This section explains how to write a plugin for Orion. It is intended for developers who want to extend Orion's functionality.

## What is a plugin?

A plugin is an HTML file containing some JavaScript that knows how to connect to the Orion client. Plugins can be hosted on any web server and installed into Orion using their URL.

In order to be useful, a plugin should provide one or more services. When Orion needs a service contributed by a plugin, it loads the plugin inside an IFrame.

Orion currently supports a small set of extension points: service types that plugins can contribute to, in order to customize the client and add more functionality. These include things like:

- Adding more commands to the editor toolbar
- Adding more commands to the navigator view
- Adding content assist for new file types
- Adding syntax highlighting rules for new file types

For a full list of available services, see the Developer Guide.

## What you need

Every plugin must include the following JavaScript library:

- `plugin.js`

You can copy-paste its contents into a <script> tag in your plugin, or load it externally like so:

    <script src="plugin.js"></script>

## Writing the plugin

Let's make a plugin that adds a button to the toolbar of the Orion editor. When clicked, it will reverse the selected text in the editor. This is not a very useful feature, but it'll be a good introduction to the concepts involved.

### Creating the HTML file

Create a new HTML file called `reversePlugin.html` with the following content:

    <!DOCTYPE html>
    <html>
    <head>
      <meta charset="UTF-8" />
      <title>Reverse Plugin</title>
    </head>
    <body></body>
    </html>

What we have now isn't a plugin yet. It's just a bare-bones HTML file. The next step is to include the API we'll need to talk to Orion. Grab the `plugin.js` file (see What you need) and put it in the same folder as `reversePlugin.html`. Then add this inside the <head> tags of the HTML file:

    <script src="plugin.js"></script>

### Making it a plugin

Next, we'll add some code that connects our file to Orion. Add the following, again inside the <head> tags:

    <script>
      window.onload = function() {
        var provider = new eclipse.PluginProvider();
        provider.connect();
      };
    </script>

At this point, we've got an honest-to-goodness Orion plugin, albeit one that does nothing. Let's go over the various parts in detail.

- `window.onload` — Runs our function after `plugin.js` has been loaded by the browser. This ensures that the `eclipse.PluginProvider` constructor is available.
- `var provider = new eclipse.PluginProvider()` — Creates a new PluginProvider. The PluginProvider may provide one or more services, but right now ours doesn't provide any.
  Optionally, an object giving metadata about the plugin can be provided as an argument to the constructor.
- `provider.connect()` — This is where the magic happens. When our plugin is activated from Orion, this call opens an asynchronous communication channel. Orion adds information about our plugin, and any service contributions it makes, to the Orion registry.

### Registering the service

Now we're going to expose a service to Orion. We'll create and register a service with the "orion.edit.command" service type. Add the additional lines as shown:

    window.onload = function() {
      var provider = new eclipse.PluginProvider();
      var serviceImpl = {  };
      var serviceProperties = {  };
      provider.registerServiceProvider("orion.edit.command", serviceImpl, serviceProperties);
      provider.connect();
    };

Let's go over what we have now:

- `var serviceImpl`: This object gives the implementation of our service, the part that will do the actual work. When someone requests our service, our plugin is loaded into an IFrame, and the service's methods are made available. The `function`-typed properties of the `serviceImpl` object define the service methods.
- `var serviceProperties`: Every service provider can supply properties, which is an object that holds metadata about the service provider. If you're familiar with Eclipse desktop, you can think of service properties as analogous to the extensions declared in a plugin.xml file.
- `provider.registerServiceProvider("orion.edit.command", serviceImpl, serviceProperties);`: This call registers our service implementation and properties with the service type "orion.edit.command". At this point, if we tried installing our plugin into Orion, we'd have enough to make the Orion editor see our contribution. However, our contribution still does nothing. Let's fix that.

### Implementing the service

We'll fill in the `serviceImpl` and `serviceProperties` objects with the actual details of the service. Change the `serviceImpl` object to look like this:

    var serviceImpl = {
      run: function(text) {
        return text.split("").reverse().join("");
      }
    };

Note that the functions defined in the service will depend on what service type you're contributing to. In our case, we're contributing to "orion.edit.command", which expects a `run()` function. (See the Developer Guide for a list of extension points and their API.)

Change the serviceProperties object to look like this:

    var serviceProperties = {
      name: "Reverse Text",
      key: ["e", true, true] // Ctrl+Shift+e
    };

### The finished plugin file

Make sure that your copy of `reversePlugin.html` looks like this:

    <!DOCTYPE html>
    <html>
    <head>
      <meta charset="UTF-8" />
      <title>Reverse Plugin</title>
      <script src="plugin.js"></script>
      <script>
      window.onload = function() {
          var provider = new eclipse.PluginProvider();
          var serviceImpl = {
                  run: function(text) {
                      return text.split("").reverse().join("");
                  }
              };
          var serviceProperties = {
                  name: "Reverse Text",
                  key: ["e", true, true] // Ctrl+Shift+e
              };
          provider.registerServiceProvider("orion.edit.command", serviceImpl, serviceProperties);
          provider.connect();
      };
    </script>
    </head>
    <body></body>
    </html>

### Testing the plugin

First we need to host our plugin somewhere.

- If you have a personal web server available, you can copy `reversePlugin.html` and `plugin.js` there.
- If you're using Orionhub, you can put the plugin in a new folder in your Orionhub workspace. Then create a Site Configuration in Orion that launches your folder. See Launching your project as a website.
- You can also use a pre-built version at http://mamacdon.github.com/0.2/plugins/reverse/reversePlugin.html.

Now that you've got a URL for reversePlugin.html, install it into Orion:

- Go to http://yourOrionServer/plugin/install.html#http://yourPluginServer/reversePlugin.html.
- You'll be prompted to install the plugin. Click Yes.

Let's try it out.

- In Orion, go to the navigator and create a new file called `test.txt`.
- Click on `test.txt` to open the editor.
- You'll see a new button on the editor toolbar (see screenshot below).
- Select some text, click the button, and it should be reversed.

## Examples

Here are some existing plugins we've written. View their source code to see how they work:

http://orionhub.org/plugins/sampleCommandsPlugin.html
  Contributes several sample actions to the Orion navigator by using the `orion.navigate.command` service type.

http://orionhub.org/plugins/webEditingPlugin.html
  Contributes syntax highlighting support for HTML files by using the `orion.edit.highlighter` service type.

http://mamacdon.github.com/0.2/plugins/beautify/jsbeautify.html
  Contributes a "Beautify JS" button to the editor toolbar by using the `orion.edit.command` service type. Visit http://mamacdon.github.com for a directory of other available plugins, organized by Orion version.

http://mamacdon.github.com/0.2/plugins/uglify/uglify-plugin.html
  Contributes an "Uglify JS" (minify, in other words) button to the editor toolbar by using the `orion.edit.command` service type.

## See also

- Installing a plugin