1package dag
2
3import (
4 "crypto/rand"
5 "encoding/json"
6 "fmt"
7 "time"
8
9 "github.com/pkg/errors"
10
11 "github.com/MichaelMure/git-bug/entity"
12 "github.com/MichaelMure/git-bug/identity"
13 "github.com/MichaelMure/git-bug/repository"
14)
15
16// OperationType is an operation type identifier
17type OperationType int
18
19// Operation is a piece of data defining a change to reflect on the state of an Entity.
20// What this Operation or Entity's state looks like is not of the resort of this package as it only deals with the
21// data structure and storage.
22type Operation interface {
23 // Id return the Operation identifier
24 //
25 // Some care need to be taken to define a correct Id derivation and enough entropy in the data used to avoid
26 // collisions. Notably:
27 // - the Id of the first Operation will be used as the Id of the Entity. Collision need to be avoided across entities
28 // of the same type (example: no collision within the "bug" namespace).
29 // - collisions can also happen within the set of Operations of an Entity. Simple Operation might not have enough
30 // entropy to yield unique Ids (example: two "close" operation within the same second, same author).
31 // If this is a concern, it is recommended to include a piece of random data in the operation's data, to guarantee
32 // a minimal amount of entropy and avoid collision.
33 //
34 // Author's note: I tried to find a clever way around that inelegance (stuffing random useless data into the stored
35 // structure is not exactly elegant), but I failed to find a proper way. Essentially, anything that would reuse some
36 // other data (parent operation's Id, lamport clock) or the graph structure (depth) impose that the Id would only
37 // make sense in the context of the graph and yield some deep coupling between Entity and Operation. This in turn
38 // make the whole thing even less elegant.
39 //
40 // A common way to derive an Id will be to use the entity.DeriveId() function on the serialized operation data.
41 Id() entity.Id
42 // Type return the type of the operation
43 Type() OperationType
44 // Validate check if the Operation data is valid
45 Validate() error
46 // Author returns the author of this operation
47 Author() identity.Interface
48 // Time return the time when the operation was added
49 Time() time.Time
50
51 // SetMetadata store arbitrary metadata about the operation
52 SetMetadata(key string, value string)
53 // GetMetadata retrieve arbitrary metadata about the operation
54 GetMetadata(key string) (string, bool)
55 // AllMetadata return all metadata for this operation
56 AllMetadata() map[string]string
57
58 // setId allow to set the Id, used when unmarshalling only
59 setId(id entity.Id)
60 // setAuthor allow to set the author, used when unmarshalling only
61 setAuthor(author identity.Interface)
62 // setExtraMetadataImmutable add a metadata not carried by the operation itself on the operation
63 setExtraMetadataImmutable(key string, value string)
64}
65
66// OperationWithFiles is an optional extension for an Operation that has files dependency, stored in git.
67type OperationWithFiles interface {
68 // GetFiles return the files needed by this operation
69 // This implies that the Operation maintain and store internally the references to those files. This is how
70 // this information is read later, when loading from storage.
71 // For example, an operation that has a text value referencing some files would maintain a mapping (text ref -->
72 // hash).
73 GetFiles() []repository.Hash
74}
75
76// OperationDoesntChangeSnapshot is an interface signaling that the Operation implementing it doesn't change the
77// snapshot, for example a metadata operation that act on other operations.
78type OperationDoesntChangeSnapshot interface {
79 DoesntChangeSnapshot()
80}
81
82// Snapshot is the minimal interface that a snapshot need to implement
83type Snapshot interface {
84 // AllOperations returns all the operations that have been applied to that snapshot, in order
85 AllOperations() []Operation
86}
87
88// OpBase implement the common feature that every Operation should support.
89type OpBase struct {
90 // Not serialized. Store the op's id in memory.
91 id entity.Id
92 // Not serialized
93 author identity.Interface
94
95 OperationType OperationType `json:"type"`
96 UnixTime int64 `json:"timestamp"`
97
98 // mandatory random bytes to ensure a better randomness of the data used to later generate the ID
99 // len(Nonce) should be > 20 and < 64 bytes
100 // It has no functional purpose and should be ignored.
101 Nonce []byte `json:"nonce"`
102
103 Metadata map[string]string `json:"metadata,omitempty"`
104 // Not serialized. Store the extra metadata in memory,
105 // compiled from SetMetadataOperation.
