/*
 * Copyright 2022 Google LLC
 *
 * 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.
 */
package com.google.android.libraries.mobiledatadownload.internal.logging;

import static com.google.android.libraries.mobiledatadownload.internal.MddConstants.SPLIT_CHAR;

import static java.util.concurrent.TimeUnit.MILLISECONDS;

import android.content.Context;
import android.content.SharedPreferences;

import com.google.android.libraries.mobiledatadownload.TimeSource;
import com.google.android.libraries.mobiledatadownload.internal.util.FileGroupsMetadataUtil;
import com.google.android.libraries.mobiledatadownload.internal.util.FileGroupsMetadataUtil.GroupKeyDeserializationException;
import com.google.android.libraries.mobiledatadownload.internal.util.SharedPreferencesUtil;
import com.google.android.libraries.mobiledatadownload.tracing.PropagatedExecutionSequencer;
import com.google.common.base.Optional;
import com.google.common.base.Splitter;
import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.common.primitives.Ints;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.mobiledatadownload.internal.MetadataProto.FileGroupLoggingState;
import com.google.mobiledatadownload.internal.MetadataProto.GroupKey;
import com.google.mobiledatadownload.internal.MetadataProto.SamplingInfo;
import com.google.protobuf.Timestamp;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.HashSet;
import java.util.List;
import java.util.Random;
import java.util.Set;
import java.util.TimeZone;
import java.util.concurrent.Executor;

/** LoggingStateStore that uses SharedPreferences for storage. */
public final class SharedPreferencesLoggingState implements LoggingStateStore {

    private static final String SHARED_PREFS_NAME = "LoggingState";

    private static final String LAST_MAINTENANCE_RUN_SECS_KEY = "last_maintenance_secs";

    private static final String SALT_KEY = "stable_log_sampling_salt";
    private static final String SALT_TIMESTAMP_MILLIS_KEY =
            "log_sampling_salt_set_timestamp_millis";

    private final Supplier<SharedPreferences> sharedPrefs;
    private final Executor backgroundExecutor;
    private final TimeSource timeSource;
    private final Random random;

    // Serialize access to SharedPref keys to avoid clobbering.
    private final PropagatedExecutionSequencer futureSerializer =
            PropagatedExecutionSequencer.create();

    /**
     * Constructs a new instance.
     *
     * @param sharedPrefs may be called multiple times, so memoization is recommended. The returned
     *                    instance must be exclusive to {@link SharedPreferencesLoggingState} since
     *                    {@link #clear}
     *                    may clear the data at any time.
     */
    public static SharedPreferencesLoggingState create(
            Supplier<SharedPreferences> sharedPrefs,
            TimeSource timeSource,
            Executor backgroundExecutor,
            Random random) {
        return new SharedPreferencesLoggingState(sharedPrefs, timeSource, backgroundExecutor,
                random);
    }

    /** Constructs a new instance. */
    public static SharedPreferencesLoggingState createFromContext(
            Context context,
            Optional<String> instanceIdOptional,
            TimeSource timeSource,
            Executor backgroundExecutor,
            Random random) {
        // Avoid calling getSharedPreferences on the main thread.
        Supplier<SharedPreferences> sharedPrefs =
                Suppliers.memoize(
                        () ->
                                SharedPreferencesUtil.getSharedPreferences(
                                        context, SHARED_PREFS_NAME, instanceIdOptional));
        return new SharedPreferencesLoggingState(sharedPrefs, timeSource, backgroundExecutor,
                random);
    }

    private SharedPreferencesLoggingState(
            Supplier<SharedPreferences> sharedPrefs,
            TimeSource timeSource,
            Executor backgroundExecutor,
            Random random) {
        this.sharedPrefs = sharedPrefs;
        this.timeSource = timeSource;
        this.backgroundExecutor = backgroundExecutor;
        this.random = random;
    }

    /** Data fields for each Entry persisted in SharedPreferences. */
    private enum Key {
        CELLULAR_USAGE("cu"),
        WIFI_USAGE("wu");

        final String sharedPrefsSuffix;

        Key(String sharedPrefsSuffix) {
            this.sharedPrefsSuffix = sharedPrefsSuffix;
        }
    }

    /** Bridge between FileGroupLoggingState and its SharedPreferences representation. */
    private static final class Entry {

        final GroupKey groupKey;
        final long buildId;
        final int fileGroupVersionNumber;

