/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.kafka.streams.processor.internals.assignment;

import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.utils.Utils;
import org.apache.kafka.streams.processor.TaskId;
import org.apache.kafka.streams.processor.internals.Task;
import org.junit.Test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Set;

import static java.util.Arrays.asList;
import static org.apache.kafka.common.utils.Utils.mkEntry;
import static org.apache.kafka.common.utils.Utils.mkMap;
import static org.apache.kafka.common.utils.Utils.mkSet;
import static org.apache.kafka.common.utils.Utils.mkSortedSet;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.EMPTY_CLIENT_TAGS;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.NAMED_TASK_T0_0_0;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.NAMED_TASK_T1_0_0;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TASK_0_0;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TASK_0_1;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TASK_0_2;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TASK_0_3;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TP_0_0;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TP_0_1;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TP_0_2;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TP_1_0;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TP_1_1;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.TP_1_2;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.UUID_1;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.UUID_2;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.UUID_3;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.hasActiveTasks;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.hasStandbyTasks;
import static org.apache.kafka.streams.processor.internals.assignment.AssignmentTestUtils.uuidForInt;
import static org.apache.kafka.streams.processor.internals.assignment.SubscriptionInfo.UNKNOWN_OFFSET_SUM;
import static org.hamcrest.CoreMatchers.equalTo;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.empty;
import static org.hamcrest.Matchers.is;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertNull;
import static org.junit.Assert.assertThrows;
import static org.junit.Assert.assertTrue;

public class ClientStateTest {
    private final ClientState client = new ClientState(1);
    private final ClientState zeroCapacityClient = new ClientState(0);

    @Test
    public void previousStateConstructorShouldCreateAValidObject() {
        final ClientState clientState = new ClientState(
            mkSet(TASK_0_0, TASK_0_1),
            mkSet(TASK_0_2, TASK_0_3),
            mkMap(mkEntry(TASK_0_0, 5L), mkEntry(TASK_0_2, -1L)),
            EMPTY_CLIENT_TAGS,
            4
        );

        // all the "next assignment" fields should be empty
        assertThat(clientState.activeTaskCount(), is(0));
        assertThat(clientState.activeTaskLoad(), is(0.0));
        assertThat(clientState.activeTasks(), is(empty()));
        assertThat(clientState.standbyTaskCount(), is(0));
        assertThat(clientState.standbyTasks(), is(empty()));
        assertThat(clientState.assignedTaskCount(), is(0));
        assertThat(clientState.assignedTasks(), is(empty()));

        // and the "previous assignment" fields should match the constructor args
        assertThat(clientState.prevActiveTasks(), is(mkSet(TASK_0_0, TASK_0_1)));
        assertThat(clientState.prevStandbyTasks(), is(mkSet(TASK_0_2, TASK_0_3)));
        assertThat(clientState.previousAssignedTasks(), is(mkSet(TASK_0_0, TASK_0_1, TASK_0_2, TASK_0_3)));
        assertThat(clientState.capacity(), is(4));
        assertThat(clientState.lagFor(TASK_0_0), is(5L));
        assertThat(clientState.lagFor(TASK_0_2), is(-1L));
    }

    @Test
    public void shouldHaveNotReachedCapacityWhenAssignedTasksLessThanCapacity() {
        assertFalse(client.reachedCapacity());
    }

    @Test
    public void shouldHaveReachedCapacityWhenAssignedTasksGreaterThanOrEqualToCapacity() {
        client.assignActive(TASK_0_1);
        assertTrue(client.reachedCapacity());
    }

    @Test
    public void shouldRefuseDoubleActiveTask() {
        final ClientState clientState = new ClientState(1);
        clientState.assignActive(TASK_0_0);
        assertThrows(IllegalArgumentException.class, () -> clientState.assignActive(TASK_0_0));
    }

