/*
 *
 * Copyright 2016 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/lib/transport/bdp_estimator.h"

#include <inttypes.h>
#include <stdlib.h>

#include <grpc/support/log.h>
#include <grpc/support/useful.h>

grpc_tracer_flag grpc_bdp_estimator_trace =
    GRPC_TRACER_INITIALIZER(false, "bdp_estimator");

void grpc_bdp_estimator_init(grpc_bdp_estimator *estimator, const char *name) {
  estimator->estimate = 65536;
  estimator->ping_state = GRPC_BDP_PING_UNSCHEDULED;
  estimator->ping_start_time = gpr_time_0(GPR_CLOCK_MONOTONIC);
  estimator->next_ping_scheduled = 0;
  estimator->name = name;
  estimator->bw_est = 0;
  estimator->inter_ping_delay = 100.0;  // start at 100ms
  estimator->stable_estimate_count = 0;
}

bool grpc_bdp_estimator_get_estimate(const grpc_bdp_estimator *estimator,
                                     int64_t *estimate) {
  *estimate = estimator->estimate;
  return true;
}

bool grpc_bdp_estimator_get_bw(const grpc_bdp_estimator *estimator,
                               double *bw) {
  *bw = estimator->bw_est;
  return true;
}

void grpc_bdp_estimator_add_incoming_bytes(grpc_bdp_estimator *estimator,
                                           int64_t num_bytes) {
  estimator->accumulator += num_bytes;
}

bool grpc_bdp_estimator_need_ping(grpc_exec_ctx *exec_ctx,
                                  const grpc_bdp_estimator *estimator) {
  switch (estimator->ping_state) {
    case GRPC_BDP_PING_UNSCHEDULED:
      return grpc_exec_ctx_now(exec_ctx) >= estimator->next_ping_scheduled;
    case GRPC_BDP_PING_SCHEDULED:
      return false;
    case GRPC_BDP_PING_STARTED:
      return false;
  }
  GPR_UNREACHABLE_CODE(return false);
}

void grpc_bdp_estimator_schedule_ping(grpc_bdp_estimator *estimator) {
  if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
    gpr_log(GPR_DEBUG, "bdp[%s]:sched acc=%" PRId64 " est=%" PRId64,
            estimator->name, estimator->accumulator, estimator->estimate);
  }
  GPR_ASSERT(estimator->ping_state == GRPC_BDP_PING_UNSCHEDULED);
  estimator->ping_state = GRPC_BDP_PING_SCHEDULED;
  estimator->accumulator = 0;
}

void grpc_bdp_estimator_start_ping(grpc_bdp_estimator *estimator) {
  if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
    gpr_log(GPR_DEBUG, "bdp[%s]:start acc=%" PRId64 " est=%" PRId64,
            estimator->name, estimator->accumulator, estimator->estimate);
  }
  GPR_ASSERT(estimator->ping_state == GRPC_BDP_PING_SCHEDULED);
  estimator->ping_state = GRPC_BDP_PING_STARTED;
  estimator->accumulator = 0;
  estimator->ping_start_time = gpr_now(GPR_CLOCK_MONOTONIC);
}

void grpc_bdp_estimator_complete_ping(grpc_exec_ctx *exec_ctx,
                                      grpc_bdp_estimator *estimator) {
  gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
  gpr_timespec dt_ts = gpr_time_sub(now, estimator->ping_start_time);
  double dt = (double)dt_ts.tv_sec + 1e-9 * (double)dt_ts.tv_nsec;
  double bw = dt > 0 ? ((double)estimator->accumulator / dt) : 0;
  int start_inter_ping_delay = estimator->inter_ping_delay;
  if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
    gpr_log(GPR_DEBUG, "bdp[%s]:complete acc=%" PRId64 " est=%" PRId64
                       " dt=%lf bw=%lfMbs bw_est=%lfMbs",
            estimator->name, estimator->accumulator, estimator->estimate, dt,
            bw / 125000.0, estimator->bw_est / 125000.0);
  }
  GPR_ASSERT(estimator->ping_state == GRPC_BDP_PING_STARTED);
  if (estimator->accumulator > 2 * estimator->estimate / 3 &&
      bw > estimator->bw_est) {
    estimator->estimate =
        GPR_MAX(estimator->accumulator, estimator->estimate * 2);
    estimator->bw_est = bw;
    if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
      gpr_log(GPR_DEBUG, "bdp[%s]: estimate increased to %" PRId64,
              estimator->name, estimator->estimate);
    }
    estimator->inter_ping_delay /= 2;  // if the ping estimate changes,
                                       // exponentially get faster at probing
  } else if (estimator->inter_ping_delay < 10000) {
    estimator->stable_estimate_count++;
    if (estimator->stable_estimate_count >= 2) {
      estimator->inter_ping_delay +=
          100 +
          (int)(rand() * 100.0 / RAND_MAX);  // if the ping estimate is steady,
                                             // slowly ramp down the probe time
    }
  }
  if (start_inter_ping_delay != estimator->inter_ping_delay) {
    estimator->stable_estimate_count = 0;
    if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
      gpr_log(GPR_DEBUG, "bdp[%s]:update_inter_time to %dms", estimator->name,
              estimator->inter_ping_delay);
    }
  }
  estimator->ping_state = GRPC_BDP_PING_UNSCHEDULED;
  estimator->accumulator = 0;
  estimator->next_ping_scheduled =
      grpc_exec_ctx_now(exec_ctx) + estimator->inter_ping_delay;
}