// Copyright 2017 The Prometheus Authors
// 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 storage

import (
	"fmt"
	"math"
	"sort"
	"testing"

	"github.com/prometheus/prometheus/pkg/labels"
	"github.com/prometheus/prometheus/tsdb/chunkenc"
	"github.com/prometheus/prometheus/tsdb/tsdbutil"
	"github.com/prometheus/prometheus/util/testutil"
)

func TestMergeStringSlices(t *testing.T) {
	for _, tc := range []struct {
		input    [][]string
		expected []string
	}{
		{},
		{[][]string{{"foo"}}, []string{"foo"}},
		{[][]string{{"foo"}, {"bar"}}, []string{"bar", "foo"}},
		{[][]string{{"foo"}, {"bar"}, {"baz"}}, []string{"bar", "baz", "foo"}},
	} {
		testutil.Equals(t, tc.expected, mergeStringSlices(tc.input))
	}
}

func TestMergeTwoStringSlices(t *testing.T) {
	for _, tc := range []struct {
		a, b, expected []string
	}{
		{[]string{}, []string{}, []string{}},
		{[]string{"foo"}, nil, []string{"foo"}},
		{nil, []string{"bar"}, []string{"bar"}},
		{[]string{"foo"}, []string{"bar"}, []string{"bar", "foo"}},
		{[]string{"foo"}, []string{"bar", "baz"}, []string{"bar", "baz", "foo"}},
		{[]string{"foo"}, []string{"foo"}, []string{"foo"}},
	} {
		testutil.Equals(t, tc.expected, mergeTwoStringSlices(tc.a, tc.b))
	}
}

func TestMergeQuerierWithChainMerger(t *testing.T) {
	for _, tc := range []struct {
		name          string
		querierSeries [][]Series
		extraQueriers []Querier

		expected SeriesSet
	}{
		{
			name:          "1 querier with no series",
			querierSeries: [][]Series{{}},
			expected:      NewMockSeriesSet(),
		},
		{
			name:          "many queriers with no series",
			querierSeries: [][]Series{{}, {}, {}, {}, {}, {}, {}},
			expected:      NewMockSeriesSet(),
		},
		{
			name: "1 querier, two series",
			querierSeries: [][]Series{{
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}}),
			}},
			expected: NewMockSeriesSet(
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}}),
			),
		},
		{
			name: "2 queriers, 1 different series each",
			querierSeries: [][]Series{{
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}}),
			}, {
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}}),
			}},
			expected: NewMockSeriesSet(
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}}),
			),
		},
		{
			name: "2 time unsorted queriers, 2 series each",
			querierSeries: [][]Series{{
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{5, 5}, sample{6, 6}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}}),
			}, {
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{3, 3}, sample{4, 4}}),
			}},
			expected: NewMockSeriesSet(
				NewListSeries(
					labels.FromStrings("bar", "baz"),
					[]tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}, sample{5, 5}, sample{6, 6}},
				),
				NewListSeries(
					labels.FromStrings("foo", "bar"),
					[]tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}, sample{3, 3}, sample{4, 4}},
				),
			),
		},
		{
			name: "5 queriers, only 2 queriers have 2 time unsorted series each",
			querierSeries: [][]Series{{}, {}, {
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{5, 5}, sample{6, 6}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}}),
			}, {
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{3, 3}, sample{4, 4}}),
			}, {}},
			expected: NewMockSeriesSet(
				NewListSeries(
					labels.FromStrings("bar", "baz"),
					[]tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}, sample{5, 5}, sample{6, 6}},
				),
				NewListSeries(
					labels.FromStrings("foo", "bar"),
					[]tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}, sample{3, 3}, sample{4, 4}},
				),
			),
		},
		{
			name: "2 queriers, only 2 queriers have 2 time unsorted series each, with 3 noop and one nil querier together",
			querierSeries: [][]Series{{}, {}, {
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{5, 5}, sample{6, 6}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}}),
			}, {
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{3, 3}, sample{4, 4}}),
			}, {}},
			extraQueriers: []Querier{NoopQuerier(), NoopQuerier(), nil, NoopQuerier()},
			expected: NewMockSeriesSet(
				NewListSeries(
					labels.FromStrings("bar", "baz"),
					[]tsdbutil.Sample{sample{1, 1}, sample{2, 2}, sample{3, 3}, sample{5, 5}, sample{6, 6}},
				),
				NewListSeries(
					labels.FromStrings("foo", "bar"),
					[]tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}, sample{3, 3}, sample{4, 4}},
				),
			),
		},
		{
			name: "2 queriers, with 2 series, one is overlapping",
			querierSeries: [][]Series{{}, {}, {
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{2, 21}, sample{3, 31}, sample{5, 5}, sample{6, 6}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}}),
			}, {
				NewListSeries(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 22}, sample{3, 32}}),
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{3, 3}, sample{4, 4}}),
			}, {}},
			expected: NewMockSeriesSet(
				NewListSeries(
					labels.FromStrings("bar", "baz"),
					[]tsdbutil.Sample{sample{1, 1}, sample{2, 21}, sample{3, 31}, sample{5, 5}, sample{6, 6}},
				),
				NewListSeries(
					labels.FromStrings("foo", "bar"),
					[]tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}, sample{3, 3}, sample{4, 4}},
				),
			),
		},
		{
			name: "2 queries, one with NaN samples series",
			querierSeries: [][]Series{{
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, math.NaN()}}),
			}, {
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{1, 1}}),
			}},
			expected: NewMockSeriesSet(
				NewListSeries(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, math.NaN()}, sample{1, 1}}),
			),
		},
	} {
		t.Run(tc.name, func(t *testing.T) {
			var qs []Querier
			for _, in := range tc.querierSeries {
				qs = append(qs, &mockQuerier{toReturn: in})
			}
			qs = append(qs, tc.extraQueriers...)