    @Test
    public void shouldRefuseActiveAndStandbyTask() {
        final ClientState clientState = new ClientState(1);
        clientState.assignActive(TASK_0_0);
        assertThrows(IllegalArgumentException.class, () -> clientState.assignStandby(TASK_0_0));
    }

    @Test
    public void shouldRefuseDoubleStandbyTask() {
        final ClientState clientState = new ClientState(1);
        clientState.assignStandby(TASK_0_0);
        assertThrows(IllegalArgumentException.class, () -> clientState.assignStandby(TASK_0_0));
    }

    @Test
    public void shouldRefuseStandbyAndActiveTask() {
        final ClientState clientState = new ClientState(1);
        clientState.assignStandby(TASK_0_0);
        assertThrows(IllegalArgumentException.class, () -> clientState.assignActive(TASK_0_0));
    }

    @Test
    public void shouldRefuseToUnassignNotAssignedActiveTask() {
        final ClientState clientState = new ClientState(1);
        assertThrows(IllegalArgumentException.class, () -> clientState.unassignActive(TASK_0_0));
    }

    @Test
    public void shouldRefuseToUnassignNotAssignedStandbyTask() {
        final ClientState clientState = new ClientState(1);
        assertThrows(IllegalArgumentException.class, () -> clientState.unassignStandby(TASK_0_0));
    }

    @Test
    public void shouldRefuseToUnassignActiveTaskAsStandby() {
        final ClientState clientState = new ClientState(1);
        clientState.assignActive(TASK_0_0);
        assertThrows(IllegalArgumentException.class, () -> clientState.unassignStandby(TASK_0_0));
    }

    @Test
    public void shouldRefuseToUnassignStandbyTaskAsActive() {
        final ClientState clientState = new ClientState(1);
        clientState.assignStandby(TASK_0_0);
        assertThrows(IllegalArgumentException.class, () -> clientState.unassignActive(TASK_0_0));
    }

    @Test
    public void shouldUnassignActiveTask() {
        final ClientState clientState = new ClientState(1);
        clientState.assignActive(TASK_0_0);
        assertThat(clientState, hasActiveTasks(1));
        clientState.unassignActive(TASK_0_0);
        assertThat(clientState, hasActiveTasks(0));
    }

    @Test
    public void shouldUnassignStandbyTask() {
        final ClientState clientState = new ClientState(1);
        clientState.assignStandby(TASK_0_0);
        assertThat(clientState, hasStandbyTasks(1));
        clientState.unassignStandby(TASK_0_0);
        assertThat(clientState, hasStandbyTasks(0));
    }

    @Test
    public void shouldNotModifyActiveView() {
        final ClientState clientState = new ClientState(1);
        final Set<TaskId> taskIds = clientState.activeTasks();
        assertThrows(UnsupportedOperationException.class, () -> taskIds.add(TASK_0_0));
        assertThat(clientState, hasActiveTasks(0));
    }

    @Test
    public void shouldNotModifyStandbyView() {
        final ClientState clientState = new ClientState(1);
        final Set<TaskId> taskIds = clientState.standbyTasks();
        assertThrows(UnsupportedOperationException.class, () -> taskIds.add(TASK_0_0));
        assertThat(clientState, hasStandbyTasks(0));
    }

    @Test
    public void shouldNotModifyAssignedView() {
        final ClientState clientState = new ClientState(1);
        final Set<TaskId> taskIds = clientState.assignedTasks();
        assertThrows(UnsupportedOperationException.class, () -> taskIds.add(TASK_0_0));
        assertThat(clientState, hasActiveTasks(0));
        assertThat(clientState, hasStandbyTasks(0));
    }

    @Test
    public void shouldAddActiveTasksToBothAssignedAndActive() {
        client.assignActive(TASK_0_1);
        assertThat(client.activeTasks(), equalTo(Collections.singleton(TASK_0_1)));
        assertThat(client.assignedTasks(), equalTo(Collections.singleton(TASK_0_1)));
        assertThat(client.assignedTaskCount(), equalTo(1));
        assertThat(client.standbyTasks().size(), equalTo(0));
    }

