// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "chrome/browser/sync/retry_verifier.h"

#include <algorithm>

#include "base/logging.h"
#include "sync/engine/polling_constants.h"
#include "sync/sessions/session_state.h"

namespace browser_sync {

namespace {
// Given the current delay calculate the minimum and maximum wait times for
// the next retry.
DelayInfo CalculateDelay(int64 current_delay) {
  int64 backoff_s = std::max(static_cast<int64>(1), current_delay *
                             browser_sync::kBackoffRandomizationFactor);

  DelayInfo delay_info;
  delay_info.min_delay = backoff_s + (-1 * current_delay/
                             browser_sync::kBackoffRandomizationFactor);
  delay_info.max_delay = backoff_s + current_delay/2;

  delay_info.min_delay = std::max(static_cast<int64>(1),
      std::min(delay_info.min_delay, browser_sync::kMaxBackoffSeconds));

  delay_info.max_delay = std::max(static_cast<int64>(1),
      std::min(delay_info.max_delay, browser_sync::kMaxBackoffSeconds));

  return delay_info;
}

// Fills the table with the maximum and minimum values for each retry, upto
// |count| number of retries.
void FillDelayTable(DelayInfo* delay_table, int count) {
  DCHECK(count > 1);

  // We start off with the minimum value of 2 seconds.
  delay_table[0].min_delay = static_cast<int64>(2);
  delay_table[0].max_delay = static_cast<int64>(2);

  for (int i = 1 ; i < count ; ++i) {
    delay_table[i].min_delay = CalculateDelay(delay_table[i-1].min_delay).
                               min_delay;
    delay_table[i].max_delay = CalculateDelay(delay_table[i-1].max_delay).
                               max_delay;
  }
}
}  // namespace

// Verifies if the current retry is on time. Note that we dont use the
// maximum value of the retry range in verifying, only the minimum. Reason
// being there is no guarantee that the retry will be on the dot. However in
// practice it is on the dot. But making that assumption for all the platforms
// would make the test flaky. However we have the global timeout for the
// verification which would make sure all retries take place in a reasonable
// amount of time. The global timeout is defined in profile sync service
// harness as |kExponentialBackoffVerificationTimeoutMs|.
bool IsRetryOnTime(DelayInfo* delay_table, int retry_count,
                   const base::TimeDelta& time_elapsed) {
  DVLOG(1) << "Retry Count : " << retry_count
           << " Time elapsed : " << time_elapsed.InSeconds()
           << " Retry table min: " << delay_table[retry_count].min_delay
           << " Retry table max: " << delay_table[retry_count].max_delay;
  return ((time_elapsed.InSeconds() >= delay_table[retry_count].min_delay));
}

RetryVerifier::RetryVerifier() : retry_count_(0),
                                 success_(false),
                                 done_(false) {
  memset(&delay_table_, 0, sizeof(delay_table_));
}

RetryVerifier::~RetryVerifier() {
}

// Initializes the state for verification.
void RetryVerifier::Initialize(
    const browser_sync::sessions::SyncSessionSnapshot& snap) {
  retry_count_ = 0;
  last_sync_time_ = snap.sync_start_time;
  FillDelayTable(delay_table_, kMaxRetry);
  done_ = false;
  success_ = false;
}

void RetryVerifier::VerifyRetryInterval(
    const browser_sync::sessions::SyncSessionSnapshot& snap) {
  DCHECK(retry_count_ < kMaxRetry);
  if (retry_count_ == 0) {
    if (snap.sync_start_time != last_sync_time_) {
      retry_count_++;
      last_sync_time_ = snap.sync_start_time;
    }
    success_ = true;
    return;
  }

  // Check if the sync start time has changed. If so indicates a new sync
  // has taken place.
  if (snap.sync_start_time != last_sync_time_) {
    base::TimeDelta delta = snap.sync_start_time - last_sync_time_;
    success_ = IsRetryOnTime(delay_table_,retry_count_ -1, delta);
    last_sync_time_ = snap.sync_start_time;
    ++retry_count_;
    done_ = (retry_count_ >= kMaxRetry);
    return;
  }
}
}  // namespace browser_sync