# Jekyll::Linkpreview

[![Build Status](https://travis-ci.org/ysk24ok/jekyll-linkpreview.svg?branch=master)](https://travis-ci.org/ysk24ok/jekyll-linkpreview)

Jekyll plugin to generate link preview by `{% linkpreview %}` tag. The plugin fetches [Open Graph protocol](http://ogp.me/) metadata of the designated page to generate preview. The og properties are saved as JSON for caching and it is used when rebuilding the site.

You can pass url directly to the tag,

```
{% linkpreview "https://github.com" %}
```

or, can pass a url variable.

```
{% assign github_toppage = 'https://github.com' %}
{% linkpreview github_toppage %}
```

The tag above generates following HTML when you run `jekyll build`.

```html
<div class="jekyll-linkpreview-wrapper">
  <p><a href="https://github.com" target="_blank">https://github.com</a></p>
  <div class="jekyll-linkpreview-wrapper-inner">
    <div class="jekyll-linkpreview-content">
      <div class="jekyll-linkpreview-image">
        <a href="https://github.com" target="_blank">
          <img src="https://github.githubassets.com/images/modules/open_graph/github-logo.png" />
        </a>
      </div>
      <div class="jekyll-linkpreview-body">
        <h2 class="jekyll-linkpreview-title">
          <a href="https://github.com" target="_blank">Build software better, together</a>
        </h2>
        <div class="jekyll-linkpreview-description">GitHub is where people build software. More than 31 million people use GitHub to discover, fork, and contribute to over 100 million projects.</div>
      </div>
    </div>
    <div class="jekyll-linkpreview-footer">
      <a href="https://github.com" target="_blank">github.com</a>
    </div>
  </div>
</div>
```

By applying appropriate CSS, the link preview will be like this.

<img width="613" alt="スクリーンショット 2019-04-03 20 52 50" src="https://user-images.githubusercontent.com/3449164/55479970-35baf100-565a-11e9-8c5d-709213917f74.png">

When the page does not have Open Graph protocol metadata, following simple HTML will be generated.

```html
<div class="jekyll-linkpreview-wrapper">
  <p><a href="https://example.com" target="_blank">https://example.com</a></p>
</div>
```

You can override the default templates, see [Custom templates](#user-content-custom-templates).

## Installation

See https://jekyllrb.com/docs/plugins/installation/ .

## Usage

1. Create `_cache` directory.

1. Embed [linkpreview.css](assets/css/linkpreview.css) into your Website.

1. Use `{% linkpreview %}` tag.

1. Run `jekyll build` or `jekyll serve`.


## Custom templates

You can override the default templates used for generating previews, both in case Open Graph protocol metadata exists or does not exist for a given page.

### Template for pages where Open Graph protocol metadata exists

 1. Place `linkpreview.html` file inside `_includes/` folder of your Jekyll site (`_includes/linkpreview.html`)

 2. Use built-in variables to extract data which you would like to render. Available variables are:
  * **link_url** i.e. `{{ link_url }}`
  * **link_title** i.e. `{{ link_title }}`
  * **link_image** i.e. `{{ link_image }}`
  * **link_description** i.e. `{{ link_description }}`
  * **link_domain** i.e. `{{ link_domain }}`

### Template for pages where Open Graph protocol metadata does not exist

1. Place `linkpreview_nog.html` file inside `_includes/` folder of your Jekyll site (`_includes/linkpreview_nog.html`)

2. Use built-in **link_url** variable to render URL data, i.e. `{{ link_url }}`

## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ysk24ok/jekyll-linkpreview.

## License

The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).