.editorconfig

+# Editor configuration, see https://editorconfig.org
+root = true
+
+[*]
+charset = utf-8
+indent_style = space
+indent_size = 4
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.ts]
+quote_type = single
+
+[*.md]
+max_line_length = off
+trim_trailing_whitespace = false

.gitignore

@@ -12,6 +12,9 @@ env/
 # Apple
 .DS_Store
 
+# VSCode
+.vscode/
+
 # NetBeans
 **/nbproject/private/
 **/nbproject/Makefile-*.mk

.versionrc

+{
+    "tagPrefix": "",
+    "commitUrlFormat": "https://transfer.hft-stuttgart.de/gitlab/unified-ticketing/-/commit/{{hash}}",
+    "compareUrlFormat": "https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/compare/{{previousTag}}...{{currentTag}}",
+    "issueUrlFormat": "https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/issues/{{id}}"
+}

CHANGELOG.md

@@ -2,19 +2,26 @@
 
 All notable changes to this project will be documented in this file. See [standard-version](https://github.com/conventional-changelog/standard-version) for commit guidelines.
 
-## [0.1.0](https://transfer.hft-stuttgart.de///compare/0.0.0...0.1.0) (2020-11-23)
+### [0.1.1](https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/compare/0.1.0...0.1.1) (2020-12-10)
 
 
 ### Features
 
-* add ci pipeline ([d6d6f3a](https://transfer.hft-stuttgart.de///commit/d6d6f3aaa7b09404cef03bb319508087e33f4982))
-* add GPLv3 License text ([6016122](https://transfer.hft-stuttgart.de///commit/6016122eb4c9e92e1befd1243b85c6ac509502b8))
-* **ci:** add maven settings file for gitlab artifactory ([aacd6b4](https://transfer.hft-stuttgart.de///commit/aacd6b494c3f49a5e6b325232b6532494e1e8bfa))
-* **ci:** add repo and dist management parts to pom ([ab131be](https://transfer.hft-stuttgart.de///commit/ab131beb5d3838327e7e1e5aca19c6120d58708c))
-* import first state of library code ([b841acd](https://transfer.hft-stuttgart.de///commit/b841acdde74a5e2969bac34db8a3051001ce860e))
+* enable mvn javadoc plugin ([c2ca81e](https://transfer.hft-stuttgart.de/gitlab/unified-ticketing/-/commit/c2ca81e80da49e37a561bad115b06a62bc5f7e91))
+
+## [0.1.0](https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/compare/0.0.0...0.1.0) (2020-11-23)
+
+
+### Features
+
+* add ci pipeline ([d6d6f3a](https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/commit/d6d6f3aaa7b09404cef03bb319508087e33f4982))
+* add GPLv3 License text ([6016122](https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/commit/6016122eb4c9e92e1befd1243b85c6ac509502b8))
+* **ci:** add maven settings file for gitlab artifactory ([aacd6b4](https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/commit/aacd6b494c3f49a5e6b325232b6532494e1e8bfa))
+* **ci:** add repo and dist management parts to pom ([ab131be](https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/commit/ab131beb5d3838327e7e1e5aca19c6120d58708c))
+* import first state of library code ([b841acd](https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/commit/b841acdde74a5e2969bac34db8a3051001ce860e))
 
 
 ### Bug Fixes
 
-* **logger:** set correct package for mainlogger after 19162378 ([04ae3ee](https://transfer.hft-stuttgart.de///commit/04ae3ee468a84e5729dcce9dfab02c6322e15ec1))
-* **systems/gitlab:** allow gitlab root at subpath on non-standard port ([baba48d](https://transfer.hft-stuttgart.de///commit/baba48d5e0b70b2c91c3232ecbc9187c504d043c))
+* **logger:** set correct package for mainlogger after 19162378 ([04ae3ee](https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/commit/04ae3ee468a84e5729dcce9dfab02c6322e15ec1))
+* **systems/gitlab:** allow gitlab root at subpath on non-standard port ([baba48d](https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/commit/baba48d5e0b70b2c91c3232ecbc9187c504d043c))

CONTRIBUTING.md

+Information on how to contribute to this project, is written in the docs.  
+See here: [docs/unified-ticketing/contributing.md](docs/unified-ticketing/contributing.md)

LICENSE.md

@@ -2,7 +2,7 @@ GNU General Public License
 ==========================
 
 _Version 3, 29 June 2007_
-_Copyright © 2007 Free Software Foundation, Inc. &lt;<http://fsf.org/>&gt;_
+_Copyright © 2007 [Free Software Foundation, Inc.](https://fsf.org)_
 
 Everyone is permitted to copy and distribute verbatim copies of this license
 document, but changing it is not allowed.

README.md

@@ -4,3 +4,8 @@ This is the repository of the unified-ticketing library.
 
 Documentation for this is done with GitLab Pages using MkDocs and is available here:  
 https://transfer.hft-stuttgart.de/pages/unified-ticketing/
+
+If you don't want to open the Webpage or it is not available for whatever reason,
+the documentation root is in [docs/index.md][docs-root]
+
+[docs-root]: docs/index.md

docs/api/core/logging.md

+# Logging
+
+The library uses the built-in logger from `java.util.logging`.
+It configures to not use the parent logger and places a new ConsoleHandler
+on static initialization. This outputs the log in formatted lines like:
+```text
+[2020-11-27T14:40:26+0100] [WARNING] [de.hftstuttgart.unifiedticketing.core.Logging.test] calling from app
+```
+
+This will _not_ change visual presentation based on any localization.
+
+## change log-level
+
+Default is to use _INFO_-level.
+You can change the used level:
+```java
+Logging.setLevel(Level);
+```
+
+The parameter passed is of type `java.util.logging.Level`.
+
+## test logging output
+
+To test if the logging as such works,
+you can pass a test string:
+```java
+Logging.test("test message");
+```
+
+This message will be logged by the `Logging`-class own Logger,
+once per level.
+
+## set custom formatter
+
+If you need another format,
+you can replace the default formatter of this lib by calling:
+```java
+Logging.setFormatter(Formatter);
+```
+
+This formatter has to be of type `java.util.logging.Formatter`

