// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "chrome/browser/performance_manager/mechanisms/page_discarder.h"

#include <utility>

#include "base/byte_size.h"
#include "base/memory/weak_ptr.h"
#include "base/metrics/histogram_functions.h"
#include "base/not_fatal_until.h"
#include "chrome/browser/performance_manager/public/user_tuning/user_tuning_utils.h"
#include "chrome/browser/resource_coordinator/lifecycle_unit_state.mojom.h"
#include "components/performance_manager/public/graph/page_node.h"
#include "content/public/browser/web_contents.h"
#include "content/public/common/content_features.h"
#include "third_party/abseil-cpp/absl/cleanup/cleanup.h"

#if BUILDFLAG(IS_ANDROID)
#include "chrome/browser/resource_coordinator/utils.h"
#else
#include "chrome/browser/resource_coordinator/tab_lifecycle_unit.h"
#include "chrome/browser/resource_coordinator/tab_lifecycle_unit_external.h"
#endif  // BUILDFLAG(IS_ANDROID)

namespace performance_manager::mechanism {
namespace {

// These values are persisted to logs. Entries should not be renumbered and
// numeric values should never be reused.
// LINT.IfChange(DiscardPageOnUIThreadOutcome)
enum class DiscardPageOnUIThreadOutcome {
  kSuccess = 0,
  kNoContents = 1,
  kDiscardTabFailure = 2,
  kNoLifecycleUnit = 3,
  kMaxValue = kNoLifecycleUnit
};
// LINT.ThenChange(/tools/metrics/histograms/metadata/tab/enums.xml:DiscardPageOnUIThreadOutcome)

}  // namespace

std::optional<base::ByteSize> PageDiscarder::DiscardPageNode(
    const PageNode* page_node,
    ::mojom::LifecycleUnitDiscardReason discard_reason) {
  base::WeakPtr<content::WebContents> contents = page_node->GetWebContents();

  std::optional<DiscardPageOnUIThreadOutcome> outcome;
  absl::Cleanup record_discard_outcome = [&]() {
    CHECK(outcome.has_value(), base::NotFatalUntil::M140);
    base::UmaHistogramEnumeration("Discarding.DiscardPageOnUIThreadOutcome",
                                  outcome.value());
  };

  CHECK(contents, base::NotFatalUntil::M140);
  if (!contents) {
    outcome = DiscardPageOnUIThreadOutcome::kNoContents;
    return std::nullopt;
  }

  base::ByteSize memory_footprint_estimate =
      user_tuning::GetDiscardedMemoryEstimateForPage(page_node);

#if BUILDFLAG(IS_ANDROID)
  CHECK(base::FeatureList::IsEnabled(features::kWebContentsDiscard));
  resource_coordinator::AttemptFastKillForDiscard(contents.get(),
                                                  discard_reason);
  contents->Discard(base::NullCallback());
#else
  auto* lifecycle_unit =
      resource_coordinator::TabLifecycleUnitSource::GetTabLifecycleUnitExternal(
          contents.get());
  if (!lifecycle_unit) {
    outcome = DiscardPageOnUIThreadOutcome::kNoLifecycleUnit;
    return std::nullopt;
  }

  if (!lifecycle_unit->DiscardTab(discard_reason,
                                  memory_footprint_estimate.InKiB())) {
    outcome = DiscardPageOnUIThreadOutcome::kDiscardTabFailure;
    return std::nullopt;
  }

#endif  // BUILDFLAG(IS_ANDROID)

  outcome = DiscardPageOnUIThreadOutcome::kSuccess;
  return memory_footprint_estimate;
}

}  // namespace performance_manager::mechanism