Merge pull request #852 from MichaelMure/move-around

move {bug,identity} to /entities, move input to /commands

28 files changed, 2205 insertions, 0 deletions

diff --git a/entities/bug/bug.go b/entities/bug/bug.go
new file mode 100644
index 00000000..213a4ca4
--- /dev/null
+++ b/entities/bug/bug.go
@@ -0,0 +1,179 @@
+// Package bug contains the bug data model and low-level related functions
+package bug
+
+import (
+	"fmt"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+)
+
+var _ Interface = &Bug{}
+var _ entity.Interface = &Bug{}
+
+// 1: original format
+// 2: no more legacy identities
+// 3: Ids are generated from the create operation serialized data instead of from the first git commit
+// 4: with DAG entity framework
+const formatVersion = 4
+
+var def = dag.Definition{
+	Typename:             "bug",
+	Namespace:            "bugs",
+	OperationUnmarshaler: operationUnmarshaller,
+	FormatVersion:        formatVersion,
+}
+
+var ClockLoader = dag.ClockLoader(def)
+
+// Bug holds the data of a bug thread, organized in a way close to
+// how it will be persisted inside Git. This is the data structure
+// used to merge two different version of the same Bug.
+type Bug struct {
+	*dag.Entity
+}
+
+// NewBug create a new Bug
+func NewBug() *Bug {
+	return &Bug{
+		Entity: dag.New(def),
+	}
+}
+
+func simpleResolvers(repo repository.ClockedRepo) entity.Resolvers {
+	return entity.Resolvers{
+		&identity.Identity{}: identity.NewSimpleResolver(repo),
+	}
+}
+
+// Read will read a bug from a repository
+func Read(repo repository.ClockedRepo, id entity.Id) (*Bug, error) {
+	return ReadWithResolver(repo, simpleResolvers(repo), id)
+}
+
+// ReadWithResolver will read a bug from its Id, with custom resolvers
+func ReadWithResolver(repo repository.ClockedRepo, resolvers entity.Resolvers, id entity.Id) (*Bug, error) {
+	e, err := dag.Read(def, repo, resolvers, id)
+	if err != nil {
+		return nil, err
+	}
+	return &Bug{Entity: e}, nil
+}
+
+type StreamedBug struct {
+	Bug *Bug
+	Err error
+}
+
+// ReadAll read and parse all local bugs
+func ReadAll(repo repository.ClockedRepo) <-chan StreamedBug {
+	return readAll(repo, simpleResolvers(repo))
+}
+
+// ReadAllWithResolver read and parse all local bugs
+func ReadAllWithResolver(repo repository.ClockedRepo, resolvers entity.Resolvers) <-chan StreamedBug {
+	return readAll(repo, resolvers)
+}
+
+// Read and parse all available bug with a given ref prefix
+func readAll(repo repository.ClockedRepo, resolvers entity.Resolvers) <-chan StreamedBug {
+	out := make(chan StreamedBug)
+
+	go func() {
+		defer close(out)
+
+		for streamedEntity := range dag.ReadAll(def, repo, resolvers) {
+			if streamedEntity.Err != nil {
+				out <- StreamedBug{
+					Err: streamedEntity.Err,
+				}
+			} else {
+				out <- StreamedBug{
+					Bug: &Bug{Entity: streamedEntity.Entity},
+				}
+			}
+		}
+	}()
+
+	return out
+}
+
+// ListLocalIds list all the available local bug ids
+func ListLocalIds(repo repository.Repo) ([]entity.Id, error) {
+	return dag.ListLocalIds(def, repo)
+}
+
+// Validate check if the Bug data is valid
+func (bug *Bug) Validate() error {
+	if err := bug.Entity.Validate(); err != nil {
+		return err
+	}
+
+	// The very first Op should be a CreateOp
+	firstOp := bug.FirstOp()
+	if firstOp == nil || firstOp.Type() != CreateOp {
+		return fmt.Errorf("first operation should be a Create op")
+	}
+
+	// Check that there is no more CreateOp op
+	for i, op := range bug.Operations() {
+		if i == 0 {
+			continue
+		}
+		if op.Type() == CreateOp {
+			return fmt.Errorf("only one Create op allowed")
+		}
+	}
+
+	return nil
+}
+
+// Append add a new Operation to the Bug
+func (bug *Bug) Append(op Operation) {
+	bug.Entity.Append(op)
+}
+
+// Operations return the ordered operations
+func (bug *Bug) Operations() []Operation {
+	source := bug.Entity.Operations()
+	result := make([]Operation, len(source))
+	for i, op := range source {
+		result[i] = op.(Operation)
+	}
+	return result
+}
+
+// Compile a bug in a easily usable snapshot
+func (bug *Bug) Compile() *Snapshot {
+	snap := &Snapshot{
+		id:     bug.Id(),
+		Status: OpenStatus,
+	}
+
+	for _, op := range bug.Operations() {
+		op.Apply(snap)
+		snap.Operations = append(snap.Operations, op)
+	}
+
+	return snap
+}
+
+// FirstOp lookup for the very first operation of the bug.
+// For a valid Bug, this operation should be a CreateOp
+func (bug *Bug) FirstOp() Operation {
+	if fo := bug.Entity.FirstOp(); fo != nil {
+		return fo.(Operation)
+	}
+	return nil
+}
+
+// LastOp lookup for the very last operation of the bug.
+// For a valid Bug, should never be nil
+func (bug *Bug) LastOp() Operation {
+	if lo := bug.Entity.LastOp(); lo != nil {
+		return lo.(Operation)
+	}
+	return nil
+}
diff --git a/entities/bug/bug_actions.go b/entities/bug/bug_actions.go
new file mode 100644
index 00000000..864c2052
--- /dev/null
+++ b/entities/bug/bug_actions.go
@@ -0,0 +1,74 @@
+package bug
+
+import (
+	"github.com/pkg/errors"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+)
+
+// Fetch retrieve updates from a remote
+// This does not change the local bugs state
+func Fetch(repo repository.Repo, remote string) (string, error) {
+	return dag.Fetch(def, repo, remote)
+}
+
+// Push update a remote with the local changes
+func Push(repo repository.Repo, remote string) (string, error) {
+	return dag.Push(def, repo, remote)
+}
+
+// Pull will do a Fetch + MergeAll
+// This function will return an error if a merge fail
+// Note: an author is necessary for the case where a merge commit is created, as this commit will
+// have an author and may be signed if a signing key is available.
+func Pull(repo repository.ClockedRepo, resolvers entity.Resolvers, remote string, mergeAuthor identity.Interface) error {
+	_, err := Fetch(repo, remote)
+	if err != nil {
+		return err
+	}
+
+	for merge := range MergeAll(repo, resolvers, remote, mergeAuthor) {
+		if merge.Err != nil {
+			return merge.Err
+		}
+		if merge.Status == entity.MergeStatusInvalid {
+			return errors.Errorf("merge failure: %s", merge.Reason)
+		}
+	}
+
+	return nil
+}
+
+// MergeAll will merge all the available remote bug
+// Note: an author is necessary for the case where a merge commit is created, as this commit will
+// have an author and may be signed if a signing key is available.
+func MergeAll(repo repository.ClockedRepo, resolvers entity.Resolvers, remote string, mergeAuthor identity.Interface) <-chan entity.MergeResult {
+	out := make(chan entity.MergeResult)
+
+	go func() {
+		defer close(out)
+
+		results := dag.MergeAll(def, repo, resolvers, remote, mergeAuthor)
+
+		// wrap the dag.Entity into a complete Bug
+		for result := range results {
+			result := result
+			if result.Entity != nil {
+				result.Entity = &Bug{
+					Entity: result.Entity.(*dag.Entity),
+				}
+			}
+			out <- result
+		}
+	}()
+
+	return out
+}
+
+// RemoveBug will remove a local bug from its entity.Id
+func RemoveBug(repo repository.ClockedRepo, id entity.Id) error {
+	return dag.Remove(def, repo, id)
+}
diff --git a/entities/bug/comment.go b/entities/bug/comment.go
new file mode 100644
index 00000000..fcf501ab
--- /dev/null
+++ b/entities/bug/comment.go
@@ -0,0 +1,45 @@
+package bug
+
+import (
+	"github.com/dustin/go-humanize"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/repository"
+	"github.com/MichaelMure/git-bug/util/timestamp"
+)
+
+// Comment represent a comment in a Bug
+type Comment struct {
+	// id should be the result of entity.CombineIds with the Bug id and the id
+	// of the Operation that created the comment
+	id      entity.Id
+	Author  identity.Interface
+	Message string
+	Files   []repository.Hash
+
+	// Creation time of the comment.
+	// Should be used only for human display, never for ordering as we can't rely on it in a distributed system.