docs/api/core/ticket-system.md

+# Ticketsystem
+
+A `TicketSystem` object represents a connection definition to a space in an external ticket system.
+Part of this is a base URL, and some system specific identifier for e.g. a project on that system.
+If the access needs some kind of authentication,
+this has to be configured in this object on creation.
+
+## create new instance
+
+The constructor of `TicketSystem` is not publicly callable.
+Acquiring an instance has to be done either by passing an URI or using the builder mechanism.
+
+### by URI
+
+This library has a global definition, for how an URI has to start.
+The end of it is defined by each system specific implementation.
+
+!!! info "global URI definition"
+    `unifiedticketing:<system identifier>:<additional information>`  
+    _For system specific details look into the systems part of this docs_
+
+To instantiate a `TicketSystem` from an URI, call the static method `fromUri(String)`:
+
+```java
+TicketSystem ts = TicketSystem.fromUri(<uri>);
+```
+
+!!! warning
+    If the given String does not match the criteria for a valid URI,
+    or the system identifier is unknown, it throws an `AssertionException`
+
+### by builder
+
+The library has a builder mechanism defined to instantiate a new `TicketSystem` object, using fluent-api.
+To start it, call the static method `fromBuilder()`.  
+The returning object gives you all supported systems as choice,
+which then brings you to the system specific builder mechanism.
+
+At the end, you'll have to finish the building process with a call to `build()`.
+
+!!! warning
+    If not all mandatory information where given before calling `build()`,
+    it will throw an `AssertionException`
+
+## configuration options
+
+You can set configurations of two kinds:
+
+- simple boolean switches to enable/disable a behaviour/feature
+- string values
+
+To set a configuration, call the instance method `config`. It provides two signatures:
+
+- `config(TicketSystem.ConfigurationOption, boolean)`
+- `config(TicketSystem.ConfigurationOption, String)`
+
+??? abstract "currently available configuration options"
+    | ConfigurationOption  | type    | default | description                                                                                       |
+    | :------------------- | :------ | :------ | :------------------------------------------------------------------------------------------------ |
+    | RETURN_NULL_ON_ERROR | boolean | `false` | If true, don't throw exception on error, but return null or the calling object, if in fluent-api. |
+
+!!! warning
+    option `RETURN_NULL_ON_ERROR` is not fully implemented and tested yet.  
+    Expect it still throws Exceptions sometimes, but returns null/self also sometimes.
+## list tickets
+
+Tickets are requested by using the filter mechanism.
+To get _all_ Tickets just don't define any filters before calling `get()`.
+They are returned as `List<Ticket>`.
+
+??? warning "default pagination"
+    many systems have an implicit default pagination enabled,
+    which could block you from simply getting _all_ tickets.
+
+    you can ask the `TicketSystem` object, to tell you if it uses a default pagination:
+
+    ```java
+    ts.hasDefaultPagination();
+    ```
+
+!!! info "assignees"
+    Tickets have a field of type `Assignee`.
+    These have final String fields,
+    where the system implementation puts values if supported.
+
+!!! example "requesting tickets"
+    ```java
+    ts.find()
+        .setPage(1)
+        .setPageSize(10)
+        .get();
+    ```
+
+You can add various filter options, before finally calling `get()`.
+Each supported systems implementation is free to define special filter options.
+These are only callable, if your variable has the dedicated child-type.
+
+The globally available ones are listed below.
+They are marked `single` or `multi` types.
+A `single` typed filter will override previous values,
+whereas `multi` typed ones will be added to the previous values.
+
+| filter option method definition  | type     | description                                                                                                      |
+| :------------------------------- | :------- | :--------------------------------------------------------------------------------------------------------------- |
+| `isClosed()`                     | `single` | returns only tickets closed, or _considered_ closed by the system specific implementation                        |
+| `isOpen()`                       | `single` | returns only tickets open, or _considered_ open by the system specific implementation                            |
+| `setPage(int)`                   | `single` | page number of pagination to request                                                                             |
+| `setPageSize(int)`               | `single` | page size of request to paginate with                                                                            |
+| `withAssigneeId(String)`         | `multi`  | tickets with given assigneeId as assignee. <br/> On multiple calls ticket must have _ALL_ given ids as assignees |
+| `withAssigneeName(String)`       | `multi`  | same as assigneeId above                                                                                         |
+| `withDescriptionContain(String)` | `single` | substring the description has to contain                                                                         |
+| `withDescriptionMatch(String)`   | `single` | fully qualified regular expression, the whole description has to match                                           |
+| `withId(String)`                 | `multi`  | id a ticket must have. <br/> multiple calls keeps tickets matching _any_ of the set ids                          |
+| `withLabel(String)`              | `multi`  | label a ticket must have. <br/> Multiple calls a ticket must have _all_ given labels                             |
+| `withTitleContain(String)`       | `single` | substring the title has to contain                                                                               |
+| `withTitleMatch(String)`         | `single` | fully qualified regular expression, the whole title has to match                                                 |
+
+## get single ticket
+
+To request a single ticket the method `getTicketById` is provided,
+available with two signatures:
+- `getTicketById(String)`
+- `getTicketById(int)`
+
+The integer variant is just for convenience, if you have the id as number.
+It calls the String one with your number transformed.
+
+!!! example
+    ```java
+    Ticket t = ts.getTicketById("5");
+    ```
+
+## create new ticket
+
+The creation of a new Ticket is started by calling `createTicket()`.  
+This starts another fluid-api chain,
+in which you can set everything your new ticket should contain.
+The chain finishes calling `create()` at the end.
+
+!!! warning
+    if a mandatory information for ticket creation is not given,
+    prior calling `create()`,
+    an `AssertionException` is thrown.
+
+!!! example
+    ```java
+    Ticket t = ts.createTicket()
+        .title("some title")
+        .create();
+    ```
+
+Global available setters for ticket creation are:
+
+| method                                         | additional information                                                  |
+| :--------------------------------------------- | :---------------------------------------------------------------------- |
+| `assignees(String[])`                          | array of assignee identifiers, check system specific part, what to pass |
+| `description(String)`                          |                                                                         |
+| `labels(Set<String>)` <br/> `labels(String[])` |                                                                         |
+| `title(String)`                                |                                                                         |

docs/api/core/ticket.md

+# Ticket
+
+A ticket instance represents one ticket of the connected space.
+
+## get/create ticket
+
+The class is not publicly constructable,
+as it always belongs to a `TicketSystem` object.
+
+Getting an instance for a existing ticket,
+or creating a new one,
+is done from a `TicketSystem` instance.
+[->For details see here <-](./ticket-system.md)
+## reading data
+
+There are various getters available.
+Below the globally defined ones are listed,
+each system specific implementation is free to provide additional ones.
+
+!!! warning
+    systems are not guaranteed to support all data,
+    a global getter is defined for.
+    Therefore it can happen, you get an null value back
+    or exception thrown in this case.
+
+| method             | return                |
+| :----------------- | :-------------------- |
+| `getAssignees()`   | `Set<TicketAssignee>` |
+| `getDescription()` | `String`              |
+| `getId()`          | `String`              |
+| `getLabels()`      | `Set<String>`         |
+| `getParent()`      | `TicketSystem`        |
+| `getTitle()`       | `String`              |
+| `isOpen()`         | `boolean`             |
+
+## changing data
+
+You can change data of supported fields through dedicated setters.
+Every changed field is flagged as changed.
+To persist the changes to the connected space,
+you need to call `save()`.
+This forms an update request for all flagged fields
+and returns a new instance of `Ticket`,
+formed off the answer from the connected system.
+
+Below the globally defined setters are listed,
+each system implementation is free to offer more.
+
+| method                                              | description                                                     |
+| :-------------------------------------------------- | :-------------------------------------------------------------- |
+| `addAssignee(String)`<br/>`removeAssignee(String)`  | adds/removes assignee, check system specific part, what to pass |
+| `addLabel(String)`                                  | add label                                                       |
+| `clearAssignees()`                                  | remove all assignees                                            |
+| `open()`<br/>`close()`                              | opens/closes the ticket                                         |
+| `setDescription(String)`                            |                                                                 |
+| `setLabels(Set<String>)`<br/>`setLabels(String[])`  | replace all labels with the passed ones                         |
+| `setTitle(String)`                                  |                                                                 |

docs/api/exceptions.md

+# Exceptions
+
+The library defines its own set of exceptions.
+Throughout the whole library, these are used.
+They are located in the package `de.hftstuttgart.unifiedticketing.exceptions`.
+
+Base for all others is `UnifiedticketingException`,
+which extends `RuntimeException`.
+Every other custom exception extends this exception.
+
+This provides you with the ability,
+to catch a specific or all library related problems.
+Both without catching exceptions of your own code,
+that happen to be in the same try block.
+
+## Possible Exceptions
+
+- `AssertionException`
+- `DeserializationException`
+- `HttpRequestException`
+- `HttpResponseException`
+- `SerializationException`
+- `UnsupportedFunctionException`