    @Test
    public void shouldAddStandbyTasksToBothStandbyAndAssigned() {
        client.assignStandby(TASK_0_1);
        assertThat(client.assignedTasks(), equalTo(Collections.singleton(TASK_0_1)));
        assertThat(client.standbyTasks(), equalTo(Collections.singleton(TASK_0_1)));
        assertThat(client.assignedTaskCount(), equalTo(1));
        assertThat(client.activeTasks().size(), equalTo(0));
    }

    @Test
    public void shouldAddPreviousActiveTasksToPreviousAssignedAndPreviousActive() {
        client.addPreviousActiveTasks(Utils.mkSet(TASK_0_1, TASK_0_2));
        assertThat(client.prevActiveTasks(), equalTo(Utils.mkSet(TASK_0_1, TASK_0_2)));
        assertThat(client.previousAssignedTasks(), equalTo(Utils.mkSet(TASK_0_1, TASK_0_2)));
    }

    @Test
    public void shouldAddPreviousStandbyTasksToPreviousAssignedAndPreviousStandby() {
        client.addPreviousStandbyTasks(Utils.mkSet(TASK_0_1, TASK_0_2));
        assertThat(client.prevActiveTasks().size(), equalTo(0));
        assertThat(client.previousAssignedTasks(), equalTo(Utils.mkSet(TASK_0_1, TASK_0_2)));
    }

    @Test
    public void shouldHaveAssignedTaskIfActiveTaskAssigned() {
        client.assignActive(TASK_0_1);
        assertTrue(client.hasAssignedTask(TASK_0_1));
    }

    @Test
    public void shouldHaveAssignedTaskIfStandbyTaskAssigned() {
        client.assignStandby(TASK_0_1);
        assertTrue(client.hasAssignedTask(TASK_0_1));
    }

    @Test
    public void shouldNotHaveAssignedTaskIfTaskNotAssigned() {
        client.assignActive(TASK_0_1);
        assertFalse(client.hasAssignedTask(TASK_0_2));
    }

    @Test
    public void shouldHaveMoreAvailableCapacityWhenCapacityTheSameButFewerAssignedTasks() {
        final ClientState otherClient = new ClientState(1);
        client.assignActive(TASK_0_1);
        assertTrue(otherClient.hasMoreAvailableCapacityThan(client));
        assertFalse(client.hasMoreAvailableCapacityThan(otherClient));
    }

    @Test
    public void shouldHaveMoreAvailableCapacityWhenCapacityHigherAndSameAssignedTaskCount() {
        final ClientState otherClient = new ClientState(2);
        assertTrue(otherClient.hasMoreAvailableCapacityThan(client));
        assertFalse(client.hasMoreAvailableCapacityThan(otherClient));
    }

    @Test
    public void shouldUseMultiplesOfCapacityToDetermineClientWithMoreAvailableCapacity() {
        final ClientState otherClient = new ClientState(2);

        for (int i = 0; i < 7; i++) {
            otherClient.assignActive(new TaskId(0, i));
        }

        for (int i = 7; i < 11; i++) {
            client.assignActive(new TaskId(0, i));
        }

        assertTrue(otherClient.hasMoreAvailableCapacityThan(client));
    }

    @Test
    public void shouldHaveMoreAvailableCapacityWhenCapacityIsTheSameButAssignedTasksIsLess() {
        final ClientState client = new ClientState(3);
        final ClientState otherClient = new ClientState(3);
        for (int i = 0; i < 4; i++) {
            client.assignActive(new TaskId(0, i));
            otherClient.assignActive(new TaskId(0, i));
        }
        otherClient.assignActive(new TaskId(0, 5));
        assertTrue(client.hasMoreAvailableCapacityThan(otherClient));
    }

