text-versioncontrol v0.9.11
Text-VersionControl
Introduction
Text-VersionControl provides version and concurrency control for text editing based on OT(Operational Transformation) and CRDT(Conflict-free Replicated Data Type) ideas. It's for use in real-time, distributed collaborative document editing and history management for text contents.
Getting Started
Install the library by npm install text-versioncontrol --save
Table of Contents
- Operations and Delta Operations Constructing Delta Working with Delta Utility Functions
- SharedString
- History
- Miscellaneous
Operations and Delta
Text-VersionControl utilizes Quill's Delta representation in JSON. It supports Operational Transformation's basic representations(retain, delete, and insert). The delta format also provides attributes and embedded objects for expressing complex content besides simple text.
Operations
Content can be expressed using insert operations
```js {insert: "Hello"}, {insert: "World", attributes: {"color": "red"}}, {insert: {"video": "http://youtube.com/sOdLN"}} ```
Operations
```js {retain: 5} {delete: 2} {insert: "Hello World!"} ```
Embedded objects can hold a map of string->string.
```js {insert: {"img": "file:///img.gif"}} ```
Content with attributes
```js {insert: "Hello", attributes: {"link": "http://github.com"}} ```
Adding attributes
```js {retain: 5, attributes: {"link": "http://github.com"}} ```
Removing attributes
```js {retain: 5, attributes: {"link": null}} ```
Constructing Delta
new Delta(ops?:Op[])
Initialize with JSON
```js new Delta([{retain: 5}, {delete: 2}, {insert: "Hello World!"}]) ```
Construct by chaining
```js new Delta().retain(5).delete(2).insert("Hello World!") ``` * Available method variants ```js delta.insert("hello") // simple text content delta.insert("world", {"color": "red"}) // text with attributes delta.insert({"img": "./ball.gif"}) // embedded content delta.insert({"video": "./ball.gif"}, {"w": "300", "h": "600"}) // embedded content with attributes delta.retain(5) delta.retain(3, {"bold": "true"}) // adding or modifying an attribute delta.retain(3, {"bold": null}) // removing an attribute delta.delete(2) ```
Working with Delta
Examples
```js let delta = new Delta().insert("hello").insert(" world").retain(2).retain(3) // normalize delta = delta.normalize() // == new Delta().insert("hello world").retain(5) // slice delta.take(1,2) // == new Delta().insert("e") // apply or compose delta.apply(new Delta().retain(1).delete(4).insert("i")) // == new Delta().insert("hi world") ```
normalize
```js normalize():Delta ``` * **Returns**: a more compact and equivalent delta by removing redundant or effect-less operations * Equivalent to `normalizeDeltas(delta)`
take
```js take(start:number, end:number):Delta ``` * **Returns**: new delta slicing the original delta by the given range * Equivalent to `cropContent(delta, start, end)`
apply or compose
```js apply(other:Delta):Delta compose(other:Delta):Delta ``` * **Returns**: Combination of two deltas into a single flattened delta. * Applying a change on a content * Combining two changes into one * Equivalent to `flattenDeltas(delta, other)`
transform
```js transform(other:Delta, priority = false):Delta ``` * **Returns** transformed `other` as if this delta has preceded it * `priority` is used for insert tie-breaking * Equivalent to `transformDeltas(delta, other, priority)`
invert
```js invert(baseContent:Delta):Delta ``` * **Returns**: the inversion of a change when applied on `baseContent`. * In other words, it returns `D'` where `baseContent.apply(D).apply(D') == baseContent` holds for content `baseContent` and change `D`. * Useful for generating an undo change. * `baseContent` is required for correctly inverting addition/removal of attributes * equivalent to `invertChange(baseConent, delta)`
Utility Functions
Text-VersionControl provides utility functions to manipulate deltas
flattenDeltas(...deltas:Delta[]):Delta
* Flattens a sequence of multiple deltas into a single equivalent deltafilterChanges(baseContent:Delta, changes:Delta[], criteria:(idx:number, change:Delta):Delta[]
* Filters changes that are fulfilling criteria given a base content and sequence of changes. Useful to rule out certain changes while keeping (the effect of) rest of changes intact
SharedString
SharedString forms the core of Text-VersionControl's OT and CRDT functionality. SharedString is a mutable object that can be edited by receiving changes as delta. It can consolidate concurrent, distributed edits by multiple users.