docs/api/index.md

+# Java-API
+
+This is the API-Documentation,
+holding detailed information for each publicly available action you can do with each class.
+Below the structure of the library is explained and some generic examples are shown.
+## library structure
+
+The library is structured into three packages:
+
+1. `de.hftstuttgart.unifiedticketing.core`
+1. `de.hftstuttgart.unifiedticketing.exceptions`
+1. `de.hftstuttgart.unifiedticketing.systems`
+
+The core package contains the classes defining the generic API,
+to be implemented by each supported system.  
+The systems package contains a sub-package per supported system,
+which then holds the implementations of the core classes.  
+The exceptions package has some own exception types,
+used throughout the lib.
+
+For each package, this documentation provides a chapter in the navigation on the left.
+
+## examples
+
+!!! info
+    These examples are not specific to a certain system.
+    Therefore they can contain placeholders for system specific parts.
+    To get these parts, you'll have to go to the dedicated API-docs part.
+
+??? example "create TicketSystem instance"
+    __from builder:__
+    ```java
+    TicketSystem ts = TicketSystem.fromBuilder()
+        .<methods specifying connection details>
+        .build();
+    ```
+
+    __from uri:__
+    ```java
+    TicketSystem ts = TicketSystem.fromUri(<uri>);
+    ```
+
+??? example "searching tickets"
+    __without filters:__
+    ```java
+    ts.find().get();
+    ```
+
+    __only open tickets and explicit pagination:__
+    ```java
+    ts.find()
+        .isOpen()
+        .setPage(1)
+        .setPageSize(10)
+        .get();
+    ```
+
+??? warning "default pagination"
+    many systems have an implicit default pagination enabled,
+    which could block you from simply getting _all_ tickets.
+
+    !!! tip
+        you can ask the `TicketSystem` object, to tell you if it uses a default pagination:
+        ```java
+        ts.hasDefaultPagination();
+        ```

docs/api/systems/gitlab/ticket-system.md

+# GitLab-Ticketsystem
+
+This documents GitLab specific things for the integration to this library.
+For the global parts, see in the [core sections Ticketsystem site][core-ts].
+
+## create new instance
+
+A `GitlabTicketSystem` object is always referencing a specific GitLab project.
+Mandatory information to instantiate it, are the GitLab instances base url and the projects id.
+
+For public accessible actions, it can be used anonymously.
+Other operations have to be authenticated using an api-key.
+
+For all calls the GitLab api V4 is used (at the time of writing this, the only available one).
+If not configured otherwise, connections will use https.
+
+### by URI
+
+```java
+// recommended option
+GitlabTicketSystem ts = (GitlabTicketSystem) TicketSystem.fromUri("<uri>");
+
+// second possible declaration
+TicketSystem<
+    GitlabTicket,
+    GitlabTicketSystem,
+    GitlabTicketBuilder,
+    GitlabFilter
+    > gl = TicketSystem.fromUri("<uri>");
+```
+
+The first declaration option uses the child-class from the GitLab implementation directly.
+The second option uses the parent-class instead,
+defining the different implementations with Generics.
+
+Use the first option, if you're sure you want to use GitLab no matter what.
+This way you can see GitLab specific methods,
+whereas the second option keeps you limited on the global defined ones.
+If you may switch ticket systems in the future,
+the second option forces you to not use system specific stuff, making a transition easier.
+
+The URI to pass has to match this format:
+```
+unifiedticketing:gitlab:[http://|https://]<base url>:<project id>[:api key]
+```
+
+- protocol for http/https is optional. If not given, https is used
+- base url can contain also non-standard port hosted gitlab instances
+- api key if authentication needed, otherwise anonymous access is used
+
+??? example "URI examples"
+    - non-https anonymous, project 234, public gitlab  
+        `unifiedticketing:gitlab:http://wwww.gitlab.com:234`
+    - implicit https authenticated, project 234, public gitlab  
+        `unifiedticketing:gitlab:gitlab.com:234:1234896102765abcddbda324bb3a3`
+    - explicit https authenticated, project 42, fictional gitlab, non-standard port  
+        `unifiedticketing:gitlab:https://gitlab.example.org:8080:42:1234896102765abcddbda324bb3a3`
+
+### by builder
+
+For instantiation from the builder,
+mostly the same like building by URI applies.
+
+!!! warning
+    Passing the base url ensure the protocol (http or https) is removed
+
+??? example "builder examples"
+    - non-https anonymous, project 234, public gitlab  
+        ```java
+        GitlabTicketSystem ts = TicketSystem.fromBuilder()
+            .gitlab()
+            .withBaseUrl("www.gitlab.com")
+            .withHttp()
+            .withProjectId(234) // String and int variant available
+            .build();
+        ```
+    - implicit https authenticated, project 234, public gitlab  
+        ```java
+        GitlabTicketSystem ts = TicketSystem.fromBuilder()
+            .gitlab()
+            .withBaseUrl("gitlab.com")
+            .withProjectId("234")
+            .withApiKey("1234896102765abcddbda324bb3a3")
+            .build();
+        ```
+    - explicit https authenticated, project 42, fictional gitlab, non-standard port  
+        ```java
+        GitlabTicketSystem ts = TicketSystem.fromBuilder()
+            .gitlab()
+            .withBaseUrl("gitlab.example.org:8080")
+            .withHttps()
+            .withProjectId(42)
+            .withApiKey("1234896102765abcddbda324bb3a3")
+            .build();
+        ```
+
+## list tickets
+
+!!! warning "default pagination"
+    GitLab has a default pagination on _20_ elements per page.
+    Highest possible value is _100_ elements. [[Link]][gl-api-docs-pagination]
+
+!!! warning "mutual exclusive filters"
+    if you filter for assignees, you can only use either assignee-ids or their usernames. [[Link]][gl-api-docs-issues-list]
+
+!!! info "assignees"
+    GitLab implementation supports the fields `id`, `username` and `full name`.
+    If ticket has no assignee, assignee field stays `null`.
+
+From the filters shown on the global `TicketSystem` docs,
+the ones for regex-matching are not natively supported by the GitLab API.
+If such a filter is used,
+this get's done locally after receiving the response from GitLab,
+before handing it to the user.
+
+## get single ticket
+
+!!! info
+    This uses the list mechanism internally,
+    with the given issue-id as filter and just unwraps it from the received list.
+
+## create new ticket
+
+For a new GitLab ticket a title is mandatory.
+Everything else is optional.
+
+!!! example "minimal example"
+    ```java
+    GitlabTicket = ts.createTicket()
+        .title("my new ticket")
+        .create();
+    ```
+
+Setting an assignee, has to be by user-id. Setting by user name is not supported.
+
+[core-ts]: ../../core/ticket-system.md
+[gl-api-docs-issues-list]: https://docs.gitlab.com/ee/api/issues.html#list-issues
+[gl-api-docs-pagination]: https://docs.gitlab.com/ee/api/#pagination