    @Test
    public void shouldThrowIllegalStateExceptionIfCapacityOfThisClientStateIsZero() {
        assertThrows(IllegalStateException.class, () -> zeroCapacityClient.hasMoreAvailableCapacityThan(client));
    }

    @Test
    public void shouldThrowIllegalStateExceptionIfCapacityOfOtherClientStateIsZero() {
        assertThrows(IllegalStateException.class, () -> client.hasMoreAvailableCapacityThan(zeroCapacityClient));
    }

    @Test
    public void shouldHaveUnfulfilledQuotaWhenActiveTaskSizeLessThanCapacityTimesTasksPerThread() {
        client.assignActive(new TaskId(0, 1));
        assertTrue(client.hasUnfulfilledQuota(2));
    }

    @Test
    public void shouldNotHaveUnfulfilledQuotaWhenActiveTaskSizeGreaterEqualThanCapacityTimesTasksPerThread() {
        client.assignActive(new TaskId(0, 1));
        assertFalse(client.hasUnfulfilledQuota(1));
    }

    @Test
    public void shouldAddTasksWithLatestOffsetToPrevActiveTasks() {
        final Map<TaskId, Long> taskOffsetSums = Collections.singletonMap(TASK_0_1, Task.LATEST_OFFSET);
        client.addPreviousTasksAndOffsetSums("c1", taskOffsetSums);
        client.initializePrevTasks(Collections.emptyMap(), false);
        assertThat(client.prevActiveTasks(), equalTo(Collections.singleton(TASK_0_1)));
        assertThat(client.previousAssignedTasks(), equalTo(Collections.singleton(TASK_0_1)));
        assertTrue(client.prevStandbyTasks().isEmpty());
    }

    @Test
    public void shouldThrowWhenSomeOwnedPartitionsAreNotRecognizedWhenInitializingPrevTasks() {
        final Map<TopicPartition, TaskId> taskForPartitionMap = Collections.singletonMap(TP_0_1, TASK_0_1);
        client.addOwnedPartitions(Collections.singleton(TP_0_0), "c1");
        client.addPreviousTasksAndOffsetSums("c1", Collections.emptyMap());
        assertThrows(IllegalStateException.class, () -> client.initializePrevTasks(taskForPartitionMap, false));
    }

    @Test
    public void shouldFilterOutUnrecognizedPartitionsAndInitializePrevTasksWhenUsingNamedTopologies() {
        final Map<TopicPartition, TaskId> taskForPartitionMap = Collections.singletonMap(TP_0_1, TASK_0_1);
        client.addOwnedPartitions(Collections.singleton(TP_0_0), "c1");
        client.addPreviousTasksAndOffsetSums("c1", Collections.emptyMap());
        client.initializePrevTasks(taskForPartitionMap, true);
        assertThat(client.prevActiveTasks().isEmpty(), is(true));
        assertThat(client.previousAssignedTasks().isEmpty(), is(true));
        assertThat(client.prevStandbyTasks().isEmpty(), is(true));
    }

    @Test
    public void shouldReturnPreviousStatefulTasksForConsumer() {
        client.addPreviousTasksAndOffsetSums("c1", mkMap(
                mkEntry(TASK_0_0, 100L),
                mkEntry(TASK_0_1, Task.LATEST_OFFSET)
        ));
        client.addPreviousTasksAndOffsetSums("c2", Collections.singletonMap(TASK_0_2, 0L));
        client.addPreviousTasksAndOffsetSums("c3", Collections.emptyMap());

        client.initializePrevTasks(Collections.emptyMap(), false);

        assertThat(client.prevOwnedStatefulTasksByConsumer("c1"), equalTo(mkSet(TASK_0_0, TASK_0_1)));
        assertThat(client.prevOwnedStatefulTasksByConsumer("c2"), equalTo(mkSet(TASK_0_2)));
        assertTrue(client.prevOwnedStatefulTasksByConsumer("c3").isEmpty());
    }

