Add versions to models (#1064)

## Description

Currently only the ModelStore populates and checks versions.

Some high-level points:
* fail any sort of get (just metadata or full model) if there's a version mismatch
* update operations automatically set things to the current version
* versions are stored as tags so there's some int->string (and vice versa) munging
* versions stored as tags so they can be repopulated even if only the metadata (BaseModel) for a model is pulled. This is done mostly for consistency

## Type of change

<!--- Please check the type of change your PR introduces: --->
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🐹 Trivial/Minor

## Issue(s)

* closes #284 

## Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

src/internal/kopia/model_store.go

@@ -2,6 +2,7 @@ package kopia
 
 import (
 	"context"
+	"strconv"
 
 	"github.com/google/uuid"
 	"github.com/kopia/kopia/repo"
@@ -11,7 +12,11 @@ import (
 	"github.com/alcionai/corso/src/internal/model"
 )
 
-const stableIDKey = "stableID"
+const (
+	stableIDKey        = "stableID"
+	modelVersionKey    = "storeVersion"
+	globalModelVersion = 1
+)
 
 var (
 	ErrNotFound           = errors.New("not found")
@@ -27,12 +32,14 @@ func NewModelStore(c *conn) (*ModelStore, error) {
 		return nil, errors.Wrap(err, "creating ModelStore")
 	}
 
-	return &ModelStore{c: c}, nil
+	return &ModelStore{c: c, modelVersion: globalModelVersion}, nil
 }
 
 // ModelStore must not be accessed after the given KopiaWrapper is closed.
 type ModelStore struct {
 	c *conn
+	// Stash a reference here so testing can easily change it.
+	modelVersion int
 }
 
 func (ms *ModelStore) Close(ctx context.Context) error {
@@ -70,6 +77,7 @@ func tagsForModel(s model.Schema, tags map[string]string) (map[string]string, er
 func tagsForModelWithID(
 	s model.Schema,
 	id model.StableID,
+	version int,
 	tags map[string]string,
 ) (map[string]string, error) {
 	if !s.Valid() {
@@ -91,6 +99,12 @@ func tagsForModelWithID(
 
 	res[stableIDKey] = string(id)
 
+	if _, ok := res[modelVersionKey]; ok {
+		return nil, errors.WithStack(errBadTagKey)
+	}
+
+	res[modelVersionKey] = strconv.Itoa(version)
+
 	return res, nil
 }
 
@@ -112,7 +126,7 @@ func putInner(
 		base.ID = model.StableID(uuid.NewString())
 	}
 
-	tmpTags, err := tagsForModelWithID(s, base.ID, base.Tags)
+	tmpTags, err := tagsForModelWithID(s, base.ID, base.Version, base.Tags)
 	if err != nil {
 		// Will be wrapped at a higher layer.
 		return err
@@ -140,6 +154,8 @@ func (ms *ModelStore) Put(
 		return errors.WithStack(errUnrecognizedSchema)
 	}
 
+	m.Base().Version = ms.modelVersion
+
 	err := repo.WriteSession(
 		ctx,
 		ms.c,
@@ -159,22 +175,45 @@ func (ms *ModelStore) Put(
 
 func stripHiddenTags(tags map[string]string) {
 	delete(tags, stableIDKey)
+	delete(tags, modelVersionKey)
 	delete(tags, manifest.TypeLabelKey)
 }
 
-func baseModelFromMetadata(m *manifest.EntryMetadata) (*model.BaseModel, error) {
+func (ms ModelStore) populateBaseModelFromMetadata(
+	base *model.BaseModel,
+	m *manifest.EntryMetadata,
+) error {
 	id, ok := m.Labels[stableIDKey]
 	if !ok {
-		return nil, errors.WithStack(errNoStableID)
+		return errors.WithStack(errNoStableID)
 	}
 
-	res := &model.BaseModel{
-		ModelStoreID: m.ID,
-		ID:           model.StableID(id),
-		Tags:         m.Labels,
+	v, err := strconv.Atoi(m.Labels[modelVersionKey])
+	if err != nil {
+		return errors.Wrap(err, "parsing model version")
 	}
 
-	stripHiddenTags(res.Tags)
+	if v != ms.modelVersion {
+		return errors.Errorf("bad model version %s", m.Labels[modelVersionKey])
+	}
+
+	base.ModelStoreID = m.ID
+	base.ID = model.StableID(id)
+	base.Version = v
+	base.Tags = m.Labels
+
+	stripHiddenTags(base.Tags)
+
+	return nil
+}
+
+func (ms ModelStore) baseModelFromMetadata(
+	m *manifest.EntryMetadata,
+) (*model.BaseModel, error) {
+	res := &model.BaseModel{}
+	if err := ms.populateBaseModelFromMetadata(res, m); err != nil {
+		return nil, err
+	}
 
 	return res, nil
 }
@@ -208,7 +247,7 @@ func (ms *ModelStore) GetIDsForType(
 	res := make([]*model.BaseModel, 0, len(metadata))
 
 	for _, m := range metadata {
-		bm, err := baseModelFromMetadata(m)
+		bm, err := ms.baseModelFromMetadata(m)
 		if err != nil {
 			return nil, errors.Wrap(err, "parsing model metadata")
 		}
@@ -304,12 +343,10 @@ func (ms *ModelStore) GetWithModelStoreID(
 		return errors.WithStack(errModelTypeMismatch)
 	}
 
-	base := data.Base()
-	base.Tags = metadata.Labels
-	stripHiddenTags(base.Tags)
-	base.ModelStoreID = id
-
-	return nil
+	return errors.Wrap(
+		ms.populateBaseModelFromMetadata(data.Base(), metadata),
+		"getting model by ID",
+	)
 }
 
