//
//
// Copyright 2021 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//

#include "src/core/xds/grpc/xds_routing.h"

#include <grpc/support/port_platform.h>
#include <stdint.h>
#include <stdlib.h>

#include <algorithm>
#include <cctype>
#include <utility>

#include "src/core/lib/channel/channel_args.h"
#include "src/core/util/grpc_check.h"
#include "src/core/util/matchers.h"
#include "src/core/xds/grpc/xds_http_filter.h"
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/match.h"
#include "absl/strings/str_cat.h"

namespace grpc_core {

namespace {
enum MatchType {
  EXACT_MATCH,
  SUFFIX_MATCH,
  PREFIX_MATCH,
  UNIVERSE_MATCH,
  INVALID_MATCH,
};

// Returns true if match succeeds.
bool DomainMatch(MatchType match_type, absl::string_view domain_pattern_in,
                 absl::string_view expected_host_name_in) {
  // Normalize the args to lower-case. Domain matching is case-insensitive.
  std::string domain_pattern = std::string(domain_pattern_in);
  std::string expected_host_name = std::string(expected_host_name_in);
  std::transform(domain_pattern.begin(), domain_pattern.end(),
                 domain_pattern.begin(),
                 [](unsigned char c) { return std::tolower(c); });
  std::transform(expected_host_name.begin(), expected_host_name.end(),
                 expected_host_name.begin(),
                 [](unsigned char c) { return std::tolower(c); });
  if (match_type == EXACT_MATCH) {
    return domain_pattern == expected_host_name;
  } else if (match_type == SUFFIX_MATCH) {
    // Asterisk must match at least one char.
    if (expected_host_name.size() < domain_pattern.size()) return false;
    absl::string_view pattern_suffix(domain_pattern.c_str() + 1);
    absl::string_view host_suffix(expected_host_name.c_str() +
                                  expected_host_name.size() -
                                  pattern_suffix.size());
    return pattern_suffix == host_suffix;
  } else if (match_type == PREFIX_MATCH) {
    // Asterisk must match at least one char.
    if (expected_host_name.size() < domain_pattern.size()) return false;
    absl::string_view pattern_prefix(domain_pattern.c_str(),
                                     domain_pattern.size() - 1);
    absl::string_view host_prefix(expected_host_name.c_str(),
                                  pattern_prefix.size());
    return pattern_prefix == host_prefix;
  } else {
    return match_type == UNIVERSE_MATCH;
  }
}

MatchType DomainPatternMatchType(absl::string_view domain_pattern) {
  if (domain_pattern.empty()) return INVALID_MATCH;
  if (!absl::StrContains(domain_pattern, '*')) return EXACT_MATCH;
  if (domain_pattern == "*") return UNIVERSE_MATCH;
  if (domain_pattern[0] == '*') return SUFFIX_MATCH;
  if (domain_pattern[domain_pattern.size() - 1] == '*') return PREFIX_MATCH;
  return INVALID_MATCH;
}

}  // namespace

std::optional<size_t> XdsRouting::FindVirtualHostForDomain(
    const VirtualHostListIterator& vhost_iterator, absl::string_view domain) {
  // Find the best matched virtual host.
  // The search order for 4 groups of domain patterns:
  //   1. Exact match.
  //   2. Suffix match (e.g., "*ABC").
  //   3. Prefix match (e.g., "ABC*").
  //   4. Universe match (i.e., "*").
  // Within each group, longest match wins.
  // If the same best matched domain pattern appears in multiple virtual
  // hosts, the first matched virtual host wins.
  std::optional<size_t> target_index;
  MatchType best_match_type = INVALID_MATCH;
  size_t longest_match = 0;
  // Check each domain pattern in each virtual host to determine the best
  // matched virtual host.
  for (size_t i = 0; i < vhost_iterator.Size(); ++i) {
    const auto& domains = vhost_iterator.GetDomainsForVirtualHost(i);
    for (const std::string& domain_pattern : domains) {
      // Check the match type first. Skip the pattern if it's not better
      // than current match.
      const MatchType match_type = DomainPatternMatchType(domain_pattern);
      // This should be caught by RouteConfigParse().
      GRPC_CHECK(match_type != INVALID_MATCH);
      if (match_type > best_match_type) continue;
      if (match_type == best_match_type &&
          domain_pattern.size() <= longest_match) {
        continue;
      }
      // Skip if match fails.
      if (!DomainMatch(match_type, domain_pattern, domain)) continue;
      // Choose this match.
      target_index = i;
      best_match_type = match_type;
      longest_match = domain_pattern.size();
      if (best_match_type == EXACT_MATCH) break;
    }
    if (best_match_type == EXACT_MATCH) break;
  }
  return target_index;
}

