/*
 *
 * Copyright 2015 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/lib/security/credentials/google_default/google_default_credentials.h"

#include <string.h>

#include "absl/strings/match.h"
#include "absl/strings/strip.h"

#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/sync.h>

#include "src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.h"
#include "src/core/ext/filters/client_channel/lb_policy/xds/xds_channel_args.h"
#include "src/core/lib/channel/channel_args.h"
#include "src/core/lib/gpr/env.h"
#include "src/core/lib/gpr/string.h"
#include "src/core/lib/gprpp/host_port.h"
#include "src/core/lib/gprpp/ref_counted_ptr.h"
#include "src/core/lib/http/httpcli.h"
#include "src/core/lib/http/parser.h"
#include "src/core/lib/iomgr/load_file.h"
#include "src/core/lib/iomgr/polling_entity.h"
#include "src/core/lib/security/credentials/alts/alts_credentials.h"
#include "src/core/lib/security/credentials/alts/check_gcp_environment.h"
#include "src/core/lib/security/credentials/credentials.h"
#include "src/core/lib/security/credentials/external/external_account_credentials.h"
#include "src/core/lib/security/credentials/jwt/jwt_credentials.h"
#include "src/core/lib/security/credentials/oauth2/oauth2_credentials.h"
#include "src/core/lib/slice/slice_internal.h"
#include "src/core/lib/slice/slice_string_helpers.h"
#include "src/core/lib/surface/api_trace.h"

using grpc_core::Json;

/* -- Constants. -- */

#define GRPC_COMPUTE_ENGINE_DETECTION_HOST "metadata.google.internal."
#define GRPC_GOOGLE_CREDENTIAL_CREATION_ERROR \
  "Failed to create Google credentials"

/* -- Default credentials. -- */

/* A sticky bit that will be set only if the result of metadata server detection
 * is positive. We do not set the bit if the result is negative. Because it
 * means the detection is done via network test that is unreliable and the
 * unreliable result should not be referred by successive calls. */
static int g_metadata_server_available = 0;
static grpc_core::Mutex* g_state_mu;
/* Protect a metadata_server_detector instance that can be modified by more than
 * one gRPC threads */
static gpr_mu* g_polling_mu;
static gpr_once g_once = GPR_ONCE_INIT;
static grpc_core::internal::grpc_gce_tenancy_checker g_gce_tenancy_checker =
    grpc_alts_is_running_on_gcp;

static void init_default_credentials(void) {
  g_state_mu = new grpc_core::Mutex();
}

struct metadata_server_detector {
  grpc_polling_entity pollent;
  int is_done;
  int success;
  grpc_http_response response;
};
grpc_core::RefCountedPtr<grpc_channel_security_connector>
grpc_google_default_channel_credentials::create_security_connector(
    grpc_core::RefCountedPtr<grpc_call_credentials> call_creds,
    const char* target, const grpc_channel_args* args,
    grpc_channel_args** new_args) {
  const bool is_grpclb_load_balancer = grpc_channel_args_find_bool(
      args, GRPC_ARG_ADDRESS_IS_GRPCLB_LOAD_BALANCER, false);
  const bool is_backend_from_grpclb_load_balancer = grpc_channel_args_find_bool(
      args, GRPC_ARG_ADDRESS_IS_BACKEND_FROM_GRPCLB_LOAD_BALANCER, false);
  const char* xds_cluster =
      grpc_channel_args_find_string(args, GRPC_ARG_XDS_CLUSTER_NAME);
  const bool is_xds_non_cfe_cluster =
      xds_cluster != nullptr && !absl::StartsWith(xds_cluster, "google_cfe_");
  const bool use_alts = is_grpclb_load_balancer ||
                        is_backend_from_grpclb_load_balancer ||
                        is_xds_non_cfe_cluster;
  /* Return failure if ALTS is selected but not running on GCE. */
  if (use_alts && alts_creds_ == nullptr) {
    gpr_log(GPR_ERROR, "ALTS is selected, but not running on GCE.");
    return nullptr;
  }
  grpc_core::RefCountedPtr<grpc_channel_security_connector> sc =
      use_alts ? alts_creds_->create_security_connector(call_creds, target,
                                                        args, new_args)
               : ssl_creds_->create_security_connector(call_creds, target, args,
                                                       new_args);
  /* grpclb-specific channel args are removed from the channel args set
   * to ensure backends and fallback adresses will have the same set of channel
   * args. By doing that, it guarantees the connections to backends will not be
   * torn down and re-connected when switching in and out of fallback mode.
   */
  if (use_alts) {
    static const char* args_to_remove[] = {
        GRPC_ARG_ADDRESS_IS_GRPCLB_LOAD_BALANCER,
        GRPC_ARG_ADDRESS_IS_BACKEND_FROM_GRPCLB_LOAD_BALANCER,
    };
    *new_args = grpc_channel_args_copy_and_add_and_remove(
        args, args_to_remove, GPR_ARRAY_SIZE(args_to_remove), nullptr, 0);
  }
  return sc;
}

