Directives

# @json-render/directives

Pre-built custom directives for `@json-render/core`. Drop them into your catalog and renderer to add formatting, math, string manipulation, and i18n.

## Quick Start

```typescript
import { standardDirectives } from '@json-render/directives';

// Wire into prompt generation
const prompt = catalog.prompt({ directives: standardDirectives });

// Wire into the renderer (React example)
import { JSONUIProvider, Renderer } from '@json-render/react';

<JSONUIProvider registry={registry} directives={standardDirectives}>
  <Renderer spec={spec} registry={registry} />
</JSONUIProvider>
```

To add factory directives like `createI18nDirective`, spread the array:

```typescript
import { standardDirectives, createI18nDirective } from '@json-render/directives';

const directives = [...standardDirectives, createI18nDirective(config)];
```

## Defining Custom Directives

Use `defineDirective` from `@json-render/core`:

```typescript
import { defineDirective, resolvePropValue } from '@json-render/core';
import { z } from 'zod';

const doubleDirective = defineDirective({
  name: '$double',
  description: 'Double a numeric value.',
  schema: z.object({
    $double: z.unknown(),
  }),
  resolve(value, ctx) {
    const resolved = resolvePropValue(value.$double, ctx);
    return (resolved as number) * 2;
  },
});
```

Rules:
- Name must start with `$`
- Name must not conflict with built-in keys (`$state`, `$cond`, `$computed`, `$template`, `$item`, `$index`, `$bindState`, `$bindItem`)
- Resolvers should call `resolvePropValue` on sub-values to support composition

## Built-in Directives

### `$format` — Locale-aware value formatting

Formats values using `Intl` formatters. Supports `date`, `currency`, `number`, and `percent`.

```json
{ "$format": "currency", "value": { "$state": "/cart/total" }, "currency": "USD" }
{ "$format": "date", "value": { "$state": "/user/createdAt" } }
{ "$format": "number", "value": 1234567, "notation": "compact" }
{ "$format": "percent", "value": 0.75 }
{ "$format": "date", "value": { "$state": "/post/createdAt" }, "style": "relative" }
```

Fields: `$format` (date | currency | number | percent), `value` (any expression), `locale?` (string), `currency?` (string, default "USD"), `notation?` (string), `style?` ("relative" for relative dates), `options?` (extra Intl options).

### `$math` — Arithmetic operations

```json
{ "$math": "add", "a": { "$state": "/subtotal" }, "b": { "$state": "/tax" } }
{ "$math": "round", "a": 3.7 }
```

Operations: `add`, `subtract`, `multiply`, `divide`, `mod`, `min`, `max`, `round`, `floor`, `ceil`, `abs`. Unary ops (`round`, `floor`, `ceil`, `abs`) only use `a`. Division by zero returns `0`.

Fields: `$math` (operation enum), `a?` (first operand, default 0), `b?` (second operand, default 0).

### `$concat` — String concatenation

```json
{ "$concat": [{ "$state": "/user/firstName" }, " ", { "$state": "/user/lastName" }] }
```

Fields: `$concat` (array of values to resolve and join into a string).

### `$count` — Array/string length

```json
{ "$count": { "$state": "/cart/items" } }
```

Returns `.length` of arrays or strings, `0` for other types.

Fields: `$count` (value to count).

### `$truncate` — Text truncation

```json
{ "$truncate": { "$state": "/post/body" }, "length": 140, "suffix": "..." }
```

Fields: `$truncate` (value to truncate), `length?` (max chars, default 100), `suffix?` (string, default "...").

### `$pluralize` — Singular/plural forms

```json
{ "$pluralize": { "$state": "/cart/itemCount" }, "one": "item", "other": "items", "zero": "no items" }
```

Output: `"3 items"`, `"1 item"`, or `"no items"`.

Fields: `$pluralize` (count val