+	UnixTime timestamp.Timestamp
+}
+
+// Id return the Comment identifier
+func (c Comment) Id() entity.Id {
+	if c.id == "" {
+		// simply panic as it would be a coding error (no id provided at construction)
+		panic("no id")
+	}
+	return c.id
+}
+
+// FormatTimeRel format the UnixTime of the comment for human consumption
+func (c Comment) FormatTimeRel() string {
+	return humanize.Time(c.UnixTime.Time())
+}
+
+func (c Comment) FormatTime() string {
+	return c.UnixTime.Time().Format("Mon Jan 2 15:04:05 2006 +0200")
+}
+
+// IsAuthored is a sign post method for gqlgen
+func (c Comment) IsAuthored() {}
diff --git a/entities/bug/err.go b/entities/bug/err.go
new file mode 100644
index 00000000..1bd174bb
--- /dev/null
+++ b/entities/bug/err.go
@@ -0,0 +1,17 @@
+package bug
+
+import (
+	"errors"
+
+	"github.com/MichaelMure/git-bug/entity"
+)
+
+var ErrBugNotExist = errors.New("bug doesn't exist")
+
+func NewErrMultipleMatchBug(matching []entity.Id) *entity.ErrMultipleMatch {
+	return entity.NewErrMultipleMatch("bug", matching)
+}
+
+func NewErrMultipleMatchOp(matching []entity.Id) *entity.ErrMultipleMatch {
+	return entity.NewErrMultipleMatch("operation", matching)
+}
diff --git a/entities/bug/interface.go b/entities/bug/interface.go
new file mode 100644
index 00000000..2ae31fd1
--- /dev/null
+++ b/entities/bug/interface.go
@@ -0,0 +1,44 @@
+package bug
+
+import (
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/repository"
+	"github.com/MichaelMure/git-bug/util/lamport"
+)
+
+type Interface interface {
+	// Id returns the Bug identifier
+	Id() entity.Id
+
+	// Validate checks if the Bug data is valid
+	Validate() error
+
+	// Append an operation into the staging area, to be committed later
+	Append(op Operation)
+
+	// Operations returns the ordered operations
+	Operations() []Operation
+
+	// NeedCommit indicates that the in-memory state changed and need to be commit in the repository
+	NeedCommit() bool
+
+	// Commit writes the staging area in Git and move the operations to the packs
+	Commit(repo repository.ClockedRepo) error
+
+	// FirstOp lookup for the very first operation of the bug.
+	// For a valid Bug, this operation should be a CreateOp
+	FirstOp() Operation
+
+	// LastOp lookup for the very last operation of the bug.
+	// For a valid Bug, should never be nil
+	LastOp() Operation
+
+	// Compile a bug in an easily usable snapshot
+	Compile() *Snapshot
+
+	// CreateLamportTime return the Lamport time of creation
+	CreateLamportTime() lamport.Time
+
+	// EditLamportTime return the Lamport time of the last edit
+	EditLamportTime() lamport.Time
+}
diff --git a/entities/bug/label.go b/entities/bug/label.go
new file mode 100644
index 00000000..79b5f591
--- /dev/null
+++ b/entities/bug/label.go
@@ -0,0 +1,95 @@
+package bug
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"image/color"
+
+	fcolor "github.com/fatih/color"
+
+	"github.com/MichaelMure/git-bug/util/text"
+)
+
+type Label string
+
+func (l Label) String() string {
+	return string(l)
+}
+
+// RGBA from a Label computed in a deterministic way
+func (l Label) Color() LabelColor {
+	// colors from: https://material-ui.com/style/color/
+	colors := []LabelColor{
+		{R: 244, G: 67, B: 54, A: 255},   // red
+		{R: 233, G: 30, B: 99, A: 255},   // pink
+		{R: 156, G: 39, B: 176, A: 255},  // purple
+		{R: 103, G: 58, B: 183, A: 255},  // deepPurple
+		{R: 63, G: 81, B: 181, A: 255},   // indigo
+		{R: 33, G: 150, B: 243, A: 255},  // blue
+		{R: 3, G: 169, B: 244, A: 255},   // lightBlue
+		{R: 0, G: 188, B: 212, A: 255},   // cyan
+		{R: 0, G: 150, B: 136, A: 255},   // teal
+		{R: 76, G: 175, B: 80, A: 255},   // green
+		{R: 139, G: 195, B: 74, A: 255},  // lightGreen
+		{R: 205, G: 220, B: 57, A: 255},  // lime
+		{R: 255, G: 235, B: 59, A: 255},  // yellow
+		{R: 255, G: 193, B: 7, A: 255},   // amber
+		{R: 255, G: 152, B: 0, A: 255},   // orange
+		{R: 255, G: 87, B: 34, A: 255},   // deepOrange
+		{R: 121, G: 85, B: 72, A: 255},   // brown
+		{R: 158, G: 158, B: 158, A: 255}, // grey
+		{R: 96, G: 125, B: 139, A: 255},  // blueGrey
+	}
+
+	id := 0
+	hash := sha256.Sum256([]byte(l))
+	for _, char := range hash {
+		id = (id + int(char)) % len(colors)
+	}
+
+	return colors[id]
+}
+
+func (l Label) Validate() error {
+	str := string(l)
+
+	if text.Empty(str) {
+		return fmt.Errorf("empty")
+	}
+
+	if !text.SafeOneLine(str) {
+		return fmt.Errorf("label has unsafe characters")
+	}
+
+	return nil
+}
+
+type LabelColor color.RGBA
+
+func (lc LabelColor) RGBA() color.RGBA {
+	return color.RGBA(lc)
+}
+
+func (lc LabelColor) Term256() Term256 {
+	red := Term256(lc.R) * 6 / 256
+	green := Term256(lc.G) * 6 / 256
+	blue := Term256(lc.B) * 6 / 256
+
+	return red*36 + green*6 + blue + 16
+}
+
+type Term256 int
+
+func (t Term256) Escape() string {
+	if fcolor.NoColor {
+		return ""
+	}
+	return fmt.Sprintf("\x1b[38;5;%dm", t)
+}
+
+func (t Term256) Unescape() string {
+	if fcolor.NoColor {
+		return ""
+	}
+	return "\x1b[0m"
+}
diff --git a/entities/bug/label_test.go b/entities/bug/label_test.go
new file mode 100644
index 00000000..49401c49
--- /dev/null
+++ b/entities/bug/label_test.go
@@ -0,0 +1,35 @@
+package bug
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestLabelRGBA(t *testing.T) {
+	rgba := Label("test1").Color()
+	expected := LabelColor{R: 0, G: 150, B: 136, A: 255}
+
+	require.Equal(t, expected, rgba)
+}
+
+func TestLabelRGBASimilar(t *testing.T) {
+	rgba := Label("test2").Color()
+	expected := LabelColor{R: 3, G: 169, B: 244, A: 255}
+
+	require.Equal(t, expected, rgba)
+}
+
+func TestLabelRGBAReverse(t *testing.T) {
+	rgba := Label("tset").Color()
+	expected := LabelColor{R: 63, G: 81, B: 181, A: 255}
+
+	require.Equal(t, expected, rgba)
+}
+
+func TestLabelRGBAEqual(t *testing.T) {
+	color1 := Label("test").Color()
+	color2 := Label("test").Color()
+
+	require.Equal(t, color1, color2)
+}
diff --git a/entities/bug/op_add_comment.go b/entities/bug/op_add_comment.go
new file mode 100644
index 00000000..2e6a39f9
--- /dev/null
+++ b/entities/bug/op_add_comment.go
@@ -0,0 +1,93 @@
+package bug
+
+import (
+	"fmt"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+	"github.com/MichaelMure/git-bug/util/text"
+	"github.com/MichaelMure/git-bug/util/timestamp"
+)
+
+var _ Operation = &AddCommentOperation{}
+var _ dag.OperationWithFiles = &AddCommentOperation{}
+
+// AddCommentOperation will add a new comment in the bug
+type AddCommentOperation struct {
+	dag.OpBase
+	Message string `json:"message"`
+	// TODO: change for a map[string]util.hash to store the filename ?