grpc_channel_args* grpc_google_default_channel_credentials::update_arguments(
    grpc_channel_args* args) {
  grpc_channel_args* updated = args;
  if (grpc_channel_args_find(args, GRPC_ARG_DNS_ENABLE_SRV_QUERIES) ==
      nullptr) {
    grpc_arg new_srv_arg = grpc_channel_arg_integer_create(
        const_cast<char*>(GRPC_ARG_DNS_ENABLE_SRV_QUERIES), true);
    updated = grpc_channel_args_copy_and_add(args, &new_srv_arg, 1);
    grpc_channel_args_destroy(args);
  }
  return updated;
}

const char* grpc_google_default_channel_credentials::type() const {
  return "GoogleDefault";
}

static void on_metadata_server_detection_http_response(
    void* user_data, grpc_error_handle error) {
  metadata_server_detector* detector =
      static_cast<metadata_server_detector*>(user_data);
  if (error == GRPC_ERROR_NONE && detector->response.status == 200 &&
      detector->response.hdr_count > 0) {
    /* Internet providers can return a generic response to all requests, so
       it is necessary to check that metadata header is present also. */
    size_t i;
    for (i = 0; i < detector->response.hdr_count; i++) {
      grpc_http_header* header = &detector->response.hdrs[i];
      if (strcmp(header->key, "Metadata-Flavor") == 0 &&
          strcmp(header->value, "Google") == 0) {
        detector->success = 1;
        break;
      }
    }
  }
  gpr_mu_lock(g_polling_mu);
  detector->is_done = 1;
  GRPC_LOG_IF_ERROR(
      "Pollset kick",
      grpc_pollset_kick(grpc_polling_entity_pollset(&detector->pollent),
                        nullptr));
  gpr_mu_unlock(g_polling_mu);
}

static void destroy_pollset(void* p, grpc_error_handle /*e*/) {
  grpc_pollset_destroy(static_cast<grpc_pollset*>(p));
}

static int is_metadata_server_reachable() {
  metadata_server_detector detector;
  grpc_http_request request;
  grpc_closure destroy_closure;
  /* The http call is local. If it takes more than one sec, it is for sure not
     on compute engine. */
  const auto max_detection_delay = grpc_core::Duration::Seconds(1);
  grpc_pollset* pollset =
      static_cast<grpc_pollset*>(gpr_zalloc(grpc_pollset_size()));
  grpc_pollset_init(pollset, &g_polling_mu);
  detector.pollent = grpc_polling_entity_create_from_pollset(pollset);
  detector.is_done = 0;
  detector.success = 0;
  memset(&request, 0, sizeof(grpc_http_request));
  auto uri =
      grpc_core::URI::Create("http", GRPC_COMPUTE_ENGINE_DETECTION_HOST, "/",
                             {} /* query params */, "" /* fragment */);
  GPR_ASSERT(uri.ok());  // params are hardcoded
  auto http_request = grpc_core::HttpRequest::Get(
      std::move(*uri), nullptr /* channel args */, &detector.pollent, &request,
      grpc_core::ExecCtx::Get()->Now() + max_detection_delay,
      GRPC_CLOSURE_CREATE(on_metadata_server_detection_http_response, &detector,
                          grpc_schedule_on_exec_ctx),
      &detector.response,
      grpc_core::RefCountedPtr<grpc_channel_credentials>(
          grpc_insecure_credentials_create()));
  http_request->Start();
  grpc_core::ExecCtx::Get()->Flush();
  /* Block until we get the response. This is not ideal but this should only be
    called once for the lifetime of the process by the default credentials. */
  gpr_mu_lock(g_polling_mu);
  while (!detector.is_done) {
    grpc_pollset_worker* worker = nullptr;
    if (!GRPC_LOG_IF_ERROR(
            "pollset_work",
            grpc_pollset_work(grpc_polling_entity_pollset(&detector.pollent),
                              &worker, grpc_core::Timestamp::InfFuture()))) {
      detector.is_done = 1;
      detector.success = 0;
    }
  }
  gpr_mu_unlock(g_polling_mu);
  http_request.reset();
  GRPC_CLOSURE_INIT(&destroy_closure, destroy_pollset,
                    grpc_polling_entity_pollset(&detector.pollent),
                    grpc_schedule_on_exec_ctx);
  grpc_pollset_shutdown(grpc_polling_entity_pollset(&detector.pollent),
                        &destroy_closure);
  g_polling_mu = nullptr;
  grpc_core::ExecCtx::Get()->Flush();
  gpr_free(grpc_polling_entity_pollset(&detector.pollent));
  grpc_http_response_destroy(&detector.response);
  return detector.success;
}

