Added all basic infrastructure.

.gitignore

@@ -0,0 +1,36 @@
+HELP.md
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+*.mv.db
+*.trace.db

.mvn/wrapper/MavenWrapperDownloader.java

@@ -0,0 +1,117 @@
+/*
+ * Copyright 2007-present the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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.
+ */
+import java.net.*;
+import java.io.*;
+import java.nio.channels.*;
+import java.util.Properties;
+
+public class MavenWrapperDownloader {
+
+    private static final String WRAPPER_VERSION = "0.5.6";
+    /**
+     * Default URL to download the maven-wrapper.jar from, if no 'downloadUrl' is provided.
+     */
+    private static final String DEFAULT_DOWNLOAD_URL = "https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/"
+        + WRAPPER_VERSION + "/maven-wrapper-" + WRAPPER_VERSION + ".jar";
+
+    /**
+     * Path to the maven-wrapper.properties file, which might contain a downloadUrl property to
+     * use instead of the default one.
+     */
+    private static final String MAVEN_WRAPPER_PROPERTIES_PATH =
+            ".mvn/wrapper/maven-wrapper.properties";
+
+    /**
+     * Path where the maven-wrapper.jar will be saved to.
+     */
+    private static final String MAVEN_WRAPPER_JAR_PATH =
+            ".mvn/wrapper/maven-wrapper.jar";
+
+    /**
+     * Name of the property which should be used to override the default download url for the wrapper.
+     */
+    private static final String PROPERTY_NAME_WRAPPER_URL = "wrapperUrl";
+
+    public static void main(String args[]) {
+        System.out.println("- Downloader started");
+        File baseDirectory = new File(args[0]);
+        System.out.println("- Using base directory: " + baseDirectory.getAbsolutePath());
+
+        // If the maven-wrapper.properties exists, read it and check if it contains a custom
+        // wrapperUrl parameter.
+        File mavenWrapperPropertyFile = new File(baseDirectory, MAVEN_WRAPPER_PROPERTIES_PATH);
+        String url = DEFAULT_DOWNLOAD_URL;
+        if(mavenWrapperPropertyFile.exists()) {
+            FileInputStream mavenWrapperPropertyFileInputStream = null;
+            try {
+                mavenWrapperPropertyFileInputStream = new FileInputStream(mavenWrapperPropertyFile);
+                Properties mavenWrapperProperties = new Properties();
+                mavenWrapperProperties.load(mavenWrapperPropertyFileInputStream);
+                url = mavenWrapperProperties.getProperty(PROPERTY_NAME_WRAPPER_URL, url);
+            } catch (IOException e) {
+                System.out.println("- ERROR loading '" + MAVEN_WRAPPER_PROPERTIES_PATH + "'");
+            } finally {
+                try {
+                    if(mavenWrapperPropertyFileInputStream != null) {
+                        mavenWrapperPropertyFileInputStream.close();
+                    }
+                } catch (IOException e) {
+                    // Ignore ...
+                }
+            }
+        }
+        System.out.println("- Downloading from: " + url);
+
+        File outputFile = new File(baseDirectory.getAbsolutePath(), MAVEN_WRAPPER_JAR_PATH);
+        if(!outputFile.getParentFile().exists()) {
+            if(!outputFile.getParentFile().mkdirs()) {
+                System.out.println(
+                        "- ERROR creating output directory '" + outputFile.getParentFile().getAbsolutePath() + "'");
+            }
+        }
+        System.out.println("- Downloading to: " + outputFile.getAbsolutePath());
+        try {
+            downloadFileFromURL(url, outputFile);
+            System.out.println("Done");
+            System.exit(0);
+        } catch (Throwable e) {
+            System.out.println("- Error downloading");
+            e.printStackTrace();
+            System.exit(1);
+        }
+    }
+
+    private static void downloadFileFromURL(String urlString, File destination) throws Exception {
+        if (System.getenv("MVNW_USERNAME") != null && System.getenv("MVNW_PASSWORD") != null) {
+            String username = System.getenv("MVNW_USERNAME");
+            char[] password = System.getenv("MVNW_PASSWORD").toCharArray();
+            Authenticator.setDefault(new Authenticator() {
+                @Override
+                protected PasswordAuthentication getPasswordAuthentication() {
+                    return new PasswordAuthentication(username, password);
+                }
+            });
+        }
+        URL website = new URL(urlString);
+        ReadableByteChannel rbc;
+        rbc = Channels.newChannel(website.openStream());
+        FileOutputStream fos = new FileOutputStream(destination);
+        fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
+        fos.close();
+        rbc.close();
+    }
+
+}

