/*
 * Copyright (C) 2018 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.
 */

package com.android.server.pm;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.apex.ApexInfo;
import android.apex.ApexInfoList;
import android.apex.ApexSessionInfo;
import android.content.Context;
import android.content.IIntentReceiver;
import android.content.IIntentSender;
import android.content.Intent;
import android.content.IntentSender;
import android.content.pm.PackageInfo;
import android.content.pm.PackageInstaller;
import android.content.pm.PackageInstaller.SessionInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageParser;
import android.content.pm.PackageParser.PackageParserException;
import android.content.pm.PackageParser.SigningDetails;
import android.content.pm.PackageParser.SigningDetails.SignatureSchemeVersion;
import android.content.pm.ParceledListSlice;
import android.content.rollback.IRollbackManager;
import android.os.Bundle;
import android.os.Handler;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;
import android.os.ParcelFileDescriptor;
import android.os.PowerManager;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.util.IntArray;
import android.util.Slog;
import android.util.SparseArray;
import android.util.apk.ApkSignatureVerifier;

import com.android.internal.annotations.GuardedBy;
import com.android.internal.os.BackgroundThread;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * This class handles staged install sessions, i.e. install sessions that require packages to
 * be installed only after a reboot.
 */
public class StagingManager {

    private static final String TAG = "StagingManager";

    private final PackageInstallerService mPi;
    private final ApexManager mApexManager;
    private final PowerManager mPowerManager;
    private final PreRebootVerificationHandler mPreRebootVerificationHandler;

    @GuardedBy("mStagedSessions")
    private final SparseArray<PackageInstallerSession> mStagedSessions = new SparseArray<>();

    StagingManager(PackageInstallerService pi, ApexManager am, Context context) {
        mPi = pi;
        mApexManager = am;
        mPowerManager = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
        mPreRebootVerificationHandler = new PreRebootVerificationHandler(
                BackgroundThread.get().getLooper());
    }

    private void updateStoredSession(@NonNull PackageInstallerSession sessionInfo) {
        synchronized (mStagedSessions) {
            PackageInstallerSession storedSession = mStagedSessions.get(sessionInfo.sessionId);
            // storedSession might be null if a call to abortSession was made before the session
            // is updated.
            if (storedSession != null) {
                mStagedSessions.put(sessionInfo.sessionId, sessionInfo);
            }
        }
    }

    ParceledListSlice<PackageInstaller.SessionInfo> getSessions() {
        final List<PackageInstaller.SessionInfo> result = new ArrayList<>();
        synchronized (mStagedSessions) {
            for (int i = 0; i < mStagedSessions.size(); i++) {
                result.add(mStagedSessions.valueAt(i).generateInfo(false));
            }
        }
        return new ParceledListSlice<>(result);
    }

    /**
     * Validates the signature used to sign the container of the new apex package
     *
     * @param newApexPkg The new apex package that is being installed
     * @throws PackageManagerException
     */
    private void validateApexSignature(PackageInfo newApexPkg)
            throws PackageManagerException {
        // Get signing details of the new package
        final String apexPath = newApexPkg.applicationInfo.sourceDir;
        final String packageName = newApexPkg.packageName;

        final SigningDetails newSigningDetails;
        try {
            newSigningDetails = ApkSignatureVerifier.verify(apexPath, SignatureSchemeVersion.JAR);
        } catch (PackageParserException e) {
            throw new PackageManagerException(SessionInfo.STAGED_SESSION_VERIFICATION_FAILED,
                    "Failed to parse APEX package " + apexPath, e);
        }

        // Get signing details of the existing package
        final PackageInfo existingApexPkg = mApexManager.getPackageInfo(packageName,
                ApexManager.MATCH_ACTIVE_PACKAGE);
        if (existingApexPkg == null) {
            // This should never happen, because submitSessionToApexService ensures that no new
            // apexes were installed.
            throw new IllegalStateException("Unknown apex package " + packageName);
        }

        final SigningDetails existingSigningDetails;
        try {
            existingSigningDetails = ApkSignatureVerifier.verify(
                existingApexPkg.applicationInfo.sourceDir, SignatureSchemeVersion.JAR);
        } catch (PackageParserException e) {
            throw new PackageManagerException(SessionInfo.STAGED_SESSION_VERIFICATION_FAILED,
                    "Failed to parse APEX package " + existingApexPkg.applicationInfo.sourceDir, e);
        }