namespace {

bool ValidateUrlField(const Json& json, const std::string& field) {
  auto it = json.object_value().find(field);
  if (it == json.object_value().end()) {
    return true;
  }
  if (it->second.type() != Json::Type::STRING ||
      it->second.string_value().empty()) {
    return false;
  }
  absl::StatusOr<grpc_core::URI> url =
      grpc_core::URI::Parse(it->second.string_value());
  if (!url.ok()) return false;
  if (!absl::EqualsIgnoreCase(url->scheme(), "https")) {
    return false;
  }
  absl::string_view host;
  absl::string_view port;
  grpc_core::SplitHostPort(url->authority(), &host, &port);
  if (absl::ConsumeSuffix(&host, ".googleapis.com")) {
    if (host == "sts" || host == "iamcredentials") {
      return true;
    } else if (absl::StartsWith(host, "sts.") ||
               absl::StartsWith(host, "iamcredentials.")) {
      return true;
    } else if (absl::EndsWith(host, ".sts") ||
               absl::EndsWith(host, ".iamcredentials")) {
      return true;
    } else if (absl::EndsWith(host, "-sts") ||
               absl::EndsWith(host, "-iamcredentials")) {
      return true;
    }
  }
  return false;
}

bool ValidateExteralAccountCredentials(const Json& json) {
  return json.type() == Json::Type::OBJECT &&
         ValidateUrlField(json, "token_url") &&
         ValidateUrlField(json, "service_account_impersonation_url") &&
         ValidateUrlField(json, "token_info_url");
}

}  // namespace

/* Takes ownership of creds_path if not NULL. */
static grpc_error_handle create_default_creds_from_path(
    const std::string& creds_path,
    grpc_core::RefCountedPtr<grpc_call_credentials>* creds) {
  grpc_auth_json_key key;
  grpc_auth_refresh_token token;
  grpc_core::RefCountedPtr<grpc_call_credentials> result;
  grpc_slice creds_data = grpc_empty_slice();
  grpc_error_handle error = GRPC_ERROR_NONE;
  Json json;
  if (creds_path.empty()) {
    error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("creds_path unset");
    goto end;
  }
  error = grpc_load_file(creds_path.c_str(), 0, &creds_data);
  if (error != GRPC_ERROR_NONE) goto end;
  json = Json::Parse(grpc_core::StringViewFromSlice(creds_data), &error);
  if (error != GRPC_ERROR_NONE) goto end;
  if (json.type() != Json::Type::OBJECT) {
    error = grpc_error_set_str(
        GRPC_ERROR_CREATE_FROM_STATIC_STRING("Failed to parse JSON"),
        GRPC_ERROR_STR_RAW_BYTES, grpc_core::StringViewFromSlice(creds_data));
    goto end;
  }

  /* First, try an auth json key. */
  key = grpc_auth_json_key_create_from_json(json);
  if (grpc_auth_json_key_is_valid(&key)) {
    result =
        grpc_service_account_jwt_access_credentials_create_from_auth_json_key(
            key, grpc_max_auth_token_lifetime());
    if (result == nullptr) {
      error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
          "grpc_service_account_jwt_access_credentials_create_from_auth_json_"
          "key failed");
    }
    goto end;
  }

  /* Then try a refresh token if the auth json key was invalid. */
  token = grpc_auth_refresh_token_create_from_json(json);
  if (grpc_auth_refresh_token_is_valid(&token)) {
    result =
        grpc_refresh_token_credentials_create_from_auth_refresh_token(token);
    if (result == nullptr) {
      error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
          "grpc_refresh_token_credentials_create_from_auth_refresh_token "
          "failed");
    }
    goto end;
  }

  /* Finally try an external account credentials.*/
  if (!ValidateExteralAccountCredentials(json)) {
    error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
        "Invalid external account credentials format.");
    goto end;
  }
  result = grpc_core::ExternalAccountCredentials::Create(json, {}, &error);

end:
  GPR_ASSERT((result == nullptr) + (error == GRPC_ERROR_NONE) == 1);
  grpc_slice_unref_internal(creds_data);
  *creds = result;
  return error;
}

static void update_tenancy() {
  gpr_once_init(&g_once, init_default_credentials);
  grpc_core::MutexLock lock(g_state_mu);

