/*
Copyright 2011 The Perkeep 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 compressor

import (
	"math/rand"
	"testing"
)

func TestSum(t *testing.T) {
	var buf [100000]uint8
	rnd := rand.New(rand.NewSource(4))
	for i := range buf {
		buf[i] = uint8(rnd.Intn(256))
	}

	roll := func(offset, length int) *RollSum {
		rs := NewRollSum()
		for count := offset; count < length; count++ {
			rs.Roll(buf[count])
		}
		return rs
	}

	sum := func(offset, length int) uint32 {
		rs := roll(offset, length)
		return rs.Digest()
	}

	sum1a := sum(0, len(buf))
	sum1b := sum(1, len(buf))
	sum2a := sum(len(buf)-windowSize*5/2, len(buf)-windowSize)
	sum2b := sum(0, len(buf)-windowSize)
	sum3a := sum(0, windowSize+3)
	sum3b := sum(3, windowSize+3)

	if sum1a != sum1b {
		t.Errorf("sum1a=%d sum1b=%d", sum1a, sum1b)
	}
	if sum2a != sum2b {
		t.Errorf("sum2a=%d sum2b=%d", sum2a, sum2b)
	}
	if sum3a != sum3b {
		t.Errorf("sum3a=%d sum3b=%d", sum3a, sum3b)
	}

	end := 500
	rs := roll(0, windowSize)
	for i := range end {
		sumRoll := rs.Digest()
		newRoll := roll(i, i+windowSize).Digest()

		if sumRoll != newRoll {
			t.Errorf("Error: i=%d, buf[i]=%d, sumRoll=%d, newRoll=%d\n", i, buf[i], sumRoll, newRoll)
		}

		rs.Roll(buf[i+windowSize])
	}
}

func BenchmarkRollsum(b *testing.B) {
	const bufSize = 5 << 20
	buf := make([]byte, bufSize)
	for i := range buf {
		buf[i] = byte(rand.Int63())
	}

	b.ResetTimer()
	rs := NewRollSum()
	splits := 0
	for range b.N {
		splits = 0
		for _, b := range buf {
			rs.Roll(b)
			if rs.OnSplit() {
				_ = rs.Bits()
				splits++
			}
		}
	}
	b.SetBytes(bufSize)
	b.Logf("num splits = %d; every %d bytes", splits, int(float64(bufSize)/float64(splits)))
}
