feat: bitpacked and base64 encoded VisitedRooms in player YAML to keep the file human readable

4 files changed, 199 insertions, 7 deletions

diff --git a/internal/player/player.go b/internal/player/player.go
index 65026e7..fcf274b 100644
--- a/internal/player/player.go
+++ b/internal/player/player.go
@@ -333,8 +333,7 @@ func New(name string) *Player {
 		RoomID:      0,
 		MapSymbols:  make(map[int]MapSymbolData),
 		Stats: PlayerStats{
-			RoomsVisited: make(map[int]bool),
-			MobKills:     make(map[string]int),
+			MobKills: make(map[string]int),
 		},
 	}
 	for _, s := range AllSkills {
diff --git a/internal/player/roomset.go b/internal/player/roomset.go
new file mode 100644
index 0000000..3565bb6
--- /dev/null
+++ b/internal/player/roomset.go
@@ -0,0 +1,109 @@
+package player
+
+import (
+	"encoding/base64"
+	"math/bits"
+
+	"gopkg.in/yaml.v3"
+)
+
+type RoomSet struct {
+	bits []byte
+}
+
+func (rs *RoomSet) Add(roomID int) {
+	if roomID < 0 {
+		return
+	}
+	byteIdx := roomID / 8
+	if byteIdx >= len(rs.bits) {
+		nb := make([]byte, byteIdx+1)
+		copy(nb, rs.bits)
+		rs.bits = nb
+	}
+	rs.bits[byteIdx] |= 1 << (roomID % 8)
+}
+
+func (rs *RoomSet) Has(roomID int) bool {
+	if roomID < 0 {
+		return false
+	}
+	byteIdx := roomID / 8
+	return byteIdx < len(rs.bits) && rs.bits[byteIdx]&(1<<(roomID%8)) != 0
+}
+
+func (rs *RoomSet) Len() int {
+	n := 0
+	for _, b := range rs.bits {
+		n += bits.OnesCount8(b)
+	}
+	return n
+}
+
+func (rs RoomSet) IsZero() bool {
+	return len(rs.bits) == 0
+}
+
+func (rs *RoomSet) Keys() []int {
+	var keys []int
+	for byteIdx, b := range rs.bits {
+		if b == 0 {
+			continue
+		}
+		base := byteIdx * 8
+		for bitIdx := 0; bitIdx < 8; bitIdx++ {
+			if b&(1<<bitIdx) != 0 {
+				keys = append(keys, base+bitIdx)
+			}
+		}
+	}
+	return keys
+}
+
+func (rs *RoomSet) Rekey(idMap map[int]int) (RoomSet, bool) {
+	var next RoomSet
+	changed := false
+	for _, k := range rs.Keys() {
+		newK, ok := idMap[k]
+		if !ok {
+			newK = k
+		} else if newK != k {
+			changed = true
+		}
+		next.Add(newK)
+	}
+	return next, changed
+}
+
+func NewRoomSetFrom(ids ...int) RoomSet {
+	var rs RoomSet
+	for _, id := range ids {
+		rs.Add(id)
+	}
+	return rs
+}
+
+func (rs RoomSet) MarshalYAML() (any, error) {
+	return base64.StdEncoding.EncodeToString(rs.bits), nil
+}
+
+func (rs *RoomSet) UnmarshalYAML(value *yaml.Node) error {
+	if value.Kind == yaml.ScalarNode && (value.Tag == "!!null" || value.Value == "null") {
+		rs.bits = nil
+		return nil
+	}
+	var s string
+	if err := value.Decode(&s); err != nil {
+		return err
+	}
+	if s == "" {
+		rs.bits = nil
+		return nil
+	}
+	b, err := base64.StdEncoding.DecodeString(s)
+	if err != nil {
+		return err
+	}
+	rs.bits = b
+	return nil
+}
diff --git a/internal/player/roomset_test.go b/internal/player/roomset_test.go
new file mode 100644
index 0000000..2b6b9cb
--- /dev/null
+++ b/internal/player/roomset_test.go
@@ -0,0 +1,87 @@
+package player
+
+import (
+	"strings"
+	"testing"
+
+	"gopkg.in/yaml.v3"
+)
+
+func TestRoomSetYAMLRoundTrip(t *testing.T) {
+	stats := PlayerStats{
+		RoomsVisited: NewRoomSetFrom(1, 5, 300),
+		MobKills:     map[string]int{"rat": 3},
+		TotalKills:   3,
+		Deaths:       0,
+	}
+	data, err := yaml.Marshal(stats)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	out := string(data)
+	if !strings.Contains(out, "rooms_visited:") {
+		t.Fatalf("expected rooms_visited key in output:\n%s", out)
+	}
+
+	var loaded PlayerStats
+	if err := yaml.Unmarshal(data, &loaded); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if loaded.RoomsVisited.Len() != 3 {
+		t.Errorf("Len = %d, want 3", loaded.RoomsVisited.Len())
+	}
+	for _, id := range []int{1, 5, 300} {
+		if !loaded.RoomsVisited.Has(id) {
+			t.Errorf("expected Has(%d) == true", id)
+		}
+	}
+	if loaded.RoomsVisited.Has(2) {
+		t.Error("expected Has(2) == false")
+	}
+}
+
+func TestRoomSetOmitEmpty(t *testing.T) {
+	stats := PlayerStats{}
+	data, err := yaml.Marshal(stats)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	out := string(data)
+	if strings.Contains(out, "rooms_visited:") {
+		t.Errorf("expected rooms_visited to be absent for empty set:\n%s", out)
+	}
+
+	var loaded PlayerStats
+	if err := yaml.Unmarshal(data, &loaded); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if loaded.RoomsVisited.Len() != 0 {
+		t.Errorf("Len = %d, want 0", loaded.RoomsVisited.Len())
+	}
+}
+
+func TestRoomSetIsZero(t *testing.T) {
+	var zero RoomSet
+	if !zero.IsZero() {
+		t.Error("zero value should be IsZero")
+	}
+	visited := NewRoomSetFrom(1)
+	if visited.IsZero() {
+		t.Error("non-empty set should not be IsZero")
+	}
+}
+
+func TestRoomSetMarshalEmpty(t *testing.T) {
+	var rs RoomSet
+	v, err := rs.MarshalYAML()
+	if err != nil {
+		t.Fatalf("MarshalYAML: %v", err)
+	}
+	s, ok := v.(string)
+	if !ok {
+		t.Fatalf("MarshalYAML returned %T, want string", v)
+	}
+	if s != "" {
+		t.Errorf("MarshalYAML empty = %q, want empty string", s)
+	}
+}
diff --git a/internal/player/stats.go b/internal/player/stats.go
index 82b741c..2b63558 100644
--- a/internal/player/stats.go
+++ b/internal/player/stats.go
@@ -1,17 +1,14 @@
 package player
 
 type PlayerStats struct {
-	RoomsVisited map[int]bool   `yaml:"rooms_visited,omitempty"`
+	RoomsVisited RoomSet        `yaml:"rooms_visited,omitempty"`
 	MobKills     map[string]int `yaml:"mob_kills,omitempty"`
 	TotalKills   int            `yaml:"total_kills"`
 	Deaths       int            `yaml:"deaths"`
 }
 
 func (s *PlayerStats) RecordRoomVisit(roomID int) {
-	if s.RoomsVisited == nil {
-		s.RoomsVisited = make(map[int]bool)
-	}
-	s.RoomsVisited[roomID] = true
+	s.RoomsVisited.Add(roomID)
 }
 
 func (s *PlayerStats) RecordMobKill(mobDefID string) {