Finalmask: Add Sudoku (TCP & UDP) (#5685)

https://github.com/SUDOKU-ASCII/sudoku/issues/23#issuecomment-3859972396

transport/internet/finalmask/sudoku/codec.go

@@ -0,0 +1,163 @@
+package sudoku
+
+import (
+	"fmt"
+	"math/rand"
+)
+
+var perm4 = [24][4]byte{
+	{0, 1, 2, 3},
+	{0, 1, 3, 2},
+	{0, 2, 1, 3},
+	{0, 2, 3, 1},
+	{0, 3, 1, 2},
+	{0, 3, 2, 1},
+	{1, 0, 2, 3},
+	{1, 0, 3, 2},
+	{1, 2, 0, 3},
+	{1, 2, 3, 0},
+	{1, 3, 0, 2},
+	{1, 3, 2, 0},
+	{2, 0, 1, 3},
+	{2, 0, 3, 1},
+	{2, 1, 0, 3},
+	{2, 1, 3, 0},
+	{2, 3, 0, 1},
+	{2, 3, 1, 0},
+	{3, 0, 1, 2},
+	{3, 0, 2, 1},
+	{3, 1, 0, 2},
+	{3, 1, 2, 0},
+	{3, 2, 0, 1},
+	{3, 2, 1, 0},
+}
+
+type codec struct {
+	tables        []*table
+	rng           *rand.Rand
+	paddingChance int
+	tableIndex    int
+}
+
+func newCodec(tables []*table, pMin, pMax int) *codec {
+	if len(tables) == 0 {
+		tables = nil
+	}
+	rng := newSeededRand()
+	return &codec{
+		tables:        tables,
+		rng:           rng,
+		paddingChance: pickPaddingChance(rng, pMin, pMax),
+	}
+}
+
+func pickPaddingChance(rng *rand.Rand, pMin, pMax int) int {
+	if pMin < 0 {
+		pMin = 0
+	}
+	if pMax < pMin {
+		pMax = pMin
+	}
+	if pMin > 100 {
+		pMin = 100
+	}
+	if pMax > 100 {
+		pMax = 100
+	}
+	if pMax == pMin {
+		return pMin
+	}
+	return pMin + rng.Intn(pMax-pMin+1)
+}
+
+func (c *codec) shouldPad() bool {
+	if c.paddingChance <= 0 {
+		return false
+	}
+	if c.paddingChance >= 100 {
+		return true
+	}
+	return c.rng.Intn(100) < c.paddingChance
+}
+
+func (c *codec) currentTable() *table {
+	if len(c.tables) == 0 {
+		return nil
+	}
+	return c.tables[c.tableIndex%len(c.tables)]
+}
+
+func (c *codec) randomPadding(t *table) byte {
+	pool := t.layout.paddingPool
+	return pool[c.rng.Intn(len(pool))]
+}
+
+func (c *codec) encode(in []byte) ([]byte, error) {
+	if len(in) == 0 {
+		return nil, nil
+	}
+
+	out := make([]byte, 0, len(in)*6+8)
+	for _, b := range in {
+		t := c.currentTable()
+		if t == nil {
+			return nil, fmt.Errorf("sudoku table set missing")
+		}
+		if c.shouldPad() {
+			out = append(out, c.randomPadding(t))
+		}
+
+		enc := t.encode[b]
+		if len(enc) == 0 {
+			return nil, fmt.Errorf("sudoku encode table missing for byte %d", b)
+		}
+
+		hints := enc[c.rng.Intn(len(enc))]
+		perm := perm4[c.rng.Intn(len(perm4))]
+		for _, idx := range perm {
+			if c.shouldPad() {
+				out = append(out, c.randomPadding(t))
+			}
+			out = append(out, hints[idx])
+		}
+		c.tableIndex++
+	}
+
+	if c.shouldPad() {
+		if t := c.currentTable(); t != nil {
+			out = append(out, c.randomPadding(t))
+		}
+	}
+
+	return out, nil
+}
+
+func decodeBytes(tables []*table, tableIndex *int, in []byte, hintBuf []byte, out []byte) ([]byte, []byte, error) {
+	if len(tables) == 0 {
+		return hintBuf, out, fmt.Errorf("sudoku table set missing")
+	}
+	for _, b := range in {
+		t := tables[*tableIndex%len(tables)]
+		if !t.layout.isHint(b) {
+			continue
+		}
+
+		hintBuf = append(hintBuf, b)
+		if len(hintBuf) < 4 {
+			continue
+		}
+
+		keyBytes := sort4([4]byte{hintBuf[0], hintBuf[1], hintBuf[2], hintBuf[3]})
+		key := packKey(keyBytes)
+		decoded, ok := t.decode[key]
+		if !ok {
+			return hintBuf[:0], out, fmt.Errorf("invalid sudoku hint tuple")
+		}
+
+		out = append(out, decoded)
+		hintBuf = hintBuf[:0]
+		*tableIndex++
+	}
+
+	return hintBuf, out, nil
+}