// Copyright 2021 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 chunkenc

import (
	"testing"

	"github.com/prometheus/prometheus/pkg/histogram"
	"github.com/stretchr/testify/require"
)

func TestHistoChunkSameBuckets(t *testing.T) {

	c := NewHistoChunk()

	type res struct {
		t int64
		h histogram.SparseHistogram
	}

	// create fresh appender and add the first histogram

	app, err := c.Appender()
	require.NoError(t, err)
	require.Equal(t, 0, c.NumSamples())

	ts := int64(1234567890)

	h := histogram.SparseHistogram{
		Count:     5,
		ZeroCount: 2,
		Sum:       18.4,
		//ZeroThreshold: 1, TODO
		Schema: 1,
		PositiveSpans: []histogram.Span{
			{Offset: 0, Length: 2},
			{Offset: 1, Length: 2},
		},
		PositiveBuckets: []int64{1, 1, -1, 0}, // counts: 1, 2, 1, 1 (total 5)
		NegativeSpans:   nil,
		NegativeBuckets: []int64{},
	}

	app.AppendHistogram(ts, h)
	require.Equal(t, 1, c.NumSamples())

	exp := []res{
		{t: ts, h: h},
	}

	// add an updated histogram

	ts += 16
	h.Count += 9
	h.ZeroCount++
	h.Sum = 24.4
	h.PositiveBuckets = []int64{5, -2, 1, -2} // counts: 5, 3, 4, 2 (total 14)

	app.AppendHistogram(ts, h)
	exp = append(exp, res{t: ts, h: h})

	require.Equal(t, 2, c.NumSamples())

	// add update with new appender

	app, err = c.Appender()
	require.NoError(t, err)
	require.Equal(t, 2, c.NumSamples())

	ts += 14
	h.Count += 13
	h.ZeroCount += 2
	h.Sum = 24.4
	h.PositiveBuckets = []int64{6, 1, -3, 6} // counts: 6, 7, 4, 10 (total 27)

	app.AppendHistogram(ts, h)
	exp = append(exp, res{t: ts, h: h})

	require.Equal(t, 3, c.NumSamples())

	// 1. Expand iterator in simple case.
	it1 := c.iterator(nil)
	require.NoError(t, it1.Err())
	var res1 []res
	for it1.Next() {
		ts, h := it1.AtHistogram()
		res1 = append(res1, res{t: ts, h: h.Copy()})
	}
	require.NoError(t, it1.Err())
	require.Equal(t, exp, res1)

	// 2. Expand second iterator while reusing first one.
	//it2 := c.Iterator(it1)
	//var res2 []pair
	//for it2.Next() {
	//	ts, v := it2.At()
	//	res2 = append(res2, pair{t: ts, v: v})
	//	}
	//	require.NoError(t, it2.Err())
	//	require.Equal(t, exp, res2)

	// 3. Test iterator Seek.
	//	mid := len(exp) / 2

	//	it3 := c.Iterator(nil)
	//	var res3 []pair
	//	require.Equal(t, true, it3.Seek(exp[mid].t))
	// Below ones should not matter.
	//	require.Equal(t, true, it3.Seek(exp[mid].t))
	//	require.Equal(t, true, it3.Seek(exp[mid].t))
	//	ts, v = it3.At()
	//	res3 = append(res3, pair{t: ts, v: v})

	//	for it3.Next() {
	//		ts, v := it3.At()
	//		res3 = append(res3, pair{t: ts, v: v})
	//	}
	//	require.NoError(t, it3.Err())
	//	require.Equal(t, exp[mid:], res3)
	//	require.Equal(t, false, it3.Seek(exp[len(exp)-1].t+1))
}

// mimics the scenario described for compareSpans()
func TestHistoChunkBucketChanges(t *testing.T) {

	c := NewHistoChunk()

	type res struct {
		t int64
		h histogram.SparseHistogram
	}

	// create fresh appender and add the first histogram

	app, err := c.Appender()
	require.NoError(t, err)
	require.Equal(t, 0, c.NumSamples())

	ts1 := int64(1234567890)

	h1 := histogram.SparseHistogram{
		Count:     5,
		ZeroCount: 2,
		Sum:       18.4,
		//ZeroThreshold: 1, TODO
		Schema: 1,
		PositiveSpans: []histogram.Span{
			{Offset: 0, Length: 2},
			{Offset: 2, Length: 1},
			{Offset: 3, Length: 2},
			{Offset: 3, Length: 1},
			{Offset: 1, Length: 1},
		},
		PositiveBuckets: []int64{6, -3, 0, -1, 2, 1, -4}, // counts: 6, 3, 3, 2, 4, 5, 1 (total 24)
		NegativeSpans:   nil,
		NegativeBuckets: []int64{},
	}

	app.AppendHistogram(ts1, h1)
	require.Equal(t, 1, c.NumSamples())

	// add an new histogram that has expanded buckets

	ts2 := ts1 + 16
	h2 := h1
	h2.PositiveSpans = []histogram.Span{
		{Offset: 0, Length: 3},
		{Offset: 1, Length: 1},
		{Offset: 1, Length: 4},
		{Offset: 3, Length: 3},
	}
	h2.Count += 9
	h2.ZeroCount++
	h2.Sum = 30
	// existing histogram should get values converted from the above to: 6 3 0 3 0 0 2 4 5 0 1 (previous values with some new empty buckets in between)
	// so the new histogram should have new counts >= these per-bucket counts, e.g.:
	h2.PositiveBuckets = []int64{7, -2, -4, 2, -2, -1, 2, 3, 0, -5, 1} // 7 5 1 3 1 0 2 5 5 0 1 (total 30)

	app.AppendHistogram(ts2, h2)

	// TODO is this okay?
	// the appender can rewrite its own bytes slice but it is not able to update the HistoChunk, so our histochunk is outdated until we update it manually
	c.b = *(app.(*HistoAppender).b)
	require.Equal(t, 2, c.NumSamples())

	// because the 2nd histogram has expanded buckets, we should expect all histograms (in particular the first)
	// to come back using the new spans metadata as well as the expanded buckets
	h1.PositiveSpans = h2.PositiveSpans
	h1.PositiveBuckets = []int64{6, -3, -3, 3, -3, 0, 2, 2, 1, -5, 1}
	exp := []res{
		{t: ts1, h: h1},
		{t: ts2, h: h2},
	}
	it1 := c.iterator(nil)
	require.NoError(t, it1.Err())
	var res1 []res
	for it1.Next() {
		ts, h := it1.AtHistogram()
		res1 = append(res1, res{t: ts, h: h.Copy()})
	}
	require.NoError(t, it1.Err())
	require.Equal(t, exp, res1)
}