        // Verify signing details for upgrade
        if (newSigningDetails.checkCapability(existingSigningDetails,
                SigningDetails.CertCapabilities.INSTALLED_DATA)
                || existingSigningDetails.checkCapability(newSigningDetails,
                SigningDetails.CertCapabilities.ROLLBACK)) {
            return;
        }

        throw new PackageManagerException(SessionInfo.STAGED_SESSION_VERIFICATION_FAILED,
                "APK-container signature of APEX package " + packageName + " with version "
                        + newApexPkg.versionCodeMajor + " and path " + apexPath + " is not"
                        + " compatible with the one currently installed on device");
    }

    private List<PackageInfo> submitSessionToApexService(
            @NonNull PackageInstallerSession session) throws PackageManagerException {
        final IntArray childSessionsIds = new IntArray();
        if (session.isMultiPackage()) {
            for (int id : session.getChildSessionIds()) {
                if (isApexSession(mStagedSessions.get(id))) {
                    childSessionsIds.add(id);
                }
            }
        }
        // submitStagedSession will throw a PackageManagerException if apexd verification fails,
        // which will be propagated to populate stagedSessionErrorMessage of this session.
        final ApexInfoList apexInfoList = mApexManager.submitStagedSession(session.sessionId,
                childSessionsIds.toArray());
        final List<PackageInfo> result = new ArrayList<>();
        for (ApexInfo apexInfo : apexInfoList.apexInfos) {
            final PackageInfo packageInfo;
            int flags = PackageManager.GET_META_DATA;
            PackageParser.Package pkg;
            try {
                File apexFile = new File(apexInfo.modulePath);
                PackageParser pp = new PackageParser();
                pkg = pp.parsePackage(apexFile, flags, false);
            } catch (PackageParserException e) {
                throw new PackageManagerException(SessionInfo.STAGED_SESSION_VERIFICATION_FAILED,
                        "Failed to parse APEX package " + apexInfo.modulePath, e);
            }
            packageInfo = PackageParser.generatePackageInfo(pkg, apexInfo, flags);
            final PackageInfo activePackage = mApexManager.getPackageInfo(packageInfo.packageName,
                    ApexManager.MATCH_ACTIVE_PACKAGE);
            if (activePackage == null) {
                Slog.w(TAG, "Attempting to install new APEX package " + packageInfo.packageName);
                throw new PackageManagerException(SessionInfo.STAGED_SESSION_VERIFICATION_FAILED,
                        "It is forbidden to install new APEX packages.");
            }
            checkRequiredVersionCode(session, activePackage);
            checkDowngrade(session, activePackage, packageInfo);
            result.add(packageInfo);
        }
        Slog.d(TAG, "Session " + session.sessionId + " has following APEX packages: ["
                + result.stream().map(p -> p.packageName).collect(Collectors.joining(",")) + "]");
        return result;
    }

    private void checkRequiredVersionCode(final PackageInstallerSession session,
            final PackageInfo activePackage) throws PackageManagerException {
        if (session.params.requiredInstalledVersionCode == PackageManager.VERSION_CODE_HIGHEST) {
            return;
        }
        final long activeVersion = activePackage.applicationInfo.longVersionCode;
        if (activeVersion != session.params.requiredInstalledVersionCode) {
            if (!mApexManager.abortActiveSession()) {
                Slog.e(TAG, "Failed to abort apex session " + session.sessionId);
            }
            throw new PackageManagerException(
                    SessionInfo.STAGED_SESSION_VERIFICATION_FAILED,
                    "Installed version of APEX package " + activePackage.packageName
                            + " does not match required. Active version: " + activeVersion
                            + " required: " + session.params.requiredInstalledVersionCode);
        }
    }

    private void checkDowngrade(final PackageInstallerSession session,
            final PackageInfo activePackage, final PackageInfo newPackage)
            throws PackageManagerException {
        final long activeVersion = activePackage.applicationInfo.longVersionCode;
        final long newVersionCode = newPackage.applicationInfo.longVersionCode;
        final boolean allowsDowngrade = PackageManagerServiceUtils.isDowngradePermitted(
                session.params.installFlags, activePackage.applicationInfo.flags);
        if (activeVersion > newVersionCode && !allowsDowngrade) {
            if (!mApexManager.abortActiveSession()) {
                Slog.e(TAG, "Failed to abort apex session " + session.sessionId);
            }
            throw new PackageManagerException(
                    SessionInfo.STAGED_SESSION_VERIFICATION_FAILED,
                    "Downgrade of APEX package " + newPackage.packageName
                            + " is not allowed. Active version: " + activeVersion
                            + " attempted: " + newVersionCode);
        }
    }

    private static boolean isApexSession(@NonNull PackageInstallerSession session) {
        return (session.params.installFlags & PackageManager.INSTALL_APEX) != 0;
    }

    private boolean sessionContains(@NonNull PackageInstallerSession session,
                                    Predicate<PackageInstallerSession> filter) {
        if (!session.isMultiPackage()) {
            return filter.test(session);
        }
        synchronized (mStagedSessions) {
            return !(Arrays.stream(session.getChildSessionIds())
                    // Retrieve cached sessions matching ids.
                    .mapToObj(i -> mStagedSessions.get(i))
                    // Filter only the ones containing APEX.
                    .filter(childSession -> filter.test(childSession))
                    .collect(Collectors.toList())
                    .isEmpty());
        }
    }