			mergedQuerier, _, _ := NewMergeQuerier(qs[0], qs, ChainedSeriesMerge).Select(false, nil)

			// Get all merged series upfront to make sure there are no incorrectly retained shared
			// buffers causing bugs.
			var mergedSeries []Series
			for mergedQuerier.Next() {
				mergedSeries = append(mergedSeries, mergedQuerier.At())
			}
			testutil.Ok(t, mergedQuerier.Err())

			for _, actualSeries := range mergedSeries {
				testutil.Assert(t, tc.expected.Next(), "Expected Next() to be true")
				expectedSeries := tc.expected.At()
				testutil.Equals(t, expectedSeries.Labels(), actualSeries.Labels())

				expSmpl, expErr := ExpandSamples(expectedSeries.Iterator())
				actSmpl, actErr := ExpandSamples(actualSeries.Iterator())
				testutil.Equals(t, expErr, actErr)
				testutil.Equals(t, expSmpl, actSmpl)
			}
			testutil.Assert(t, !tc.expected.Next(), "Expected Next() to be false")
		})
	}
}

func TestMergeChunkQuerierWithNoVerticalChunkSeriesMerger(t *testing.T) {
	for _, tc := range []struct {
		name             string
		chkQuerierSeries [][]ChunkSeries
		extraQueriers    []ChunkQuerier

