# @cerulea/lexicon

define AT Protocol lexicon schemas in TypeScript

- no deps :D
- runtime validation via `schema.validate(value)`
  - returns `{ success: true, value }` or `{ success: false, issues }` with a path per issue
- emit lexicon JSON documents via `toLexicons(...roots)`
  - easily generate a `lexicons/` dir of json from typescript defs; it's like a three-liner
- simple record builder via `schema.build(...)`
  - will auto-fill `$type` for records
  - will expand short `#fragment` strings for unions

## usage

```typescript
import * as l from "@cerulea/lexicon";

const facetRange = { start: l.integer, end: l.integer };
const Facet = l.union("example.myapp.facet", {
  "#mention": l.object({ ...facetRange, did: l.did }),
  "#link": l.object({ ...facetRange, uri: l.uri }),
});

const Post = l.record("example.myapp.post", { key: "tid" }, {
  text: l.stringWith({ maxGraphemes: 300 }),
  facets: l.optional(l.array(Facet)),
  createdAt: l.datetime,
});
type Post = l.Infer<typeof Post>;

const getPost = l.query("example.myapp.getPost", {
  parameters: l.params({ uri: l.atUri }),
  output: Post,
  errors: [{ name: "NotFound" }],
});

const post: Post = Post.build({
  text: "hi @alice",
  facets: [{ $type: "#mention", start: 3, end: 9, did: "did:example:alice" }],
  createdAt: new Date().toISOString(),
});

const untrusted: unknown = {
  $type: "example.myapp.post",
  text: "hello",
  createdAt: "my evil invalid date",
};
const result = Post.validate(untrusted);
if (!result.success) console.error(result.issues);

const lexicons = l.toLexicons(Post, getPost);
/* [
  { lexicon: 1, id: "example.myapp.facet", … },
  { lexicon: 1, id: "example.myapp.getPost", … },
  …
] */
```