    private boolean sessionContainsApex(@NonNull PackageInstallerSession session) {
        return sessionContains(session, (s) -> isApexSession(s));
    }

    private boolean sessionContainsApk(@NonNull PackageInstallerSession session) {
        return sessionContains(session, (s) -> !isApexSession(s));
    }

    private void resumeSession(@NonNull PackageInstallerSession session) {
        Slog.d(TAG, "Resuming session " + session.sessionId);
        final boolean hasApex = sessionContainsApex(session);
        if (hasApex) {
            // Check with apexservice whether the apex packages have been activated.
            ApexSessionInfo apexSessionInfo = mApexManager.getStagedSessionInfo(session.sessionId);
            if (apexSessionInfo == null) {
                session.setStagedSessionFailed(SessionInfo.STAGED_SESSION_ACTIVATION_FAILED,
                        "apexd did not know anything about a staged session supposed to be"
                        + "activated");
                return;
            }
            if (isApexSessionFailed(apexSessionInfo)) {
                session.setStagedSessionFailed(SessionInfo.STAGED_SESSION_ACTIVATION_FAILED,
                        "APEX activation failed. Check logcat messages from apexd for "
                                + "more information.");
                return;
            }
            if (apexSessionInfo.isVerified) {
                // Session has been previously submitted to apexd, but didn't complete all the
                // pre-reboot verification, perhaps because the device rebooted in the meantime.
                // Greedily re-trigger the pre-reboot verification.
                Slog.d(TAG, "Found pending staged session " + session.sessionId + " still to be "
                        + "verified, resuming pre-reboot verification");
                mPreRebootVerificationHandler.startPreRebootVerification(session.sessionId);
                return;
            }
            if (!apexSessionInfo.isActivated && !apexSessionInfo.isSuccess) {
                // In all the remaining cases apexd will try to apply the session again at next
                // boot. Nothing to do here for now.
                Slog.w(TAG, "Staged session " + session.sessionId + " scheduled to be applied "
                        + "at boot didn't activate nor fail. This usually means that apexd will "
                        + "retry at next reboot.");
                return;
            }
            Slog.i(TAG, "APEX packages in session " + session.sessionId
                    + " were successfully activated. Proceeding with APK packages, if any");
        }
        // The APEX part of the session is activated, proceed with the installation of APKs.
        try {
            Slog.d(TAG, "Installing APK packages in session " + session.sessionId);
            installApksInSession(session);
        } catch (PackageManagerException e) {
            session.setStagedSessionFailed(e.error, e.getMessage());

            if (!hasApex) {
                return;
            }

            if (!mApexManager.abortActiveSession()) {
                Slog.e(TAG, "Failed to abort APEXd session");
            } else {
                Slog.e(TAG,
                        "Successfully aborted apexd session. Rebooting device in order to revert "
                                + "to the previous state of APEXd.");
                mPowerManager.reboot(null);
            }
            return;
        }

        Slog.d(TAG, "Marking session " + session.sessionId + " as applied");
        session.setStagedSessionApplied();
        if (hasApex) {
            mApexManager.markStagedSessionSuccessful(session.sessionId);
        }
    }

    private List<String> findAPKsInDir(File stageDir) {
        List<String> ret = new ArrayList<>();
        if (stageDir != null && stageDir.exists()) {
            for (File file : stageDir.listFiles()) {
                if (file.getAbsolutePath().toLowerCase().endsWith(".apk")) {
                    ret.add(file.getAbsolutePath());
                }
            }
        }
        return ret;
    }

    @NonNull
    private PackageInstallerSession createAndWriteApkSession(
            @NonNull PackageInstallerSession originalSession, boolean preReboot)
            throws PackageManagerException {
        final int errorCode = preReboot ? SessionInfo.STAGED_SESSION_VERIFICATION_FAILED
                : SessionInfo.STAGED_SESSION_ACTIVATION_FAILED;
        if (originalSession.stageDir == null) {
            Slog.wtf(TAG, "Attempting to install a staged APK session with no staging dir");
            throw new PackageManagerException(errorCode,
                    "Attempting to install a staged APK session with no staging dir");
        }
        List<String> apkFilePaths = findAPKsInDir(originalSession.stageDir);
        if (apkFilePaths.isEmpty()) {
            Slog.w(TAG, "Can't find staged APK in " + originalSession.stageDir.getAbsolutePath());
            throw new PackageManagerException(errorCode,
                    "Can't find staged APK in " + originalSession.stageDir.getAbsolutePath());
        }