		expected ChunkSeriesSet
	}{
		{
			name:             "one querier with no series",
			chkQuerierSeries: [][]ChunkSeries{{}},
			expected:         NewMockChunkSeriesSet(),
		},
		{
			name:             "many queriers with no series",
			chkQuerierSeries: [][]ChunkSeries{{}, {}, {}, {}, {}, {}, {}},
			expected:         NewMockChunkSeriesSet(),
		},
		{
			name: "one querier, two series",
			chkQuerierSeries: [][]ChunkSeries{{
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}}, []tsdbutil.Sample{sample{3, 3}}),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}}, []tsdbutil.Sample{sample{2, 2}}),
			}},
			expected: NewMockChunkSeriesSet(
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}}, []tsdbutil.Sample{sample{3, 3}}),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}}, []tsdbutil.Sample{sample{2, 2}}),
			),
		},
		{
			name: "two queriers, one different series each",
			chkQuerierSeries: [][]ChunkSeries{{
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}}, []tsdbutil.Sample{sample{3, 3}}),
			}, {
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}}, []tsdbutil.Sample{sample{2, 2}}),
			}},
			expected: NewMockChunkSeriesSet(
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}}, []tsdbutil.Sample{sample{3, 3}}),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}}, []tsdbutil.Sample{sample{2, 2}}),
			),
		},
		{
			name: "two queriers, two not in time order series each",
			chkQuerierSeries: [][]ChunkSeries{{
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{5, 5}}, []tsdbutil.Sample{sample{6, 6}}),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}}, []tsdbutil.Sample{sample{2, 2}}),
			}, {
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}}, []tsdbutil.Sample{sample{3, 3}}),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{3, 3}}, []tsdbutil.Sample{sample{4, 4}}),
			}},
			expected: NewMockChunkSeriesSet(
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
					[]tsdbutil.Sample{sample{1, 1}, sample{2, 2}},
					[]tsdbutil.Sample{sample{3, 3}},
					[]tsdbutil.Sample{sample{5, 5}},
					[]tsdbutil.Sample{sample{6, 6}},
				),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"),
					[]tsdbutil.Sample{sample{0, 0}, sample{1, 1}},
					[]tsdbutil.Sample{sample{2, 2}},
					[]tsdbutil.Sample{sample{3, 3}},
					[]tsdbutil.Sample{sample{4, 4}},
				),
			),
		},
		{
			name: "five queriers, only two have two not in time order series each",
			chkQuerierSeries: [][]ChunkSeries{{}, {}, {
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{5, 5}}, []tsdbutil.Sample{sample{6, 6}}),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}}, []tsdbutil.Sample{sample{2, 2}}),
			}, {
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}}, []tsdbutil.Sample{sample{3, 3}}),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{3, 3}}, []tsdbutil.Sample{sample{4, 4}}),
			}, {}},
			expected: NewMockChunkSeriesSet(
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
					[]tsdbutil.Sample{sample{1, 1}, sample{2, 2}},
					[]tsdbutil.Sample{sample{3, 3}},
					[]tsdbutil.Sample{sample{5, 5}},
					[]tsdbutil.Sample{sample{6, 6}},
				),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"),
					[]tsdbutil.Sample{sample{0, 0}, sample{1, 1}},
					[]tsdbutil.Sample{sample{2, 2}},
					[]tsdbutil.Sample{sample{3, 3}},
					[]tsdbutil.Sample{sample{4, 4}},
				),
			),
		},
		{
			name: "two queriers, with two not in time order series each, with 3 noop queries and one nil together",
			chkQuerierSeries: [][]ChunkSeries{{
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{5, 5}}, []tsdbutil.Sample{sample{6, 6}}),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, 0}, sample{1, 1}}, []tsdbutil.Sample{sample{2, 2}}),
			}, {
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"), []tsdbutil.Sample{sample{1, 1}, sample{2, 2}}, []tsdbutil.Sample{sample{3, 3}}),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{3, 3}}, []tsdbutil.Sample{sample{4, 4}}),
			}},
			extraQueriers: []ChunkQuerier{NoopChunkedQuerier(), NoopChunkedQuerier(), nil, NoopChunkedQuerier()},
			expected: NewMockChunkSeriesSet(
				NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
					[]tsdbutil.Sample{sample{1, 1}, sample{2, 2}},
					[]tsdbutil.Sample{sample{3, 3}},
					[]tsdbutil.Sample{sample{5, 5}},
					[]tsdbutil.Sample{sample{6, 6}},
				),
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"),
					[]tsdbutil.Sample{sample{0, 0}, sample{1, 1}},
					[]tsdbutil.Sample{sample{2, 2}},
					[]tsdbutil.Sample{sample{3, 3}},
					[]tsdbutil.Sample{sample{4, 4}},
				),
			),
		},
		{
			name: "two queries, one with NaN samples series",
			chkQuerierSeries: [][]ChunkSeries{{
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, math.NaN()}}),
			}, {
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{1, 1}}),
			}},
			expected: NewMockChunkSeriesSet(
				NewListChunkSeriesFromSamples(labels.FromStrings("foo", "bar"), []tsdbutil.Sample{sample{0, math.NaN()}}, []tsdbutil.Sample{sample{1, 1}}),
			),
		},
	} {
		t.Run(tc.name, func(t *testing.T) {
			var qs []ChunkQuerier
			for _, in := range tc.chkQuerierSeries {
				qs = append(qs, &mockChunkQurier{toReturn: in})
			}
			qs = append(qs, tc.extraQueriers...)

			merged, _, _ := NewMergeChunkQuerier(qs[0], qs, NewVerticalChunkSeriesMerger(nil)).Select(false, nil)
			for merged.Next() {
				testutil.Assert(t, tc.expected.Next(), "Expected Next() to be true")
				actualSeries := merged.At()
				expectedSeries := tc.expected.At()
				testutil.Equals(t, expectedSeries.Labels(), actualSeries.Labels())

				expChks, expErr := ExpandChunks(expectedSeries.Iterator())
				actChks, actErr := ExpandChunks(actualSeries.Iterator())
				testutil.Equals(t, expErr, actErr)
				testutil.Equals(t, expChks, actChks)