namespace {

bool HeadersMatch(const std::vector<HeaderMatcher>& header_matchers,
                  grpc_metadata_batch* initial_metadata) {
  for (const auto& header_matcher : header_matchers) {
    std::string concatenated_value;
    if (!header_matcher.Match(XdsRouting::GetHeaderValue(
            initial_metadata, header_matcher.name(), &concatenated_value))) {
      return false;
    }
  }
  return true;
}

bool UnderFraction(const uint32_t fraction_per_million) {
  // Generate a random number in [0, 1000000).
  const uint32_t random_number = rand() % 1000000;
  return random_number < fraction_per_million;
}

}  // namespace

std::optional<size_t> XdsRouting::GetRouteForRequest(
    const RouteListIterator& route_list_iterator, absl::string_view path,
    grpc_metadata_batch* initial_metadata) {
  for (size_t i = 0; i < route_list_iterator.Size(); ++i) {
    const XdsRouteConfigResource::Route::Matchers& matchers =
        route_list_iterator.GetMatchersForRoute(i);
    if (matchers.path_matcher.Match(path) &&
        HeadersMatch(matchers.header_matchers, initial_metadata) &&
        (!matchers.fraction_per_million.has_value() ||
         UnderFraction(*matchers.fraction_per_million))) {
      return i;
    }
  }
  return std::nullopt;
}

bool XdsRouting::IsValidDomainPattern(absl::string_view domain_pattern) {
  return DomainPatternMatchType(domain_pattern) != INVALID_MATCH;
}

std::optional<absl::string_view> XdsRouting::GetHeaderValue(
    grpc_metadata_batch* initial_metadata, absl::string_view header_name,
    std::string* concatenated_value) {
  // Note: If we ever allow binary headers here, we still need to
  // special-case ignore "grpc-tags-bin" and "grpc-trace-bin", since
  // they are not visible to the LB policy in grpc-go.
  if (absl::EndsWith(header_name, "-bin")) {
    return std::nullopt;
  } else if (header_name == "content-type") {
    return "application/grpc";
  }
  return initial_metadata->GetStringValue(header_name, concatenated_value);
}

XdsRouting::PerRouteFilterChainBuilder::PerRouteFilterChainBuilder(
    const std::vector<XdsListenerResource::HttpConnectionManager::HttpFilter>&
        hcm_filter_configs,
    const XdsHttpFilterRegistry& http_filter_registry,
    const XdsRouteConfigResource::VirtualHost& vhost,
    FilterChainBuilder& builder,
    absl::AnyInvocable<void(FilterChainBuilder&)> add_last_filter,
    Blackboard& blackboard)
    : hcm_filter_configs_(hcm_filter_configs),
      vhost_(vhost),
      builder_(builder),
      add_last_filter_(std::move(add_last_filter)),
      blackboard_(blackboard) {
  filter_impls_.reserve(hcm_filter_configs.size());
  for (const auto& http_filter : hcm_filter_configs) {
    // Find filter.  This is guaranteed to succeed, because it's checked
    // at config validation time.
    const XdsHttpFilterImpl* filter_impl =
        http_filter_registry.GetFilterForTopLevelType(
            http_filter.config_proto_type);
    GRPC_CHECK_NE(filter_impl, nullptr);
    // Add filter to list.
    filter_impls_.push_back(filter_impl);
  }
}

namespace {

RefCountedPtr<const FilterConfig> GetOverrideConfig(
    const XdsHttpFilterImpl* filter_impl,
    const XdsRouteConfigResource::TypedPerFilterConfig& typed_per_filter_config,
    const std::string& name) {
  auto it = typed_per_filter_config.find(name);
  if (it == typed_per_filter_config.end()) return nullptr;
  if (it->second.config_proto_type != filter_impl->OverrideConfigProtoName()) {
    return nullptr;
  }
  return it->second.filter_config;
}

