package repository

import (
	"io"
	"math/rand"
	"os"
	"restic/backend"
	"restic/backend/mem"
	"restic/crypto"
	"restic/pack"
	"testing"
)

type randReader struct {
	src  rand.Source
	rand *rand.Rand
}

func newRandReader(src rand.Source) *randReader {
	return &randReader{
		src:  src,
		rand: rand.New(src),
	}
}

// Read generates len(p) random bytes and writes them into p. It
// always returns len(p) and a nil error.
func (r *randReader) Read(p []byte) (n int, err error) {
	for i := 0; i < len(p); i += 7 {
		val := r.src.Int63()
		for j := 0; i+j < len(p) && j < 7; j++ {
			p[i+j] = byte(val)
			val >>= 8
		}
	}
	return len(p), nil
}

func randomID(rd io.Reader) backend.ID {
	id := backend.ID{}
	_, err := io.ReadFull(rd, id[:])
	if err != nil {
		panic(err)
	}
	return id
}

const maxBlobSize = 1 << 20

func saveFile(t testing.TB, be Saver, filename string, n int) {
	f, err := os.Open(filename)
	if err != nil {
		t.Fatal(err)
	}

	data := make([]byte, n)
	m, err := io.ReadFull(f, data)

	if m != n {
		t.Fatalf("read wrong number of bytes from %v: want %v, got %v", filename, m, n)
	}

	if err = f.Close(); err != nil {
		t.Fatal(err)
	}

	h := backend.Handle{Type: backend.Data, Name: backend.Hash(data).String()}

	err = be.Save(h, data)
	if err != nil {
		t.Fatal(err)
	}

	err = os.Remove(filename)
	if err != nil {
		t.Fatal(err)
	}
}

func fillPacks(t testing.TB, rnd *randReader, be Saver, pm *packerManager, buf []byte) (bytes int) {
	for i := 0; i < 100; i++ {
		l := rnd.rand.Intn(1 << 20)
		seed := rnd.rand.Int63()

		packer, err := pm.findPacker(uint(l))
		if err != nil {
			t.Fatal(err)
		}

		rd := rand.New(rand.NewSource(seed))
		id := randomID(rd)
		buf = buf[:l]
		_, err = io.ReadFull(rd, buf)
		if err != nil {
			t.Fatal(err)
		}

		n, err := packer.Add(pack.Data, id, buf)
		if n != l {
			t.Errorf("Add() returned invalid number of bytes: want %v, got %v", n, l)
		}
		bytes += l

		if packer.Size() < minPackSize && pm.countPacker() < maxPackers {
			pm.insertPacker(packer)
			continue
		}

		bytesWritten, err := packer.Finalize()
		if err != nil {
			t.Fatal(err)
		}

		tmpfile := packer.Writer().(*os.File)
		saveFile(t, be, tmpfile.Name(), int(bytesWritten))
	}

	return bytes
}

func flushRemainingPacks(t testing.TB, rnd *randReader, be Saver, pm *packerManager) (bytes int) {
	if pm.countPacker() > 0 {
		for _, packer := range pm.packs {
			n, err := packer.Finalize()
			if err != nil {
				t.Fatal(err)
			}
			bytes += int(n)

			tmpfile := packer.Writer().(*os.File)
			saveFile(t, be, tmpfile.Name(), bytes)
		}
	}

	return bytes
}

type fakeBackend struct{}

func (f *fakeBackend) Save(h backend.Handle, data []byte) error {
	return nil
}

func TestPackerManager(t *testing.T) {
	rnd := newRandReader(rand.NewSource(23))

	be := mem.New()
	pm := NewPackerManager(be, crypto.NewRandomKey())

	blobBuf := make([]byte, maxBlobSize)

	bytes := fillPacks(t, rnd, be, pm, blobBuf)
	bytes += flushRemainingPacks(t, rnd, be, pm)

	t.Logf("saved %d bytes", bytes)
}

func BenchmarkPackerManager(t *testing.B) {
	rnd := newRandReader(rand.NewSource(23))

	be := &fakeBackend{}
	pm := NewPackerManager(be, crypto.NewRandomKey())
	blobBuf := make([]byte, maxBlobSize)

	t.ResetTimer()

	bytes := 0
	for i := 0; i < t.N; i++ {
		bytes += fillPacks(t, rnd, be, pm, blobBuf)
	}

	bytes += flushRemainingPacks(t, rnd, be, pm)
	t.Logf("saved %d bytes", bytes)
}