docs/api/systems/gitlab/ticket.md

+# Gitlab-Ticket
+
+!!! todo
+    write usage api docs

docs/developers-guide/machine-setup.md

+# Machine Setup
+
+## General
+
+### Git
+
+The whole project is a Git repository,
+to do anything you'll need to have Git setup on your machine.
+
+!!! tip
+    We highly recommend you use Git directly typing commands to your terminal,
+    instead of relying on any GUI tools, IDE integration's whatsoever.
+    They make life easy, sure.
+    But do you know, what exact calls they do under the hood?
+
+#### Installation
+
+=== "*nix"
+    Should be part of all major systems default software distribution path.
+
+=== "Windows"
+    !!! warning "disclaimer"
+        This is for people having not much experience.
+        If you e.g. use Cygwin, you could just install Git from there and ignore this^^
+
+    - Download Git: [Git-SCM][gitscm-win]
+    - Installation recommendations:
+        - opt-out from `Enable Git Credential Manager`  
+            _We had bad experiences with it, storing wrong passwords an no one knew where to remove them as none of the pros used this thing^^_
+
+#### Configuration
+
+After installing Git, you'll have to set a few information,
+in order to be able to work with it.
+Mandatory is your username and email.
+
+Globally set your most used username and email address you'll be using.
+
+```bash
+git config --global user.name "<username>"
+git config --global user.email "<email address>"
+```
+
+!!! attention
+    If your global email is different from the one for this projects GitLab,
+    make sure to either add your main email address as committer email in your profile,
+    or change the git config for this project individually after cloning it.
+
+#### Clone project
+
+As of writing, the project can be accessed with HTTPS and SSH.
+If this is not working,
+check the repository from the link in the upper right corner of the page.
+(Maybe the path changed and someone forgot to update this part of the docs)
+
+=== "SSH"
+    ```bash
+    git clone git@transfer.hft-stuttgart.de:9Lukas5/unified-ticketing.git
+    ```
+
+=== "HTTPS"
+    ```bash
+    git clone https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing.git
+    ```
+
+## Java Development
+
+The Java library is development with OpenJDK 8 and Maven 3.6
+
+### Requirements
+
+- Git setup
+- OpenJDK 1.8.0+
+- Maven 3.6.0+
+
+### Installation
+
+#### OpenJDK
+
+=== "*nix"
+    Check your specific systems package names.
+
+    __Ubuntu 20.04__:  
+    ```bash
+    sudo apt install openjdk-11-jdk
+    ```
+
+=== "Windows"
+
+    - download OpenJDK: [jdk.java.net][java-net]
+    - extract archive to permanent place
+    - create/update system environment variable `JAVA_HOME`,
+        to the path you extracted OpenJDK to.
+    - update `PATH` variable including the `bin` folder of your newly placed OpenJDK
+    - check with a terminal that `java --version` works
+
+#### Maven
+
+=== "*nix"
+    Same as before, check your specific systems package names.
+
+    __Ubuntu:__  
+    ```bash
+    sudo apt install maven
+    ```
+
+=== "Windows"
+
+    - download Maven binary: [maven.apache.org][maven-dl]
+    - extract archive to permanent place
+    - create/update system environment variable `MAVEN_HOME`,
+        to the path you extracted Maven to.
+    - update `PATH` including `bin` folder of maven home
+    - check that `mvn --version` works
+
+### Import project to IDE
+
+Following is described, how to import the maven project to your IDE.
+I really hope, you're familiar enough to know how to use your IDE,
+so this is a just-in-case service.
+
+Also, this does not claim to be up-to-date/correct/cover all available IDE's.
+You are invited to contribute to this list below
+if you're IDE of choice is not listed yet or has some faults.
+
+=== "IntelliJ IDEA"
+    - Select `Open or Import`
+    - Choose the folder you cloned the project into
+
+## MkDocs (Documentation)
+
+This project is documented using MkDocs Material.
+It means we write Markdown files, organize them in a configuration file
+and MkDocs generates a static Website out of it we host and you are reading right now.
+
+### Requirements
+
+- Python 3.5+
+- pip
+- Python virtual environment _(optional)_
+
+### Installation
+
+=== "*nix"
+    check system specific names and commands, below are some examples collected over time:
+
+    __Ubuntu:__  
+    ```bash
+    sudo apt install python3 python3-pip python3-venv
+    ```
+
+=== "Windows"
+    - download & install Python: [python.org][python-win-dl] (use executable installer version)
+
+- open a terminal inside the project's root directory
+- _optional:_ create & activate new virtual environment:
+
+    === "*unix"
+        ```bash
+        python3 -m venv env
+        . ./env/bin/activate
+        ```
+
+    === "Windows"
+        === "CMD"
+            ```cmd
+            python -m venv env
+            env\scripts\activate.bat
+            ```
+        === "Power Shell"
+            !!! attention "execution policy"
+                You may have to first set the correct execution policy,
+                before able to run the activation script.
+
+                ```powershell
+                Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser
+                ```
+
+            ```powershell
+            python -m venv env
+            env\scripts\Activate.ps1
+            ```
+
+- install all required packages:  
+    ```
+    pip install -Ur requirements.txt
+    ```
+
+### Usage
+
+To work on the documentation, the mkdocs development server has to run.
+On start it tells you on which port it runs (default is `8000`).
+
+Open the Browser on the shown URL and edit the Markdown files.
+On saving changes your Browser should automatically reload the page.
+
+- _optional:_ enter python virtual environment
+
+    === "*unix"
+        ```bash
+        . ./env/bin/activate
+        ```
+
+    === "Windows"
+        === "CMD"
+            ```cmd
+            env\scripts\activate.bat
+            ```
+        === "Power Shell"
+            !!! attention "execution policy"
+                You may have to first set the correct execution policy,
+                before able to run the activation script.
+
+                ```powershell
+                Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser
+                ```
+
+            ```powershell
+            env\scripts\Activate.ps1
+            ```
+
+- start MkDocs development server:  
+    ```bash
+    mkdocs serve
+    ```
+- work
+- kill dev server by pressing `ctrl+c`
+- _optional:_ exit python virtual environment:  
+    ```bash
+    deactivate
+    ```
+
+### Editor/IDE
+
+You don't need any special IDE, as a bare minimum a text editor would work (even vim is possible).  
+__But don't you dare to use this crappy Microsoft built in editor!__
+
+Practically it's very supportive of course,
+to use a IDE that has good markdown support in terms of code-highlighting,
+table formatting, etc.  
+Below are collected tips for different IDE's.
+
+=== "VSCode"
+    recommended extensions:  
+    _these are the extension id's searchable from vscode_
+
+    - `editorconfig.editorconfig`
+    - `waderyan.gitblame`
+    - `yzhang.markdown-all-in-one`
+    - `jebbs.plantuml`
+
+[gitscm-win]: https://git-scm.com/download/win
+[java-net]: https://jdk.java.net/
+[maven-dl]: https://maven.apache.org/download.cgi
+[python-win-dl]: https://www.python.org/downloads/windows/

docs/developers-guide/styleguide.md

+# Styleguide
+
+If not explicitly stated otherwise,
+the following takes effect for all files:
+
+- character encoding __utf-8__
+- line endings with __lf__
+- indentation with __4 spaces__
+- final new line
+
+In general,
+it's a good idea to have a look into the yet existing code,
+to check how certain things were done up to now.
+
+## Java
+
+The most important thing to say here is: opening braces are written into the next line.  
+_(more to come if s.o. does s.th. differently I didn't think of)_
+
+## Markdown
+
+most important bullet points:
+
+- leave always an empty line above and beneath of lists.
+    It may render fine in normal markdown viewers,
+    but not in the MkDocs Pages docs (like this)  
+
+    ??? example inline end
+        __bad:__
+        ```markdown
+        some text
+        - bullet point
+        - another item
+        more normal text
+        ```
+        __good:__
+        ```markdown
+        some text
+
+        - bullet point
+        - another item
+
+        more normal text
+        ```
+
+- if you insert a link,
+    __always__ write the link to the bottom of the file with an alias,
+    ordered alphabetically.  
+
+    ??? example
+        __bad:__
+        ```markdown
+        Look [here](https://www.coolsite.not/with/ultra/long/url) to read more about this.
+        ```
+        __good:__
+        ```markdown
+        Look [here][coolsite] to read more about this.
+
+        [coolsite]: https://www.coolsite.not/with/ultra/long/url
+        ```
+
+- split long sentences on punctuation and connection words like `and` & `or`.  
+    It will have the same appearance in viewers,
+    but be much easier to maintain on code side.
+
+    ??? example
+        __bad__:
+        ```markdown
+        Some sentence that is very long, therefore it has punctuation and has absolutely no sense at all.
+        ```
+        > Some sentence that is very long, therefore it has punctuation and has absolutely no sense at all.
+
+        __good:__
+        ```markdown
+        Some sentence that is very long,
+        therefore it has punctuation
+        and has absolutely no sense at all.
+        ```
+
+        > Some sentence that is very long,
+        > therefore it has punctuation
+        > and has absolutely no sense at all.
+
+- tables have to be formatted in code
+
+    ??? example
+        __bad:__
+        ```markdown
+        ||column 1|
+        |:-|:-|
+        |__row 1__|cell 1|
+        ```
+
+        __good:__
+        ```markdown
+        |           | column 1 |
+        | :-------- | :------- |
+        | __row 1__ | cell 1   |
+        ```

