= Development Guide
:Notice: Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at. http://www.apache.org/licenses/LICENSE-2.0 . Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR  CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

image::WheatFieldWithCrows.png[]

== Quickstart

. Build Causeway with kroviz
+
----
cd ~/causeway
mvn -T 1C clean install \
 -Dmodule-kroviz \
 -Dmaven.source.skip=true
----

. Start kroviz
+
[source]
----
cd ~/causeway/incubator/clients/kroviz/
#gradle build
./gradlew.sh -t run
----
+
. Start the Server App
. Enter in the Browser:
+
[source]
----
http://localhost:3000
----

. Select 'Connect' in the Burger Menu


TIP: Originally Apache Causeway SimpleApp 1.16.0 was used as the reference RO backend.
This required some extra steps in order to deal with CORS setup, see sections on pre 2.0.0-M3 and CORS.
Currently (2.0.0-M6) Demo is used as reference - at the moment  it's the only CORS enabled application.
=== Frontend

=== Requirements

Kotlin/JS uses `Gradle` for the build, for the JS runtime `NodeJS`, and for the JS dependency management part `npm`.
You should have installed:
* node js (https://nodejs.org/en/download/current/)
* Apache Gradle
* Google Chrome (72.0.3626.81 or higher)
* &lt;Moesif CORS Plugin (for Chrome)

=== Build

gradle can be run under Windows with git-bash:

* ./gradlew.bat tasks # list all gradle tasks
* ./gradlew.bat webpack-bundle # create main.bundle.js
* ./gradlew.bat test –exclude-task npm-install

Internally gradle uses npm for the JS part.

In IntelliJ import the gradle project residing in ~/causeway/incubator/clients/kroviz/.
TIP: In case the project isn't working as expected, you may try File -> Invalidate Caches ...
Alternatively you can e.g. in IntelliJ a Run/Debug Configuration:

image::kroviz_Run_Debug_Configuration.png[Preview]

----
 npm --verbose
----

If task npm-install hangs, try

----
 ./gradlew.bat npm-install --info --debug --stacktrace
----

Helps in identifying thing that may go wrong (e.g. due to proxy settings).

=== Run

----
gradlew.bat -t run
----

=== Backend

==== Via Docker Image

// TODO insert to AI reference /doc

== Design

In the following section you'll find information that likely helps understanding the implementation.

=== Overview

include::partial$design/uml-overview.adoc[]


=== Patterns Applied

==== Redux

The implementation is an (independent) reinvention of Redux.
I prefer the name Aggregator over Reducer though - IIRC Aggregator is prior art.

==== Half Object Protocol

The HOP pattern dates back to the early 2000, namely CanooULC.
IMO Naked Objects together with the RO API and kroViz resembles something similar.

==== Transfer Object (JEE / EAA)

TO's are created from JSON responses

==== Event Sourcing (EAA)

Requests, reponses, and resulting TO's are logged.
Before requests are sent out to the server this log is consulted and used as a cache.

==== Proxy (GOF)

The event source acts as a Proxy and thereby saves time and bandwidth.

==== Aggregator (EAI)

Various aggregators are responsible to collect or assemble displayable objects.
Once all layout information is there, the UI will be rendered, even if not all data elements of a list
have arrived. Those elements will be added as they arrive. This is done with the help of
mutable lists.

include::partial$design/seq-aggregator.adoc[]


==== Chain of Responsibility (GOF)

A chain of handlers is used to identify what kind of TO is to be generated from the
JSON response. Handlers are responsible for initial assignment of aggregators.

include::partial$design/uml-handler.adoc[]


==== Template Method (GOF)

The Handler base class makes use of this pattern. Some methods have to be implemented
in each subclass, in some cases the default implementation in the base class is used.

==== Composite Pattern (GOF)

UI elements are hierarchically grouped, cf. *layout.xml

==== Factory (GOF)

Used for building tables dynamically.

==== Remote Facade

The Restful Objects API.

== Code

Thanks to Kotlin, code is very compact and readable.
And, since Kotlin is a typed language and IDE's can infer a lot about the code, there are only few surprises.
Nevertheless, Kotlin/JS allows to use JavaScript features alongside the typed part, what effectively makes it a dynamic language.