        /** Prefix used in SharedPreference keys. */
        final String spKeyPrefix;

        static Entry fromLoggingState(FileGroupLoggingState loggingState) {
            return new Entry(
                    /* groupKey= */ loggingState.getGroupKey(),
                    /* buildId= */ loggingState.getBuildId(),
                    /* fileGroupVersionNumber= */ loggingState.getFileGroupVersionNumber());
        }

        /**
         * @throws IllegalArgumentException if the key can't be parsed
         */
        static Entry fromSpKey(String spKey) {
            List<String> parts = Splitter.on(SPLIT_CHAR).splitToList(spKey);
            try {
                return new Entry(
                        /* groupKey= */ FileGroupsMetadataUtil.deserializeGroupKey(parts.get(0)),
                        /* buildId= */ Long.parseLong(parts.get(1)),
                        /* fileGroupVersionNumber= */ Integer.parseInt(parts.get(2)));
            } catch (GroupKeyDeserializationException | ArrayIndexOutOfBoundsException e) {
                throw new IllegalArgumentException("Failed to parse SharedPrefs key: " + spKey, e);
            }
        }

        private Entry(GroupKey groupKey, long buildId, int fileGroupVersionNumber) {
            this.groupKey = groupKey;
            this.buildId = buildId;
            this.fileGroupVersionNumber = fileGroupVersionNumber;
            this.spKeyPrefix =
                    FileGroupsMetadataUtil.getSerializedGroupKey(groupKey)
                            + SPLIT_CHAR
                            + buildId
                            + SPLIT_CHAR
                            + fileGroupVersionNumber;
        }

        String getSharedPrefsKey(Key key) {
            return spKeyPrefix + SPLIT_CHAR + key.sharedPrefsSuffix;
        }
    }

    @Override
    public ListenableFuture<Optional<Integer>> getAndResetDaysSinceLastMaintenance() {
        return futureSerializer.submit(
                () -> {
                    long currentTimestamp = timeSource.currentTimeMillis();

                    Optional<Integer> daysSinceLastMaintenance;
                    boolean hasEverDoneMaintenance =
                            sharedPrefs.get().contains(LAST_MAINTENANCE_RUN_SECS_KEY);
                    if (hasEverDoneMaintenance) {
                        long persistedTimestamp = sharedPrefs.get().getLong(
                                LAST_MAINTENANCE_RUN_SECS_KEY, 0);
                        long currentStartOfDay = truncateTimestampToStartOfDay(currentTimestamp);
                        long previousStartOfDay = truncateTimestampToStartOfDay(persistedTimestamp);
                        // Note: ignore MillisTo_Days java optional suggestion because Duration
                        // is api
                        // 26+.
                        daysSinceLastMaintenance =
                                Optional.of(
                                        Ints.saturatedCast(
                                                MILLISECONDS.toDays(
                                                        currentStartOfDay - previousStartOfDay)));
                    } else {
                        daysSinceLastMaintenance = Optional.absent();
                    }

                    SharedPreferences.Editor editor = sharedPrefs.get().edit();
                    editor.putLong(LAST_MAINTENANCE_RUN_SECS_KEY, currentTimestamp);
                    commitOrThrow(editor);

                    return daysSinceLastMaintenance;
                },
                backgroundExecutor);
    }

    @Override
    public ListenableFuture<Void> incrementDataUsage(FileGroupLoggingState dataUsageIncrements) {
        return futureSerializer.submit(
                () -> {
                    Entry entry = Entry.fromLoggingState(dataUsageIncrements);

                    long currentCellarUsage =
                            sharedPrefs.get().getLong(entry.getSharedPrefsKey(Key.CELLULAR_USAGE),
                                    0);
                    long currentWifiUsage =
                            sharedPrefs.get().getLong(entry.getSharedPrefsKey(Key.WIFI_USAGE), 0);
                    long updatedCellarUsage =
                            currentCellarUsage + dataUsageIncrements.getCellularUsage();
                    long updatedWifiUsage = currentWifiUsage + dataUsageIncrements.getWifiUsage();

                    SharedPreferences.Editor editor = sharedPrefs.get().edit();
                    editor.putLong(entry.getSharedPrefsKey(Key.CELLULAR_USAGE), updatedCellarUsage);
                    editor.putLong(entry.getSharedPrefsKey(Key.WIFI_USAGE), updatedWifiUsage);

                    return commitOrThrow(editor);
                },
                backgroundExecutor);
    }