docs/developers-guide/uml.md

+# Library UML-Diagram
+
+This is the full UML-diagram for the Unified-Ticketing library.
+
+!!! tip
+    You most likely can't read anything embedded to the site,
+    please open the graphics-URL in an extra tab and zoom in.
+
+```plantuml
+
+abstract Filter {
+    __ generics definition __
+    T extends Ticket
+    F extends Filter
+    ==
+    - {static} logger: Logger
+
+    # {static} addToSet(\n\tfilterName: FilterNames,\n\tmap: Map<String, Object>,\n\tnewValue: String\n)
+
+    __ instance definition __
+    # setFilters: Map<String, Object>
+
+    + constructor()
+
+    + withAssigneeId(id: String): F
+    + withAssigneeName(name: String): F
+    + withDescriptionContain(substring: String): F
+    + withDescriptionMatch(regex: String): F
+    + withId(id: string): F
+    + isOpen(): F
+    + isClosed(): F
+    + withLabel(label: String): F
+    + setPage(page: int): F
+    + setPageSize(size: int): F
+    + withTitleContain(substring: String): F
+    + withTitleMatch(regex: String): F
+
+    + {abstract} get(): List<T>
+}
+
+enum FilterNames {
+    + ASSIGNEEID
+    + ASSIGNEENAME
+    + DESCRIPTION_CONTAIN
+    + DESCRIPTION_MATCH
+    + IDS
+    + LABELS
+    + OPEN
+    + PAGE
+    + PAGINATION
+    + TITLE_CONTAINS
+    + TITLE_MATCH
+}
+
+class Logging {
+    - {static} handler: Handler
+    - {static} mainLogger: Logger
+    - {static} logger: Logger
+
+    + {static} getLogger(name: String): Logger
+    + {static} setFormatter(formatter: Formatter): void
+    + {static} setLevel(level: Level): void
+    + {static} test(message: String): void
+}
+
+class RegisteredSystems <<(S, orange)>> {
+    - {static} logger: Logger
+    - {static} instance: RegisteredSystems
+
+    # {static} getInstance(): RegisteredSystems
+
+    __ instance definition __
+    + constructor()
+
+    + gitlab(): GitlabTicketSystemBuilder
+}
+
+abstract Ticket {
+    __ generics definition __
+    T \t extends Ticket
+    TS \t extends TicketSystem
+    ==
+    - {static} logger: Logger
+
+    __ instance definition __
+    # assignees: Set<TicketAssignee>
+    # description: String
+    # id: String
+    # labels: Set<String>
+    # open: boolean
+    # title: String
+
+    # updatedFields: Set<String>
+    # parent: TS
+
+    # constructor(parent: TS)
+
+    + getAssignees(): Set<? extends TicketAssignee>
+    + {abstract} addAssignee(identifier: String): T
+    + clearAssignees(): T
+    + {asbtract} removeAssignee(identifier: String): T
+    + getDescription(): String
+    + setDescription(description: String): T
+    + getId(): String
+    + addLabel(label: String): T
+    + getLabels(): Set<String>
+    + setLabels(labels: Set<String>): T
+    + setLabels(labels: String[]): T
+    + isOpen(): boolean
+    + open(): T
+    + close(): T
+    + getParent(): TS
+    + getTitle(): String
+    + setTitle(title: String): T
+
+    + {abstract} save(): T
+
+    + equals(o: Object): boolean
+    + hashCode(): int
+    + toString(): String
+}
+
+enum FieldNames {
+    + ASSIGNEES
+    + DESCRIPTION
+    + ID
+    + LABELS
+    + OPEN
+    + TITLE
+}
+
+abstract TicketAssignee {
+    + email: String
+    + id: String
+    + fullName: String
+    + username: String
+
+    # constructor(\n\temail: String,\n\tid: String,\n\tusername: String,\n\tfullName: String\n)
+
+    + equals(o: Object): boolean
+    + hashCode(): int
+    + toString(): String
+}
+
+abstract TicketBuilder {
+    __ generics definition __
+    B \t extends TicketBuilder
+    T \t extends Ticket
+    TS \t extends TicketSystem
+    ==
+    - {static} logger: Logger
+
+    __ instance definition __
+    # assignees: Set<String>
+    # description: String
+    # labels: Set<String>
+    # title: String
+
+    # constructor(parent: TS)
+
+    + assignees(identifiers: String...): B
+    + description(description: String): B
+    + labels(labels: Set<String>): B
+    + labels(labels: String[]): B
+    + title(title: String): B
+
+    + {abstract} create(): T
+}
+
+abstract TicketSystem {
+    __ generics definition __
+    B \t extends TicketBuilder
+    F \t extends Filter
+    T \t extends Ticket
+    TS \t extends TicketSystem
+    ==
+    - {static} logger: Logger
+
+    + {static} fromBuilder(): RegisteredSystems
+    + {static} fromUri(uri: String): TicketSystem
+
+    __ instance definition __
+    + apiKey: String
+    + baseUrl: String
+    + password: String
+    + username: String
+
+    # configuration: Map<String, String>
+
+    + constructor()
+
+    + config(option: ConfigurationOptions, value: String): TS
+    + config(option: ConfigurationOptions, value: boolean): TS
+    + getConfigTrue(option: ConfigurationOptions): boolean
+    + getConfigValue(option: ConfigurationOptions): Object
+    + {abstract} createTicket(): TB
+    + {abstract} find(): F
+    + {abstract} getTicketById(id: String): T
+    + {abstract} getTicketById(id: int): T
+
+    + {abstract} hasAssigneeSupport(): boolean
+    + {abstract} hasDefaultPagination(): boolean
+    + {abstract} hasLabelSupport(): boolean
+    + {abstract} hasPaginationSupport(): boolean
+    + {abstract} hasReturnNullOnErrorSupport(): boolean
+}
+
+enum ConfigurationOptions {
+    + RETURN_NULL_ON_ERROR
+}
+
+abstract TicketSystemBuilder {
+    __ generics definition __
+    B \t extends TicketBuilder
+    TS \t extends TicketSystem
+    ==
+    - {static} logger: Logger
+
+    __ instance definition __
+    + baseUrl: String
+
+    + withBaseUrl(url: String): B
+
+    + {abstract} build(): TS
+}
+
+' package connections
+Filter *-- FilterNames: "inner class"
+TicketSystem --> RegisteredSystems: "fromBuilder()"
+TicketSystem *-- ConfigurationOptions: "inner class"
+Ticket *-- FieldNames: "inner class"
+Ticket --> Ticket: "save()"
+Ticket o-- TicketSystem: "parent"
+Ticket o-- TicketAssignee
+TicketSystem --> TicketBuilder: "createTicket()"
+TicketBuilder --> Ticket: "create()"
+
+class AssertionException {
+    + constructor()
+    + constructor(msg: String)
+    + constructor(msg: String, cause: Throwable)
+    + constructor(suppressed: Throwable)
+}
+
+class DeserializationException {
+    + constructor()
+    + constructor(msg: String)
+    + constructor(msg: String, cause: Throwable)
+    + constructor(suppressed: Throwable)
+}
+
+class HttpRequestException {
+    + constructor()
+    + constructor(msg: String)
+    + constructor(msg: String, cause: Throwable)
+    + constructor(suppressed: Throwable)
+}
+
+class HttpResponseException {
+    + constructor()
+    + constructor(msg: String)
+    + constructor(msg: String, cause: Throwable)
+    + constructor(suppressed: Throwable)
+}
+
+class SerializationException {
+    + constructor()
+    + constructor(msg: String)
+    + constructor(msg: String, cause: Throwable)
+    + constructor(suppressed: Throwable)
+}
+
+class UnifiedticketingException {
+    + constructor()
+    + constructor(msg: String)
+    + constructor(msg: String, cause: Throwable)
+    + constructor(suppressed: Throwable)
+}
+
+class UnsupportedFunctionException {
+    + constructor()
+    + constructor(msg: String)
+    + constructor(msg: String, cause: Throwable)
+    + constructor(suppressed: Throwable)
+}
+
+AssertionException -[hidden]down- DeserializationException
+DeserializationException -[hidden]down- HttpRequestException
+HttpRequestException -[hidden]down- HttpResponseException
+HttpResponseException -[hidden]down- SerializationException
+SerializationException -[hidden]down- UnifiedticketingException
+UnifiedticketingException -[hidden]down- UnsupportedFunctionException
+
+class GitlabFilter {
+    - {static} logger: Logger
+
+    __ instance definition __
+    # parent: GitlabTicketSystem
+
+    # getHttpClient(): OkHttpClient
+    + get(): List<GitlabTicket>
+}
+
+class GitlabTicket {
+    - {static} logger: Logger
+
+    # {static} fromTicketResponse(\n\tparent: GitlabTicketSystem,\n\tresponse: GitlabTicketResponse\n): GitlabTicket
+
+    __ instance definition __
+    # constructor(parent: GitLabTicketSystem)
+
+    + addAssignee(userId: String): GitlabTicket
+    + addAssignee(userId: int): GitlabTicket
+    + removeAssignee(userId: String): GitlabTicket
+    + removeAssignee(userId: int): GitlabTicket
+    + save(): GitlabTicket
+
+    + deepEquals(o: Object): boolean
+}
+
+class GitlabTicketAssignee {
+    # constructor(id: int, fullName: String, username: String)
+}
+
+class GitlabTicketBuilder {
+    - {static} logger: Logger
+
+    __ instant definition __
+    # constructor(parent: GitlabTicketSystem)
+
+    + assignees(identifiers: String...): GitlabTicketBuilder
+    + assignees(identifiers: int...): GitlabTicketBuilder
+
+    # getHttpClient(): OkHttpClient
+    + create(): GitlabTicket
+}
+
+class GitlabTicketResponse {
+    + assignees: List<Assignee>
+    + description: String
+    + iid: int
+    + labels: Set<String>
+    + state: String
+    + title: String
+
+    # constructor()
+}
+
+class Assignee {
+    + id: int
+    + name: String
+    + username: String
+}
+
+class GitlabTicketSystem {
+    - {static} logger: Logger
+
+    + {static} fromUri(uri: String): GitlabTicketSystem
+
+    __ instance definition __
+    # constructor()
+    + createTicket(): GitlabTicketBuilder
+    + find(): GitlabFilter
+    + getTicketById(id: String): GitlabTicket
+
+    + hasAssigneeSupport(): boolean
+    + hasDefaultPagination(): boolean
+    + hasLabelSupport(): boolean
+    + hasPaginationSupport(): boolean
+    + hasReturnNullOnErrorSupport(): boolean
+}
+
+class GitlabTicketSystemBuilder {
+    - {static} logger: Logger
+
+    __ instance definition __
+    # apiKey: String
+    # apiVersion: String
+    # projectId: int
+    # https: boolean
+
+    + constructor()
+
+    + withApiKey(apiKey: String): GitlabTicketSystemBuilder
+    + withHttp(): GitlabTicketSystemBuilder
+    + withHttps(): GitlabTicketSystemBuilder
+    + withProjectId(projectId: int): GitlabTicketSystemBuilder
+    + withProjectId(projectId: String): GitlabTicketSystemBuilder
+
+    + build(): GitlabTicketSystem
+}
+
+' package connections
+GitlabFilter o-- GitlabTicketSystem: "parent"
+GitlabTicketResponse o- Assignee: "inner class"
+GitlabTicketSystemBuilder --> GitlabTicketSystem: "build()"
+GitlabTicketSystem --> GitlabTicketBuilder: "createTicket()"
+GitlabTicketBuilder --> GitlabTicket: "create()"
+GitlabTicketSystem *-- GitlabTicketResponse
+
+' core package connections
+GitlabFilter --|> Filter
+GitlabTicket --|> Ticket
+GitlabTicketAssignee --|> TicketAssignee
+GitlabTicketBuilder --|> TicketBuilder
+GitlabTicketSystem --|> TicketSystem
+GitlabTicketSystemBuilder --|> TicketSystemBuilder
+
+RegisteredSystems --> GitlabTicketSystemBuilder: "gitlab()"
+
+```