        PackageInstaller.SessionParams params = originalSession.params.copy();
        params.isStaged = false;
        params.installFlags |= PackageManager.INSTALL_STAGED;
        // TODO(b/129744602): use the userid from the original session.
        if (preReboot) {
            params.installFlags &= ~PackageManager.INSTALL_ENABLE_ROLLBACK;
            params.installFlags |= PackageManager.INSTALL_DRY_RUN;
        } else {
            params.installFlags |= PackageManager.INSTALL_DISABLE_VERIFICATION;
        }
        int apkSessionId = mPi.createSession(
                params, originalSession.getInstallerPackageName(),
                0 /* UserHandle.SYSTEM */);
        PackageInstallerSession apkSession = mPi.getSession(apkSessionId);

        try {
            apkSession.open();
            for (String apkFilePath : apkFilePaths) {
                File apkFile = new File(apkFilePath);
                ParcelFileDescriptor pfd = ParcelFileDescriptor.open(apkFile,
                        ParcelFileDescriptor.MODE_READ_ONLY);
                long sizeBytes = pfd.getStatSize();
                if (sizeBytes < 0) {
                    Slog.e(TAG, "Unable to get size of: " + apkFilePath);
                    throw new PackageManagerException(errorCode,
                            "Unable to get size of: " + apkFilePath);
                }
                apkSession.write(apkFile.getName(), 0, sizeBytes, pfd);
            }
        } catch (IOException e) {
            Slog.e(TAG, "Failure to install APK staged session " + originalSession.sessionId, e);
            throw new PackageManagerException(errorCode, "Failed to write APK session", e);
        }
        return apkSession;
    }

    /**
     * Extract apks in the given session into a new session. Returns {@code null} if there is no
     * apks in the given session. Only parent session is returned for multi-package session.
     */
    @Nullable
    private PackageInstallerSession extractApksInSession(PackageInstallerSession session,
            boolean preReboot) throws PackageManagerException {
        final int errorCode = preReboot ? SessionInfo.STAGED_SESSION_VERIFICATION_FAILED
                : SessionInfo.STAGED_SESSION_ACTIVATION_FAILED;
        if (!session.isMultiPackage() && !isApexSession(session)) {
            return createAndWriteApkSession(session, preReboot);
        } else if (session.isMultiPackage()) {
            // For multi-package staged sessions containing APKs, we identify which child sessions
            // contain an APK, and with those then create a new multi-package group of sessions,
            // carrying over all the session parameters and unmarking them as staged. On commit the
            // sessions will be installed atomically.
            final List<PackageInstallerSession> childSessions;
            synchronized (mStagedSessions) {
                childSessions =
                        Arrays.stream(session.getChildSessionIds())
                                // Retrieve cached sessions matching ids.
                                .mapToObj(i -> mStagedSessions.get(i))
                                // Filter only the ones containing APKs.s
                                .filter(childSession -> !isApexSession(childSession))
                                .collect(Collectors.toList());
            }
            if (childSessions.isEmpty()) {
                // APEX-only multi-package staged session, nothing to do.
                return null;
            }
            final PackageInstaller.SessionParams params = session.params.copy();
            params.isStaged = false;
            if (preReboot) {
                params.installFlags &= ~PackageManager.INSTALL_ENABLE_ROLLBACK;
            }
            // TODO(b/129744602): use the userid from the original session.
            final int apkParentSessionId = mPi.createSession(
                    params, session.getInstallerPackageName(),
                    0 /* UserHandle.SYSTEM */);
            final PackageInstallerSession apkParentSession = mPi.getSession(apkParentSessionId);
            try {
                apkParentSession.open();
            } catch (IOException e) {
                Slog.e(TAG, "Unable to prepare multi-package session for staged session "
                        + session.sessionId);
                throw new PackageManagerException(errorCode,
                        "Unable to prepare multi-package session for staged session");
            }

            for (PackageInstallerSession sessionToClone : childSessions) {
                PackageInstallerSession apkChildSession =
                        createAndWriteApkSession(sessionToClone, preReboot);
                try {
                    apkParentSession.addChildSessionId(apkChildSession.sessionId);
                } catch (IllegalStateException e) {
                    Slog.e(TAG, "Failed to add a child session for installing the APK files", e);
                    throw new PackageManagerException(errorCode,
                            "Failed to add a child session " + apkChildSession.sessionId);
                }
            }
            return apkParentSession;
        }
        return null;
    }

    private void verifyApksInSession(PackageInstallerSession session)
            throws PackageManagerException {

        final PackageInstallerSession apksToVerify = extractApksInSession(
                session,  /* preReboot */ true);
        if (apksToVerify == null) {
            return;
        }

