//
// Copyright 2020 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/credentials/transport/tls/grpc_tls_certificate_provider.h"

#include <grpc/credentials.h>
#include <grpc/slice.h>
#include <grpc/support/port_platform.h>
#include <grpc/support/time.h>
#include <stdint.h>
#include <time.h>

#include <algorithm>
#include <utility>
#include <vector>

#include "absl/log/check.h"
#include "absl/log/log.h"
#include "absl/status/status.h"
#include "absl/strings/string_view.h"
#include "src/core/credentials/transport/tls/ssl_utils.h"
#include "src/core/lib/debug/trace.h"
#include "src/core/lib/iomgr/error.h"
#include "src/core/lib/iomgr/exec_ctx.h"
#include "src/core/lib/slice/slice.h"
#include "src/core/lib/slice/slice_internal.h"
#include "src/core/tsi/ssl_transport_security_utils.h"
#include "src/core/util/load_file.h"
#include "src/core/util/stat.h"
#include "src/core/util/status_helper.h"

namespace grpc_core {
namespace {

absl::Status ValidateRootCertificates(absl::string_view root_certificates) {
  if (root_certificates.empty()) return absl::OkStatus();
  absl::StatusOr<std::vector<X509*>> parsed_roots =
      ParsePemCertificateChain(root_certificates);
  if (!parsed_roots.ok()) {
    return absl::Status(
        parsed_roots.status().code(),
        absl::StrCat("Failed to parse root certificates as PEM: ",
                     parsed_roots.status().message()));
  }
  for (X509* x509 : *parsed_roots) {
    X509_free(x509);
  }
  return absl::OkStatus();
}

absl::Status ValidatePemKeyCertPair(absl::string_view cert_chain,
                                    absl::string_view private_key) {
  if (cert_chain.empty() && private_key.empty()) return absl::OkStatus();
  // Check that the cert chain consists of valid PEM blocks.
  absl::StatusOr<std::vector<X509*>> parsed_certs =
      ParsePemCertificateChain(cert_chain);
  if (!parsed_certs.ok()) {
    return absl::Status(
        parsed_certs.status().code(),
        absl::StrCat("Failed to parse certificate chain as PEM: ",
                     parsed_certs.status().message()));
  }
  for (X509* x509 : *parsed_certs) {
    X509_free(x509);
  }
  // Check that the private key consists of valid PEM blocks.
  absl::StatusOr<EVP_PKEY*> parsed_private_key =
      ParsePemPrivateKey(private_key);
  if (!parsed_private_key.ok()) {
    return absl::Status(parsed_private_key.status().code(),
                        absl::StrCat("Failed to parse private key as PEM: ",
                                     parsed_private_key.status().message()));
  }
  EVP_PKEY_free(*parsed_private_key);
  return absl::OkStatus();
}

