# API: hyper-p2p-autobase-view-sync

**Protocol:** `autobase-view-sync/v1`

**Export:** `HyperP2PAutobaseViewSync`

## Overview

Gossip-synced Autobase view version + content hash; reactive UIs can mirror via `hyper-p2p-reactive-state`.

## Constructor

```js
const mod = new HyperP2PAutobaseViewSync(opts)
```

| Option | Type | Default | Description |
|--------|------|---------|-------------|
| `topic` | string \| Buffer \| null | null | Hyperswarm topic; gossip attaches when set |
| `keyPair` | Ed25519 KeyPair | random | Signing identity for swarm |
| `autobase` | object \| null | null | Attached autobase instance (`attach()` also supported) |

## Methods

### `attach(autobase) → this`

Validates autobase via `assertAutobase`.

### `publishView(version) → view`

Updates local view when `version >= _view.version`, gossips `view-sync`, emits `publish`.

- **Returns:** `{ version, hash, at }` where `hash` is `sha256("view:" + version)` hex
- **Throws:** `version must be non-negative`

### `mergeRemoteView(view) → boolean`

Advances when remote `version` is newer; rejects same version with conflicting `hash`.

- **Returns:** `true` when merged, `false` when rejected
- **Emits:** `merged` on success

### `currentView() → view`

- **Returns:** shallow copy of `{ version, hash, at, mergedAt? }`

### `isAtLeast(version) → boolean`

### `behindBy(version) → number`

- **Returns:** `max(0, version - _view.version)`
- **Throws:** `version must be non-negative`

### `getStats() → object`

`{ published, merged, gossipIn, gossipOut, view, protocol }`.

### `async ready() → this`

Joins gossip when `topic` is set; inbound `view-sync` calls `mergeRemoteView`.

### `async close() → void`

Destroys swarm; emits `closed`.

## Events

| Event | Payload |
|-------|---------|
| `publish` | published view |
| `merged` | merged view state |
| `closed` | no payload |

## getStats()

Returns `{ ...this._stats, protocol }` plus module-specific counters (pending queues, registry sizes, gossip in/out when P2P).
Local modules report hot-path counters only; P2P modules include gossip traffic when `topic` is set.

## Errors

Stable message substrings: see [`../../_shared/ERROR_CODES.md`](../../_shared/ERROR_CODES.md).

Validation helpers may throw `ValidationError` (e.g. `peer is required`, `path is required`).

### Documented `throw new Error(...)` strings

- `version must be non-negative`

## P2P

When `topic` is set, `ready()` joins Hyperswarm and opens gossip for `autobase-view-sync/v1`.
Outbound payloads use `sendGossip` (Protomux peer map); inbound handled in `_onGossip`.

### Gossip message types

- `view-sync`

## Testing

```bash
npm install && npm test
```

## Common flows

1. `publishView(version)` — gossip `view-sync`.
2. `mergeRemoteView(view)` — monotonic version merge.
3. `currentView()` — local snapshot.