 // checkPrevModelVersion compares the ModelType and ModelStoreID in this model
@@ -368,6 +405,8 @@ func (ms *ModelStore) Update(
 		return errors.WithStack(errNoModelStoreID)
 	}
 
+	base.Version = ms.modelVersion
+
 	// TODO(ashmrtnz): Can remove if bottleneck.
 	if err := ms.checkPrevModelVersion(ctx, s, base); err != nil {
 		return err

src/internal/kopia/model_store_test.go

@@ -29,7 +29,7 @@ func getModelStore(t *testing.T, ctx context.Context) *ModelStore {
 	c, err := openKopiaRepo(t, ctx)
 	require.NoError(t, err)
 
-	return &ModelStore{c}
+	return &ModelStore{c: c, modelVersion: globalModelVersion}
 }
 
 // ---------------
@@ -101,6 +101,12 @@ func (suite *ModelStoreIntegrationSuite) TestBadTagsErrors() {
 				manifest.TypeLabelKey: "foo",
 			},
 		},
+		{
+			name: "storeVersion",
+			tags: map[string]string{
+				manifest.TypeLabelKey: "foo",
+			},
+		},
 	}
 
 	for _, test := range table {
@@ -204,6 +210,23 @@ func (suite *ModelStoreIntegrationSuite) TestBadTypeErrors() {
 	)
 }
 
+func (suite *ModelStoreIntegrationSuite) TestPutGetBadVersion() {
+	t := suite.T()
+	schema := model.BackupOpSchema
+	foo := &fooModel{Bar: uuid.NewString()}
+	// Avoid some silly test errors from comparing nil to empty map.
+	foo.Tags = map[string]string{}
+
+	err := suite.m.Put(suite.ctx, schema, foo)
+	require.NoError(t, err)
+
+	suite.m.modelVersion = 42
+
+	returned := &fooModel{}
+	err = suite.m.Get(suite.ctx, schema, foo.ID, returned)
+	assert.Error(t, err)
+}
+
 func (suite *ModelStoreIntegrationSuite) TestPutGet() {
 	table := []struct {
 		s      model.Schema
@@ -247,6 +270,7 @@ func (suite *ModelStoreIntegrationSuite) TestPutGet() {
 
 			require.NotEmpty(t, foo.ModelStoreID)
 			require.NotEmpty(t, foo.ID)
+			require.Equal(t, globalModelVersion, foo.Version)
 
 			returned := &fooModel{}
 			err = suite.m.Get(suite.ctx, test.s, foo.ID, returned)
@@ -340,6 +364,22 @@ func (suite *ModelStoreIntegrationSuite) TestGet_NotFoundErrors() {
 		t, suite.m.GetWithModelStoreID(suite.ctx, model.BackupOpSchema, "baz", nil), ErrNotFound)
 }
 
+func (suite *ModelStoreIntegrationSuite) TestPutGetOfTypeBadVersion() {
+	t := suite.T()
+	schema := model.BackupOpSchema
+
+	foo := &fooModel{Bar: uuid.NewString()}
+
+	err := suite.m.Put(suite.ctx, schema, foo)
+	require.NoError(t, err)
+
+	suite.m.modelVersion = 42
+
+	ids, err := suite.m.GetIDsForType(suite.ctx, schema, nil)
+	assert.Error(t, err)
+	assert.Empty(t, ids)
+}
+
 func (suite *ModelStoreIntegrationSuite) TestPutGetOfType() {
 	table := []struct {
 		s      model.Schema
@@ -527,12 +567,14 @@ func (suite *ModelStoreIntegrationSuite) TestPutUpdate() {
 			name: "NoTags",
 			mutator: func(m *fooModel) {
 				m.Bar = "baz"
+				m.Version = 42
 			},
 		},
 		{
 			name: "WithTags",
 			mutator: func(m *fooModel) {
 				m.Bar = "baz"
+				m.Version = 42
 				m.Tags = map[string]string{
 					"a": "42",
 				}
@@ -558,11 +600,15 @@ func (suite *ModelStoreIntegrationSuite) TestPutUpdate() {
 
 			oldModelID := foo.ModelStoreID
 			oldStableID := foo.ID
+			oldVersion := foo.Version
 
 			test.mutator(foo)
 
 			require.NoError(t, m.Update(ctx, theModelType, foo))
 			assert.Equal(t, oldStableID, foo.ID)
+			// The version in the model store has not changed so we get the old
+			// version back.
+			assert.Equal(t, oldVersion, foo.Version)
 
 			returned := &fooModel{}
 			require.NoError(
@@ -571,7 +617,8 @@ func (suite *ModelStoreIntegrationSuite) TestPutUpdate() {
 
 			ids, err := m.GetIDsForType(ctx, theModelType, nil)
 			require.NoError(t, err)
-			assert.Len(t, ids, 1)
+			require.Len(t, ids, 1)
+			assert.Equal(t, globalModelVersion, ids[0].Version)
 
 			if oldModelID == foo.ModelStoreID {
 				// Unlikely, but we don't control ModelStoreID generation and can't

src/internal/model/model.go

@@ -44,6 +44,9 @@ type BaseModel struct {
 	// to refer to this one. This field may change if the model is updated. This
 	// field should be treated as read-only by users.
 	ModelStoreID manifest.ID `json:"-"`
+	// Version is a version number that can help track changes across models.
+	// TODO(ashmrtn): Reference version control documentation.
+	Version int `json:"-"`
 	// Tags associated with this model in the store to facilitate lookup. Tags in
 	// the struct are not serialized directly into the stored model, but are part
 	// of the metadata for the model.