}  // namespace

absl::StatusOr<RefCountedPtr<const FilterChain>>
XdsRouting::PerRouteFilterChainBuilder::GetDefaultFilterChain() {
  if (default_filter_chain_.ok() && *default_filter_chain_ == nullptr) {
    GRPC_TRACE_LOG(xds_resolver, INFO) << "Building default filter chain:";
    for (size_t i = 0; i < filter_impls_.size(); ++i) {
      auto* filter_impl = filter_impls_[i];
      const auto& filter_config = hcm_filter_configs_[i];
      RefCountedPtr<const FilterConfig> config;
      if (filter_config.filter_config != nullptr) {
        auto vhost_override_config = GetOverrideConfig(
            filter_impl, vhost_.typed_per_filter_config, filter_config.name);
        config = filter_impl->MergeConfigs(filter_config.filter_config,
                                           std::move(vhost_override_config),
                                           nullptr, nullptr, blackboard_);
      }
      GRPC_TRACE_LOG(xds_resolver, INFO)
          << "  Adding filter=" << filter_config.name
          << " config=" << (config == nullptr ? "<null>" : config->ToString());
      filter_impl->AddFilter(builder_, std::move(config));
    }
    if (add_last_filter_ != nullptr) add_last_filter_(builder_);
    default_filter_chain_ = builder_.Build();
    GRPC_TRACE_LOG(xds_resolver, INFO)
        << "Filter chain creation status: " << default_filter_chain_.status();
  }
  return default_filter_chain_;
}

absl::StatusOr<RefCountedPtr<const FilterChain>>
XdsRouting::PerRouteFilterChainBuilder::BuildFilterChainForRoute(
    const XdsRouteConfigResource::Route& route) {
  GRPC_TRACE_LOG(xds_resolver, INFO)
      << "Building filter chain for route:" << route.ToString();
  // If there are no per-route overrides, use the default filter chain.
  if (route.typed_per_filter_config.empty()) return GetDefaultFilterChain();
  // Otherwise, build a new filter chain for the route.
  for (size_t i = 0; i < filter_impls_.size(); ++i) {
    auto* filter_impl = filter_impls_[i];
    const auto& filter_config = hcm_filter_configs_[i];
    RefCountedPtr<const FilterConfig> config;
    if (filter_config.filter_config != nullptr) {
      auto vhost_override_config = GetOverrideConfig(
          filter_impl, vhost_.typed_per_filter_config, filter_config.name);
      auto route_override_config = GetOverrideConfig(
          filter_impl, route.typed_per_filter_config, filter_config.name);
      config = filter_impl->MergeConfigs(
          filter_config.filter_config, std::move(vhost_override_config),
          std::move(route_override_config), nullptr, blackboard_);
    }
    GRPC_TRACE_LOG(xds_resolver, INFO)
        << "  Adding filter=" << filter_config.name
        << " config=" << (config == nullptr ? "<null>" : config->ToString());
    filter_impl->AddFilter(builder_, std::move(config));
  }
  if (add_last_filter_ != nullptr) add_last_filter_(builder_);
  absl::StatusOr<RefCountedPtr<const FilterChain>> route_filter_chain =
      builder_.Build();
  GRPC_TRACE_LOG(xds_resolver, INFO)
      << "Filter chain creation status: " << route_filter_chain.status();
  return route_filter_chain;
}

