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 * to you under the Apache License, Version 2.0 (the            *
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package org.apache.james.utils;

import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatThrownBy;

import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

import org.apache.james.utils.DiscreteDistribution.DistributionEntry;
import org.assertj.core.data.Offset;
import org.junit.jupiter.api.Test;

import com.google.common.collect.ImmutableList;

class DiscreteDistributionTest {
    public static final Offset<Long> OFFSET = Offset.offset(10_000L);

    @Test
    void createShouldNotSupportNegativeDistribution() {
        assertThatThrownBy(() -> new DistributionEntry<>("a", -1))
            .isInstanceOf(IllegalArgumentException.class);
    }

    @Test
    void createShouldSupportZeroDistribution() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 0),
                new DistributionEntry<>("b", 1)));

        assertThat(testee.generateRandomStream().limit(10)).containsOnly("b");
    }

    @Test
    void createShouldNotSupportEmptyDistribution() {
        assertThatThrownBy(() -> DiscreteDistribution.create(ImmutableList.of()))
            .isInstanceOf(IllegalArgumentException.class);
    }

    @Test
    void createShouldNotSupportEffectivelyEmptyDistribution() {
        assertThatThrownBy(() -> DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 0),
                new DistributionEntry<>("b", 0))))
            .isInstanceOf(IllegalArgumentException.class);
    }


    @Test
    void streamOfSingleDistributionMapShouldAlwaysReturnSameElement() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 1)));

        assertThat(testee.generateRandomStream().limit(10)).containsOnly("a");
    }

    @Test
    void streamOfEvenDistributionMapShouldReturnSameNumberOfEachElement() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 10),
                new DistributionEntry<>("b", 10)));

        Map<String, Long> experimentOutcome = testee.generateRandomStream().limit(1_000_000)
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
        assertThat(experimentOutcome.get("a"))
            .isCloseTo(experimentOutcome.get("b"), OFFSET);
    }

    @Test
    void streamOfSpecificDistributionMapShouldReturnTwiceMoreA() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 20),
                new DistributionEntry<>("b", 10)));

        Map<String, Long> experimentOutcome = testee.generateRandomStream().limit(1_000_000)
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
        assertThat(experimentOutcome.get("a"))
            .isCloseTo(experimentOutcome.get("b") * 2, OFFSET);
    }

    @Test
    void partitionShouldSupportDuplicatedDistributionEntry() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 10),
                new DistributionEntry<>("b", 10),
                new DistributionEntry<>("a", 10)));

        Map<String, Long> experimentOutcome = testee.generateRandomStream().limit(1_000_000)
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
        assertThat(experimentOutcome.get("a"))
            .isCloseTo(experimentOutcome.get("b") * 2, OFFSET);
    }

}