# @theme-ui/prism

A syntax highlighting component based on
[prism-react-renderer](https://github.com/FormidableLabs/prism-react-renderer)
that works seamlessly with Theme UI.

## Installation

```
npm i @theme-ui/prism
```

## Usage

The syntax highlighting component needs to be passed to Theme UI context via the
`ThemeProvider`.

```js
// src/components/layout.js
import { ThemeUIProvider } from 'theme-ui'
import { MDXProvider } from '@mdx-js/react'
import { useThemedStylesWithMdx } from '@theme-ui/mdx'
import Prism from '@theme-ui/prism'

import theme from './theme'

const components = {
  pre: ({ children }) => <>{children}</>,
  code: Prism,
}

function Provider({ children }) {
  const componentsWithStyles = useThemedStylesWithMdx(
    useMDXComponents(components)
  )

  return (
    <ThemeProvider theme={theme}>
      <MDXProvider components={componentsWithStyles}>{children}</MDXProvider>
    </ThemeProvider>
  )
}

export default Provider
```

Then, all code blocks in MDX documents wrapped by Layout will be syntax
highlighted.

### Gatsby plugin

When using `gatsby-plugin-theme-ui`, shadow the
`src/gatsby-plugin-theme-ui/components.js` module to add the Prism component to
MDX scope.

```js
// src/gatsby-plugin-theme-ui/components.js
import Prism from '@theme-ui/prism'

export default {
  pre: (props) => props.children,
  code: Prism,
}
```

## Syntax themes

This package includes the default syntax color themes from the `prismjs` and
`prism-react-renderer` packages. To add these to your Theme UI `theme` object,
import a preset and add the styles to `theme.styles.code`.

```js
// theme.js
import nightOwl from '@theme-ui/prism/presets/night-owl.json'

const theme = {
  // ...theme
  styles: {
    code: {
      ...nightOwl,
    },
  },
}
```

The following themes are available and can be found in the
[`presets/`](https://github.com/system-ui/theme-ui/tree/stable/packages/prism/presets)
directory.

- `dracula.json`
- `duotone-dark.json`
- `duotone-light.json`
- `github.json`
- `night-owl-light.json`
- `night-owl.json`
- `oceanic-next.json`
- `prism-coy.json`
- `prism-dark.json`
- `prism-funky.json`
- `prism-okaidia.json`
- `prism-solarizedlight.json`
- `prism-tomorrow.json`
- `prism-twilight.json`
- `prism.json`
- `shades-of-purple.json`
- `ultramin.json`
- `vs-dark.json`

### Theme UI colors

To theme the prism styles based on the colors defined in your `theme.colors`
object, use the `theme-ui` preset, which will use the following color keys for
syntax highlight.

- `gray`
- `primary`
- `secondary`
- `accent`

```js
// src/gatsby-plugin-theme-ui/index.js
import prism from '@theme-ui/prism/presets/theme-ui'

export default {
  colors: {
    text: '#000',
    background: '#fff',
    primary: '#33e',
    secondary: '#119',
    accent: '#639',
    gray: '#666',
  },
  styles: {
    code: {
      ...prism,
    },
  },
}
```

## Highlight support

This package supports highlighting inside code blocks. The following two
syntaxes are supported:

Single-line highlight by placing `// highlight-line` at the end of the line.

```js
let singleLineHighlight = 'there is a // highlight-line comment here ->' // highlight-line
```

Multi-line highlights by wrapping lines with `// highlight-start` and
`// highlight-end`. Multiple highlight wrappers are supported in a single code
block.

```js
// highlight-start
let multiLineHighlight = `
  this multiline string is wrapped by 
  // highlight-start and // highlight-end 
  comments
`
// highlight-end
```

The highlight styling is controlled in `styles.pre` under `.highlight`. For
example:

```json
".highlight": {
  "background": "hsla(0, 0%, 30%, .5)"
}
```

## Additional languages

Please note that `@theme-ui/prism` uses
[`prism-react-renderer`](https://github.com/FormidableLabs/prism-react-renderer),
[which does not include all languages supported in Prism](https://github.com/FormidableLabs/prism-react-renderer/blob/master/src/vendor/prism/includeLangs.js)
by default. So, if you happen to use one of the missing languages, your code
block simply won't show up as highlighted.

For example, to add support for the `R` language, import the language and pass a
custom `Prism` instance to the Theme UI component:

```js
// src/gatsby-plugin-theme-ui/components.js
import ThemeUIPrism from '@theme-ui/prism'
import PrismCore from 'prismjs/components/prism-core'
import 'prismjs/components/prism-r'

export default {
  pre: (props) => props.children,
  code: (props) => <ThemeUIPrism {...props} Prism={PrismCore} />,
}
```