        final LocalIntentReceiverAsync receiver = new LocalIntentReceiverAsync(
                (Intent result) -> {
                    int status = result.getIntExtra(PackageInstaller.EXTRA_STATUS,
                            PackageInstaller.STATUS_FAILURE);
                    if (status != PackageInstaller.STATUS_SUCCESS) {
                        final String errorMessage = result.getStringExtra(
                                PackageInstaller.EXTRA_STATUS_MESSAGE);
                        Slog.e(TAG, "Failure to verify APK staged session "
                                + session.sessionId + " [" + errorMessage + "]");
                        session.setStagedSessionFailed(
                                SessionInfo.STAGED_SESSION_VERIFICATION_FAILED, errorMessage);
                        return;
                    }
                    mPreRebootVerificationHandler.notifyPreRebootVerification_Apk_Complete(
                            session.sessionId);
                });

        apksToVerify.commit(receiver.getIntentSender(), false);
    }

    private void installApksInSession(@NonNull PackageInstallerSession session)
            throws PackageManagerException {

        final PackageInstallerSession apksToInstall = extractApksInSession(
                session, /* preReboot */ false);
        if (apksToInstall == null) {
            return;
        }

        if ((apksToInstall.params.installFlags & PackageManager.INSTALL_ENABLE_ROLLBACK) != 0) {
            // If rollback is available for this session, notify the rollback
            // manager of the apk session so it can properly enable rollback.
            final IRollbackManager rm = IRollbackManager.Stub.asInterface(
                    ServiceManager.getService(Context.ROLLBACK_SERVICE));
            try {
                rm.notifyStagedApkSession(session.sessionId, apksToInstall.sessionId);
            } catch (RemoteException re) {
                Slog.e(TAG, "Failed to notifyStagedApkSession for session: "
                        + session.sessionId, re);
            }
        }

        final LocalIntentReceiverSync receiver = new LocalIntentReceiverSync();
        apksToInstall.commit(receiver.getIntentSender(), false);
        final Intent result = receiver.getResult();
        final int status = result.getIntExtra(PackageInstaller.EXTRA_STATUS,
                PackageInstaller.STATUS_FAILURE);
        if (status != PackageInstaller.STATUS_SUCCESS) {
            final String errorMessage = result.getStringExtra(
                    PackageInstaller.EXTRA_STATUS_MESSAGE);
            Slog.e(TAG, "Failure to install APK staged session "
                    + session.sessionId + " [" + errorMessage + "]");
            throw new PackageManagerException(
                    SessionInfo.STAGED_SESSION_ACTIVATION_FAILED, errorMessage);
        }
    }

    void commitSession(@NonNull PackageInstallerSession session) {
        updateStoredSession(session);
        mPreRebootVerificationHandler.startPreRebootVerification(session.sessionId);
    }

    /**
     * <p> Check if the session provided is non-overlapping with the active staged sessions.
     *
     * <p> A session is non-overlapping if it meets one of the following conditions: </p>
     * <ul>
     *     <li>It is a parent session</li>
     *     <li>It is already one of the active sessions</li>
     *     <li>Its package name is not same as any of the active sessions</li>
     * </ul>
     * @throws PackageManagerException if session fails the check
     */
    void checkNonOverlappingWithStagedSessions(@NonNull PackageInstallerSession session)
            throws PackageManagerException {
        if (session.isMultiPackage()) {
            // We cannot say a parent session overlaps until we process its children
            return;
        }
        if (session.getPackageName() == null) {
            throw new PackageManagerException(PackageManager.INSTALL_FAILED_INVALID_APK,
                    "Cannot stage session " + session.sessionId + " with package name null");
        }

        synchronized (mStagedSessions) {
            for (int i = 0; i < mStagedSessions.size(); i++) {
                final PackageInstallerSession stagedSession = mStagedSessions.valueAt(i);
                if (!stagedSession.isCommitted() || stagedSession.isStagedAndInTerminalState()) {
                    continue;
                }
                if (stagedSession.isMultiPackage()) {
                    // This active parent staged session is useless as it doesn't have a package
                    // name and the session we are checking is not a parent session either.
                    continue;
                }

                // From here on, stagedSession is a non-parent active staged session

                // Check if stagedSession has an active parent session or not
                if (stagedSession.hasParentSessionId()) {
                    int parentId = stagedSession.getParentSessionId();
                    PackageInstallerSession parentSession = mStagedSessions.get(parentId);
                    if (parentSession == null || parentSession.isStagedAndInTerminalState()) {
                        // Parent session has been abandoned or terminated already
                        continue;
                    }
                }

                // Check if session is one of the active sessions
                if (session.sessionId == stagedSession.sessionId) {
                    Slog.w(TAG, "Session " + session.sessionId + " is already staged");
                    continue;
                }