Initialization
ss = SharedString.fromDelta({ops:[{insert:"Hello World"}]})
ss = SharedString.fromString("Hello World")
Applying changes
applyChange(change:Delta, branch:string):Delta
- Edits the content by applying change. This mutates SharedString.
- Returns transformed change as if the change was made in linear fashion
Multiple users with their own sequence of changes independently can be applied by alternating branch.
```js ss.applyChange(changeByAlice, "Alice") ss.applyChange(changeByBob, "Bob") // Bob is unaware of Alice's change ss.applyChange(changeByAlice2, "Alice") // second edit by Alice, while unaware of Bob's change ss.applyChange(changeByCharlie, "Charlie") // Charlie is unaware of Alice's or Bob's changes ``` * As long as you keep the order of changes within each branch, the result content will be the same no matter how you order the changes of different branches. This satisfies CRDT characteristics. * `branch` also takes a role as a tiebreaker for concurrent inserts.
Wildcard branch lets you simulate a checkpoint, where the change is applied as if it's aware of all other changes from different branches
The star wildcard branch sees the previous changes of all branches and can be seen by all branches later on
```js ss.applyChange(changeByStar, "*") ss.applyChange(changeByCharlie, "Charlie") // Charlie is aware of change by '*' ```
The underscore wildcard branch sees the previous changes of all branches but cannot be seen by other branches later on
```js ss.applyChange(changeByUnderScore, "_") ss.applyChange(changeByCharlie, "Charlie") // Charlie is unaware of change by '_' ```
Rendering current content
ss.toDelta() // the content seen as if changes in all branches were consolidated
ss.toDelta(branch) // the content visible on specific branch
Other methods
Clone current state
```js ss.clone() ```
History
History utilizes SharedString to provide higher level functionalities such as snapshot access, append, merge, or rebase. It keeps the content and changes as Delta.
Initialization
new History(name:string, initialContent: Delta | string)
name
here exists for tie-breaking concurrent inserts during merge or rebase.
Applying changes
By appending at current revision:
```js history.append(deltas) ```
By merging forked sequence of changes diverged from a base revision:
```js history.merge({rev: baseRev, changes: deltasByAlice, branch: "Alice"}) ``` ![Image of merging](./doc/merge.png) * **Returns**: `MergeResult` ```js { rev: number, // latest revision after applying merge content: Delta, // result content reqChanges: Delta[], // request changes (passed changes transformed) resChanges: Delta[] } // response changes (base changes) ``` * `branchName` works as the insert tiebreaker by comparing with History's `name` value
By rebasing forked sequence of changes diverged from a base revision.
```js history.rebase({rev: baseRev, changes: deltasByAlice, branch: "Alice"}) ``` ![Image of rebasing](./doc/rebase.png) * **Returns**: `MergeResult` ```js { rev: number, // latest revision after applying rebase content: Delta, // result content reqChanges: Delta[], // request changes (passed changes) resChanges: Delta[] } // response changes (base changes transformed) ``` * Unlike merging, rebasing forces new set of changes to be first applied on the base revision, followed by existing changes (transformed) in the history since the base revision. Beware rebasing replaces changes already recorded in the history.
Revisions, snapshots, and changes
Getting the current revision
```js history.getCurrentRev() ```
Getting the content
```js history.getContent() // content at current revision history.getContentAt(rev) // snapshot content at rev ```
Getting the changes
```js history.getChangeAt(rev) // change made on content at rev history.getChangesFrom(rev) history.getChangesFromTo(revFrom, revTo) ```
Miscellaneous
Notes on similarity and difference to Quill's Delta
Text-VersionControl borrows Quill Delta's representation and many of method names but does not behave the same in a few cases. For example, many of the methods of Quill's Delta reorder adjacent delete and insert (which in most cases does not change the effect), but Text-VersionControl's equivalent methods preserve it. See the following examples:
Result of
new Delta().retain(2).delete(2).insert('Hello')
```js [{retain: 2}, {insert: 'Hello'}, {delete: 2}] // Quill [{retain: 2}, {delete: 2}, {insert: 'Hello'}] // Text-VersionControl ```
Result of
new Delta([{insert: 'ab'}, {delete: 1}, {insert: 'cd'}]).compose([{retain: 4}]
```js [{insert: 'abcd'}, {delete: 1}] // Quill [{insert: 'ab'}, {delete: 1}, {insert: 'cd'}] // Text-VersionControl ```
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