void XdsRouting::PerRouteFilterChainBuilder::
    BuildFilterChainForRouteWithWeightedClusters(
        const XdsRouteConfigResource::Route& route,
        absl::FunctionRef<
            void(size_t, absl::StatusOr<RefCountedPtr<const FilterChain>>)>
            set_filter_chain_for_cluster_weight) {
  // If any cluster weight does not have any filter config overrides,
  // we'll reuse the route-level filter chain.  We construct it lazily
  // and cache it so that we never construct it more than we need to.
  absl::StatusOr<RefCountedPtr<const FilterChain>> route_filter_chain = nullptr;
  const auto& route_action =
      std::get<XdsRouteConfigResource::Route::RouteAction>(route.action);
  const auto& cluster_weights = std::get<
      std::vector<XdsRouteConfigResource::Route::RouteAction::ClusterWeight>>(
      route_action.action);
  for (size_t j = 0; j < cluster_weights.size(); ++j) {
    const auto& cluster_weight = cluster_weights[j];
    if (cluster_weight.typed_per_filter_config.empty()) {
      // No per-ClusterWeight overrides, so use the route-level filter chain.
      if (route_filter_chain.ok() && *route_filter_chain == nullptr) {
        route_filter_chain = BuildFilterChainForRoute(route);
      }
      set_filter_chain_for_cluster_weight(j, route_filter_chain);
    } else {
      GRPC_TRACE_LOG(xds_resolver, INFO)
          << "Building filter chain for route:" << route.ToString()
          << " ClusterWeight:" << cluster_weight.ToString();
      for (size_t i = 0; i < filter_impls_.size(); ++i) {
        auto* filter_impl = filter_impls_[i];
        const auto& filter_config = hcm_filter_configs_[i];
        RefCountedPtr<const FilterConfig> config;
        if (filter_config.filter_config != nullptr) {
          auto vhost_override_config = GetOverrideConfig(
              filter_impl, vhost_.typed_per_filter_config, filter_config.name);
          auto route_override_config = GetOverrideConfig(
              filter_impl, route.typed_per_filter_config, filter_config.name);
          auto cluster_weight_override_config = GetOverrideConfig(
              filter_impl, cluster_weight.typed_per_filter_config,
              filter_config.name);
          config = filter_impl->MergeConfigs(
              filter_config.filter_config, std::move(vhost_override_config),
              std::move(route_override_config),
              std::move(cluster_weight_override_config), blackboard_);
        }
        GRPC_TRACE_LOG(xds_resolver, INFO)
            << "  Adding filter=" << filter_config.name << " config="
            << (config == nullptr ? "<null>" : config->ToString());
        filter_impl->AddFilter(builder_, std::move(config));
      }
      if (add_last_filter_ != nullptr) add_last_filter_(builder_);
      auto filter_chain = builder_.Build();
      GRPC_TRACE_LOG(xds_resolver, INFO)
          << "Filter chain creation status: " << filter_chain.status();
      set_filter_chain_for_cluster_weight(j, std::move(filter_chain));
    }
  }
}

namespace {

const XdsRouteConfigResource::FilterConfigOverride* FindFilterConfigOverride(
    const std::string& instance_name,
    const XdsRouteConfigResource::VirtualHost& vhost,
    const XdsRouteConfigResource::Route& route,
    const XdsRouteConfigResource::Route::RouteAction::ClusterWeight*
        cluster_weight) {
  // Check ClusterWeight, if any.
  if (cluster_weight != nullptr) {
    auto it = cluster_weight->typed_per_filter_config.find(instance_name);
    if (it != cluster_weight->typed_per_filter_config.end()) return &it->second;
  }
  // Check Route.
  auto it = route.typed_per_filter_config.find(instance_name);
  if (it != route.typed_per_filter_config.end()) return &it->second;
  // Check VirtualHost.
  it = vhost.typed_per_filter_config.find(instance_name);
  if (it != vhost.typed_per_filter_config.end()) return &it->second;
  // Not found.
  return nullptr;
}