                // If session is not among the active sessions, then it cannot have same package
                // name as any of the active sessions.
                if (session.getPackageName().equals(stagedSession.getPackageName())) {
                    throw new PackageManagerException(
                            PackageManager.INSTALL_FAILED_OTHER_STAGED_SESSION_IN_PROGRESS,
                            "Package: " + session.getPackageName() + " in session: "
                                    + session.sessionId + " has been staged already by session: "
                                    + stagedSession.sessionId, null);
                }

                // TODO(b/141843321): Add support for staging multiple sessions in apexd
                // Since apexd doesn't support multiple staged sessions yet, we have to careful how
                // we handle apex sessions. We want to allow a set of apex sessions under the same
                // parent to be staged when there is no previously staged apex sessions.
                if (isApexSession(session) && isApexSession(stagedSession)) {
                    // session is apex and it can co-exist with stagedSession only if they are from
                    // same parent
                    final boolean coExist;
                    if (!session.hasParentSessionId() && !stagedSession.hasParentSessionId()) {
                        // Both single package apex sessions. Cannot co-exist.
                        coExist = false;
                    } else {
                        // At least one of the session has parent. Both must be from same parent.
                        coExist =
                                session.getParentSessionId() == stagedSession.getParentSessionId();
                    }
                    if (!coExist) {
                        throw new PackageManagerException(
                                PackageManager.INSTALL_FAILED_OTHER_STAGED_SESSION_IN_PROGRESS,
                                "Package: " + session.getPackageName() + " in session: "
                                        + session.sessionId + " cannot be staged as there is "
                                        + "already another apex staged session: "
                                        + stagedSession.sessionId, null);
                    }
                }
            }
        }
    }

    void createSession(@NonNull PackageInstallerSession sessionInfo) {
        synchronized (mStagedSessions) {
            mStagedSessions.append(sessionInfo.sessionId, sessionInfo);
        }
    }

    void abortSession(@NonNull PackageInstallerSession session) {
        synchronized (mStagedSessions) {
            mStagedSessions.remove(session.sessionId);
        }
    }

    void abortCommittedSession(@NonNull PackageInstallerSession session) {
        if (session.isStagedSessionApplied()) {
            Slog.w(TAG, "Cannot abort applied session : " + session.sessionId);
            return;
        }
        abortSession(session);

        boolean hasApex = sessionContainsApex(session);
        if (hasApex) {
            ApexSessionInfo apexSession = mApexManager.getStagedSessionInfo(session.sessionId);
            if (apexSession == null || isApexSessionFinalized(apexSession)) {
                Slog.w(TAG,
                        "Cannot abort session " + session.sessionId
                                + " because it is not active or APEXD is not reachable");
                return;
            }
            mApexManager.abortActiveSession();
        }
    }

    private boolean isApexSessionFinalized(ApexSessionInfo session) {
        /* checking if the session is in a final state, i.e., not active anymore */
        return session.isUnknown || session.isActivationFailed || session.isSuccess
                || session.isReverted;
    }

    private static boolean isApexSessionFailed(ApexSessionInfo apexSessionInfo) {
        // isRevertInProgress is included to cover the scenario, when a device is rebooted
        // during the revert, and apexd fails to resume the revert after reboot.
        return apexSessionInfo.isActivationFailed || apexSessionInfo.isUnknown
                || apexSessionInfo.isReverted || apexSessionInfo.isRevertInProgress
                || apexSessionInfo.isRevertFailed;
    }

    @GuardedBy("mStagedSessions")
    private boolean isMultiPackageSessionComplete(@NonNull PackageInstallerSession session) {
        // This method assumes that the argument is either a parent session of a multi-package
        // i.e. isMultiPackage() returns true, or that it is a child session, i.e.
        // hasParentSessionId() returns true.
        if (session.isMultiPackage()) {
            // Parent session of a multi-package group. Check that we restored all the children.
            for (int childSession : session.getChildSessionIds()) {
                if (mStagedSessions.get(childSession) == null) {
                    return false;
                }
            }
            return true;
        }
        if (session.hasParentSessionId()) {
            PackageInstallerSession parent = mStagedSessions.get(session.getParentSessionId());
            if (parent == null) {
                return false;
            }
            return isMultiPackageSessionComplete(parent);
        }
        Slog.wtf(TAG, "Attempting to restore an invalid multi-package session.");
        return false;
    }

    void restoreSession(@NonNull PackageInstallerSession session) {
        PackageInstallerSession sessionToResume = session;
        synchronized (mStagedSessions) {
            mStagedSessions.append(session.sessionId, session);
            // For multi-package sessions, we don't know in which order they will be restored. We
            // need to wait until we have restored all the session in a group before restoring them.
            if (session.isMultiPackage() || session.hasParentSessionId()) {
                if (!isMultiPackageSessionComplete(session)) {
                    // Still haven't recovered all sessions of the group, return.
                    return;
                }
                // Group recovered, find the parent if necessary and resume the installation.
                if (session.hasParentSessionId()) {
                    sessionToResume = mStagedSessions.get(session.getParentSessionId());
                }
            }
        }
        checkStateAndResume(sessionToResume);
    }