106 extraMetadata map[string]string
107}
108
109func NewOpBase(opType OperationType, author identity.Interface, unixTime int64) OpBase {
110 return OpBase{
111 OperationType: opType,
112 author: author,
113 UnixTime: unixTime,
114 Nonce: makeNonce(20),
115 id: entity.UnsetId,
116 }
117}
118
119func makeNonce(len int) []byte {
120 result := make([]byte, len)
121 _, err := rand.Read(result)
122 if err != nil {
123 panic(err)
124 }
125 return result
126}
127
128func IdOperation(op Operation, base *OpBase) entity.Id {
129 if base.id == "" {
130 // something went really wrong
131 panic("op's id not set")
132 }
133 if base.id == entity.UnsetId {
134 // This means we are trying to get the op's Id *before* it has been stored, for instance when
135 // adding multiple ops in one go in an OperationPack.
136 // As the Id is computed based on the actual bytes written on the disk, we are going to predict
137 // those and then get the Id. This is safe as it will be the exact same code writing on disk later.
138
139 data, err := json.Marshal(op)
140 if err != nil {
141 panic(err)
142 }
143
144 base.id = entity.DeriveId(data)
145 }
146 return base.id
147}
148
149func (base *OpBase) Type() OperationType {
150 return base.OperationType
151}
152
153// Time return the time when the operation was added
154func (base *OpBase) Time() time.Time {
155 return time.Unix(base.UnixTime, 0)
156}
157
158// Validate check the OpBase for errors
159func (base *OpBase) Validate(op Operation, opType OperationType) error {
160 if base.OperationType == 0 {
161 return fmt.Errorf("operation type unset")
162 }
163 if base.OperationType != opType {
164 return fmt.Errorf("incorrect operation type (expected: %v, actual: %v)", opType, base.OperationType)
165 }
166
167 if op.Time().Unix() == 0 {
168 return fmt.Errorf("time not set")
169 }
170
171 if base.author == nil {
172 return fmt.Errorf("author not set")
173 }
174
175 if err := op.Author().Validate(); err != nil {
176 return errors.Wrap(err, "author")
177 }
178
179 if op, ok := op.(OperationWithFiles); ok {
180 for _, hash := range op.GetFiles() {
181 if !hash.IsValid() {
182 return fmt.Errorf("file with invalid hash %v", hash)
183 }
184 }
185 }
186
187 if len(base.Nonce) > 64 {
188 return fmt.Errorf("nonce is too big")
189 }
190 if len(base.Nonce) < 20 {
191 return fmt.Errorf("nonce is too small")
192 }
193
194 return nil
195}
196
197// IsAuthored is a sign post method for gqlgen
198func (base *OpBase) IsAuthored() {}
199
200// Author return author identity
201func (base *OpBase) Author() identity.Interface {
202 return base.author
203}
204
205// IdIsSet returns true if the id has been set already
206func (base *OpBase) IdIsSet() bool {
207 return base.id != "" && base.id != entity.UnsetId
208}
209
210// SetMetadata store arbitrary metadata about the operation
211func (base *OpBase) SetMetadata(key string, value string) {
212 if base.IdIsSet() {
213 panic("set metadata on an operation with already an Id")
214 }
215
216 if base.Metadata == nil {
217 base.Metadata = make(map[string]string)
218 }
219 base.Metadata[key] = value
220}
221
222// GetMetadata retrieve arbitrary metadata about the operation
223func (base *OpBase) GetMetadata(key string) (string, bool) {
224 val, ok := base.Metadata[key]
225
226 if ok {
227 return val, true
228 }
229
230 // extraMetadata can't replace the original operations value if any
231 val, ok = base.extraMetadata[key]
232
233 return val, ok
234}
235
236// AllMetadata return all metadata for this operation
237func (base *OpBase) AllMetadata() map[string]string {
238 result := make(map[string]string)
239
240 for key, val := range base.extraMetadata {
241 result[key] = val
242 }
243
244 // Original metadata take precedence
245 for key, val := range base.Metadata {
246 result[key] = val
247 }
248
249 return result
250}
251
252// setId allow to set the Id, used when unmarshalling only
253func (base *OpBase) setId(id entity.Id) {
254 if base.id != "" && base.id != entity.UnsetId {
255 panic("trying to set id again")
256 }
257 base.id = id
258}
259
260// setAuthor allow to set the author, used when unmarshalling only
261func (base *OpBase) setAuthor(author identity.Interface) {
262 base.author = author
263}
264
265func (base *OpBase) setExtraMetadataImmutable(key string, value string) {
266 if base.extraMetadata == nil {
267 base.extraMetadata = make(map[string]string)
268 }
269 if _, exist := base.extraMetadata[key]; !exist {
270 base.extraMetadata[key] = value
271 }
272}