.mvn/wrapper/maven-wrapper.properties

@@ -0,0 +1,2 @@
+distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.8.3/apache-maven-3.8.3-bin.zip
+wrapperUrl=https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar

mvnw

@@ -0,0 +1,310 @@
+#!/bin/sh
+# ----------------------------------------------------------------------------
+# 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
+#
+#    https://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.
+# ----------------------------------------------------------------------------
+
+# ----------------------------------------------------------------------------
+# Maven Start Up Batch script
+#
+# Required ENV vars:
+# ------------------
+#   JAVA_HOME - location of a JDK home dir
+#
+# Optional ENV vars
+# -----------------
+#   M2_HOME - location of maven2's installed home dir
+#   MAVEN_OPTS - parameters passed to the Java VM when running Maven
+#     e.g. to debug Maven itself, use
+#       set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000
+#   MAVEN_SKIP_RC - flag to disable loading of mavenrc files
+# ----------------------------------------------------------------------------
+
+if [ -z "$MAVEN_SKIP_RC" ] ; then
+
+  if [ -f /etc/mavenrc ] ; then
+    . /etc/mavenrc
+  fi
+
+  if [ -f "$HOME/.mavenrc" ] ; then
+    . "$HOME/.mavenrc"
+  fi
+
+fi
+
+# OS specific support.  $var _must_ be set to either true or false.
+cygwin=false;
+darwin=false;
+mingw=false
+case "`uname`" in
+  CYGWIN*) cygwin=true ;;
+  MINGW*) mingw=true;;
+  Darwin*) darwin=true
+    # Use /usr/libexec/java_home if available, otherwise fall back to /Library/Java/Home
+    # See https://developer.apple.com/library/mac/qa/qa1170/_index.html
+    if [ -z "$JAVA_HOME" ]; then
+      if [ -x "/usr/libexec/java_home" ]; then
+        export JAVA_HOME="`/usr/libexec/java_home`"
+      else
+        export JAVA_HOME="/Library/Java/Home"
+      fi
+    fi
+    ;;
+esac
+
+if [ -z "$JAVA_HOME" ] ; then
+  if [ -r /etc/gentoo-release ] ; then
+    JAVA_HOME=`java-config --jre-home`
+  fi
+fi
+
+if [ -z "$M2_HOME" ] ; then
+  ## resolve links - $0 may be a link to maven's home
+  PRG="$0"
+
+  # need this for relative symlinks
+  while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+      PRG="$link"
+    else
+      PRG="`dirname "$PRG"`/$link"
+    fi
+  done
+
+  saveddir=`pwd`
+
+  M2_HOME=`dirname "$PRG"`/..
+
+  # make it fully qualified
+  M2_HOME=`cd "$M2_HOME" && pwd`
+
+  cd "$saveddir"
+  # echo Using m2 at $M2_HOME
+fi
+
+# For Cygwin, ensure paths are in UNIX format before anything is touched
+if $cygwin ; then
+  [ -n "$M2_HOME" ] &&
+    M2_HOME=`cygpath --unix "$M2_HOME"`
+  [ -n "$JAVA_HOME" ] &&
+    JAVA_HOME=`cygpath --unix "$JAVA_HOME"`
+  [ -n "$CLASSPATH" ] &&
+    CLASSPATH=`cygpath --path --unix "$CLASSPATH"`
+fi
+
+# For Mingw, ensure paths are in UNIX format before anything is touched
+if $mingw ; then
+  [ -n "$M2_HOME" ] &&
+    M2_HOME="`(cd "$M2_HOME"; pwd)`"
+  [ -n "$JAVA_HOME" ] &&
+    JAVA_HOME="`(cd "$JAVA_HOME"; pwd)`"
+fi
+
+if [ -z "$JAVA_HOME" ]; then
+  javaExecutable="`which javac`"
