power/stats: Add default implementation

Bug: 181592995
Test: atest VtsHalPowerStatsTargetTest
Change-Id: I87ea4974f857ebd126b80a45c7d7403307bceb03
diff --git a/power/stats/aidl/default/FakeEnergyConsumer.h b/power/stats/aidl/default/FakeEnergyConsumer.h
new file mode 100644
index 0000000..f41aa6e
--- /dev/null
+++ b/power/stats/aidl/default/FakeEnergyConsumer.h
@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <PowerStats.h>
+
+#include <android-base/chrono_utils.h>
+
+#include <chrono>
+#include <random>
+
+namespace aidl {
+namespace android {
+namespace hardware {
+namespace power {
+namespace stats {
+
+class FakeEnergyConsumer : public PowerStats::IEnergyConsumer {
+  public:
+    FakeEnergyConsumer(EnergyConsumerType type, std::string name) : mType(type), mName(name) {
+        mResult.timestampMs = 0;
+        mResult.energyUWs = 0;
+        mResult.attribution = {};
+    }
+
+    ~FakeEnergyConsumer() = default;
+
+    std::string getName() override { return mName; }
+
+    EnergyConsumerType getType() override { return mType; }
+
+    std::optional<EnergyConsumerResult> getEnergyConsumed() override {
+        mFakeEnergyConsumerResult.update(&mResult);
+        return mResult;
+    }
+
+  private:
+    class FakeEnergyConsumerResult {
+      public:
+        FakeEnergyConsumerResult() : mDistribution(1, 100) {}
+        void update(EnergyConsumerResult* result) {
+            // generates number in the range 1..100
+            auto randNum = std::bind(mDistribution, mGenerator);
+
+            // Get current time since boot in milliseconds
+            uint64_t now = std::chrono::time_point_cast<std::chrono::milliseconds>(
+                                   ::android::base::boot_clock::now())
+                                   .time_since_epoch()
+                                   .count();
+            result->timestampMs = now;
+            result->energyUWs += randNum() * 100;
+        }
+
+      private:
+        std::default_random_engine mGenerator;
+        std::uniform_int_distribution<int> mDistribution;
+    };
+
+    EnergyConsumerType mType;
+    std::string mName;
+    FakeEnergyConsumerResult mFakeEnergyConsumerResult;
+    EnergyConsumerResult mResult;
+};
+
+}  // namespace stats
+}  // namespace power
+}  // namespace hardware
+}  // namespace android
+}  // namespace aidl
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