    @Test
    public void shouldReturnPreviousActiveStandbyTasksForConsumer() {
        client.addOwnedPartitions(mkSet(TP_0_1, TP_1_1), "c1");
        client.addOwnedPartitions(mkSet(TP_0_2, TP_1_2), "c2");
        client.initializePrevTasks(
            mkMap(
                mkEntry(TP_0_0, TASK_0_0),
                mkEntry(TP_0_1, TASK_0_1),
                mkEntry(TP_0_2, TASK_0_2),
                mkEntry(TP_1_0, TASK_0_0),
                mkEntry(TP_1_1, TASK_0_1),
                mkEntry(TP_1_2, TASK_0_2)),
            false
        );

        client.addPreviousTasksAndOffsetSums("c1", mkMap(
                mkEntry(TASK_0_1, Task.LATEST_OFFSET),
                mkEntry(TASK_0_0, 10L)));
        client.addPreviousTasksAndOffsetSums("c2", Collections.singletonMap(TASK_0_2, 0L));

        assertThat(client.prevOwnedStatefulTasksByConsumer("c1"), equalTo(mkSet(TASK_0_1, TASK_0_0)));
        assertThat(client.prevOwnedStatefulTasksByConsumer("c2"), equalTo(mkSet(TASK_0_2)));
        assertThat(client.prevOwnedActiveTasksByConsumer(), equalTo(
                mkMap(
                        mkEntry("c1", Collections.singleton(TASK_0_1)),
                        mkEntry("c2", Collections.singleton(TASK_0_2))
                ))
        );
        assertThat(client.prevOwnedStandbyByConsumer(), equalTo(
                mkMap(
                        mkEntry("c1", Collections.singleton(TASK_0_0)),
                        mkEntry("c2", Collections.emptySet())
                ))
        );
    }

    @Test
    public void shouldReturnAssignedTasksForConsumer() {
        final List<TaskId> allTasks = new ArrayList<>(asList(TASK_0_0, TASK_0_1, TASK_0_2));
        client.assignActiveTasks(allTasks);

        client.assignActiveToConsumer(TASK_0_0, "c1");
        // calling it multiple tasks should be idempotent
        client.assignActiveToConsumer(TASK_0_0, "c1");
        client.assignActiveToConsumer(TASK_0_1, "c1");
        client.assignActiveToConsumer(TASK_0_2, "c2");

        client.assignStandbyToConsumer(TASK_0_2, "c1");
        client.assignStandbyToConsumer(TASK_0_0, "c2");
        // calling it multiple tasks should be idempotent
        client.assignStandbyToConsumer(TASK_0_0, "c2");

        client.revokeActiveFromConsumer(TASK_0_1, "c1");
        // calling it multiple tasks should be idempotent
        client.revokeActiveFromConsumer(TASK_0_1, "c1");

        assertThat(client.assignedActiveTasksByConsumer(), equalTo(mkMap(
                mkEntry("c1", mkSet(TASK_0_0, TASK_0_1)),
                mkEntry("c2", mkSet(TASK_0_2))
        )));
        assertThat(client.assignedStandbyTasksByConsumer(), equalTo(mkMap(
                mkEntry("c1", mkSet(TASK_0_2)),
                mkEntry("c2", mkSet(TASK_0_0))
        )));
        assertThat(client.revokingActiveTasksByConsumer(), equalTo(Collections.singletonMap("c1", mkSet(TASK_0_1))));
    }

    @Test
    public void shouldAddTasksInOffsetSumsMapToPrevStandbyTasks() {
        final Map<TaskId, Long> taskOffsetSums = mkMap(
            mkEntry(TASK_0_1, 0L),
            mkEntry(TASK_0_2, 100L)
        );
        client.addPreviousTasksAndOffsetSums("c1", taskOffsetSums);
        client.initializePrevTasks(Collections.emptyMap(), false);
        assertThat(client.prevStandbyTasks(), equalTo(mkSet(TASK_0_1, TASK_0_2)));
        assertThat(client.previousAssignedTasks(), equalTo(mkSet(TASK_0_1, TASK_0_2)));
        assertTrue(client.prevActiveTasks().isEmpty());
    }