    private void checkStateAndResume(@NonNull PackageInstallerSession session) {
        if (!session.isCommitted()) {
            // Session hasn't been committed yet, ignore.
            return;
        }
        // Check the state of the session and decide what to do next.
        if (session.isStagedSessionFailed() || session.isStagedSessionApplied()) {
            // Final states, nothing to do.
            return;
        }
        if (!session.isStagedSessionReady()) {
            // The framework got restarted before the pre-reboot verification could complete,
            // restart the verification.
            mPreRebootVerificationHandler.startPreRebootVerification(session.sessionId);
        } else {
            // Session had already being marked ready. Start the checks to verify if there is any
            // follow-up work.
            resumeSession(session);
        }
    }

    private static class LocalIntentReceiverAsync {
        final Consumer<Intent> mConsumer;

        LocalIntentReceiverAsync(Consumer<Intent> consumer) {
            mConsumer = consumer;
        }

        private IIntentSender.Stub mLocalSender = new IIntentSender.Stub() {
            @Override
            public void send(int code, Intent intent, String resolvedType, IBinder whitelistToken,
                    IIntentReceiver finishedReceiver, String requiredPermission, Bundle options) {
                mConsumer.accept(intent);
            }
        };

        public IntentSender getIntentSender() {
            return new IntentSender((IIntentSender) mLocalSender);
        }
    }

    private static class LocalIntentReceiverSync {
        private final LinkedBlockingQueue<Intent> mResult = new LinkedBlockingQueue<>();

        private IIntentSender.Stub mLocalSender = new IIntentSender.Stub() {
            @Override
            public void send(int code, Intent intent, String resolvedType, IBinder whitelistToken,
                    IIntentReceiver finishedReceiver, String requiredPermission,
                    Bundle options) {
                try {
                    mResult.offer(intent, 5, TimeUnit.SECONDS);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        };

        public IntentSender getIntentSender() {
            return new IntentSender((IIntentSender) mLocalSender);
        }

        public Intent getResult() {
            try {
                return mResult.take();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }

    private final class PreRebootVerificationHandler extends Handler {

        PreRebootVerificationHandler(Looper looper) {
            super(looper);
        }

        /**
         * Handler for states of pre reboot verification. The states are arranged linearly (shown
         * below) with each state either calling the next state, or calling some other method that
         * eventually calls the next state.
         *
         * <p><ul>
         *     <li>MSG_PRE_REBOOT_VERIFICATION_START</li>
         *     <li>MSG_PRE_REBOOT_VERIFICATION_APEX</li>
         *     <li>MSG_PRE_REBOOT_VERIFICATION_APK</li>
         *     <li>MSG_PRE_REBOOT_VERIFICATION_END</li>
         * </ul></p>
         *
         * Details about each of state can be found in corresponding handler of node.
         */
        private static final int MSG_PRE_REBOOT_VERIFICATION_START = 1;
        private static final int MSG_PRE_REBOOT_VERIFICATION_APEX = 2;
        private static final int MSG_PRE_REBOOT_VERIFICATION_APK = 3;
        private static final int MSG_PRE_REBOOT_VERIFICATION_END = 4;

        @Override
        public void handleMessage(Message msg) {
            final int sessionId = msg.arg1;
            final PackageInstallerSession session;
            synchronized (mStagedSessions) {
                session = mStagedSessions.get(sessionId);
            }
            // Maybe session was aborted before pre-reboot verification was complete
            if (session == null) {
                Slog.d(TAG, "Stopping pre-reboot verification for sessionId: " + sessionId);
                return;
            }
            switch (msg.what) {
                case MSG_PRE_REBOOT_VERIFICATION_START:
                    handlePreRebootVerification_Start(session);
                    break;
                case MSG_PRE_REBOOT_VERIFICATION_APEX:
                    handlePreRebootVerification_Apex(session);
                    break;
                case MSG_PRE_REBOOT_VERIFICATION_APK:
                    handlePreRebootVerification_Apk(session);
                    break;
                case MSG_PRE_REBOOT_VERIFICATION_END:
                    handlePreRebootVerification_End(session);
                    break;
            }
        }