}  // namespace

StaticDataCertificateProvider::StaticDataCertificateProvider(
    std::string root_certificate, PemKeyCertPairList pem_key_cert_pairs)
    : distributor_(MakeRefCounted<grpc_tls_certificate_distributor>()),
      root_certificate_(std::move(root_certificate)),
      pem_key_cert_pairs_(std::move(pem_key_cert_pairs)) {
  distributor_->SetWatchStatusCallback([this](std::string cert_name,
                                              bool root_being_watched,
                                              bool identity_being_watched) {
    MutexLock lock(&mu_);
    std::optional<std::string> root_certificate;
    std::optional<PemKeyCertPairList> pem_key_cert_pairs;
    StaticDataCertificateProvider::WatcherInfo& info = watcher_info_[cert_name];
    if (!info.root_being_watched && root_being_watched &&
        !root_certificate_.empty()) {
      root_certificate = root_certificate_;
    }
    info.root_being_watched = root_being_watched;
    if (!info.identity_being_watched && identity_being_watched &&
        !pem_key_cert_pairs_.empty()) {
      pem_key_cert_pairs = pem_key_cert_pairs_;
    }
    info.identity_being_watched = identity_being_watched;
    if (!info.root_being_watched && !info.identity_being_watched) {
      watcher_info_.erase(cert_name);
    }
    const bool root_has_update = root_certificate.has_value();
    const bool identity_has_update = pem_key_cert_pairs.has_value();
    if (root_has_update || identity_has_update) {
      distributor_->SetKeyMaterials(cert_name, std::move(root_certificate),
                                    std::move(pem_key_cert_pairs));
    }
    grpc_error_handle root_cert_error;
    grpc_error_handle identity_cert_error;
    if (root_being_watched && !root_has_update) {
      root_cert_error =
          GRPC_ERROR_CREATE("Unable to get latest root certificates.");
    }
    if (identity_being_watched && !identity_has_update) {
      identity_cert_error =
          GRPC_ERROR_CREATE("Unable to get latest identity certificates.");
    }
    if (!root_cert_error.ok() || !identity_cert_error.ok()) {
      distributor_->SetErrorForCert(cert_name, root_cert_error,
                                    identity_cert_error);
    }
  });
}

StaticDataCertificateProvider::~StaticDataCertificateProvider() {
  // Reset distributor's callback to make sure the callback won't be invoked
  // again after this object(provider) is destroyed.
  distributor_->SetWatchStatusCallback(nullptr);
}

UniqueTypeName StaticDataCertificateProvider::type() const {
  static UniqueTypeName::Factory kFactory("StaticData");
  return kFactory.Create();
}

absl::Status StaticDataCertificateProvider::ValidateCredentials() const {
  absl::Status status = ValidateRootCertificates(root_certificate_);
  if (!status.ok()) {
    return status;
  }
  for (const PemKeyCertPair& pair : pem_key_cert_pairs_) {
    absl::Status status =
        ValidatePemKeyCertPair(pair.cert_chain(), pair.private_key());
    if (!status.ok()) {
      return status;
    }
  }
  return absl::OkStatus();
}

namespace {

gpr_timespec TimeoutSecondsToDeadline(int64_t seconds) {
  return gpr_time_add(gpr_now(GPR_CLOCK_MONOTONIC),
                      gpr_time_from_seconds(seconds, GPR_TIMESPAN));
}

}  // namespace

static constexpr int64_t kMinimumFileWatcherRefreshIntervalSeconds = 1;