    @Test
    public void shouldComputeTaskLags() {
        final Map<TaskId, Long> taskOffsetSums = mkMap(
            mkEntry(TASK_0_1, 0L),
            mkEntry(TASK_0_2, 100L)
        );
        final Map<TaskId, Long> allTaskEndOffsetSums = mkMap(
            mkEntry(TASK_0_1, 500L),
            mkEntry(TASK_0_2, 100L)
        );
        client.addPreviousTasksAndOffsetSums("c1", taskOffsetSums);
        client.computeTaskLags(null, allTaskEndOffsetSums);

        assertThat(client.lagFor(TASK_0_1), equalTo(500L));
        assertThat(client.lagFor(TASK_0_2), equalTo(0L));
    }

    @Test
    public void shouldNotTryToLookupTasksThatWerePreviouslyAssignedButNoLongerExist() {
        final Map<TaskId, Long> clientReportedTaskEndOffsetSums = mkMap(
            mkEntry(NAMED_TASK_T0_0_0, 500L),
            mkEntry(NAMED_TASK_T1_0_0, 500L)
            );
        final Map<TaskId, Long> allTaskEndOffsetSumsComputedByAssignor = Collections.singletonMap(NAMED_TASK_T0_0_0, 500L);
        client.addPreviousTasksAndOffsetSums("c1", clientReportedTaskEndOffsetSums);
        client.computeTaskLags(null, allTaskEndOffsetSumsComputedByAssignor);

        assertThrows(IllegalStateException.class, () -> client.lagFor(NAMED_TASK_T1_0_0));

        client.assignActive(NAMED_TASK_T0_0_0);
        assertThat(client.prevTasksByLag("c1"), equalTo(mkSortedSet(NAMED_TASK_T0_0_0)));
    }

    @Test
    public void shouldReturnEndOffsetSumForLagOfTaskWeDidNotPreviouslyOwn() {
        final Map<TaskId, Long> taskOffsetSums = Collections.emptyMap();
        final Map<TaskId, Long> allTaskEndOffsetSums = Collections.singletonMap(TASK_0_1, 500L);
        client.addPreviousTasksAndOffsetSums("c1", taskOffsetSums);
        client.computeTaskLags(null, allTaskEndOffsetSums);
        assertThat(client.lagFor(TASK_0_1), equalTo(500L));
    }

    @Test
    public void shouldReturnLatestOffsetForLagOfPreviousActiveRunningTask() {
        final Map<TaskId, Long> taskOffsetSums = Collections.singletonMap(TASK_0_1, Task.LATEST_OFFSET);
        final Map<TaskId, Long> allTaskEndOffsetSums = Collections.singletonMap(TASK_0_1, 500L);
        client.addPreviousTasksAndOffsetSums("c1", taskOffsetSums);
        client.computeTaskLags(null, allTaskEndOffsetSums);
        assertThat(client.lagFor(TASK_0_1), equalTo(Task.LATEST_OFFSET));
    }

    @Test
    public void shouldReturnUnknownOffsetSumForLagOfTaskWithUnknownOffset() {
        final Map<TaskId, Long> taskOffsetSums = Collections.singletonMap(TASK_0_1, UNKNOWN_OFFSET_SUM);
        final Map<TaskId, Long> allTaskEndOffsetSums = Collections.singletonMap(TASK_0_1, 500L);
        client.addPreviousTasksAndOffsetSums("c1", taskOffsetSums);
        client.computeTaskLags(null, allTaskEndOffsetSums);
        assertThat(client.lagFor(TASK_0_1), equalTo(UNKNOWN_OFFSET_SUM));
    }