			}
			testutil.Ok(t, merged.Err())
			testutil.Assert(t, !tc.expected.Next(), "Expected Next() to be false")
		})
	}
}

type mockQuerier struct {
	baseQuerier

	toReturn []Series
}

type seriesByLabel []Series

func (a seriesByLabel) Len() int           { return len(a) }
func (a seriesByLabel) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
func (a seriesByLabel) Less(i, j int) bool { return labels.Compare(a[i].Labels(), a[j].Labels()) < 0 }

func (m *mockQuerier) Select(sortSeries bool, _ *SelectHints, _ ...*labels.Matcher) (SeriesSet, Warnings, error) {
	cpy := make([]Series, len(m.toReturn))
	copy(cpy, m.toReturn)
	if sortSeries {
		sort.Sort(seriesByLabel(cpy))
	}

	return NewMockSeriesSet(cpy...), nil, nil
}

type mockChunkQurier struct {
	baseQuerier

	toReturn []ChunkSeries
}

type chunkSeriesByLabel []ChunkSeries

func (a chunkSeriesByLabel) Len() int      { return len(a) }
func (a chunkSeriesByLabel) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a chunkSeriesByLabel) Less(i, j int) bool {
	return labels.Compare(a[i].Labels(), a[j].Labels()) < 0
}

func (m *mockChunkQurier) Select(sortSeries bool, _ *SelectHints, _ ...*labels.Matcher) (ChunkSeriesSet, Warnings, error) {
	cpy := make([]ChunkSeries, len(m.toReturn))
	copy(cpy, m.toReturn)
	if sortSeries {
		sort.Sort(chunkSeriesByLabel(cpy))
	}

	return NewMockChunkSeriesSet(cpy...), nil, nil
}

type mockSeriesSet struct {
	idx    int
	series []Series
}

func NewMockSeriesSet(series ...Series) SeriesSet {
	return &mockSeriesSet{
		idx:    -1,
		series: series,
	}
}

func (m *mockSeriesSet) Next() bool {
	m.idx++
	return m.idx < len(m.series)
}

func (m *mockSeriesSet) At() Series { return m.series[m.idx] }

func (m *mockSeriesSet) Err() error { return nil }

type mockChunkSeriesSet struct {
	idx    int
	series []ChunkSeries
}

func NewMockChunkSeriesSet(series ...ChunkSeries) ChunkSeriesSet {
	return &mockChunkSeriesSet{
		idx:    -1,
		series: series,
	}
}

func (m *mockChunkSeriesSet) Next() bool {
	m.idx++
	return m.idx < len(m.series)
}

func (m *mockChunkSeriesSet) At() ChunkSeries { return m.series[m.idx] }

func (m *mockChunkSeriesSet) Err() error { return nil }

func TestChainSampleIterator(t *testing.T) {
	for _, tc := range []struct {
		input    []chunkenc.Iterator
		expected []tsdbutil.Sample
	}{
		{
			input: []chunkenc.Iterator{
				NewListSeriesIterator([]tsdbutil.Sample{sample{0, 0}, sample{1, 1}}),
			},
			expected: []tsdbutil.Sample{sample{0, 0}, sample{1, 1}},
		},
		{
			input: []chunkenc.Iterator{
				NewListSeriesIterator([]tsdbutil.Sample{sample{0, 0}, sample{1, 1}}),
				NewListSeriesIterator([]tsdbutil.Sample{sample{2, 2}, sample{3, 3}}),
			},
			expected: []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}, sample{3, 3}},
		},
		{
			input: []chunkenc.Iterator{
				NewListSeriesIterator([]tsdbutil.Sample{sample{0, 0}, sample{3, 3}}),
				NewListSeriesIterator([]tsdbutil.Sample{sample{1, 1}, sample{4, 4}}),
				NewListSeriesIterator([]tsdbutil.Sample{sample{2, 2}, sample{5, 5}}),
			},
			expected: []tsdbutil.Sample{
				sample{0, 0}, sample{1, 1}, sample{2, 2}, sample{3, 3}, sample{4, 4}, sample{5, 5}},
		},
		// Overlap.
		{
			input: []chunkenc.Iterator{
				NewListSeriesIterator([]tsdbutil.Sample{sample{0, 0}, sample{1, 1}}),
				NewListSeriesIterator([]tsdbutil.Sample{sample{0, 0}, sample{2, 2}}),
				NewListSeriesIterator([]tsdbutil.Sample{sample{2, 2}, sample{3, 3}}),
				NewListSeriesIterator([]tsdbutil.Sample{}),
				NewListSeriesIterator([]tsdbutil.Sample{}),
				NewListSeriesIterator([]tsdbutil.Sample{}),
			},
			expected: []tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}, sample{3, 3}},
		},
	} {
		merged := newChainSampleIterator(tc.input)
		actual, err := ExpandSamples(merged)
		testutil.Ok(t, err)
		testutil.Equals(t, tc.expected, actual)
	}
}