FileWatcherCertificateProvider::FileWatcherCertificateProvider(
    std::string private_key_path, std::string identity_certificate_path,
    std::string root_cert_path, int64_t refresh_interval_sec)
    : private_key_path_(std::move(private_key_path)),
      identity_certificate_path_(std::move(identity_certificate_path)),
      root_cert_path_(std::move(root_cert_path)),
      refresh_interval_sec_(refresh_interval_sec),
      distributor_(MakeRefCounted<grpc_tls_certificate_distributor>()) {
  if (refresh_interval_sec_ < kMinimumFileWatcherRefreshIntervalSeconds) {
    VLOG(2) << "FileWatcherCertificateProvider refresh_interval_sec_ set to "
               "value less than minimum. Overriding configured value to "
               "minimum.";
    refresh_interval_sec_ = kMinimumFileWatcherRefreshIntervalSeconds;
  }
  // Private key and identity cert files must be both set or both unset.
  CHECK(private_key_path_.empty() == identity_certificate_path_.empty());
  // Must be watching either root or identity certs.
  CHECK(!private_key_path_.empty() || !root_cert_path_.empty());
  gpr_event_init(&shutdown_event_);
  ForceUpdate();
  auto thread_lambda = [](void* arg) {
    FileWatcherCertificateProvider* provider =
        static_cast<FileWatcherCertificateProvider*>(arg);
    CHECK_NE(provider, nullptr);
    while (true) {
      void* value = gpr_event_wait(
          &provider->shutdown_event_,
          TimeoutSecondsToDeadline(provider->refresh_interval_sec_));
      if (value != nullptr) {
        return;
      };
      provider->ForceUpdate();
    }
  };
  refresh_thread_ = Thread("FileWatcherCertificateProvider_refreshing_thread",
                           thread_lambda, this);
  refresh_thread_.Start();
  distributor_->SetWatchStatusCallback([this](std::string cert_name,
                                              bool root_being_watched,
                                              bool identity_being_watched) {
    MutexLock lock(&mu_);
    std::optional<std::string> root_certificate;
    std::optional<PemKeyCertPairList> pem_key_cert_pairs;
    FileWatcherCertificateProvider::WatcherInfo& info =
        watcher_info_[cert_name];
    if (!info.root_being_watched && root_being_watched &&
        !root_certificate_.empty()) {
      root_certificate = root_certificate_;
    }
    info.root_being_watched = root_being_watched;
    if (!info.identity_being_watched && identity_being_watched &&
        !pem_key_cert_pairs_.empty()) {
      pem_key_cert_pairs = pem_key_cert_pairs_;
    }
    info.identity_being_watched = identity_being_watched;
    if (!info.root_being_watched && !info.identity_being_watched) {
      watcher_info_.erase(cert_name);
    }
    ExecCtx exec_ctx;
    if (root_certificate.has_value() || pem_key_cert_pairs.has_value()) {
      distributor_->SetKeyMaterials(cert_name, root_certificate,
                                    pem_key_cert_pairs);
    }
    grpc_error_handle root_cert_error;
    grpc_error_handle identity_cert_error;
    if (root_being_watched && !root_certificate.has_value()) {
      root_cert_error =
          GRPC_ERROR_CREATE("Unable to get latest root certificates.");
    }
    if (identity_being_watched && !pem_key_cert_pairs.has_value()) {
      identity_cert_error =
          GRPC_ERROR_CREATE("Unable to get latest identity certificates.");
    }
    if (!root_cert_error.ok() || !identity_cert_error.ok()) {
      distributor_->SetErrorForCert(cert_name, root_cert_error,
                                    identity_cert_error);
    }
  });
}

FileWatcherCertificateProvider::~FileWatcherCertificateProvider() {
  // Reset distributor's callback to make sure the callback won't be invoked
  // again after this object(provider) is destroyed.
  distributor_->SetWatchStatusCallback(nullptr);
  gpr_event_set(&shutdown_event_, reinterpret_cast<void*>(1));
  refresh_thread_.Join();
}

UniqueTypeName FileWatcherCertificateProvider::type() const {
  static UniqueTypeName::Factory kFactory("FileWatcher");
  return kFactory.Create();
}

absl::Status FileWatcherCertificateProvider::ValidateCredentials() const {
  MutexLock lock(&mu_);
  absl::Status status = ValidateRootCertificates(root_certificate_);
  if (!status.ok()) {
    return status;
  }
  for (const PemKeyCertPair& pair : pem_key_cert_pairs_) {
    absl::Status status =
        ValidatePemKeyCertPair(pair.cert_chain(), pair.private_key());
    if (!status.ok()) {
      return status;
    }
  }
  return absl::OkStatus();
}