    @Override
    public ListenableFuture<List<FileGroupLoggingState>> getAndResetAllDataUsage() {
        return futureSerializer.submit(
                () -> {
                    List<FileGroupLoggingState> allLoggingStates = new ArrayList<>();
                    Set<String> allLoggingStateKeys = new HashSet<>();
                    SharedPreferences.Editor editor = sharedPrefs.get().edit();

                    for (String key : sharedPrefs.get().getAll().keySet()) {
                        Entry entry;
                        try {
                            entry = Entry.fromSpKey(key);
                        } catch (IllegalArgumentException e) {
                            continue; // This isn't a LoggingState entry
                        }
                        if (allLoggingStateKeys.contains(entry.spKeyPrefix)) {
                            continue;
                        }
                        allLoggingStateKeys.add(entry.spKeyPrefix);

                        FileGroupLoggingState loggingState =
                                FileGroupLoggingState.newBuilder()
                                        .setGroupKey(entry.groupKey)
                                        .setBuildId(entry.buildId)
                                        .setFileGroupVersionNumber(entry.fileGroupVersionNumber)
                                        .setCellularUsage(
                                                sharedPrefs.get().getLong(
                                                        entry.getSharedPrefsKey(Key.CELLULAR_USAGE),
                                                        0))
                                        .setWifiUsage(
                                                sharedPrefs.get().getLong(
                                                        entry.getSharedPrefsKey(Key.WIFI_USAGE), 0))
                                        .build();
                        allLoggingStates.add(loggingState);

                        editor.remove(entry.getSharedPrefsKey(Key.CELLULAR_USAGE));
                        editor.remove(entry.getSharedPrefsKey(Key.WIFI_USAGE));
                    }
                    commitOrThrow(editor);

                    return allLoggingStates;
                },
                backgroundExecutor);
    }

    @Override
    public ListenableFuture<Void> clear() {
        return futureSerializer.submit(
                () -> {
                    SharedPreferences.Editor editor = sharedPrefs.get().edit();
                    editor.clear();
                    return commitOrThrow(editor);
                },
                backgroundExecutor);
    }

    @Override
    public ListenableFuture<SamplingInfo> getStableSamplingInfo() {
        return futureSerializer.submit(
                () -> {
                    long salt;
                    long persistedTimestampMillis;

                    boolean hasCreatedSalt = sharedPrefs.get().contains(SALT_KEY);
                    if (hasCreatedSalt) {
                        salt = sharedPrefs.get().getLong(SALT_KEY, 0);
                        persistedTimestampMillis = sharedPrefs.get().getLong(
                                SALT_TIMESTAMP_MILLIS_KEY, 0);
                    } else {
                        salt = random.nextLong();
                        persistedTimestampMillis = timeSource.currentTimeMillis();

                        SharedPreferences.Editor editor = sharedPrefs.get().edit();
                        editor.putLong(SALT_KEY, salt);
                        editor.putLong(SALT_TIMESTAMP_MILLIS_KEY, persistedTimestampMillis);
                        commitOrThrow(editor);
                    }

                    Timestamp timestamp = TimestampsUtil.fromMillis(persistedTimestampMillis);
                    return SamplingInfo.newBuilder()
                            .setStableLogSamplingSalt(salt)
                            .setLogSamplingSaltSetTimestamp(timestamp)
                            .build();
                },
                backgroundExecutor);
    }

    // Use UTC time zone here so we don't have to worry about time zone change or daylight savings.
    private static final TimeZone UTC_TIMEZONE = TimeZone.getTimeZone("UTC");

    // TODO(b/237533403): extract as shareable code with ProtoDataStoreLoggingState
    private static long truncateTimestampToStartOfDay(long timestampMillis) {
        // We use the regular java.util.Calendar classes here since neither Joda time nor java.time is
        // supported across all client apps.
        Calendar cal = new GregorianCalendar(UTC_TIMEZONE);
        cal.setTimeInMillis(timestampMillis);
        cal.set(Calendar.HOUR_OF_DAY, 0);
        cal.set(Calendar.MINUTE, 0);
        cal.set(Calendar.SECOND, 0);
        cal.set(Calendar.MILLISECOND, 0);
        return cal.getTimeInMillis();
    }

    /** Calls {@code editor.commit()} and returns void, or throws IOException if the commit failed. */
    private static Void commitOrThrow(SharedPreferences.Editor editor) throws IOException {
        if (!editor.commit()) {
            throw new IOException("Failed to commit");
        }
        return null;
    }
}