=== Hot Spots

Look out for places where typing is escaped and the DOM is manipulated directly:

* asDynamic()
* hasOwnProperty()
* stopPropagation()
* getElementById()

=== Layout Aggregation


== Trouble Shooting

=== Corporate Firewall with SSL 'inspection'

There are some questionable setups in corporate settings that are based on SSL replacement.
In order to cope with it, you may try to import the Certificate into cacerts,
see https://intellij-support.jetbrains.com/hc/en-us/community/posts/115000094584-IDEA-Ultimate-2016-3-4-throwing-unable-to-find-valid-certification-path-to-requested-target-when-trying-to-refresh-gradle

=== Network Proxy

 Depending on the network you are in, you may need to configure the proxy settings. Among the relevant files are:
 `bash
    ~/.npmrc
    ~/.gitconfig
    ~/.ssh/config
    ~/.ssh/id_rsa
`
 ### References
 * https://jjasonclark.com/how-to-setup-node-behind-web-proxy/
 * https://gist.github.com/EudesSilva/0329645b9c258e0495544b8a5ccd1454

=== Access to git from npm

==== Problem

[source,bash]
----
   npm ERR! Error while executing:
   npm ERR! C:\Program Files\Git\bin\git.EXE ls-remote -h -t ssh://git@github.com/jarecsni/font-awesome-webpack.git
   npm ERR!
   npm ERR! git@ssh.github.com: Permission denied (publickey).
   npm ERR! fatal: Could not read from remote repository.
   npm ERR!
   npm ERR! Please make sure you have the correct access rights
   npm ERR! and the repository exists.
   npm ERR!
   npm ERR! exited with error code: 128
----

==== Solution

.~/.ssh/config
[source]
----
ProxyCommand /bin/connect.exe -H proxy.server.name:3128 %h %p
----

[source]
----
Host github.com
 User git
 Port 22
 Hostname github.com
 IdentityFile "C:\users\username.ssh\id_rsa"
 TCPKeepAlive yes
 IdentitiesOnly yes
----

[source]
----
Host ssh.github.com
 User git
 Port 443
 Hostname ssh.github.com
 IdentityFile "C:\users\username.ssh\id_rsa"
 TCPKeepAlive yes
 IdentitiesOnly yes
----


=== Karma-Tests do not respond to code changes

Windows:

    taskkill /f /im node.exe

Linux:

    killall node


== Misc

=== Toolchain Overview

When you are accustomed to the well settled Java ecosystem with integrated development environments, prepare yourself for learning new tools and addressing new problems.

Kotlin is straightforward and once you know it, you may not want to go back.

include::partial$design/dev-mindmap.adoc[]

* JSON structures can be visualized via kroki (cf. History -> Details)
* Layout: for FLEX see https://css-tricks.com/snippets/css/a-guide-to-flexbox/

=== The Browser as Client Runtime Environment

Google Chrome is used as browser. It has a very feature rich debugger (<CTRL>-<SHIFT>-I) which can even be connected to IntelliJ's debugger (Settings -> Preferences -> Extension -> Link handling). For a nice introduction to Chrome, see: https://www.google.com/googlebooks/chrome/.

All current browsers implement some security features in order to counteract Cross-Site-Resource-Forgery (XSRF). CORS (Cross-Origin-Resource-Sharing) is beeing devised to allow access to resources from a different host-port under certain circumstances. It is said to be bypassable via https://www.npmjs.com/package/node-iframe, cf. https://stackoverflow.com/questions/33143776/ajax-request-refused-to-set-unsafe-header/66782595#66782595

=== Visualize JS dependencies
E.g. via https://npmgraph.js.org/

=== Measure Test Coverage

----
nyc npm test
----

References: link:https://github.com/istanbuljs/nyc[]

=== Gradle Build Overview

include::partial$design/dev-overview.adoc[]

=== Build the Backend Yourself

==== Tool Chain

* (Oracle) JDK 11 (or higher)
* Apache Maven 3.6.3 (or later)

