Add docs

README.md

@@ -1,26 +1,75 @@
 # Native Bridge Android
+This Kotlin library is the native part of a RPC communication bridge between your app and the webview javascript. [To function it relies on a javascript counterpart to be setup](https://github.com/nrkno/nativebridge-android/). 
 
-The Android library is written in Kotlin.
+**Note:** For simplicity, we're using the term *"webview javascript"* to mean *"the javascript hosted in a site shown in the webview"*.
 
 ## Download
-Add the dependency to your app level build.gradle file:
-```java
-dependencies {
-  compile 'no.nrk.nativebridge:nativebridge:1.0.0-SNAPSHOT'
-}
-```
+The library will soon be made available in a public Maven repo. Until then use the latest `.aar` in [Releases](https://github.com/nrkno/nativebridge-android/releases).
 
-Note that the library has a dependency on Jackson.
+The library has a dependency on Jackson 2.8.9, which needs to be added for the `.aar` to compile:
+```gradle
+compile "com.fasterxml.jackson.core:jackson-core:2.8.9"
+compile "com.fasterxml.jackson.core:jackson-databind:2.8.9"
+compile "com.fasterxml.jackson.module:jackson-module-kotlin:2.8.9"
+```
 
 ## Usage
 Instead of using ```android.webkit.WebView```, use ```no.nrk.NativeBridgeWebView```. If you're already extending ```WebView```, you must instead extend ```NativeBridgeWebView```.
 
-Create classes implementing the ```TopicData.In``` and ```TopicData.Out``` interfaces. ```TopicData.In``` corresponds to the JSON received _from_ the webview, while ```TopicData.Out``` corresponds to the data we want to pass _to_ the webview.
+For dezerialising and serializing data, create classes implementing the ```TopicData.In``` and ```TopicData.Out``` interfaces. ```TopicData.In``` corresponds to the JSON received _from_ the webview javascript, while ```TopicData.Out``` corresponds to the data we want to pass _to_ the webview javascript.
 
-Register a handler for the datatype, and you've successfully established a bridge between your app and the webview:
+You will then need to add a handler, that makes it possible for the native app and the webview javascript to communicate. To do this, use the `nativeBridgeWebView.connection.addHandler(topic: String, callback: (T, WebViewConnection) -> Unit)`. The first parameter `topic` is a string that you and the developer responsible for implementing the javascript has agreed on. The webview javascript and the native app use the same `topic` to communicate. The second parameter is a closure, where `T` is your class implementing `TopicData.In`, and `WebViewConnection` is the `webview.connection` that can be used to send `TopicData.Out` to the webview javascript. 
+
+#### Example:
 ```java
 webview.connection.addHandler("someTopic", { _ : SomeTopic.In, connection ->
     connection.send("someTopic", SomeTopic.Out("data"))
   }
 )
 ```
+
+## Error handling
+If an error occurs, the app will pass data about this to the webview javascript, so the webview javascript can act accordingly. 
+
+If we have a `topic` available, the errors will be passed on the same `topic`. If not, the errors will be passed on the topic `errors`.
+
+### Possible errors
+As of version 1.0.0, the following errors can be returned:
+
+| Error situation | Error code | Error message |
+| --- | --- | --- |
+| Payload passed from webview cannot be deserialized to a topic.  | 1  | ```Illegal payload format``` |
+| Missing topic object in payload: a `topic` object was not found in the payload passed from the webview  | 2  | ```Missing field: 'topic'```  |
+| Missing data object in payload: a `data` object was not found in the payload passed from the webview  | 3  | ```Missing field: 'data'```  |
+| No topic handler defined for topic  | 4  | ```Missing topic handler```  |
+| Data doesn't match data expected by the topic handler  | 5  | ```Invalid data for topic. Expected data topic '$topic'```  |
+
+### Example error response:
+When we're able to determine a `topic`:
+```json
+{
+  "topic": "someTopic",
+  "errors": [
+    {
+      "code": 1,
+      "message": "Missing topic handler"
+    }
+  ]
+}
+```
+
+When we're not able to determine the `topic`, we will pass the errors on the `errors` topic:
+```json
+{
+  "topic": "errors",
+  "errors": [
+    {
+      "code": 2,
+      "message": "Missing field: 'topic'"
+    }
+  ]
+}
+```
+
+## License
+MIT. See [LICENSE.txt](https://github.com/nrkno/nativebridge-android/blob/master/LICENSE.txt) for details.