docs/developers-guide/workflow.md

+# Workflow
+
+This project is maintained in a GitLab repository,
+hosted on the [M4Lab's][m4lab] [Transfer-Portal][tr-portal] [GitLab instance][tr-gitlab].  
+Source code for the maven Java library and the markdown docs are managed together in a [single repository][lib-repo-home].
+
+This page tells you for the different parts of this project,
+how to do it.  
+The following applies project wide:
+
+- language is english: code, comments, documentation, tickets, discussion, ...
+
+## Git/GitLab
+
+!!! danger "disclaimer"
+    There are a few rules any developer HAS TO follow,
+    in order to get any chance his merge-requests will be accepted.
+
+This project is managed using Git, hosted on the universities GitLab instance.
+
+### Issues/Merge Requests handling
+
+Project management happens in the GitLab repositories issue board.
+
+First of all, make sure for everything you do a ticket exists.
+Extending this, also check regularly your tickets are:
+
+- assigned to you
+- are in the correct column
+
+There are three columns as of writing this documentation: `To Do`, `Doing` and `review`.  
+Planning something, a new ticket get's created and placed into the `To Do` column.
+
+If you start to work on this ticket
+
+- move it to `Doing`
+- create a new feature branch from the master
+    - named like: `<ticket-id>-<some-descriptive-name>`
+- push the new branch
+- create a new merge request
+    - title starting with `wip: `
+    - description containing `closes #<ticket-id>`
+    - assign it to you (even if you're not able to merge)
+- start working
+
+After implementing your change
+
+- move your ticket to `review` column
+- change your merge requests labels: remove `Doing` and add `review`
+- change assignee to someone to review your work
+
+### Branch Names
+
+Branches should always start with the number of the related ticket, followed by a dash.
+This way the branch get's automatically shown in the ticket.
+
+### Committing
+
+!!! tip "golden rules"
+    - __many small__ > ~~few big~~ commits
+    - unrelated changes in separate commit
+
+We encourage everyone to make heavy use of `git status` and `git diff`.
+Please always check before committing, what exactly you have changed.  
+What we won't accept:
+
+- whole file content removed and added back  
+    This most likely happens if you make great use of auto format,
+    messing everything up.
+    Another one error source is something changed line endings.
+- empty lines containing spaces, or trailing spaces on line end (without technical reason)  
+    No big deal to fix, but time waste if we have to block your MR because of this.
+- multiple changes in one commit, that have nothing to do with each other  
+    Great you have fixed a typo in a comment at the other end of the file.
+    What do you think happens, if five people fix the same typo in their commits?
+    We would have four merge conflicts, needing manual work to fix this mess.
+    So create a new ticket for what you found,
+    instead of just doing it as it doesn't hurt.
+    It hurts, trust me.
+- commit messages not following conventional commits specification
+
+!!! tip "view diff of not yet tracked files"
+    If you want to check a new file for flaws, sure `git diff` doesn't show anything.
+    But you can add the file and before committing check with `git diff --cached`.
+
+!!! tip "add only parts of changes in a file"
+    As we want to have more small commits, than one single big one,
+    it can be useful to split your changes into multiple commits,
+    even inside the same file.  
+    You can use `git add -p [path|file]`.
+    This allows you to exactly decide which lines of your changes should be staged
+    , before committing.
+
+#### Commit Messages
+
+We use the [conventional commits][conv-comm] specification in this repository,
+to auto generate a changelog with [conventional-changelog][conv-change].
+
+### Protected Branches/Tags
+
+The repository has the master branch and release tags (format `^[0-9]+\.[0-9]+\.[0-9]+$`)
+protected to project maintainers.
+
+### Branching-Model
+
+We use a branch per feature based branching model.
+Base and target to merge is always latest `master`.
+
+## Java Development
+
+First step before changing the source code,
+would be to check if there's something going on yet,
+or this topic possibly was discussed yet and abandoned for some reason.
+For this, check the [defined GitLab workflow](#gitgitlab).
+
+This library is a maven project.
+In order to contribute to it,
+make sure your machine is setup according to the [setup guide][setup-guide].
+
+### Change an existing functionality
+
+- check with the [source structure below](#source-code-structure),
+    where to find the part you want to change.
+- make your changes
+- make sure all unittests still pass
+- commit your changes following the Git/GitLab workflow defined.
+
+### Add integration for new system
+
+- familiarize with the [code structure](#source-code-structure)
+- create a new package under `de.hftstuttgart.unifiedticketing.systems`,
+    identifying the new system
+- prepare to implement all abstract classes from the `core` package
+    - class names have to be the same as the `core` ones,
+        prefixed with the identifier you named your package after
+- create unittests for the planned integration,
+    either by putting a `fail();` into each testmethod,
+    or really writing tests first for TDD
+- commit & push this skeleton-like state
+- create WIP merge-request
+- implement
+
+### Source code structure
+
+After cloning the repository,
+you'll have to open/import an existing maven project in your IDE of choice.
+There WILL NOT be any configuration files for a specific IDE committed into the code.
+In regards to the maven project parts,
+only the `pom.xml` and the contents under `/src` are committed.
+
+The main package for everything of this library is `de.hftstuttgart.unifiedticketing`.  
+Beneath it is split into three sub-packages:
+
+| subpackage   | content                                                                    |
+| :----------- | :------------------------------------------------------------------------- |
+| `core`       | root classes defining lib core, generic public interface                   |
+| `exceptions` | library own exceptions                                                     |
+| `systems`    | subpackage per system integration, implementation of abstract core-classes |
+
+__core:__  
+The majority of the classes are abstract ones.
+They define the generic interface available to the user of this lib.
+Logic identical for all system integrations are found in these classes.  
+Only few methods are really declared abstract,
+in most cases it's the part calling the external system.
+
+__exceptions:__  
+The library defines its own exceptions, based on `RuntimeException`.
+If you throw any exception,
+__only__ use exceptions from this package,
+never anything else.
+
+If you miss an exception you'd like to throw,
+add a new one that extends `UnifiedTicketingException`.
+
+__systems:__  
+Each system that's integrated into this lib,
+will have a sub-package under `de.hftstuttgart.unifiedticketing.systems`.
+In this very own package every abstract class from the `core`-package has to be implemented.
+Apart from that,
+every system can define as many helper classes
+or additional sub-packages.
+
+### Unittests
+
+The logical code is structured under `/src/main/java`.
+For unittests the same package structure is created under `/src/test/java`.
