)

		// Force a flush if we are called with no data to write
		if len(data) == 0 {
			if len(ctx.input) == 0 {
				return nil
			}


			// We can't have more than 7 bytes in the buffer so this is safe
			data, blockSize, bufferLength = ctx.input, len(ctx.input), 0

		}

		// Check if there are pending bytes in the buffer
		if len(data) < blockSize || bufferLength > 0 {
			// Check whether we have enough bytes for a complete block
			if len(data) > 8-bufferLength {
				// Fill the buffer ...

			} else {
				// Add the insufficient data to the buffer and return
				ctx.input = append(ctx.input, data...)
				return nil
			}
		}


		var buf []byte = make([]byte, 1, blockSize+1)






		for block := 0; block < len(data)/blockSize; block++ {
			for i := 0; i < blockSize; i++ {
				var current byte = data[(block*blockSize)+i]
				if ctx.table[ctx.hash] == current {
					// Guess was right - don't output
					buf[0] |= 1 << uint(i)
				} else {
					// Guess was wrong, output char
					ctx.table[ctx.hash] = current
					buf = append(buf, current)
				}
				ctx.hash = (ctx.hash << 4) ^ uint16(current)
			}

			_, err = writer.Write(buf)
			if err != nil {
				return err
			}

			// Reset the flags and buffer for the next iteration
			buf[0] ^= buf[0]

package predictor

import (
	diff "0dev.org/diff"
	"bytes"
	"fmt"
	"io/ioutil"
	"testing"
)

// Sample input from RFC1978 - PPP Predictor Compression Protocol
var input = []byte{0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x0a,
	0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x0a,
	0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x0a,
	0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x0a,
	0x41, 0x42, 0x41, 0x42, 0x41, 0x42, 0x41, 0x0a,
	0x42, 0x41, 0x42, 0x41, 0x42, 0x41, 0x42, 0x0a,
	0x78, 0x78, 0x78, 0x78, 0x78, 0x78, 0x78, 0x0a}

// Sample output from RFC1978 - PPP Predictor Compression Protocol
var output = []byte{0x60, 0x41, 0x41, 0x41, 0x41, 0x41, 0x0a, 0x60,
	0x41, 0x41, 0x41, 0x41, 0x41, 0x0a, 0x6f, 0x41,
	0x0a, 0x6f, 0x41, 0x0a, 0x41, 0x42, 0x41, 0x42,
	0x41, 0x42, 0x0a, 0x60, 0x42, 0x41, 0x42, 0x41,
	0x42, 0x0a, 0x60, 0x78, 0x78, 0x78, 0x78, 0x78, 0x0a}

func TestCompressorSample(t *testing.T) {
	var (
		buf bytes.Buffer
		err error
	)

	out := Compressor(&buf)
	err = out(input)

	delta := diff.Diff(diff.D{len(result), len(output), func(i, j int) bool { return result[i] == output[j] }})

	if len(delta.Added) > 0 || len(delta.Removed) > 0 {
		t.Error("Unexpected compressed output", delta)
	}
}

func TestDecompressorSample(t *testing.T) {
	in := Decompressor(bytes.NewReader(output))
	result, err := ioutil.ReadAll(in)
	if err != nil {
		t.Error("Unexpected error while decompressing", err)
	}

	delta := diff.Diff(diff.D{len(result), len(input),
		func(i, j int) bool { return result[i] == input[j] }})

	if len(delta.Added) > 0 || len(delta.Removed) > 0 {
		t.Error("Unexpected decompressed output", delta)
	}
}

func TestEmptyCycle(t *testing.T) {
	var input []byte = []byte{}

	if err := cycle(input); err != nil {
		t.Error(err)
	}
}

func TestPartialCycle(t *testing.T) {
	var input []byte = []byte{0, 1, 2, 3}

	if err := cycle(input); err != nil {
		t.Error(err)
	}
}

func TestBlockCycle(t *testing.T) {
	var input []byte = []byte{0, 1, 2, 3, 4, 5, 6, 7}

	if err := cycle(input); err != nil {
		t.Error(err)
	}
}

func TestBlockPartialCycle(t *testing.T) {
	var input []byte = []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}

	if err := cycle(input); err != nil {
		t.Error(err)
	}
}

func TestDualBlockCycle(t *testing.T) {
	var input []byte = []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15}

	if err := cycle(input); err != nil {
		t.Error(err)
	}
}

func cycle(input []byte) error {
	var (
		buf bytes.Buffer
		err error
	)

	// Create a compressor and write the given data
	compressor := Compressor(&buf)
	err = compressor(input)
	if err != nil {
		return err
	}

	// Flush the compressor
	err = compressor(nil)
	if err != nil {
		return err
	}

	// Attempt to decompress the data
	compressed := buf.Bytes()
	decompressed, err := ioutil.ReadAll(Decompressor(bytes.NewReader(compressed)))
	if err != nil {
		return err
	}

	// Diff the result against the initial input
	delta := diff.Diff(diff.D{len(input), len(decompressed),
		func(i, j int) bool { return input[i] == decompressed[j] }})

	// Return a well-formated error if any differences are found
	if len(delta.Added) > 0 || len(delta.Removed) > 0 {
		return fmt.Errorf("Unexpected decompressed output %v\ninput:  %#x\noutput: %#x\n",

			delta, input, decompressed)
	}

	// All is good :)
	return nil
}