+	Files []repository.Hash `json:"files"`
+}
+
+func (op *AddCommentOperation) Id() entity.Id {
+	return dag.IdOperation(op, &op.OpBase)
+}
+
+func (op *AddCommentOperation) Apply(snapshot *Snapshot) {
+	snapshot.addActor(op.Author())
+	snapshot.addParticipant(op.Author())
+
+	comment := Comment{
+		id:       entity.CombineIds(snapshot.Id(), op.Id()),
+		Message:  op.Message,
+		Author:   op.Author(),
+		Files:    op.Files,
+		UnixTime: timestamp.Timestamp(op.UnixTime),
+	}
+
+	snapshot.Comments = append(snapshot.Comments, comment)
+
+	item := &AddCommentTimelineItem{
+		CommentTimelineItem: NewCommentTimelineItem(comment),
+	}
+
+	snapshot.Timeline = append(snapshot.Timeline, item)
+}
+
+func (op *AddCommentOperation) GetFiles() []repository.Hash {
+	return op.Files
+}
+
+func (op *AddCommentOperation) Validate() error {
+	if err := op.OpBase.Validate(op, AddCommentOp); err != nil {
+		return err
+	}
+
+	if !text.Safe(op.Message) {
+		return fmt.Errorf("message is not fully printable")
+	}
+
+	return nil
+}
+
+func NewAddCommentOp(author identity.Interface, unixTime int64, message string, files []repository.Hash) *AddCommentOperation {
+	return &AddCommentOperation{
+		OpBase:  dag.NewOpBase(AddCommentOp, author, unixTime),
+		Message: message,
+		Files:   files,
+	}
+}
+
+// AddCommentTimelineItem hold a comment in the timeline
+type AddCommentTimelineItem struct {
+	CommentTimelineItem
+}
+
+// IsAuthored is a sign post method for gqlgen
+func (a *AddCommentTimelineItem) IsAuthored() {}
+
+// AddComment is a convenience function to add a comment to a bug
+func AddComment(b Interface, author identity.Interface, unixTime int64, message string, files []repository.Hash, metadata map[string]string) (*AddCommentOperation, error) {
+	op := NewAddCommentOp(author, unixTime, message, files)
+	for key, val := range metadata {
+		op.SetMetadata(key, val)
+	}
+	if err := op.Validate(); err != nil {
+		return nil, err
+	}
+	b.Append(op)
+	return op, nil
+}
diff --git a/entities/bug/op_add_comment_test.go b/entities/bug/op_add_comment_test.go
new file mode 100644
index 00000000..6f29cb01
--- /dev/null
+++ b/entities/bug/op_add_comment_test.go
@@ -0,0 +1,18 @@
+package bug
+
+import (
+	"testing"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+)
+
+func TestAddCommentSerialize(t *testing.T) {
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *AddCommentOperation {
+		return NewAddCommentOp(author, unixTime, "message", nil)
+	})
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *AddCommentOperation {
+		return NewAddCommentOp(author, unixTime, "message", []repository.Hash{"hash1", "hash2"})
+	})
+}
diff --git a/entities/bug/op_create.go b/entities/bug/op_create.go
new file mode 100644
index 00000000..fdfa131b
--- /dev/null
+++ b/entities/bug/op_create.go
@@ -0,0 +1,112 @@
+package bug
+
+import (
+	"fmt"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+	"github.com/MichaelMure/git-bug/util/text"
+	"github.com/MichaelMure/git-bug/util/timestamp"
+)
+
+var _ Operation = &CreateOperation{}
+var _ dag.OperationWithFiles = &CreateOperation{}
+
+// CreateOperation define the initial creation of a bug
+type CreateOperation struct {
+	dag.OpBase
+	Title   string            `json:"title"`
+	Message string            `json:"message"`
+	Files   []repository.Hash `json:"files"`
+}
+
+func (op *CreateOperation) Id() entity.Id {
+	return dag.IdOperation(op, &op.OpBase)
+}
+
+func (op *CreateOperation) Apply(snapshot *Snapshot) {
+	// sanity check: will fail when adding a second Create
+	if snapshot.id != "" && snapshot.id != entity.UnsetId && snapshot.id != op.Id() {
+		return
+	}
+
+	snapshot.id = op.Id()
+
+	snapshot.addActor(op.Author())
+	snapshot.addParticipant(op.Author())
+
+	snapshot.Title = op.Title
+
+	comment := Comment{
+		id:       entity.CombineIds(snapshot.Id(), op.Id()),
+		Message:  op.Message,
+		Author:   op.Author(),
+		UnixTime: timestamp.Timestamp(op.UnixTime),
+	}
+
+	snapshot.Comments = []Comment{comment}
+	snapshot.Author = op.Author()
+	snapshot.CreateTime = op.Time()
+
+	snapshot.Timeline = []TimelineItem{
+		&CreateTimelineItem{
+			CommentTimelineItem: NewCommentTimelineItem(comment),
+		},
+	}
+}
+
+func (op *CreateOperation) GetFiles() []repository.Hash {
+	return op.Files
+}
+
+func (op *CreateOperation) Validate() error {
+	if err := op.OpBase.Validate(op, CreateOp); err != nil {
+		return err
+	}
+
+	if text.Empty(op.Title) {
+		return fmt.Errorf("title is empty")
+	}
+	if !text.SafeOneLine(op.Title) {
+		return fmt.Errorf("title has unsafe characters")
+	}
+
+	if !text.Safe(op.Message) {
+		return fmt.Errorf("message is not fully printable")
+	}
+
+	return nil
+}
+
+func NewCreateOp(author identity.Interface, unixTime int64, title, message string, files []repository.Hash) *CreateOperation {
+	return &CreateOperation{
+		OpBase:  dag.NewOpBase(CreateOp, author, unixTime),
+		Title:   title,
+		Message: message,
+		Files:   files,
+	}
+}
+
+// CreateTimelineItem replace a Create operation in the Timeline and hold its edition history
+type CreateTimelineItem struct {
+	CommentTimelineItem
+}
+
+// IsAuthored is a sign post method for gqlgen
+func (c *CreateTimelineItem) IsAuthored() {}
+
+// Create is a convenience function to create a bug
+func Create(author identity.Interface, unixTime int64, title, message string, files []repository.Hash, metadata map[string]string) (*Bug, *CreateOperation, error) {
+	b := NewBug()
+	op := NewCreateOp(author, unixTime, title, message, files)
+	for key, val := range metadata {
+		op.SetMetadata(key, val)
+	}
+	if err := op.Validate(); err != nil {
+		return nil, op, err
+	}
+	b.Append(op)
+	return b, op, nil
+}
diff --git a/entities/bug/op_create_test.go b/entities/bug/op_create_test.go
new file mode 100644
index 00000000..f2c9e675
--- /dev/null
+++ b/entities/bug/op_create_test.go
@@ -0,0 +1,67 @@
+package bug
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+	"github.com/MichaelMure/git-bug/util/timestamp"
+)
+
+func TestCreate(t *testing.T) {
+	snapshot := Snapshot{}
+
+	repo := repository.NewMockRepoClock()
+
+	rene, err := identity.NewIdentity(repo, "René Descartes", "rene@descartes.fr")
+	require.NoError(t, err)
+
+	unix := time.Now().Unix()
+
+	create := NewCreateOp(rene, unix, "title", "message", nil)
+
+	create.Apply(&snapshot)
+
+	id := create.Id()
+	require.NoError(t, id.Validate())
+
+	comment := Comment{
+		id:       entity.CombineIds(create.Id(), create.Id()),
+		Author:   rene,
+		Message:  "message",
+		UnixTime: timestamp.Timestamp(create.UnixTime),
+	}
+
+	expected := Snapshot{
+		id:    create.Id(),
+		Title: "title",
+		Comments: []Comment{
+			comment,
+		},
+		Author:       rene,
+		Participants: []identity.Interface{rene},
+		Actors:       []identity.Interface{rene},
+		CreateTime:   create.Time(),
+		Timeline: []TimelineItem{
+			&CreateTimelineItem{
+				CommentTimelineItem: NewCommentTimelineItem(comment),
+			},
+		},
+	}
+
+	require.Equal(t, expected, snapshot)
+}
+
+func TestCreateSerialize(t *testing.T) {
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *CreateOperation {
+		return NewCreateOp(author, unixTime, "title", "message", nil)
+	})
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *CreateOperation {
+		return NewCreateOp(author, unixTime, "title", "message", []repository.Hash{"hash1", "hash2"})
+	})
+}
diff --git a/entities/bug/op_edit_comment.go b/entities/bug/op_edit_comment.go
new file mode 100644
index 00000000..41079f45
--- /dev/null
+++ b/entities/bug/op_edit_comment.go
@@ -0,0 +1,129 @@
+package bug
+
+import (
+	"fmt"
+
+	"github.com/pkg/errors"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+	"github.com/MichaelMure/git-bug/util/timestamp"
+
+	"github.com/MichaelMure/git-bug/util/text"
+)
+
+var _ Operation = &EditCommentOperation{}
+var _ dag.OperationWithFiles = &EditCommentOperation{}
+
+// EditCommentOperation will change a comment in the bug
+type EditCommentOperation struct {
+	dag.OpBase
+	Target  entity.Id         `json:"target"`
+	Message string            `json:"message"`
+	Files   []repository.Hash `json:"files"`
+}
+
+func (op *EditCommentOperation) Id() entity.Id {
+	return dag.IdOperation(op, &op.OpBase)
+}
+
+func (op *EditCommentOperation) Apply(snapshot *Snapshot) {
+	// Todo: currently any message can be edited, even by a different author
+	// crypto signature are needed.