void FileWatcherCertificateProvider::ForceUpdate() {
  std::optional<std::string> root_certificate;
  std::optional<PemKeyCertPairList> pem_key_cert_pairs;
  if (!root_cert_path_.empty()) {
    root_certificate = ReadRootCertificatesFromFile(root_cert_path_);
  }
  if (!private_key_path_.empty()) {
    pem_key_cert_pairs = ReadIdentityKeyCertPairFromFiles(
        private_key_path_, identity_certificate_path_);
  }
  MutexLock lock(&mu_);
  const bool root_cert_changed =
      (!root_certificate.has_value() && !root_certificate_.empty()) ||
      (root_certificate.has_value() && root_certificate_ != *root_certificate);
  if (root_cert_changed) {
    if (root_certificate.has_value()) {
      root_certificate_ = std::move(*root_certificate);
    } else {
      root_certificate_ = "";
    }
  }
  const bool identity_cert_changed =
      (!pem_key_cert_pairs.has_value() && !pem_key_cert_pairs_.empty()) ||
      (pem_key_cert_pairs.has_value() &&
       pem_key_cert_pairs_ != *pem_key_cert_pairs);
  if (identity_cert_changed) {
    if (pem_key_cert_pairs.has_value()) {
      pem_key_cert_pairs_ = std::move(*pem_key_cert_pairs);
    } else {
      pem_key_cert_pairs_ = {};
    }
  }
  if (root_cert_changed || identity_cert_changed) {
    ExecCtx exec_ctx;
    grpc_error_handle root_cert_error =
        GRPC_ERROR_CREATE("Unable to get latest root certificates.");
    grpc_error_handle identity_cert_error =
        GRPC_ERROR_CREATE("Unable to get latest identity certificates.");
    for (const auto& p : watcher_info_) {
      const std::string& cert_name = p.first;
      const WatcherInfo& info = p.second;
      std::optional<std::string> root_to_report;
      std::optional<PemKeyCertPairList> identity_to_report;
      // Set key materials to the distributor if their contents changed.
      if (info.root_being_watched && !root_certificate_.empty() &&
          root_cert_changed) {
        root_to_report = root_certificate_;
      }
      if (info.identity_being_watched && !pem_key_cert_pairs_.empty() &&
          identity_cert_changed) {
        identity_to_report = pem_key_cert_pairs_;
      }
      if (root_to_report.has_value() || identity_to_report.has_value()) {
        distributor_->SetKeyMaterials(cert_name, std::move(root_to_report),
                                      std::move(identity_to_report));
      }
      // Report errors to the distributor if the contents are empty.
      const bool report_root_error =
          info.root_being_watched && root_certificate_.empty();
      const bool report_identity_error =
          info.identity_being_watched && pem_key_cert_pairs_.empty();
      if (report_root_error || report_identity_error) {
        distributor_->SetErrorForCert(
            cert_name, report_root_error ? root_cert_error : absl::OkStatus(),
            report_identity_error ? identity_cert_error : absl::OkStatus());
      }
    }
  }
}

std::optional<std::string>
FileWatcherCertificateProvider::ReadRootCertificatesFromFile(
    const std::string& root_cert_full_path) {
  // Read the root file.
  auto root_slice =
      LoadFile(root_cert_full_path, /*add_null_terminator=*/false);
  if (!root_slice.ok()) {
    LOG(ERROR) << "Reading file " << root_cert_full_path
               << " failed: " << root_slice.status();
    return std::nullopt;
  }
  return std::string(root_slice->as_string_view());
}

namespace {

// This helper function gets the last-modified time of |filename|. When failed,
// it logs the error and returns 0.
time_t GetModificationTime(const char* filename) {
  time_t ts = 0;
  (void)GetFileModificationTime(filename, &ts);
  return ts;
}

