//
//
// 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 <grpc/support/port_platform.h>

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

#include <cctype>

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 (domain_pattern.find('*') == std::string::npos) 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

absl::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.
  absl::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().
      GPR_ASSERT(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

absl::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 absl::nullopt;
}

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

absl::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 absl::nullopt;
  } else if (header_name == "content-type") {
    return "application/grpc";
  }
  return initial_metadata->GetStringValue(header_name, concatenated_value);
}

namespace {

const XdsHttpFilterImpl::FilterConfig* 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;
}

}  // namespace

XdsRouting::GeneratePerHttpFilterConfigsResult
XdsRouting::GeneratePerHTTPFilterConfigs(
    const std::vector<XdsListenerResource::HttpConnectionManager::HttpFilter>&
        http_filters,
    const XdsRouteConfigResource::VirtualHost& vhost,
    const XdsRouteConfigResource::Route& route,
    const XdsRouteConfigResource::Route::RouteAction::ClusterWeight*
        cluster_weight,
    grpc_channel_args* args) {
  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 XdsApi code.
    const XdsHttpFilterImpl* filter_impl =
        XdsHttpFilterRegistry::GetFilterForType(
            http_filter.config.config_proto_type_name);
    GPR_ASSERT(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);
    // Find config override, if any.
    const XdsHttpFilterImpl::FilterConfig* config_override =
        FindFilterConfigOverride(http_filter.name, vhost, route,
                                 cluster_weight);
    // Generate service config for filter.
    auto method_config_field =
        filter_impl->GenerateServiceConfig(http_filter.config, config_override);
    if (!method_config_field.ok()) {
      grpc_channel_args_destroy(result.args);
      result.args = nullptr;
      result.error = GRPC_ERROR_CREATE_FROM_CPP_STRING(absl::StrCat(
          "failed to generate method config for HTTP filter ", http_filter.name,
          ": ", method_config_field.status().ToString()));
      break;
    }
    result.per_filter_configs[method_config_field->service_config_field_name]
        .push_back(method_config_field->element);
  }
  return result;
}

}  // namespace grpc_core