+
+	// Recreate the Comment Id to match on
+	commentId := entity.CombineIds(snapshot.Id(), op.Target)
+
+	var target TimelineItem
+	for i, item := range snapshot.Timeline {
+		if item.Id() == commentId {
+			target = snapshot.Timeline[i]
+			break
+		}
+	}
+
+	if target == nil {
+		// Target not found, edit is a no-op
+		return
+	}
+
+	comment := Comment{
+		id:       commentId,
+		Message:  op.Message,
+		Files:    op.Files,
+		UnixTime: timestamp.Timestamp(op.UnixTime),
+	}
+
+	switch target := target.(type) {
+	case *CreateTimelineItem:
+		target.Append(comment)
+	case *AddCommentTimelineItem:
+		target.Append(comment)
+	default:
+		// somehow, the target matched on something that is not a comment
+		// we make the op a no-op
+		return
+	}
+
+	snapshot.addActor(op.Author())
+
+	// Updating the corresponding comment
+
+	for i := range snapshot.Comments {
+		if snapshot.Comments[i].Id() == commentId {
+			snapshot.Comments[i].Message = op.Message
+			snapshot.Comments[i].Files = op.Files
+			break
+		}
+	}
+}
+
+func (op *EditCommentOperation) GetFiles() []repository.Hash {
+	return op.Files
+}
+
+func (op *EditCommentOperation) Validate() error {
+	if err := op.OpBase.Validate(op, EditCommentOp); err != nil {
+		return err
+	}
+
+	if err := op.Target.Validate(); err != nil {
+		return errors.Wrap(err, "target hash is invalid")
+	}
+
+	if !text.Safe(op.Message) {
+		return fmt.Errorf("message is not fully printable")
+	}
+
+	return nil
+}
+
+func NewEditCommentOp(author identity.Interface, unixTime int64, target entity.Id, message string, files []repository.Hash) *EditCommentOperation {
+	return &EditCommentOperation{
+		OpBase:  dag.NewOpBase(EditCommentOp, author, unixTime),
+		Target:  target,
+		Message: message,
+		Files:   files,
+	}
+}
+
+// EditComment is a convenience function to apply the operation
+func EditComment(b Interface, author identity.Interface, unixTime int64, target entity.Id, message string, files []repository.Hash, metadata map[string]string) (*EditCommentOperation, error) {
+	op := NewEditCommentOp(author, unixTime, target, message, files)
+	for key, val := range metadata {
+		op.SetMetadata(key, val)
+	}
+	if err := op.Validate(); err != nil {
+		return nil, err
+	}
+	b.Append(op)
+	return op, nil
+}
+
+// EditCreateComment is a convenience function to edit the body of a bug (the first comment)
+func EditCreateComment(b Interface, author identity.Interface, unixTime int64, message string, files []repository.Hash, metadata map[string]string) (*EditCommentOperation, error) {
+	createOp := b.FirstOp().(*CreateOperation)
+	return EditComment(b, author, unixTime, createOp.Id(), message, files, metadata)
+}
diff --git a/entities/bug/op_edit_comment_test.go b/entities/bug/op_edit_comment_test.go
new file mode 100644
index 00000000..1b649cd1
--- /dev/null
+++ b/entities/bug/op_edit_comment_test.go
@@ -0,0 +1,84 @@
+package bug
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+)
+
+func TestEdit(t *testing.T) {
+	snapshot := Snapshot{}
+
+	repo := repository.NewMockRepo()
+
+	rene, err := identity.NewIdentity(repo, "René Descartes", "rene@descartes.fr")
+	require.NoError(t, err)
+
+	unix := time.Now().Unix()
+
+	create := NewCreateOp(rene, unix, "title", "create", nil)
+	create.Apply(&snapshot)
+
+	require.NoError(t, create.Id().Validate())
+
+	comment1 := NewAddCommentOp(rene, unix, "comment 1", nil)
+	comment1.Apply(&snapshot)
+
+	require.NoError(t, comment1.Id().Validate())
+
+	// add another unrelated op in between
+	setTitle := NewSetTitleOp(rene, unix, "edited title", "title")
+	setTitle.Apply(&snapshot)
+
+	comment2 := NewAddCommentOp(rene, unix, "comment 2", nil)
+	comment2.Apply(&snapshot)
+
+	require.NoError(t, comment2.Id().Validate())
+
+	edit := NewEditCommentOp(rene, unix, create.Id(), "create edited", nil)
+	edit.Apply(&snapshot)
+
+	require.Len(t, snapshot.Timeline, 4)
+	require.Len(t, snapshot.Timeline[0].(*CreateTimelineItem).History, 2)
+	require.Len(t, snapshot.Timeline[1].(*AddCommentTimelineItem).History, 1)
+	require.Len(t, snapshot.Timeline[3].(*AddCommentTimelineItem).History, 1)
+	require.Equal(t, snapshot.Comments[0].Message, "create edited")
+	require.Equal(t, snapshot.Comments[1].Message, "comment 1")
+	require.Equal(t, snapshot.Comments[2].Message, "comment 2")
+
+	edit2 := NewEditCommentOp(rene, unix, comment1.Id(), "comment 1 edited", nil)
+	edit2.Apply(&snapshot)
+
+	require.Len(t, snapshot.Timeline, 4)
+	require.Len(t, snapshot.Timeline[0].(*CreateTimelineItem).History, 2)
+	require.Len(t, snapshot.Timeline[1].(*AddCommentTimelineItem).History, 2)
+	require.Len(t, snapshot.Timeline[3].(*AddCommentTimelineItem).History, 1)
+	require.Equal(t, snapshot.Comments[0].Message, "create edited")
+	require.Equal(t, snapshot.Comments[1].Message, "comment 1 edited")
+	require.Equal(t, snapshot.Comments[2].Message, "comment 2")
+
+	edit3 := NewEditCommentOp(rene, unix, comment2.Id(), "comment 2 edited", nil)
+	edit3.Apply(&snapshot)
+
+	require.Len(t, snapshot.Timeline, 4)
+	require.Len(t, snapshot.Timeline[0].(*CreateTimelineItem).History, 2)
+	require.Len(t, snapshot.Timeline[1].(*AddCommentTimelineItem).History, 2)
+	require.Len(t, snapshot.Timeline[3].(*AddCommentTimelineItem).History, 2)
+	require.Equal(t, snapshot.Comments[0].Message, "create edited")
+	require.Equal(t, snapshot.Comments[1].Message, "comment 1 edited")
+	require.Equal(t, snapshot.Comments[2].Message, "comment 2 edited")
+}
+
+func TestEditCommentSerialize(t *testing.T) {
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *EditCommentOperation {
+		return NewEditCommentOp(author, unixTime, "target", "message", nil)
+	})
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *EditCommentOperation {
+		return NewEditCommentOp(author, unixTime, "target", "message", []repository.Hash{"hash1", "hash2"})
+	})
+}
diff --git a/entities/bug/op_label_change.go b/entities/bug/op_label_change.go
new file mode 100644
index 00000000..45441f7c
--- /dev/null
+++ b/entities/bug/op_label_change.go
@@ -0,0 +1,292 @@
+package bug
+
+import (
+	"fmt"
+	"io"
+	"sort"
+	"strconv"
+
+	"github.com/pkg/errors"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/util/timestamp"
+)
+
+var _ Operation = &LabelChangeOperation{}
+
+// LabelChangeOperation define a Bug operation to add or remove labels
+type LabelChangeOperation struct {
+	dag.OpBase
+	Added   []Label `json:"added"`
+	Removed []Label `json:"removed"`
+}
+
+func (op *LabelChangeOperation) Id() entity.Id {
+	return dag.IdOperation(op, &op.OpBase)
+}
+
+// Apply applies the operation
+func (op *LabelChangeOperation) Apply(snapshot *Snapshot) {
+	snapshot.addActor(op.Author())
+
+	// Add in the set
+AddLoop:
+	for _, added := range op.Added {
+		for _, label := range snapshot.Labels {
+			if label == added {
+				// Already exist
+				continue AddLoop
+			}
+		}
+
+		snapshot.Labels = append(snapshot.Labels, added)
+	}
+
+	// Remove in the set
+	for _, removed := range op.Removed {
+		for i, label := range snapshot.Labels {
+			if label == removed {
+				snapshot.Labels[i] = snapshot.Labels[len(snapshot.Labels)-1]
+				snapshot.Labels = snapshot.Labels[:len(snapshot.Labels)-1]
+			}
+		}
+	}
+
+	// Sort
+	sort.Slice(snapshot.Labels, func(i, j int) bool {
+		return string(snapshot.Labels[i]) < string(snapshot.Labels[j])
+	})
+
+	item := &LabelChangeTimelineItem{
+		id:       op.Id(),
+		Author:   op.Author(),
+		UnixTime: timestamp.Timestamp(op.UnixTime),
+		Added:    op.Added,
+		Removed:  op.Removed,
+	}
+
+	snapshot.Timeline = append(snapshot.Timeline, item)
+}
+
+func (op *LabelChangeOperation) Validate() error {
+	if err := op.OpBase.Validate(op, LabelChangeOp); err != nil {
+		return err
+	}
+
+	for _, l := range op.Added {
+		if err := l.Validate(); err != nil {
+			return errors.Wrap(err, "added label")
+		}
+	}
+
+	for _, l := range op.Removed {
