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Merkle DAG on top of LevelDB

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# merkle-dag

Merkle DAG on top of LevelDB

```
npm install merkle-dag
```

## Usage

``` js
var merkle = require('merkle-dag')
var db = require('level')('test.db')

var graph = merkle(db)

// add a node with value "hello" and no links
graph.add(null, 'hello', function(err, node) {
  console.log('added:', node)
  // add a node with value "world" linking to the "hello" node
  graph.add([node.key], 'world', function(err, node) {
    console.log('added:', node)
    // retrive a node
    graph.get(node.key, function(err, node) {
      console.log('retrieved:', node)
    })
  })
})
```

## API

#### `var node = graph.add(links, value, [callback])`

Add a new node to the graph. `links` should be an array of keys of other nodes this node links to.
If this node does not link to anything pass in `null` or an empty array.

The links *must* be present in the graph or else an error will be passed to the callback.
The node that will be inserted is returned (and passed to the callback).

#### `graph.get(key, callback)`

Lookup a node using its key.

#### `graph.changes([options], [callback])`

Everytime a node is inserted a reference to it is added to a local change feed.
The order of this feed guarantees that all linked nodes come before a node.

``` js
var changes = graph.changes()

changes.on('data', function(node) {
  console.log('change #'+node.change, node)
})
```

Optionally you can provide a callback which will be called with a list of changes

``` js
graph.changes(function(err, nodes) {
  console.log('changes:', nodes)
})
```

Pass in `options.since = change` to start the change feed from a given change index

``` js
var changes = graph.changes({since:100}) // only get changes > 100
```

The change stream also support a realtime mode using `options.live`

``` js
var changes = graph.changes({live:true}) // will never end but keep emitting data
```

#### `graph.heads([options], [callback])`

To get the `heads` of the graph (nodes that no one has a link to) use `graph.heads()`

``` js
// graph.heads() returns a stream of hashes of the heads
var heads = graph.heads()

heads.on('data', function(node) {
  console.log('head:', node)
})
```

Optionally you can provide a callback which will be called with a list of heads

``` js
graph.heads(function(err, nodes) {
  console.log(nodes) // an array of heads
})
```

Options include

```
{
  limit: 10     // only get 10 heads at max
  reverse: true // get them in reverse order
}
```

## License

MIT

merkle-dag

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