# `opfs-adapter` — default `OpfsLike` and feature detector

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## Purpose

Provides the production binding of the `OpfsLike` structural interface to the browser's `navigator.storage.getDirectory()` API, plus a side-effect-free feature detector consumers call before constructing an `OpfsStorage`. Keeping this in its own module — rather than inside `OpfsStorage` — lets the storage class take an injected `OpfsLike` and stay environment-agnostic, while the production path resolves the real browser API lazily on first `getDirectory()`.

## Features

- `defaultOpfs()` returns an `OpfsLike` whose `getDirectory()` calls the live browser API.
- Missing API surfaces as `OpfsError(OPFS.UNAVAILABLE)` rather than `TypeError` from a missing-property access.
- `isOpfsAvailable()` is synchronous, has no side effects, and never throws — safe to call during render.
- Resolves `navigator` from `globalThis` so the module loads cleanly in Node, Bun, and worker environments.

## Usage: Basic Example

```ts
import {
    defaultOpfs,
    isOpfsAvailable,
    OpfsStorage,
} from "@suaveplan/storage-browser-opfs";

if (!isOpfsAvailable()) {
    // Fall back to MemoryStorage or another adapter.
}
const storage = new OpfsStorage({ opfs: defaultOpfs() });
```

## Usage: Advanced Example

```ts
import {
    defaultOpfs,
    isOpfsAvailable,
    MemoryStorage,
    OpfsStorage,
} from "@suaveplan/storage-browser-opfs";
import type { AbstractStorage } from "@suaveplan/storage/abstract";

export function pickStorage(): AbstractStorage {
    if (isOpfsAvailable()) return new OpfsStorage({ opfs: defaultOpfs() });
    return new MemoryStorage();
}
```

## API Reference

- `defaultOpfs(): OpfsLike` — `getDirectory()` throws `OpfsError(OPFS.UNAVAILABLE)` when missing.
- `isOpfsAvailable(): boolean` — pure feature detector.

## Implementation Notes

`defaultOpfs()` returns a fresh `OpfsLike` object on every call so callers can hold different references; the underlying `getDirectory` getter is read at each invocation so consumers that polyfill `navigator.storage` after this module loads still benefit. The Boolean detector deliberately checks `typeof getDirectory === "function"` rather than `"getDirectory" in storage` to weed out polyfills that stub the property without a callable.