+		if err := l.Validate(); err != nil {
+			return errors.Wrap(err, "removed label")
+		}
+	}
+
+	if len(op.Added)+len(op.Removed) <= 0 {
+		return fmt.Errorf("no label change")
+	}
+
+	return nil
+}
+
+func NewLabelChangeOperation(author identity.Interface, unixTime int64, added, removed []Label) *LabelChangeOperation {
+	return &LabelChangeOperation{
+		OpBase:  dag.NewOpBase(LabelChangeOp, author, unixTime),
+		Added:   added,
+		Removed: removed,
+	}
+}
+
+type LabelChangeTimelineItem struct {
+	id       entity.Id
+	Author   identity.Interface
+	UnixTime timestamp.Timestamp
+	Added    []Label
+	Removed  []Label
+}
+
+func (l LabelChangeTimelineItem) Id() entity.Id {
+	return l.id
+}
+
+// IsAuthored is a sign post method for gqlgen
+func (l LabelChangeTimelineItem) IsAuthored() {}
+
+// ChangeLabels is a convenience function to change labels on a bug
+func ChangeLabels(b Interface, author identity.Interface, unixTime int64, add, remove []string, metadata map[string]string) ([]LabelChangeResult, *LabelChangeOperation, error) {
+	var added, removed []Label
+	var results []LabelChangeResult
+
+	snap := b.Compile()
+
+	for _, str := range add {
+		label := Label(str)
+
+		// check for duplicate
+		if labelExist(added, label) {
+			results = append(results, LabelChangeResult{Label: label, Status: LabelChangeDuplicateInOp})
+			continue
+		}
+
+		// check that the label doesn't already exist
+		if labelExist(snap.Labels, label) {
+			results = append(results, LabelChangeResult{Label: label, Status: LabelChangeAlreadySet})
+			continue
+		}
+
+		added = append(added, label)
+		results = append(results, LabelChangeResult{Label: label, Status: LabelChangeAdded})
+	}
+
+	for _, str := range remove {
+		label := Label(str)
+
+		// check for duplicate
+		if labelExist(removed, label) {
+			results = append(results, LabelChangeResult{Label: label, Status: LabelChangeDuplicateInOp})
+			continue
+		}
+
+		// check that the label actually exist
+		if !labelExist(snap.Labels, label) {
+			results = append(results, LabelChangeResult{Label: label, Status: LabelChangeDoesntExist})
+			continue
+		}
+
+		removed = append(removed, label)
+		results = append(results, LabelChangeResult{Label: label, Status: LabelChangeRemoved})
+	}
+
+	if len(added) == 0 && len(removed) == 0 {
+		return results, nil, fmt.Errorf("no label added or removed")
+	}
+
+	op := NewLabelChangeOperation(author, unixTime, added, removed)
+	for key, val := range metadata {
+		op.SetMetadata(key, val)
+	}
+	if err := op.Validate(); err != nil {
+		return nil, nil, err
+	}
+
+	b.Append(op)
+
+	return results, op, nil
+}
+
+// ForceChangeLabels is a convenience function to apply the operation
+// The difference with ChangeLabels is that no checks of deduplications are done. You are entirely
+// responsible for what you are doing. In the general case, you want to use ChangeLabels instead.
+// The intended use of this function is to allow importers to create legal but unexpected label changes,
+// like removing a label with no information of when it was added before.
+func ForceChangeLabels(b Interface, author identity.Interface, unixTime int64, add, remove []string, metadata map[string]string) (*LabelChangeOperation, error) {
+	added := make([]Label, len(add))
+	for i, str := range add {
+		added[i] = Label(str)
+	}
+
+	removed := make([]Label, len(remove))
+	for i, str := range remove {
+		removed[i] = Label(str)
+	}
+
+	op := NewLabelChangeOperation(author, unixTime, added, removed)
+
+	for key, val := range metadata {
+		op.SetMetadata(key, val)
+	}
+	if err := op.Validate(); err != nil {
+		return nil, err
+	}
+
+	b.Append(op)
+
+	return op, nil
+}
+
+func labelExist(labels []Label, label Label) bool {
+	for _, l := range labels {
+		if l == label {
+			return true
+		}
+	}
+
+	return false
+}
+
+type LabelChangeStatus int
+
+const (
+	_ LabelChangeStatus = iota
+	LabelChangeAdded
+	LabelChangeRemoved
+	LabelChangeDuplicateInOp
+	LabelChangeAlreadySet
+	LabelChangeDoesntExist
+)
+
+func (l LabelChangeStatus) MarshalGQL(w io.Writer) {
+	switch l {
+	case LabelChangeAdded:
+		_, _ = fmt.Fprintf(w, strconv.Quote("ADDED"))
+	case LabelChangeRemoved:
+		_, _ = fmt.Fprintf(w, strconv.Quote("REMOVED"))
+	case LabelChangeDuplicateInOp:
+		_, _ = fmt.Fprintf(w, strconv.Quote("DUPLICATE_IN_OP"))
+	case LabelChangeAlreadySet:
+		_, _ = fmt.Fprintf(w, strconv.Quote("ALREADY_EXIST"))
+	case LabelChangeDoesntExist:
+		_, _ = fmt.Fprintf(w, strconv.Quote("DOESNT_EXIST"))
+	default:
+		panic("missing case")
+	}
+}
+
+func (l *LabelChangeStatus) UnmarshalGQL(v interface{}) error {
+	str, ok := v.(string)
+	if !ok {
+		return fmt.Errorf("enums must be strings")
+	}
+	switch str {
+	case "ADDED":
+		*l = LabelChangeAdded
+	case "REMOVED":
+		*l = LabelChangeRemoved
+	case "DUPLICATE_IN_OP":
+		*l = LabelChangeDuplicateInOp
+	case "ALREADY_EXIST":
+		*l = LabelChangeAlreadySet
+	case "DOESNT_EXIST":
+		*l = LabelChangeDoesntExist
+	default:
+		return fmt.Errorf("%s is not a valid LabelChangeStatus", str)
+	}
+	return nil
+}
+
+type LabelChangeResult struct {
+	Label  Label
+	Status LabelChangeStatus
+}
+
+func (l LabelChangeResult) String() string {
+	switch l.Status {
+	case LabelChangeAdded:
+		return fmt.Sprintf("label %s added", l.Label)
+	case LabelChangeRemoved:
+		return fmt.Sprintf("label %s removed", l.Label)
+	case LabelChangeDuplicateInOp:
+		return fmt.Sprintf("label %s is a duplicate", l.Label)
+	case LabelChangeAlreadySet:
+		return fmt.Sprintf("label %s was already set", l.Label)
+	case LabelChangeDoesntExist:
+		return fmt.Sprintf("label %s doesn't exist on this bug", l.Label)
+	default:
+		panic(fmt.Sprintf("unknown label change status %v", l.Status))
+	}
+}
diff --git a/entities/bug/op_label_change_test.go b/entities/bug/op_label_change_test.go
new file mode 100644
index 00000000..edbe4714
--- /dev/null
+++ b/entities/bug/op_label_change_test.go
@@ -0,0 +1,20 @@
+package bug
+
+import (
+	"testing"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+)
+
+func TestLabelChangeSerialize(t *testing.T) {
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *LabelChangeOperation {
+		return NewLabelChangeOperation(author, unixTime, []Label{"added"}, []Label{"removed"})
+	})
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *LabelChangeOperation {
+		return NewLabelChangeOperation(author, unixTime, []Label{"added"}, nil)
+	})
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *LabelChangeOperation {
+		return NewLabelChangeOperation(author, unixTime, nil, []Label{"removed"})
+	})
+}
diff --git a/entities/bug/op_set_metadata.go b/entities/bug/op_set_metadata.go
new file mode 100644
index 00000000..b4aab78c
--- /dev/null
+++ b/entities/bug/op_set_metadata.go
@@ -0,0 +1,21 @@
+package bug
+
+import (
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+)
+
+func NewSetMetadataOp(author identity.Interface, unixTime int64, target entity.Id, newMetadata map[string]string) *dag.SetMetadataOperation[*Snapshot] {
+	return dag.NewSetMetadataOp[*Snapshot](SetMetadataOp, author, unixTime, target, newMetadata)
+}
+
+// SetMetadata is a convenience function to add metadata on another operation
+func SetMetadata(b Interface, author identity.Interface, unixTime int64, target entity.Id, newMetadata map[string]string) (*dag.SetMetadataOperation[*Snapshot], error) {
+	op := NewSetMetadataOp(author, unixTime, target, newMetadata)
+	if err := op.Validate(); err != nil {
+		return nil, err
+	}
+	b.Append(op)
+	return op, nil
+}
diff --git a/entities/bug/op_set_status.go b/entities/bug/op_set_status.go
new file mode 100644
index 00000000..5e73d982
--- /dev/null
+++ b/entities/bug/op_set_status.go
@@ -0,0 +1,95 @@
+package bug
+
+import (
+	"github.com/pkg/errors"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/util/timestamp"
+)
+
+var _ Operation = &SetStatusOperation{}
+