absl::StatusOr<XdsRouting::GeneratePerHttpFilterConfigsResult>
GeneratePerHTTPFilterConfigs(
    const XdsHttpFilterRegistry& http_filter_registry,
    const std::vector<XdsListenerResource::HttpConnectionManager::HttpFilter>&
        http_filters,
    const ChannelArgs& args,
    absl::FunctionRef<absl::StatusOr<XdsHttpFilterImpl::ServiceConfigJsonEntry>(
        const XdsHttpFilterImpl&,
        const XdsListenerResource::HttpConnectionManager::HttpFilter&)>
        generate_service_config) {
  XdsRouting::GeneratePerHttpFilterConfigsResult result;
  result.args = args;
  for (const auto& http_filter : http_filters) {
    // Find filter.  This is guaranteed to succeed, because it's checked
    // at config validation time in the listener parsing code.
    const XdsHttpFilterImpl* filter_impl =
        http_filter_registry.GetFilterForTopLevelType(
            http_filter.config_proto_type);
    GRPC_CHECK_NE(filter_impl, nullptr);
    // If there is not actually any C-core filter associated with this
    // xDS filter, then it won't need any config, so skip it.
    if (filter_impl->channel_filter() == nullptr) continue;
    // Allow filter to add channel args that may affect service config
    // parsing.
    result.args = filter_impl->ModifyChannelArgs(result.args);
    // Generate service config for filter.
    auto service_config_field =
        generate_service_config(*filter_impl, http_filter);
    if (!service_config_field.ok()) {
      return absl::FailedPreconditionError(absl::StrCat(
          "failed to generate service config for HTTP filter ",
          http_filter.name, ": ", service_config_field.status().ToString()));
    }
    if (service_config_field->service_config_field_name.empty()) continue;
    result.per_filter_configs[service_config_field->service_config_field_name]
        .push_back(service_config_field->element);
  }
  return result;
}

}  // namespace

absl::StatusOr<XdsRouting::GeneratePerHttpFilterConfigsResult>
XdsRouting::GeneratePerHTTPFilterConfigsForMethodConfig(
    const XdsHttpFilterRegistry& http_filter_registry,
    const std::vector<XdsListenerResource::HttpConnectionManager::HttpFilter>&
        http_filters,
    const XdsRouteConfigResource::VirtualHost& vhost,
    const XdsRouteConfigResource::Route& route,
    const XdsRouteConfigResource::Route::RouteAction::ClusterWeight*
        cluster_weight,
    const ChannelArgs& args) {
  return GeneratePerHTTPFilterConfigs(
      http_filter_registry, http_filters, args,
      [&](const XdsHttpFilterImpl& filter_impl,
          const XdsListenerResource::HttpConnectionManager::HttpFilter&
              http_filter) {
        // Find override config, if any.
        const XdsRouteConfigResource::FilterConfigOverride*
            filter_config_override = FindFilterConfigOverride(
                http_filter.name, vhost, route, cluster_weight);
        const Json* config_override = nullptr;
        if (filter_config_override != nullptr &&
            filter_config_override->config_proto_type ==
                filter_impl.OverrideConfigProtoName()) {
          config_override = &filter_config_override->config;
        }
        // Generate service config for filter.
        return filter_impl.GenerateMethodConfig(http_filter.config,
                                                config_override);
      });
}

absl::StatusOr<XdsRouting::GeneratePerHttpFilterConfigsResult>
XdsRouting::GeneratePerHTTPFilterConfigsForServiceConfig(
    const XdsHttpFilterRegistry& http_filter_registry,
    const std::vector<XdsListenerResource::HttpConnectionManager::HttpFilter>&
        http_filters,
    const ChannelArgs& args) {
  return GeneratePerHTTPFilterConfigs(
      http_filter_registry, http_filters, args,
      [&](const XdsHttpFilterImpl& filter_impl,
          const XdsListenerResource::HttpConnectionManager::HttpFilter&
              http_filter) {
        return filter_impl.GenerateServiceConfig(http_filter.config);
      });
}

}  // namespace grpc_core
