package cli

import (
	"bytes"
	"context"
	"hash/fnv"
	"io/ioutil"
	"sort"

	"github.com/pkg/errors"

	"github.com/kopia/kopia/internal/clock"
	"github.com/kopia/kopia/internal/units"
	"github.com/kopia/kopia/repo/compression"
)

var (
	benchmarkCompressionCommand      = benchmarkCommands.Command("compression", "Run compression benchmarks")
	benchmarkCompressionBlockSize    = benchmarkCompressionCommand.Flag("block-size", "Size of a block to compress").Default("1MB").Bytes()
	benchmarkCompressionRepeat       = benchmarkCompressionCommand.Flag("repeat", "Number of repetitions").Default("100").Int()
	benchmarkCompressionDataFile     = benchmarkCompressionCommand.Flag("data-file", "Use data from the given file instead of empty").ExistingFile()
	benchmarkCompressionBySize       = benchmarkCompressionCommand.Flag("by-size", "Sort results by size").Bool()
	benchmarkCompressionVerifyStable = benchmarkCompressionCommand.Flag("verify-stable", "Verify that compression is stable").Bool()
	benchmarkCompressionOptionPrint  = benchmarkCompressionCommand.Flag("print-options", "Print out options usable for repository creation").Bool()
)

func runBenchmarkCompressionAction(ctx context.Context) error {
	type benchResult struct {
		compression    compression.Name
		throughput     float64
		compressedSize int64
	}

	var results []benchResult

	data := make([]byte, *benchmarkCompressionBlockSize)

	if *benchmarkCompressionDataFile != "" {
		d, err := ioutil.ReadFile(*benchmarkCompressionDataFile)
		if err != nil {
			return errors.Wrap(err, "error reading compression data file")
		}

		data = d
	}

	for name, comp := range compression.ByName {
		log(ctx).Infof("Benchmarking compressor '%v' (%v x %v bytes)", name, *benchmarkCompressionRepeat, len(data))

		t0 := clock.Now()

		var compressedSize int64

		var lastHash uint64

		cnt := *benchmarkCompressionRepeat

		var compressed bytes.Buffer

		for i := 0; i < cnt; i++ {
			compressed.Reset()

			if err := comp.Compress(&compressed, data); err != nil {
				log(ctx).Errorf("compression %q failed: %v", name, err)
				continue
			}

			compressedSize = int64(compressed.Len())

			if *benchmarkCompressionVerifyStable {
				h := hashOf(compressed.Bytes())

				if i == 0 {
					lastHash = h
				} else if h != lastHash {
					log(ctx).Errorf("compression %q is not stable", name)
					continue
				}
			}
		}

		hashTime := clock.Since(t0)
		bytesPerSecond := float64(len(data)) * float64(cnt) / hashTime.Seconds()

		results = append(results, benchResult{compression: name, throughput: bytesPerSecond, compressedSize: compressedSize})
	}

	if *benchmarkCompressionBySize {
		sort.Slice(results, func(i, j int) bool {
			return results[i].compressedSize < results[j].compressedSize
		})
	} else {
		sort.Slice(results, func(i, j int) bool {
			return results[i].throughput > results[j].throughput
		})
	}

	printStdout("     %-30v %-15v %v\n", "Compression", "Compressed Size", "Throughput")
	printStdout("-----------------------------------------------------------------\n")

	for ndx, r := range results {
		printStdout("%3d. %-30v %-15v %v / second", ndx, r.compression, r.compressedSize, units.BytesStringBase2(int64(r.throughput)))

		if *benchmarkCompressionOptionPrint {
			printStdout(", --compression=%s", r.compression)
		}

		printStdout("\n")
	}

	return nil
}

func init() {
	benchmarkCompressionCommand.Action(noRepositoryAction(runBenchmarkCompressionAction))
}

func hashOf(b []byte) uint64 {
	h := fnv.New64a()
	h.Write(b) //nolint:errcheck

	return h.Sum64()
}