+// SetStatusOperation will change the status of a bug
+type SetStatusOperation struct {
+	dag.OpBase
+	Status Status `json:"status"`
+}
+
+func (op *SetStatusOperation) Id() entity.Id {
+	return dag.IdOperation(op, &op.OpBase)
+}
+
+func (op *SetStatusOperation) Apply(snapshot *Snapshot) {
+	snapshot.Status = op.Status
+	snapshot.addActor(op.Author())
+
+	item := &SetStatusTimelineItem{
+		id:       op.Id(),
+		Author:   op.Author(),
+		UnixTime: timestamp.Timestamp(op.UnixTime),
+		Status:   op.Status,
+	}
+
+	snapshot.Timeline = append(snapshot.Timeline, item)
+}
+
+func (op *SetStatusOperation) Validate() error {
+	if err := op.OpBase.Validate(op, SetStatusOp); err != nil {
+		return err
+	}
+
+	if err := op.Status.Validate(); err != nil {
+		return errors.Wrap(err, "status")
+	}
+
+	return nil
+}
+
+func NewSetStatusOp(author identity.Interface, unixTime int64, status Status) *SetStatusOperation {
+	return &SetStatusOperation{
+		OpBase: dag.NewOpBase(SetStatusOp, author, unixTime),
+		Status: status,
+	}
+}
+
+type SetStatusTimelineItem struct {
+	id       entity.Id
+	Author   identity.Interface
+	UnixTime timestamp.Timestamp
+	Status   Status
+}
+
+func (s SetStatusTimelineItem) Id() entity.Id {
+	return s.id
+}
+
+// IsAuthored is a sign post method for gqlgen
+func (s SetStatusTimelineItem) IsAuthored() {}
+
+// Open is a convenience function to change a bugs state to Open
+func Open(b Interface, author identity.Interface, unixTime int64, metadata map[string]string) (*SetStatusOperation, error) {
+	op := NewSetStatusOp(author, unixTime, OpenStatus)
+	for key, value := range metadata {
+		op.SetMetadata(key, value)
+	}
+	if err := op.Validate(); err != nil {
+		return nil, err
+	}
+	b.Append(op)
+	return op, nil
+}
+
+// Close is a convenience function to change a bugs state to Close
+func Close(b Interface, author identity.Interface, unixTime int64, metadata map[string]string) (*SetStatusOperation, error) {
+	op := NewSetStatusOp(author, unixTime, ClosedStatus)
+	for key, value := range metadata {
+		op.SetMetadata(key, value)
+	}
+	if err := op.Validate(); err != nil {
+		return nil, err
+	}
+	b.Append(op)
+	return op, nil
+}
diff --git a/entities/bug/op_set_status_test.go b/entities/bug/op_set_status_test.go
new file mode 100644
index 00000000..7ec78704
--- /dev/null
+++ b/entities/bug/op_set_status_test.go
@@ -0,0 +1,14 @@
+package bug
+
+import (
+	"testing"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+)
+
+func TestSetStatusSerialize(t *testing.T) {
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *SetStatusOperation {
+		return NewSetStatusOp(author, unixTime, ClosedStatus)
+	})
+}
diff --git a/entities/bug/op_set_title.go b/entities/bug/op_set_title.go
new file mode 100644
index 00000000..75efd08e
--- /dev/null
+++ b/entities/bug/op_set_title.go
@@ -0,0 +1,112 @@
+package bug
+
+import (
+	"fmt"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/util/timestamp"
+
+	"github.com/MichaelMure/git-bug/util/text"
+)
+
+var _ Operation = &SetTitleOperation{}
+
+// SetTitleOperation will change the title of a bug
+type SetTitleOperation struct {
+	dag.OpBase
+	Title string `json:"title"`
+	Was   string `json:"was"`
+}
+
+func (op *SetTitleOperation) Id() entity.Id {
+	return dag.IdOperation(op, &op.OpBase)
+}
+
+func (op *SetTitleOperation) Apply(snapshot *Snapshot) {
+	snapshot.Title = op.Title
+	snapshot.addActor(op.Author())
+
+	item := &SetTitleTimelineItem{
+		id:       op.Id(),
+		Author:   op.Author(),
+		UnixTime: timestamp.Timestamp(op.UnixTime),
+		Title:    op.Title,
+		Was:      op.Was,
+	}
+
+	snapshot.Timeline = append(snapshot.Timeline, item)
+}
+
+func (op *SetTitleOperation) Validate() error {
+	if err := op.OpBase.Validate(op, SetTitleOp); err != nil {
+		return err
+	}
+
+	if text.Empty(op.Title) {
+		return fmt.Errorf("title is empty")
+	}
+
+	if !text.SafeOneLine(op.Title) {
+		return fmt.Errorf("title has unsafe characters")
+	}
+
+	if !text.SafeOneLine(op.Was) {
+		return fmt.Errorf("previous title has unsafe characters")
+	}
+
+	return nil
+}
+
+func NewSetTitleOp(author identity.Interface, unixTime int64, title string, was string) *SetTitleOperation {
+	return &SetTitleOperation{
+		OpBase: dag.NewOpBase(SetTitleOp, author, unixTime),
+		Title:  title,
+		Was:    was,
+	}
+}
+
+type SetTitleTimelineItem struct {
+	id       entity.Id
+	Author   identity.Interface
+	UnixTime timestamp.Timestamp
+	Title    string
+	Was      string
+}
+
+func (s SetTitleTimelineItem) Id() entity.Id {
+	return s.id
+}
+
+// IsAuthored is a sign post method for gqlgen
+func (s SetTitleTimelineItem) IsAuthored() {}
+
+// SetTitle is a convenience function to change a bugs title
+func SetTitle(b Interface, author identity.Interface, unixTime int64, title string, metadata map[string]string) (*SetTitleOperation, error) {
+	var lastTitleOp *SetTitleOperation
+	for _, op := range b.Operations() {
+		switch op := op.(type) {
+		case *SetTitleOperation:
+			lastTitleOp = op
+		}
+	}
+
+	var was string
+	if lastTitleOp != nil {
+		was = lastTitleOp.Title
+	} else {
+		was = b.FirstOp().(*CreateOperation).Title
+	}
+
+	op := NewSetTitleOp(author, unixTime, title, was)
+	for key, value := range metadata {
+		op.SetMetadata(key, value)
+	}
+	if err := op.Validate(); err != nil {
+		return nil, err
+	}
+
+	b.Append(op)
+	return op, nil
+}
diff --git a/entities/bug/op_set_title_test.go b/entities/bug/op_set_title_test.go
new file mode 100644
index 00000000..7960ec4f
--- /dev/null
+++ b/entities/bug/op_set_title_test.go
@@ -0,0 +1,14 @@
+package bug
+
+import (
+	"testing"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+)
+
+func TestSetTitleSerialize(t *testing.T) {
+	dag.SerializeRoundTripTest(t, func(author identity.Interface, unixTime int64) *SetTitleOperation {
+		return NewSetTitleOp(author, unixTime, "title", "was")
+	})
+}
diff --git a/entities/bug/operation.go b/entities/bug/operation.go
new file mode 100644
index 00000000..a02fc780
--- /dev/null
+++ b/entities/bug/operation.go
@@ -0,0 +1,73 @@
+package bug
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+)
+
+const (
+	_ dag.OperationType = iota
+	CreateOp
+	SetTitleOp
+	AddCommentOp
+	SetStatusOp
+	LabelChangeOp
+	EditCommentOp
+	NoOpOp
+	SetMetadataOp
+)
+
+// Operation define the interface to fulfill for an edit operation of a Bug
+type Operation interface {
+	dag.Operation
+
+	// Apply the operation to a Snapshot to create the final state
+	Apply(snapshot *Snapshot)
+}
+
+// make sure that package external operations do conform to our interface
+var _ Operation = &dag.NoOpOperation[*Snapshot]{}
+var _ Operation = &dag.SetMetadataOperation[*Snapshot]{}
+
+func operationUnmarshaller(raw json.RawMessage, resolvers entity.Resolvers) (dag.Operation, error) {
+	var t struct {
+		OperationType dag.OperationType `json:"type"`
+	}
+
+	if err := json.Unmarshal(raw, &t); err != nil {
+		return nil, err
+	}
+
+	var op dag.Operation
+
+	switch t.OperationType {
+	case AddCommentOp:
+		op = &AddCommentOperation{}
+	case CreateOp:
+		op = &CreateOperation{}
+	case EditCommentOp:
+		op = &EditCommentOperation{}
+	case LabelChangeOp:
+		op = &LabelChangeOperation{}
+	case NoOpOp:
+		op = &dag.NoOpOperation[*Snapshot]{}
+	case SetMetadataOp:
+		op = &dag.SetMetadataOperation[*Snapshot]{}
+	case SetStatusOp:
+		op = &SetStatusOperation{}
+	case SetTitleOp:
+		op = &SetTitleOperation{}
+	default:
+		panic(fmt.Sprintf("unknown operation type %v", t.OperationType))
+	}
+
+	err := json.Unmarshal(raw, &op)
+	if err != nil {
+		return nil, err
+	}
+
+	return op, nil
+}
diff --git a/entities/bug/operation_test.go b/entities/bug/operation_test.go
new file mode 100644
index 00000000..fe8080c3
--- /dev/null
+++ b/entities/bug/operation_test.go
@@ -0,0 +1,131 @@
+package bug
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+)
+
+// TODO: move to entity/dag?