  /* Try a platform-provided hint for GCE. */
  if (!g_metadata_server_available) {
    g_metadata_server_available = g_gce_tenancy_checker();
  }
  /* TODO: Add a platform-provided hint for GAE. */

  /* Do a network test for metadata server. */
  if (!g_metadata_server_available) {
    g_metadata_server_available = is_metadata_server_reachable();
  }
}

static bool metadata_server_available() {
  grpc_core::MutexLock lock(g_state_mu);
  return static_cast<bool>(g_metadata_server_available);
}

static grpc_core::RefCountedPtr<grpc_call_credentials> make_default_call_creds(
    grpc_error_handle* error) {
  grpc_core::RefCountedPtr<grpc_call_credentials> call_creds;
  grpc_error_handle err;

  /* First, try the environment variable. */
  char* path_from_env = gpr_getenv(GRPC_GOOGLE_CREDENTIALS_ENV_VAR);
  if (path_from_env != nullptr) {
    err = create_default_creds_from_path(path_from_env, &call_creds);
    gpr_free(path_from_env);
    if (err == GRPC_ERROR_NONE) return call_creds;
    *error = grpc_error_add_child(*error, err);
  }

  /* Then the well-known file. */
  err = create_default_creds_from_path(
      grpc_get_well_known_google_credentials_file_path(), &call_creds);
  if (err == GRPC_ERROR_NONE) return call_creds;
  *error = grpc_error_add_child(*error, err);

  update_tenancy();

  if (metadata_server_available()) {
    call_creds = grpc_core::RefCountedPtr<grpc_call_credentials>(
        grpc_google_compute_engine_credentials_create(nullptr));
    if (call_creds == nullptr) {
      *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
          GRPC_GOOGLE_CREDENTIAL_CREATION_ERROR);
      *error = grpc_error_add_child(
          *error, GRPC_ERROR_CREATE_FROM_STATIC_STRING(
                      "Failed to get credentials from network"));
    }
  }

  return call_creds;
}

grpc_channel_credentials* grpc_google_default_credentials_create(
    grpc_call_credentials* call_credentials) {
  grpc_channel_credentials* result = nullptr;
  grpc_core::RefCountedPtr<grpc_call_credentials> call_creds(call_credentials);
  grpc_error_handle error = GRPC_ERROR_NONE;
  grpc_core::ExecCtx exec_ctx;

  GRPC_API_TRACE("grpc_google_default_credentials_create(%p)", 1,
                 (call_credentials));

  if (call_creds == nullptr) {
    call_creds = make_default_call_creds(&error);
  }

  if (call_creds != nullptr) {
    /* Create google default credentials. */
    grpc_channel_credentials* ssl_creds =
        grpc_ssl_credentials_create(nullptr, nullptr, nullptr, nullptr);
    GPR_ASSERT(ssl_creds != nullptr);
    grpc_alts_credentials_options* options =
        grpc_alts_credentials_client_options_create();
    grpc_channel_credentials* alts_creds =
        grpc_alts_credentials_create(options);
    grpc_alts_credentials_options_destroy(options);
    auto creds =
        grpc_core::MakeRefCounted<grpc_google_default_channel_credentials>(
            grpc_core::RefCountedPtr<grpc_channel_credentials>(alts_creds),
            grpc_core::RefCountedPtr<grpc_channel_credentials>(ssl_creds));
    result = grpc_composite_channel_credentials_create(
        creds.get(), call_creds.get(), nullptr);
    GPR_ASSERT(result != nullptr);
  } else {
    gpr_log(GPR_ERROR, "Could not create google default credentials: %s",
            grpc_error_std_string(error).c_str());
  }
  GRPC_ERROR_UNREF(error);
  return result;
}

namespace grpc_core {
namespace internal {

void set_gce_tenancy_checker_for_testing(grpc_gce_tenancy_checker checker) {
  g_gce_tenancy_checker = checker;
}

void grpc_flush_cached_google_default_credentials(void) {
  ExecCtx exec_ctx;
  gpr_once_init(&g_once, init_default_credentials);
  MutexLock lock(g_state_mu);
  g_metadata_server_available = 0;
}

}  // namespace internal
}  // namespace grpc_core

/* -- Well known credentials path. -- */

static grpc_well_known_credentials_path_getter creds_path_getter = nullptr;

std::string grpc_get_well_known_google_credentials_file_path(void) {
  if (creds_path_getter != nullptr) return creds_path_getter();
  return grpc_get_well_known_google_credentials_file_path_impl();
}

void grpc_override_well_known_credentials_path_getter(
    grpc_well_known_credentials_path_getter getter) {
  creds_path_getter = getter;
}