    @Test
    public void shouldReturnEndOffsetSumIfOffsetSumIsGreaterThanEndOffsetSum() {
        final Map<TaskId, Long> taskOffsetSums = Collections.singletonMap(TASK_0_1, 5L);
        final Map<TaskId, Long> allTaskEndOffsetSums = Collections.singletonMap(TASK_0_1, 1L);
        client.addPreviousTasksAndOffsetSums("c1", taskOffsetSums);
        client.computeTaskLags(null, allTaskEndOffsetSums);
        assertThat(client.lagFor(TASK_0_1), equalTo(1L));
    }

    @Test
    public void shouldThrowIllegalStateExceptionIfTaskLagsMapIsNotEmpty() {
        final Map<TaskId, Long> taskOffsetSums = Collections.singletonMap(TASK_0_1, 5L);
        final Map<TaskId, Long> allTaskEndOffsetSums = Collections.singletonMap(TASK_0_1, 1L);
        client.computeTaskLags(null, taskOffsetSums);
        assertThrows(IllegalStateException.class, () -> client.computeTaskLags(null, allTaskEndOffsetSums));
    }

    @Test
    public void shouldThrowIllegalStateExceptionOnLagForUnknownTask() {
        final Map<TaskId, Long> taskOffsetSums = Collections.singletonMap(TASK_0_1, 0L);
        final Map<TaskId, Long> allTaskEndOffsetSums = Collections.singletonMap(TASK_0_1, 500L);
        client.addPreviousTasksAndOffsetSums("c1", taskOffsetSums);
        client.computeTaskLags(null, allTaskEndOffsetSums);
        assertThrows(IllegalStateException.class, () -> client.lagFor(TASK_0_2));
    }

    @Test
    public void shouldThrowIllegalStateExceptionIfAttemptingToInitializeNonEmptyPrevTaskSets() {
        client.addPreviousActiveTasks(Collections.singleton(TASK_0_1));
        assertThrows(IllegalStateException.class, () -> client.initializePrevTasks(Collections.emptyMap(), false));
    }

    @Test
    public void shouldThrowIllegalStateExceptionIfAssignedTasksForConsumerToNonClientAssignActive() {
        assertThrows(IllegalStateException.class, () -> client.assignActiveToConsumer(TASK_0_0, "c1"));
    }

    @Test
    public void shouldReturnClientTags() {
        final Map<String, String> clientTags = mkMap(mkEntry("k1", "v1"));
        assertEquals(clientTags, new ClientState(null, 0, clientTags).clientTags());
    }

    @Test
    public void shouldReturnEmptyClientTagsMapByDefault() {
        assertTrue(new ClientState().clientTags().isEmpty());
    }

    @Test
    public void shouldSetProcessId() {
        assertEquals(UUID_1, new ClientState(UUID_1, 1).processId());
        assertEquals(UUID_2, new ClientState(UUID_2, mkMap()).processId());
        assertEquals(UUID_3, new ClientState(UUID_3, 1, mkMap()).processId());
        assertNull(new ClientState().processId());
    }

    @Test
    public void shouldCopyState() {
        final ClientState clientState = new ClientState(mkSet(new TaskId(0, 0)), mkSet(new TaskId(0, 1)), Collections.emptyMap(), EMPTY_CLIENT_TAGS, 1, uuidForInt(1));
        final ClientState clientStateCopy = new ClientState(clientState);

        assertEquals(clientStateCopy.processId(), clientState.processId());
        assertEquals(clientStateCopy.capacity(), clientState.capacity());
        assertEquals(clientStateCopy.prevActiveTasks(), clientStateCopy.prevActiveTasks());
        assertEquals(clientStateCopy.prevStandbyTasks(), clientStateCopy.prevStandbyTasks());
        assertThat(clientStateCopy.prevActiveTasks(), equalTo(clientState.prevActiveTasks()));
        assertThat(clientStateCopy.prevStandbyTasks(), equalTo(clientState.prevStandbyTasks()));
    }
}