+Tests are written using the `jupiter-engine` from JUnit5,
+combined with `Mockito3`.
+
+- test-classes are named identical to the class under test,
+    suffixed with `Test`
+- test-classes have to be in the same package than the class under test
+
+What has to be tested:
+
+- constructors
+- getters/setters
+- calculations/transformations/...
+- fluent-api to return the same instance
+- serializing request data before request
+- failing web-request
+- successful web-request & deserializing of received data
+
+!!! warning "testing external resources"
+    All tests _have to_ run offline.
+    To test external resources,
+    e.g. a web-request,
+    use Mockito to block the code under test to really access the external resource
+    and transparently return your mock answer expected for the assertions following.
+
+??? tip "test abstract classes"
+    To test non-abstract code of abstract classes,
+    you can instantiate a mock of it through Mockito,
+    set to call the real methods:
+
+    ```java
+    instance = mock(ClassUnderTest.class,
+        withSettings().useConstructor().defaultAnswer(CALLS_REAL_METHODS));
+    ```
+
+## Documentation
+
+Documentation for the project is done entirely in Markdown
+and rendered through MkDocs to a Website.
+The repository global `README.md` just points to the documentation root,
+which is `/docs/index.md`.
+The same applies for the `CONTRIBUTING.md`.  
+`CHANGELOG.md` and `LICENSE.md` are kept with content in project root,
+they are linked with a relative soft-link into the documentation folder.
+
+Files related to the documentation:
+
+| path               | description                                     |
+| :----------------- | :---------------------------------------------- |
+| `mkdocs.yml`       | configuration file for mkdocs                   |
+| `requirements.txt` | needed pypi packages to pass to pip for install |
+| `/docs/**/*`       | documentation files                             |
+| `/docs/index.md`   | Pages root                                      |
+
+With the aim to give the documentation an appealing appearance,
+additional to the default markdown specification,
+a few extensions are enabled in the mkdocs config.  
+Please have a look at them and make use of,
+where it seems adequate.
+Reference for them can be found in the [MkDocs-Material site][mat-mkdocs-ext-ref].
+
+To make any kind of diagram, sketch or similar,
+use [PlantUML][puml].
+You have to surround the PlantUML code with code fences,
+marked as `plantuml` as language identifier.
+Then they will be rendered into an svg on pages creation.
+
+!!! bug
+    I tried to put this into an collapsed example admonition,
+    but the PlantUML diagram get's always placed outside the admonition.
+    Same applies for a tabbed environment.
+
+Example:  
+__code:__  
+``````
+```plantuml
+queue "write\nmarkdown" as write
+queue "commit/push/\nmerge changes" as update
+queue "pipeline\ntriggered" as cicd
+queue "MkDocs\nMaterial" as MkDocsMat
+queue "transpiled HTML\nonline" as deployed
+
+write -right-> update
+update -right-> cicd
+cicd -right-> MkDocsMat
+MkDocsMat -right-> deployed
+```
+``````
+
+__result:__  
+```plantuml
+queue "write\nmarkdown" as write
+queue "commit/push/\nmerge changes" as update
+queue "pipeline\ntriggered" as cicd
+queue "MkDocs\nMaterial" as MkDocsMat
+queue "transpiled HTML\nonline" as deployed
+
+write -right-> update
+update -right-> cicd
+cicd -right-> MkDocsMat
+MkDocsMat -right-> deployed
+```
+
+## Schedule a release
+
+For releases this project uses [standard-version][std-ver].
+This generates an automatic changelog based on the commits
+and tags it.
+The version of the library has three numbers
+and has to follow the [semantic-version][semver] scheme.
+
+Tags marking a release have the format `^[0-9]+\.[0-9]+\.[0-9]+$`.
+Pushing these tags is restricted in the GitLab Repo settings
+for maintainers only.  
+Pushing a release tag triggers the CI/CD release pipeline for the maven project.
+
+## CI/CD
+
+This project uses GitLab-CI pipelines for
+
+- publishing the maven library to the repository own package registry
+- deploying this pages documentation
+
+These pipelines are defined in several files:
+
+| file                    | content                                                       |
+| :---------------------- | :------------------------------------------------------------ |
+| `.gitlab-ci.yml`        | root file, stages definition, include of other pipeline parts |
+| `.gitlab-ci-maven.yml`  | jobs regarding java library                                   |
+| `.gitlab-ci-mkdocs.yml` | jobs regarding pages documentation                            |
+
+pipeline graph overview:  
+```plantuml
+rectangle "compile" as stageCompile {
+    ' maven
+    agent "maven:compile" as mvnCompile
+
+    ' mkdocs
+    agent "mkdocs:compile" as mkdocsCompile
+}
+rectangle "test" as stageTest {
+    ' maven
+    agent "maven:test" as mvnTest
+
+    ' mkdocs
+    agent "none" as mkdocsTest
+}
+rectangle "deploy" as stageDeploy {
+    ' maven
+    agent "maven:publish:master" as mvnPublMaster
+    agent "maven:publish:release" as mvnPublRelease
+    label "get's deployed with\n'devel' as version" as labelMvnPublMaster
+    label "get's deployed\nwith release version" as labelMvnPublRelease
+
+    ' mkdocs
+    agent "mkdocs:bundle" as mkdocsBundle
+    agent "mkdocs:deploy" as mkdocsDeploy
+    label "creates tar archive as\ndownloadable job artifact" as labelMkdocsBundle
+    label "only triggered\non master branch" as labelMkdocsDeploy
+}
+
+' maven pipeline connections
+mvnCompile -right-> mvnTest
+mvnTest -right-> mvnPublMaster
+mvnTest -right-> mvnPublRelease
+
+mvnPublMaster -right- labelMvnPublMaster
+mvnPublRelease -right- labelMvnPublRelease
+
+' mkdocs pipeline connections
+mkdocsCompile -right-> mkdocsTest
+mkdocsTest -right-> mkdocsBundle
+mkdocsTest -right-> mkdocsDeploy
+
+mkdocsBundle -right- labelMkdocsBundle
+mkdocsDeploy -right- labelMkdocsDeploy
+
+' compile stage keep in place
+mvnCompile --[hidden]down- mkdocsCompile
+
+' test stage keep in place
+mvnTest --[hidden]down-mkdocsTest
+
+' deploy stage keep in place
+mvnPublMaster -[hidden]down- mvnPublRelease
+mvnPublRelease -[hidden]down- mkdocsBundle
+mkdocsBundle -[hidden]down- mkdocsDeploy
+```
+
+These jobs are defined with the `needs` keyword,
+to make them only depend on exactly the needed previous jobs.
+This makes it possible to run docs and library pipelines in parallel,
+without waiting that all jobs of a stage must have finished before entering the next stage.
+
+With the `only` keyword the trigger of these pipelines is optimized,
+to only run if necessary.  
+In general the final deployment jobs have configurations to run only on the secured branches/tags.
+Additionally all jobs are configured to only run,
+if changes on related files of this pipeline were made.
+
+[conv-comm]: https://www.conventionalcommits.org/en/v1.0.0/
+[conv-change]: https://github.com/conventional-changelog/conventional-changelog
+[lib-repo-home]: https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/
+[m4lab]: https://www.hft-stuttgart.de/forschung/innovative-hochschule-m4-lab
+[mat-mkdocs-ext-ref]: https://squidfunk.github.io/mkdocs-material/reference/abbreviations/
+[puml]: https://plantuml.com/
+[setup-guide]: /404.html
+[semver]: https://semver.org/
+[std-ver]: https://github.com/conventional-changelog/standard-version
+[tr-gitlab]: https://transfer.hft-stuttgart.de/gitlab/explore/projects
+[tr-portal]: https://transfer.hft-stuttgart.de/