+
+func TestValidate(t *testing.T) {
+	repo := repository.NewMockRepoClock()
+
+	makeIdentity := func(t *testing.T, name, email string) *identity.Identity {
+		i, err := identity.NewIdentity(repo, name, email)
+		require.NoError(t, err)
+		return i
+	}
+
+	rene := makeIdentity(t, "René Descartes", "rene@descartes.fr")
+
+	unix := time.Now().Unix()
+
+	good := []Operation{
+		NewCreateOp(rene, unix, "title", "message", nil),
+		NewSetTitleOp(rene, unix, "title2", "title1"),
+		NewAddCommentOp(rene, unix, "message2", nil),
+		NewSetStatusOp(rene, unix, ClosedStatus),
+		NewLabelChangeOperation(rene, unix, []Label{"added"}, []Label{"removed"}),
+	}
+
+	for _, op := range good {
+		if err := op.Validate(); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	bad := []Operation{
+		// opbase
+		NewSetStatusOp(makeIdentity(t, "", "rene@descartes.fr"), unix, ClosedStatus),
+		NewSetStatusOp(makeIdentity(t, "René Descartes\u001b", "rene@descartes.fr"), unix, ClosedStatus),
+		NewSetStatusOp(makeIdentity(t, "René Descartes", "rene@descartes.fr\u001b"), unix, ClosedStatus),
+		NewSetStatusOp(makeIdentity(t, "René \nDescartes", "rene@descartes.fr"), unix, ClosedStatus),
+		NewSetStatusOp(makeIdentity(t, "René Descartes", "rene@\ndescartes.fr"), unix, ClosedStatus),
+		&CreateOperation{OpBase: dag.NewOpBase(CreateOp, rene, 0),
+			Title:   "title",
+			Message: "message",
+		},
+
+		NewCreateOp(rene, unix, "multi\nline", "message", nil),
+		NewCreateOp(rene, unix, "title", "message", []repository.Hash{repository.Hash("invalid")}),
+		NewCreateOp(rene, unix, "title\u001b", "message", nil),
+		NewCreateOp(rene, unix, "title", "message\u001b", nil),
+		NewSetTitleOp(rene, unix, "multi\nline", "title1"),
+		NewSetTitleOp(rene, unix, "title", "multi\nline"),
+		NewSetTitleOp(rene, unix, "title\u001b", "title2"),
+		NewSetTitleOp(rene, unix, "title", "title2\u001b"),
+		NewAddCommentOp(rene, unix, "message\u001b", nil),
+		NewAddCommentOp(rene, unix, "message", []repository.Hash{repository.Hash("invalid")}),
+		NewSetStatusOp(rene, unix, 1000),
+		NewSetStatusOp(rene, unix, 0),
+		NewLabelChangeOperation(rene, unix, []Label{}, []Label{}),
+		NewLabelChangeOperation(rene, unix, []Label{"multi\nline"}, []Label{}),
+	}
+
+	for i, op := range bad {
+		if err := op.Validate(); err == nil {
+			t.Fatal("validation should have failed", i, op)
+		}
+	}
+}
+
+func TestMetadata(t *testing.T) {
+	repo := repository.NewMockRepoClock()
+
+	rene, err := identity.NewIdentity(repo, "René Descartes", "rene@descartes.fr")
+	require.NoError(t, err)
+
+	op := NewCreateOp(rene, time.Now().Unix(), "title", "message", nil)
+
+	op.SetMetadata("key", "value")
+
+	val, ok := op.GetMetadata("key")
+	require.True(t, ok)
+	require.Equal(t, val, "value")
+}
+
+func TestID(t *testing.T) {
+	repo := repository.CreateGoGitTestRepo(t, false)
+
+	repos := []repository.ClockedRepo{
+		repository.NewMockRepo(),
+		repo,
+	}
+
+	for _, repo := range repos {
+		rene, err := identity.NewIdentity(repo, "René Descartes", "rene@descartes.fr")
+		require.NoError(t, err)
+		err = rene.Commit(repo)
+		require.NoError(t, err)
+
+		b, op, err := Create(rene, time.Now().Unix(), "title", "message", nil, nil)
+		require.NoError(t, err)
+
+		id1 := op.Id()
+		require.NoError(t, id1.Validate())
+
+		err = b.Commit(repo)
+		require.NoError(t, err)
+
+		op2 := b.FirstOp()
+
+		id2 := op2.Id()
+		require.NoError(t, id2.Validate())
+		require.Equal(t, id1, id2)
+
+		b2, err := Read(repo, b.Id())
+		require.NoError(t, err)
+
+		op3 := b2.FirstOp()
+
+		id3 := op3.Id()
+		require.NoError(t, id3.Validate())
+		require.Equal(t, id1, id3)
+	}
+}
diff --git a/entities/bug/resolver.go b/entities/bug/resolver.go
new file mode 100644
index 00000000..e7beb0e4
--- /dev/null
+++ b/entities/bug/resolver.go
@@ -0,0 +1,21 @@
+package bug
+
+import (
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/repository"
+)
+
+var _ entity.Resolver = &SimpleResolver{}
+
+// SimpleResolver is a Resolver loading Bugs directly from a Repo
+type SimpleResolver struct {
+	repo repository.ClockedRepo
+}
+
+func NewSimpleResolver(repo repository.ClockedRepo) *SimpleResolver {
+	return &SimpleResolver{repo: repo}
+}
+
+func (r *SimpleResolver) Resolve(id entity.Id) (entity.Interface, error) {
+	return Read(r.repo, id)
+}
diff --git a/entities/bug/snapshot.go b/entities/bug/snapshot.go
new file mode 100644
index 00000000..cece09b8
--- /dev/null
+++ b/entities/bug/snapshot.go
@@ -0,0 +1,144 @@
+package bug
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/entity/dag"
+)
+
+var _ dag.Snapshot = &Snapshot{}
+
+// Snapshot is a compiled form of the Bug data structure used for storage and merge
+type Snapshot struct {
+	id entity.Id
+
+	Status       Status
+	Title        string
+	Comments     []Comment
+	Labels       []Label
+	Author       identity.Interface
+	Actors       []identity.Interface
+	Participants []identity.Interface
+	CreateTime   time.Time
+
+	Timeline []TimelineItem
+
+	Operations []dag.Operation
+}
+
+// Id returns the Bug identifier
+func (snap *Snapshot) Id() entity.Id {
+	if snap.id == "" {
+		// simply panic as it would be a coding error (no id provided at construction)
+		panic("no id")
+	}
+	return snap.id
+}
+
+func (snap *Snapshot) AllOperations() []dag.Operation {
+	return snap.Operations
+}
+
+// EditTime returns the last time a bug was modified
+func (snap *Snapshot) EditTime() time.Time {
+	if len(snap.Operations) == 0 {
+		return time.Unix(0, 0)
+	}
+
+	return snap.Operations[len(snap.Operations)-1].Time()
+}
+
+// GetCreateMetadata return the creation metadata
+func (snap *Snapshot) GetCreateMetadata(key string) (string, bool) {
+	return snap.Operations[0].GetMetadata(key)
+}
+
+// SearchTimelineItem will search in the timeline for an item matching the given hash
+func (snap *Snapshot) SearchTimelineItem(id entity.Id) (TimelineItem, error) {
+	for i := range snap.Timeline {
+		if snap.Timeline[i].Id() == id {
+			return snap.Timeline[i], nil
+		}
+	}
+
+	return nil, fmt.Errorf("timeline item not found")
+}
+
+// SearchComment will search for a comment matching the given hash
+func (snap *Snapshot) SearchComment(id entity.Id) (*Comment, error) {
+	for _, c := range snap.Comments {
+		if c.id == id {
+			return &c, nil
+		}
+	}
+
+	return nil, fmt.Errorf("comment item not found")
+}
+
+// append the operation author to the actors list
+func (snap *Snapshot) addActor(actor identity.Interface) {
+	for _, a := range snap.Actors {
+		if actor.Id() == a.Id() {
+			return
+		}
+	}
+
+	snap.Actors = append(snap.Actors, actor)
+}
+
+// append the operation author to the participants list
+func (snap *Snapshot) addParticipant(participant identity.Interface) {
+	for _, p := range snap.Participants {
+		if participant.Id() == p.Id() {
+			return
+		}
+	}
+
+	snap.Participants = append(snap.Participants, participant)
+}
+
+// HasParticipant return true if the id is a participant
+func (snap *Snapshot) HasParticipant(id entity.Id) bool {
+	for _, p := range snap.Participants {
+		if p.Id() == id {
+			return true
+		}
+	}
+	return false
+}
+
+// HasAnyParticipant return true if one of the ids is a participant
+func (snap *Snapshot) HasAnyParticipant(ids ...entity.Id) bool {
+	for _, id := range ids {
+		if snap.HasParticipant(id) {
+			return true
+		}
+	}
+	return false
+}
+
+// HasActor return true if the id is a actor
+func (snap *Snapshot) HasActor(id entity.Id) bool {
+	for _, p := range snap.Actors {
+		if p.Id() == id {
+			return true
+		}
+	}
+	return false
+}
+
+// HasAnyActor return true if one of the ids is a actor
+func (snap *Snapshot) HasAnyActor(ids ...entity.Id) bool {
+	for _, id := range ids {
+		if snap.HasActor(id) {
+			return true
+		}
+	}
+	return false
+}
+
+// IsAuthored is a sign post method for gqlgen
+func (snap *Snapshot) IsAuthored() {}
diff --git a/entities/bug/sorting.go b/entities/bug/sorting.go
new file mode 100644
index 00000000..2e64b92d
--- /dev/null
+++ b/entities/bug/sorting.go
@@ -0,0 +1,57 @@
+package bug
+
+type BugsByCreationTime []*Bug
+
+func (b BugsByCreationTime) Len() int {
+	return len(b)
+}
+
+func (b BugsByCreationTime) Less(i, j int) bool {
+	if b[i].CreateLamportTime() < b[j].CreateLamportTime() {
+		return true
+	}
+
+	if b[i].CreateLamportTime() > b[j].CreateLamportTime() {
+		return false
+	}
+
+	// When the logical clocks are identical, that means we had a concurrent
+	// edition. In this case we rely on the timestamp. While the timestamp might
+	// be incorrect due to a badly set clock, the drift in sorting is bounded
+	// by the first sorting using the logical clock. That means that if users
+	// synchronize their bugs regularly, the timestamp will rarely be used, and
+	// should still provide a kinda accurate sorting when needed.
