/*
 * Copyright (c) 2020, 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.
 */

#ifndef CPP_WATCHDOG_SERVER_SRC_UIDPROCSTATSCOLLECTOR_H_
#define CPP_WATCHDOG_SERVER_SRC_UIDPROCSTATSCOLLECTOR_H_

#include <android-base/result.h>
#include <android-base/stringprintf.h>
#include <gtest/gtest_prod.h>
#include <utils/Mutex.h>
#include <utils/RefBase.h>

#include <inttypes.h>
#include <stdint.h>

#include <string>
#include <unordered_map>
#include <vector>

namespace android {
namespace automotive {
namespace watchdog {

using ::android::base::StringPrintf;

#define PID_FOR_INIT 1

constexpr const char kProcDirPath[] = "/proc";
constexpr const char kStatFileFormat[] = "/%" PRIu32 "/stat";
constexpr const char kTaskDirFormat[] = "/%" PRIu32 "/task";
constexpr const char kStatusFileFormat[] = "/%" PRIu32 "/status";

// Per-process stats.
struct ProcessStats {
    std::string comm = "";
    uint64_t startTime = 0;  // Useful when identifying PID reuse
    uint64_t totalMajorFaults = 0;
    int totalTasksCount = 0;
    int ioBlockedTasksCount = 0;
    std::string toString() const;
};

// Per-UID stats.
struct UidProcStats {
    uint64_t totalMajorFaults = 0;
    int totalTasksCount = 0;
    int ioBlockedTasksCount = 0;
    std::unordered_map<pid_t, ProcessStats> processStatsByPid = {};
    std::string toString() const;
};

/**
 * Collector/parser for `/proc/[pid]/stat`, `/proc/[pid]/task/[tid]/stat` and /proc/[pid]/status`
 * files.
 */
class UidProcStatsCollectorInterface : public RefBase {
public:
    // Collects the per-uid stats from /proc directory.
    virtual android::base::Result<void> collect() = 0;
    // Returns the latest per-uid process stats.
    virtual const std::unordered_map<uid_t, UidProcStats> latestStats() const = 0;
    // Returns the delta of per-uid process stats since the last before collection.
    virtual const std::unordered_map<uid_t, UidProcStats> deltaStats() const = 0;
    // Returns true only when the /proc files for the init process are accessible.
    virtual bool enabled() const = 0;
    // Returns the /proc files common ancestor directory path.
    virtual const std::string dirPath() const = 0;
};

class UidProcStatsCollector final : public UidProcStatsCollectorInterface {
public:
    explicit UidProcStatsCollector(const std::string& path = kProcDirPath) :
          mLatestStats({}),
          mPath(path) {
        std::string pidStatPath = StringPrintf((mPath + kStatFileFormat).c_str(), PID_FOR_INIT);
        std::string tidStatPath = StringPrintf((mPath + kTaskDirFormat + kStatFileFormat).c_str(),
                                               PID_FOR_INIT, PID_FOR_INIT);
        std::string pidStatusPath = StringPrintf((mPath + kStatusFileFormat).c_str(), PID_FOR_INIT);

        mEnabled = !access(pidStatPath.c_str(), R_OK) && !access(tidStatPath.c_str(), R_OK) &&
                !access(pidStatusPath.c_str(), R_OK);
    }

    ~UidProcStatsCollector() {}

    android::base::Result<void> collect() override;

    const std::unordered_map<uid_t, UidProcStats> latestStats() const {
        Mutex::Autolock lock(mMutex);
        return mLatestStats;
    }

    const std::unordered_map<uid_t, UidProcStats> deltaStats() const {
        Mutex::Autolock lock(mMutex);
        return mDeltaStats;
    }

    bool enabled() const { return mEnabled; }

    const std::string dirPath() const { return mPath; }

private:
    android::base::Result<std::unordered_map<uid_t, UidProcStats>> readUidProcStatsLocked() const;

    /**
     * Reads the contents of the below files:
     * 1. Pid stat file at |mPath| + |kStatFileFormat|
     * 2. Aggregated per-process status at |mPath| + |kStatusFileFormat|
     * 3. Tid stat file at |mPath| + |kTaskDirFormat| + |kStatFileFormat|
     */
    android::base::Result<std::tuple<uid_t, ProcessStats>> readProcessStatsLocked(pid_t pid) const;

    // Makes sure only one collection is running at any given time.
    mutable Mutex mMutex;

    // Latest dump of per-UID stats.
    std::unordered_map<uid_t, UidProcStats> mLatestStats GUARDED_BY(mMutex);

    // Latest delta of per-uid stats.
    std::unordered_map<uid_t, UidProcStats> mDeltaStats GUARDED_BY(mMutex);

    /**
     * True if the below files are accessible:
     * 1. Pid stat file at |mPath| + |kTaskStatFileFormat|
     * 2. Tid stat file at |mPath| + |kTaskDirFormat| + |kStatFileFormat|
     * 3. Pid status file at |mPath| + |kStatusFileFormat|
     * Otherwise, set to false.
     */
    bool mEnabled;

    /**
     * Proc directory path. Default value is |kProcDirPath|.
     * Updated by tests to point to a different location when needed.
     */
    std::string mPath;

    FRIEND_TEST(IoPerfCollectionTest, TestValidProcPidContents);
    FRIEND_TEST(UidProcStatsCollectorTest, TestValidStatFiles);
    FRIEND_TEST(UidProcStatsCollectorTest, TestHandlesProcessTerminationBetweenScanningAndParsing);
    FRIEND_TEST(UidProcStatsCollectorTest, TestHandlesPidTidReuse);
};

}  // namespace watchdog
}  // namespace automotive
}  // namespace android

#endif  //  CPP_WATCHDOG_SERVER_SRC_UIDPROCSTATSCOLLECTOR_H_