docs/index.md

+[![maven][badge-latest-tag]][project-packages]
+[![pipeline state][badge-master-pipe]][project-pipelines]
+[![latest dev pipeline][badge-latest-pipe]][project-pipelines]
+[![License GPLv3][badge-gplv3]][gplv3]
+[![Conventional Commits][badge-conventional-commits]][convcomm]
+
 # Unified Ticketing
 
-!!! Todo
+This is the documentation for a Java-library called `unified-ticketing`.
+This lib provides generic interfaces to interact with tickets
+from different ticket systems out of your Java code.
+
+This library is a maven artifact,
+published under the [GNU GPL-v3][gplv3] license.
+The source code is publicly available from the [transfer portal][transferportal] of the [University of Applied Sciences Stuttgart][hfthome].
+
+## What to find where
+
+The documentation is split in three main parts, navigable on the top-bar.
+Each main-part gives you a navigation of it's content on the left.
+On the right, the currents page table of contents is shown.  
+The icon in the upper left brings you from anywhere back to this start-page.
+In the upper right you can go to the source code repository of this library and documentation.
+Leftwards a full-text search is provided.
+
+The part you are reading right now (__Home__), is the main website.
+Following is a list, what each site contains:
+
+ - __Changelog:__ auto-generated changelog from the commits
+ - __Contributing:__
+     - Prerequisites to be able to be a contributor to this project
+ - __License:__ GNU GPLv3 content
+ - __Usage:__
+     - needed entries to get this library into your own maven-project
+     - some code-snippets showing the libs capabilites
+
+The __API__ part holds a detailed description, for each publicly accessible class and their methods.
+There is an own index file, explaining the package structure of the library
+and how it is documented.
+
+The __Developers Guide__ is the part, you have to lookup how to setup your machine and conventions and workflows used in this project,
+if you decide to contribute to it.
+
+## Maintainer
+
+This library and it's development belongs to the University of Applied Sciences Stuttgart.  
+
+It was originally developed as bachelors-thesis by Lukas Wiest
+[:material-email-send:{: style="color: black"}][9l5-hft-mail]
+[:fontawesome-brands-twitter:{: style="color: #1DA1F2"}][9l5Twitter]
+[:fontawesome-brands-github:{: style="color: black"}][9l5GH]
+[:fontawesome-brands-gitlab:{: style="color: orange"}][9l5GL].  
+The guardian professor was Prof. Dr. Gero Lueckemeyer
+[:material-email-send:{: style="color: black"}][lueck-hft-mail]
+[:fontawesome-solid-university:{: style="color: black"}][lueck-hft-profile]
+[:fontawesome-brands-github:{: style="color: black"}][lueck-GH]
+[:fontawesome-brands-xing:{: style="color: teal"}][lueck-Xing].
+He is the current maintainer for this project and the appropriate contact for questions, access request, etc.
+
+[9l5-hft-mail]: mailto:62wilu1bif@hft-stuttgart.de
+[9l5GH]: https://www.github.com/9Lukas5
+[9l5GL]: https://www.gitlab.com/9Lukas5
+[9l5Twitter]: https://twitter.com/9Lukas5
+[badge-conventional-commits]: https://img.shields.io/badge/Conventional%20Commits-1.0.0-orange.svg
+[badge-gplv3]: https://img.shields.io/badge/License-GPLv3-blue.svg
+[badge-latest-pipe]: https://img.shields.io/badge/dynamic/json?color=lightgrey&label=latest%20dev%20pipeline&query=%24%5B0%5D.status&url=https%3A%2F%2Ftransfer.hft-stuttgart.de%2Fgitlab%2Fapi%2Fv4%2F%2Fprojects%2F154%2Fpipelines%3Fper_page%3D1
+[badge-latest-tag]: https://img.shields.io/badge/dynamic/json?color=green&label=maven&query=%24%5B0%5D.name&url=https%3A%2F%2Ftransfer.hft-stuttgart.de%2Fgitlab%2Fapi%2Fv4%2Fprojects%2F154%2Frepository%2Ftags%3Fper_page%3D1
+[badge-master-pipe]: https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/badges/master/pipeline.svg
+[convcomm]: https://conventionalcommits.org
+[gplv3]: unified-ticketing/license-softlink.md
+[hfthome]: https://www.hft-stuttgart.de
+[lueck-GH]: https://github.com/lueckemeyer
+[lueck-hft-mail]: mailto:gero.lueckemeyer@hft-stuttgart.de
+[lueck-hft-profile]: https://www.hft-stuttgart.de/p/gero-lueckemeyer
+[lueck-Xing]: https://www.xing.com/profile/Gero_Lueckemeyer
+[project-packages]: https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/-/packages
+[project-pipelines]: https://transfer.hft-stuttgart.de/gitlab/9Lukas5/unified-ticketing/pipelines
+[transferportal]: https://transfer.hft-stuttgart.de

docs/unified-ticketing/changelog-softlink.md

+../../CHANGELOG.md
\ No newline at end of file