}  // namespace

std::optional<PemKeyCertPairList>
FileWatcherCertificateProvider::ReadIdentityKeyCertPairFromFiles(
    const std::string& private_key_path,
    const std::string& identity_certificate_path) {
  const int kNumRetryAttempts = 3;
  for (int i = 0; i < kNumRetryAttempts; ++i) {
    // TODO(ZhenLian): replace the timestamp approach with key-match approach
    //  once the latter is implemented.
    // Checking the last modification of identity files before reading.
    time_t identity_key_ts_before =
        GetModificationTime(private_key_path.c_str());
    if (identity_key_ts_before == 0) {
      LOG(ERROR) << "Failed to get the file's modification time of "
                 << private_key_path << ". Start retrying...";
      continue;
    }
    time_t identity_cert_ts_before =
        GetModificationTime(identity_certificate_path.c_str());
    if (identity_cert_ts_before == 0) {
      LOG(ERROR) << "Failed to get the file's modification time of "
                 << identity_certificate_path << ". Start retrying...";
      continue;
    }
    // Read the identity files.
    auto key_slice = LoadFile(private_key_path, /*add_null_terminator=*/false);
    if (!key_slice.ok()) {
      LOG(ERROR) << "Reading file " << private_key_path
                 << " failed: " << key_slice.status() << ". Start retrying...";
      continue;
    }
    auto cert_slice =
        LoadFile(identity_certificate_path, /*add_null_terminator=*/false);
    if (!cert_slice.ok()) {
      LOG(ERROR) << "Reading file " << identity_certificate_path
                 << " failed: " << cert_slice.status() << ". Start retrying...";
      continue;
    }
    std::string private_key(key_slice->as_string_view());
    std::string cert_chain(cert_slice->as_string_view());
    PemKeyCertPairList identity_pairs;
    identity_pairs.emplace_back(private_key, cert_chain);
    // Checking the last modification of identity files before reading.
    time_t identity_key_ts_after =
        GetModificationTime(private_key_path.c_str());
    if (identity_key_ts_before != identity_key_ts_after) {
      LOG(ERROR) << "Last modified time before and after reading "
                 << private_key_path << " is not the same. Start retrying...";
      continue;
    }
    time_t identity_cert_ts_after =
        GetModificationTime(identity_certificate_path.c_str());
    if (identity_cert_ts_before != identity_cert_ts_after) {
      LOG(ERROR) << "Last modified time before and after reading "
                 << identity_certificate_path
                 << " is not the same. Start retrying...";
      continue;
    }
    return identity_pairs;
  }
  LOG(ERROR) << "All retry attempts failed. Will try again after the next "
                "interval.";
  return std::nullopt;
}

int64_t FileWatcherCertificateProvider::TestOnlyGetRefreshIntervalSecond()
    const {
  return refresh_interval_sec_;
}

}  // namespace grpc_core

/// -- Wrapper APIs declared in grpc_security.h -- *

grpc_tls_certificate_provider* grpc_tls_certificate_provider_static_data_create(
    const char* root_certificate, grpc_tls_identity_pairs* pem_key_cert_pairs) {
  CHECK(root_certificate != nullptr || pem_key_cert_pairs != nullptr);
  grpc_core::ExecCtx exec_ctx;
  grpc_core::PemKeyCertPairList identity_pairs_core;
  if (pem_key_cert_pairs != nullptr) {
    identity_pairs_core = std::move(pem_key_cert_pairs->pem_key_cert_pairs);
    delete pem_key_cert_pairs;
  }
  std::string root_cert_core;
  if (root_certificate != nullptr) {
    root_cert_core = root_certificate;
  }
  return new grpc_core::StaticDataCertificateProvider(
      std::move(root_cert_core), std::move(identity_pairs_core));
}

grpc_tls_certificate_provider*
grpc_tls_certificate_provider_file_watcher_create(
    const char* private_key_path, const char* identity_certificate_path,
    const char* root_cert_path, unsigned int refresh_interval_sec) {
  grpc_core::ExecCtx exec_ctx;
  return new grpc_core::FileWatcherCertificateProvider(
      private_key_path == nullptr ? "" : private_key_path,
      identity_certificate_path == nullptr ? "" : identity_certificate_path,
      root_cert_path == nullptr ? "" : root_cert_path, refresh_interval_sec);
}

void grpc_tls_certificate_provider_release(
    grpc_tls_certificate_provider* provider) {
  GRPC_TRACE_LOG(api, INFO)
      << "grpc_tls_certificate_provider_release(provider=" << provider << ")";
  grpc_core::ExecCtx exec_ctx;
  if (provider != nullptr) provider->Unref();
}
