# source

## Purpose

Validates the `manifestSource` configuration before the plugin starts wiring its read middleware. The function is small but load-bearing: it short-circuits the `"server-only"` branch when no `manifestServerUrl` is supplied so the rest of the plugin can assume the source is well-formed by the time it runs.

## Features

- `resolveManifestSource(source, manifestServerUrl?): { source, url }` — returns the normalised configuration tuple.
- Eager validation — throws synchronously instead of failing inside the read pipeline.
- Pure function — no I/O, no global state, deterministic for fixed inputs.
- Unaware of `getChunk` / `fetch` — those concerns live in `load.ts`.

## Usage: Basic Example

```ts
import { resolveManifestSource } from "@suaveplan/drive-plugin-chunks";

const cfg = resolveManifestSource("manifest-as-chunk");
```

## Usage: Advanced Example

```ts
import { resolveManifestSource } from "@suaveplan/drive-plugin-chunks";

const cfg = resolveManifestSource("server-only", "https://manifests.example.com");
console.log(cfg.url); // "https://manifests.example.com"

try {
    resolveManifestSource("server-only");
} catch (err) {
    console.error("missing manifestServerUrl");
}
```

## API Reference

- `resolveManifestSource(source: ManifestSource, manifestServerUrl?: string): { source: ManifestSource; url: string | undefined }`.
- Throws a plain `Error` (not `ChunksError`) when `source === "server-only"` and `manifestServerUrl` is missing, because this is a programmer error in plugin construction, not a runtime fault that consumers should branch on.

## Implementation Notes

The two valid `ManifestSource` values are intentionally narrow: `"manifest-as-chunk"` reuses the chunk-storage substrate as the manifest store, while `"server-only"` keeps manifests out-of-band on a separate HTTPS endpoint. Future sources (e.g. a libp2p PubSub channel) would slot in by extending the union type and the dispatcher in `load.ts`. The plain `Error` is surfaced as soon as the plugin object is constructed so misconfigurations show up at boot, not during the first `read`.