_resolver *r = arg;
  grpc_client_config *config = NULL;
  grpc_subchannel **subchannels;
  grpc_subchannel_args args;
  grpc_lb_policy *lb_policy;
  size_t i;
  if (addresses)
    {
      grpc_lb_policy_args lb_policy_args;
      config = grpc_client_config_create ();
      subchannels = gpr_malloc (sizeof (grpc_subchannel *) * addresses->naddrs);
      for (i = 0; i < addresses->naddrs; i++)
	{
	  memset (&args, 0, sizeof (args));
	  args.addr = (struct sockaddr *) (addresses->addrs[i].addr);
	  args.addr_len = (size_t) addresses->addrs[i].len;
	  subchannels[i] = grpc_subchannel_factory_create_subchannel (exec_ctx, r->subchannel_factory, &args);
	}
      memset (&lb_policy_args, 0, sizeof (lb_policy_args));
      lb_policy_args.subchannels = subchannels;
      lb_policy_args.num_subchannels = addresses->naddrs;
      lb_policy = grpc_lb_policy_create (r->lb_policy_name, &lb_policy_args);
      grpc_client_config_set_lb_policy (config, lb_policy);
      GRPC_LB_POLICY_UNREF (exec_ctx, lb_policy, "construction");
      grpc_resolved_addresses_destroy (addresses);
      gpr_free (subchannels);
    }
  gpr_mu_lock (&r->mu);
  GPR_ASSERT (r->resolving);
  r->resolving = 0;
  if (r->resolved_config)
    {
      grpc_client_config_unref (exec_ctx, r->resolved_config);
    }
  r->resolved_config = config;
  r->resolved_version++;
  dns_maybe_finish_next_locked (exec_ctx, r);
  gpr_mu_unlock (&r->mu);

  GRPC_RESOLVER_UNREF (exec_ctx, &r->base, "dns-resolving");
}

static void
dns_start_resolving_locked (dns_resolver * r)
{
  GRPC_RESOLVER_REF (&r->base, "dns-resolving");
  GPR_ASSERT (!r->resolving);
  r->resolving = 1;
  grpc_resolve_address (r->name, r->default_port, dns_on_resolved, r);
}

static void
dns_maybe_finish_next_locked (grpc_exec_ctx * exec_ctx, dns_resolver * r)
{
  if (r->next_completion != NULL && r->resolved_version != r->published_version)
    {
      *r->target_config = r->resolved_config;
      if (r->resolved_config)
	{
	  grpc_client_config_ref (r->resolved_config);
	}
      grpc_exec_ctx_enqueue (exec_ctx, r->next_completion, 1);
      r->next_completion = NULL;
      r->published_version = r->resolved_version;
    }
}

static void
dns_destroy (grpc_exec_ctx * exec_ctx, grpc_resolver * gr)
{
  dns_resolver *r = (dns_resolver *) gr;
  gpr_mu_destroy (&r->mu);
  if (r->resolved_config)
    {
      grpc_client_config_unref (exec_ctx, r->resolved_config);
    }
  grpc_subchannel_factory_unref (exec_ctx, r->subchannel_factory);
  gpr_free (r->name);
  gpr_free (r->default_port);
  gpr_free (r->lb_policy_name);
  gpr_free (r);
}

static grpc_resolver *
dns_create (grpc_resolver_args * args, const char *default_port, const char *lb_policy_name)
{
  dns_resolver *r;
  const char *path = args->uri->path;

  if (0 != strcmp (args->uri->authority, ""))
    {
      gpr_log (GPR_ERROR, "authority based dns uri's not supported");
      return NULL;
    }

  if (path[0] == '/')
    ++path;

  r = gpr_malloc (sizeof (dns_resolver));
  memset (r, 0, sizeof (*r));
  gpr_ref_init (&r->refs, 1);
  gpr_mu_init (&r->mu);
  grpc_resolver_init (&r->base, &dns_resolver_vtable);
  r->name = gpr_strdup (path);
  r->default_port = gpr_strdup (default_port);
  r->subchannel_factory = args->subchannel_factory;
  grpc_subchannel_factory_ref (r->subchannel_factory);
  r->lb_policy_name = gpr_strdup (lb_policy_name);
  return &r->base;
}

/*
 * FACTORY
 */

static void
dns_factory_ref (grpc_resolver_factory * factory)
{
}

static void
dns_factory_unref (grpc_resolver_factory * factory)
{
}

static grpc_resolver *
dns_factory_create_resolver (grpc_resolver_factory * factory, grpc_resolver_args * args)
{
  return dns_create (args, "https", "pick_first");
}

char *
dns_factory_get_default_host_name (grpc_resolver_factory * factory, grpc_uri * uri)
{
  const char *path = uri->path;
  if (path[0] == '/')
    ++path;
  return gpr_strdup (path);
}

static const grpc_resolver_factory_vtable dns_factory_vtable = {
  dns_factory_ref, dns_factory_unref, dns_factory_create_resolver,
  dns_factory_get_default_host_name, "dns"
};
static grpc_resolver_factory dns_resolver_factory = { &dns_factory_vtable };

grpc_resolver_factory *
grpc_dns_resolver_factory_create ()
{
  return &dns_resolver_factory;
}