        // Method for starting the pre-reboot verification
        private void startPreRebootVerification(int sessionId) {
            obtainMessage(MSG_PRE_REBOOT_VERIFICATION_START, sessionId, 0).sendToTarget();
        }

        private void notifyPreRebootVerification_Start_Complete(int sessionId) {
            obtainMessage(MSG_PRE_REBOOT_VERIFICATION_APEX, sessionId, 0).sendToTarget();
        }

        private void notifyPreRebootVerification_Apex_Complete(int sessionId) {
            obtainMessage(MSG_PRE_REBOOT_VERIFICATION_APK, sessionId, 0).sendToTarget();
        }

        private void notifyPreRebootVerification_Apk_Complete(int sessionId) {
            obtainMessage(MSG_PRE_REBOOT_VERIFICATION_END, sessionId, 0).sendToTarget();
        }

        /**
         * A dummy state for starting the pre reboot verification.
         *
         * See {@link PreRebootVerificationHandler} to see all nodes of pre reboot verification
         */
        private void handlePreRebootVerification_Start(@NonNull PackageInstallerSession session) {
            Slog.d(TAG, "Starting preRebootVerification for session " + session.sessionId);
            notifyPreRebootVerification_Start_Complete(session.sessionId);
        }

        /**
         * Pre-reboot verification state for apex files:
         *
         * <p><ul>
         *     <li>submits session to apex service</li>
         *     <li>validates signatures of apex files</li>
         * </ul></p>
         */
        private void handlePreRebootVerification_Apex(@NonNull PackageInstallerSession session) {
            final boolean hasApex = sessionContainsApex(session);

            // APEX checks. For single-package sessions, check if they contain an APEX. For
            // multi-package sessions, find all the child sessions that contain an APEX.
            if (hasApex) {
                try {
                    final List<PackageInfo> apexPackages =
                            submitSessionToApexService(session);
                    for (PackageInfo apexPackage : apexPackages) {
                        validateApexSignature(apexPackage);
                    }
                } catch (PackageManagerException e) {
                    session.setStagedSessionFailed(e.error, e.getMessage());
                    return;
                }
            }

            notifyPreRebootVerification_Apex_Complete(session.sessionId);
        }

        /**
         * Pre-reboot verification state for apk files:
         *   <p><ul>
         *       <li>performs a dry-run install of apk</li>
         *   </ul></p>
         */
        private void handlePreRebootVerification_Apk(@NonNull PackageInstallerSession session) {
            if (!sessionContainsApk(session)) {
                notifyPreRebootVerification_Apk_Complete(session.sessionId);
                return;
            }

            try {
                Slog.d(TAG, "Running a pre-reboot verification for APKs in session "
                        + session.sessionId + " by performing a dry-run install");

                // verifyApksInSession will notify the handler when APK verification is complete
                verifyApksInSession(session);
                // TODO(b/118865310): abort the session on apexd.
            } catch (PackageManagerException e) {
                session.setStagedSessionFailed(e.error, e.getMessage());
            }
        }

        /**
         * Pre-reboot verification state for wrapping up:
         * <p><ul>
         *     <li>enables rollback if required</li>
         *     <li>marks session as ready</li>
         * </ul></p>
         */
        private void handlePreRebootVerification_End(@NonNull PackageInstallerSession session) {
            if ((session.params.installFlags & PackageManager.INSTALL_ENABLE_ROLLBACK) != 0) {
                // If rollback is enabled for this session, we call through to the RollbackManager
                // with the list of sessions it must enable rollback for. Note that
                // notifyStagedSession is a synchronous operation.
                final IRollbackManager rm = IRollbackManager.Stub.asInterface(
                        ServiceManager.getService(Context.ROLLBACK_SERVICE));
                try {
                    // NOTE: To stay consistent with the non-staged install flow, we don't fail the
                    // entire install if rollbacks can't be enabled.
                    if (!rm.notifyStagedSession(session.sessionId)) {
                        Slog.e(TAG, "Unable to enable rollback for session: "
                                + session.sessionId);
                    }
                } catch (RemoteException re) {
                    Slog.e(TAG, "Failed to notifyStagedSession for session: "
                            + session.sessionId, re);
                }
            }

            // Proactively mark session as ready before calling apexd. Although this call order
            // looks counter-intuitive, this is the easiest way to ensure that session won't end up
            // in the inconsistent state:
            //  - If device gets rebooted right before call to apexd, then apexd will never activate
            //      apex files of this staged session. This will result in StagingManager failing
            //      the session.
            // On the other hand, if the order of the calls was inverted (first call apexd, then
            // mark session as ready), then if a device gets rebooted right after the call to apexd,
            // only apex part of the train will be applied, leaving device in an inconsistent state.
            Slog.d(TAG, "Marking session " + session.sessionId + " as ready");
            session.setStagedSessionReady();
            final boolean hasApex = sessionContainsApex(session);
            if (!hasApex) {
                // Session doesn't contain apex, nothing to do.
                return;
            }
            try {
                mApexManager.markStagedSessionReady(session.sessionId);
            } catch (PackageManagerException e) {
                session.setStagedSessionFailed(e.error, e.getMessage());
            }
        }
    }
}