func TestChainSampleIteratorSeek(t *testing.T) {
	for _, tc := range []struct {
		input    []chunkenc.Iterator
		seek     int64
		expected []tsdbutil.Sample
	}{
		{
			input: []chunkenc.Iterator{
				NewListSeriesIterator([]tsdbutil.Sample{sample{0, 0}, sample{1, 1}, sample{2, 2}}),
			},
			seek:     1,
			expected: []tsdbutil.Sample{sample{1, 1}, sample{2, 2}},
		},
		{
			input: []chunkenc.Iterator{
				NewListSeriesIterator([]tsdbutil.Sample{sample{0, 0}, sample{1, 1}}),
				NewListSeriesIterator([]tsdbutil.Sample{sample{2, 2}, sample{3, 3}}),
			},
			seek:     2,
			expected: []tsdbutil.Sample{sample{2, 2}, sample{3, 3}},
		},
		{
			input: []chunkenc.Iterator{
				NewListSeriesIterator([]tsdbutil.Sample{sample{0, 0}, sample{3, 3}}),
				NewListSeriesIterator([]tsdbutil.Sample{sample{1, 1}, sample{4, 4}}),
				NewListSeriesIterator([]tsdbutil.Sample{sample{2, 2}, sample{5, 5}}),
			},
			seek:     2,
			expected: []tsdbutil.Sample{sample{2, 2}, sample{3, 3}, sample{4, 4}, sample{5, 5}},
		},
	} {
		merged := newChainSampleIterator(tc.input)
		actual := []tsdbutil.Sample{}
		if merged.Seek(tc.seek) {
			t, v := merged.At()
			actual = append(actual, sample{t, v})
		}
		s, err := ExpandSamples(merged)
		testutil.Ok(t, err)
		actual = append(actual, s...)
		testutil.Equals(t, tc.expected, actual)
	}
}

var result []tsdbutil.Sample

func makeSeriesSet(numSeries, numSamples int) SeriesSet {
	series := []Series{}
	for j := 0; j < numSeries; j++ {
		labels := labels.Labels{{Name: "foo", Value: fmt.Sprintf("bar%d", j)}}
		samples := []tsdbutil.Sample{}
		for k := 0; k < numSamples; k++ {
			samples = append(samples, sample{t: int64(k), v: float64(k)})
		}
		series = append(series, NewListSeries(labels, samples))
	}
	return NewMockSeriesSet(series...)
}

func makeMergeSeriesSet(numSeriesSets, numSeries, numSamples int) SeriesSet {
	seriesSets := []genericSeriesSet{}
	for i := 0; i < numSeriesSets; i++ {
		seriesSets = append(seriesSets, &genericSeriesSetAdapter{makeSeriesSet(numSeries, numSamples)})
	}
	return &seriesSetAdapter{newGenericMergeSeriesSet(seriesSets, nil, (&seriesMergerAdapter{VerticalSeriesMergeFunc: ChainedSeriesMerge}).Merge)}
}

func benchmarkDrain(seriesSet SeriesSet, b *testing.B) {
	var err error
	for n := 0; n < b.N; n++ {
		for seriesSet.Next() {
			result, err = ExpandSamples(seriesSet.At().Iterator())
			testutil.Ok(b, err)
		}
	}
}

func BenchmarkNoMergeSeriesSet_100_100(b *testing.B) {
	seriesSet := makeSeriesSet(100, 100)
	benchmarkDrain(seriesSet, b)
}

func BenchmarkMergeSeriesSet(b *testing.B) {
	for _, bm := range []struct {
		numSeriesSets, numSeries, numSamples int
	}{
		{1, 100, 100},
		{10, 100, 100},
		{100, 100, 100},
	} {
		seriesSet := makeMergeSeriesSet(bm.numSeriesSets, bm.numSeries, bm.numSamples)
		b.Run(fmt.Sprintf("%d_%d_%d", bm.numSeriesSets, bm.numSeries, bm.numSamples), func(b *testing.B) {
			benchmarkDrain(seriesSet, b)
		})
	}
}