==== Create from Archetype

Create from the Apache Causeway SimpleApp archetype:

[source,bash]
----
mvn archetype:generate \
    -D archetypeGroupId=org.apache.causeway.archetype \
    -D archetypeArtifactId=simpleapp-archetype \
    -D archetypeVersion=2.0.0-M3 \
    -D groupId=org.my \
    -D artifactId=myapp-2.0.0-M3 \
    -D version=1.0.0 -B
----

==== Compile

[source,bash]
----
mvn clean install -DskipTests
----

==== Run

[source,bash]
----
cd webapp
mvn -Djetty.port=8080 jetty:run -DPROTOTYPING
----

== Appendix

=== JSON Terminology

See: elp.kapowsoftware.com/9.4/index.jsp?topic=/doc/rm/JSONTerminology.html

|===
| |

|JSON Text |JSON Object &vert; JSON Array
|JSON&nbsp;Object |{} &vert; { Properties }
|JSON Array |[] &vert; [ Items ]
|Properties |Property, Properties
|Property |String : JSON Value
|Items |JSON Value, Items
|JSON Value |JSON Text &vert; String &vert; Number &vert; false &vert; null &vert; true
|String |&quot;" &vert; " Characters " |
| Characters | Character Characters |
| Character | any Unicode character except ", \ or control character &vert; &quot; &vert; \ &vert; \/ &vert; \b &vert; \f &vert; \n &vert; \r &vert; \t &vert; \u 4 hex digits
|Number |a number very much like a C or Java number, see RFC 4627 for details.
|===

=== CORS

CORS stands for 'Cross Origin Resource Sharing' aka: 'Same Origin Policy' was designed to improve security and is implemented in browsers.
 In short it means: your browser will allow loading of resources only if host and port are identical to the url you are on.
 Ie. webpage loaded from http://localhost:8088/ resources from http://localhost:8080/restful will not be accessible.

==== Solution 1 (Q&amp;D):

 Disable CORS in your browser, e.g. for Chrome with the MOESIF plugin.

Nicely done introduction:

 * https://www.moesif.com/blog/technical/cors/Authoritative-Guide-to-CORS-Cross-Origin-Resource-Sharing-for-REST-APIs/#how-is-origin-definedhttps://www.moesif.com/blog/technical/cors/Authoritative-Guide-to-CORS-Cross-Origin-Resource-Sharing-for-REST-APIs/#how-is-origin-defined

==== Solution 2:

 Add to webapp\src\main\webapp\WEB-INF\web.xml

[source,xml]
----
<!-- CORS filter for XmlHttpRequests -->
<filter>
    <filter-name>cross-origin</filter-name>
    <filter-class>org.eclipse.jetty.servlets.CrossOriginFilter</filter-class>
    <init-param>
        <param-name>allowedOrigins</param-name>
        <param-value>*</param-value>
    </init-param>
    <init-param>
        <param-name>allowedMethods</param-name>
        <value>*</value>
    </init-param>
    <init-param>
        <param-name>allowedHeaders</param-name>
        <param-value>*</param-value>
    </init-param>
    <init-param>
        <param-name>supportsCredentials</param-name>
        <param-value>true</param-value>
    </init-param>
    <init-param>
        <param-name>chainPreflight</param-name>
        <param-value>false</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>cross-origin</filter-name>
    <url-pattern>/restful/*</url-pattern>
</filter-mapping>
----
`

Put into webapp/src/main/webapp/WEB-INF/lib:
 * https://search.maven.org/artifact/org.eclipse.jetty/jetty-util/9.4.12.v20180830/jar
 * https://search.maven.org/artifact/org.eclipse.jetty/jetty-servlets/9.4.12.v20180830/jar

==== Solution 3:

 Incorporate kroviz.js e.g. in the WAR containing your Apache Causeway backend.

== Extensions

=== OSM/Leaflet
 * 2.5D, buildings see https://osmbuildings.org/documentation/leaflet/
 * Magnifying Glass
 * Wikipedia markers
 * Routing

=== Chart.js

* SanKey diagarms, see CodePen example