+	return b[i].FirstOp().Time().Before(b[j].FirstOp().Time())
+}
+
+func (b BugsByCreationTime) Swap(i, j int) {
+	b[i], b[j] = b[j], b[i]
+}
+
+type BugsByEditTime []*Bug
+
+func (b BugsByEditTime) Len() int {
+	return len(b)
+}
+
+func (b BugsByEditTime) Less(i, j int) bool {
+	if b[i].EditLamportTime() < b[j].EditLamportTime() {
+		return true
+	}
+
+	if b[i].EditLamportTime() > b[j].EditLamportTime() {
+		return false
+	}
+
+	// When the logical clocks are identical, that means we had a concurrent
+	// edition. In this case we rely on the timestamp. While the timestamp might
+	// be incorrect due to a badly set clock, the drift in sorting is bounded
+	// by the first sorting using the logical clock. That means that if users
+	// synchronize their bugs regularly, the timestamp will rarely be used, and
+	// should still provide a kinda accurate sorting when needed.
+	return b[i].LastOp().Time().Before(b[j].LastOp().Time())
+}
+
+func (b BugsByEditTime) Swap(i, j int) {
+	b[i], b[j] = b[j], b[i]
+}
diff --git a/entities/bug/status.go b/entities/bug/status.go
new file mode 100644
index 00000000..b8fba609
--- /dev/null
+++ b/entities/bug/status.go
@@ -0,0 +1,86 @@
+package bug
+
+import (
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+type Status int
+
+const (
+	_ Status = iota
+	OpenStatus
+	ClosedStatus
+)
+
+func (s Status) String() string {
+	switch s {
+	case OpenStatus:
+		return "open"
+	case ClosedStatus:
+		return "closed"
+	default:
+		return "unknown status"
+	}
+}
+
+func (s Status) Action() string {
+	switch s {
+	case OpenStatus:
+		return "opened"
+	case ClosedStatus:
+		return "closed"
+	default:
+		return "unknown status"
+	}
+}
+
+func StatusFromString(str string) (Status, error) {
+	cleaned := strings.ToLower(strings.TrimSpace(str))
+
+	switch cleaned {
+	case "open":
+		return OpenStatus, nil
+	case "closed":
+		return ClosedStatus, nil
+	default:
+		return 0, fmt.Errorf("unknown status")
+	}
+}
+
+func (s Status) Validate() error {
+	if s != OpenStatus && s != ClosedStatus {
+		return fmt.Errorf("invalid")
+	}
+
+	return nil
+}
+
+func (s Status) MarshalGQL(w io.Writer) {
+	switch s {
+	case OpenStatus:
+		_, _ = fmt.Fprintf(w, strconv.Quote("OPEN"))
+	case ClosedStatus:
+		_, _ = fmt.Fprintf(w, strconv.Quote("CLOSED"))
+	default:
+		panic("missing case")
+	}
+}
+
+func (s *Status) UnmarshalGQL(v interface{}) error {
+	str, ok := v.(string)
+	if !ok {
+		return fmt.Errorf("enums must be strings")
+	}
+	switch str {
+	case "OPEN":
+		*s = OpenStatus
+	case "CLOSED":
+		*s = ClosedStatus
+	default:
+		return fmt.Errorf("%s is not a valid Status", str)
+	}
+	return nil
+}
diff --git a/entities/bug/timeline.go b/entities/bug/timeline.go
new file mode 100644
index 00000000..d7f042db
--- /dev/null
+++ b/entities/bug/timeline.go
@@ -0,0 +1,80 @@
+package bug
+
+import (
+	"strings"
+
+	"github.com/MichaelMure/git-bug/entities/identity"
+	"github.com/MichaelMure/git-bug/entity"
+	"github.com/MichaelMure/git-bug/repository"
+	"github.com/MichaelMure/git-bug/util/timestamp"
+)
+
+type TimelineItem interface {
+	// Id return the identifier of the item
+	Id() entity.Id
+}
+
+// CommentHistoryStep hold one version of a message in the history
+type CommentHistoryStep struct {
+	// The author of the edition, not necessarily the same as the author of the
+	// original comment
+	Author identity.Interface
+	// The new message
+	Message  string
+	UnixTime timestamp.Timestamp
+}
+
+// CommentTimelineItem is a TimelineItem that holds a Comment and its edition history
+type CommentTimelineItem struct {
+	// id should be the same as in Comment
+	id        entity.Id
+	Author    identity.Interface
+	Message   string
+	Files     []repository.Hash
+	CreatedAt timestamp.Timestamp
+	LastEdit  timestamp.Timestamp
+	History   []CommentHistoryStep
+}
+
+func NewCommentTimelineItem(comment Comment) CommentTimelineItem {
+	return CommentTimelineItem{
+		id:        comment.id,
+		Author:    comment.Author,
+		Message:   comment.Message,
+		Files:     comment.Files,
+		CreatedAt: comment.UnixTime,
+		LastEdit:  comment.UnixTime,
+		History: []CommentHistoryStep{
+			{
+				Message:  comment.Message,
+				UnixTime: comment.UnixTime,
+			},
+		},
+	}
+}
+
+func (c *CommentTimelineItem) Id() entity.Id {
+	return c.id
+}
+
+// Append will append a new comment in the history and update the other values
+func (c *CommentTimelineItem) Append(comment Comment) {
+	c.Message = comment.Message
+	c.Files = comment.Files
+	c.LastEdit = comment.UnixTime
+	c.History = append(c.History, CommentHistoryStep{
+		Author:   comment.Author,
+		Message:  comment.Message,
+		UnixTime: comment.UnixTime,
+	})
+}
+
+// Edited say if the comment was edited
+func (c *CommentTimelineItem) Edited() bool {
+	return len(c.History) > 1
+}
+
+// MessageIsEmpty return true is the message is empty or only made of spaces
+func (c *CommentTimelineItem) MessageIsEmpty() bool {
+	return len(strings.TrimSpace(c.Message)) == 0
+}
diff --git a/entities/bug/with_snapshot.go b/entities/bug/with_snapshot.go
new file mode 100644
index 00000000..0474cac7
--- /dev/null
+++ b/entities/bug/with_snapshot.go
@@ -0,0 +1,53 @@
+package bug
+
+import (
+	"github.com/MichaelMure/git-bug/repository"
+)
+
+var _ Interface = &WithSnapshot{}
+
+// WithSnapshot encapsulate a Bug and maintain the corresponding Snapshot efficiently
+type WithSnapshot struct {
+	*Bug
+	snap *Snapshot
+}
+
+func (b *WithSnapshot) Compile() *Snapshot {
+	if b.snap == nil {
+		snap := b.Bug.Compile()
+		b.snap = snap
+	}
+	return b.snap
+}
+
+// Append intercept Bug.Append() to update the snapshot efficiently
+func (b *WithSnapshot) Append(op Operation) {
+	b.Bug.Append(op)
+
+	if b.snap == nil {
+		return
+	}
+
+	op.Apply(b.snap)
+	b.snap.Operations = append(b.snap.Operations, op)
+}
+
+// Commit intercept Bug.Commit() to update the snapshot efficiently
+func (b *WithSnapshot) Commit(repo repository.ClockedRepo) error {
+	err := b.Bug.Commit(repo)
+
+	if err != nil {
+		b.snap = nil
+		return err
+	}
+
+	// Commit() shouldn't change anything of the bug state apart from the
+	// initial ID set
+
+	if b.snap == nil {
+		return nil
+	}
+
+	b.snap.id = b.Bug.Id()
+	return nil
+}