+  if [ -n "$javaExecutable" ] && ! [ "`expr \"$javaExecutable\" : '\([^ ]*\)'`" = "no" ]; then
+    # readlink(1) is not available as standard on Solaris 10.
+    readLink=`which readlink`
+    if [ ! `expr "$readLink" : '\([^ ]*\)'` = "no" ]; then
+      if $darwin ; then
+        javaHome="`dirname \"$javaExecutable\"`"
+        javaExecutable="`cd \"$javaHome\" && pwd -P`/javac"
+      else
+        javaExecutable="`readlink -f \"$javaExecutable\"`"
+      fi
+      javaHome="`dirname \"$javaExecutable\"`"
+      javaHome=`expr "$javaHome" : '\(.*\)/bin'`
+      JAVA_HOME="$javaHome"
+      export JAVA_HOME
+    fi
+  fi
+fi
+
+if [ -z "$JAVACMD" ] ; then
+  if [ -n "$JAVA_HOME"  ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+      # IBM's JDK on AIX uses strange locations for the executables
+      JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+      JAVACMD="$JAVA_HOME/bin/java"
+    fi
+  else
+    JAVACMD="`which java`"
+  fi
+fi
+
+if [ ! -x "$JAVACMD" ] ; then
+  echo "Error: JAVA_HOME is not defined correctly." >&2
+  echo "  We cannot execute $JAVACMD" >&2
+  exit 1
+fi
+
+if [ -z "$JAVA_HOME" ] ; then
+  echo "Warning: JAVA_HOME environment variable is not set."
+fi
+
+CLASSWORLDS_LAUNCHER=org.codehaus.plexus.classworlds.launcher.Launcher
+
+# traverses directory structure from process work directory to filesystem root
+# first directory with .mvn subdirectory is considered project base directory
+find_maven_basedir() {
+
+  if [ -z "$1" ]
+  then
+    echo "Path not specified to find_maven_basedir"
+    return 1
+  fi
+
+  basedir="$1"
+  wdir="$1"
+  while [ "$wdir" != '/' ] ; do
+    if [ -d "$wdir"/.mvn ] ; then
+      basedir=$wdir
+      break
+    fi
+    # workaround for JBEAP-8937 (on Solaris 10/Sparc)
+    if [ -d "${wdir}" ]; then
+      wdir=`cd "$wdir/.."; pwd`
+    fi
+    # end of workaround
+  done
+  echo "${basedir}"
+}
+
+# concatenates all lines of a file
+concat_lines() {
+  if [ -f "$1" ]; then
+    echo "$(tr -s '\n' ' ' < "$1")"
+  fi
+}
+
+BASE_DIR=`find_maven_basedir "$(pwd)"`
+if [ -z "$BASE_DIR" ]; then
+  exit 1;
+fi
+
+##########################################################################################
+# Extension to allow automatically downloading the maven-wrapper.jar from Maven-central
+# This allows using the maven wrapper in projects that prohibit checking in binary data.
+##########################################################################################
+if [ -r "$BASE_DIR/.mvn/wrapper/maven-wrapper.jar" ]; then
+    if [ "$MVNW_VERBOSE" = true ]; then
+      echo "Found .mvn/wrapper/maven-wrapper.jar"
+    fi
+else
+    if [ "$MVNW_VERBOSE" = true ]; then
+      echo "Couldn't find .mvn/wrapper/maven-wrapper.jar, downloading it ..."
+    fi
+    if [ -n "$MVNW_REPOURL" ]; then
+      jarUrl="$MVNW_REPOURL/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+    else
+      jarUrl="https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+    fi
+    while IFS="=" read key value; do
+      case "$key" in (wrapperUrl) jarUrl="$value"; break ;;
+      esac
+    done < "$BASE_DIR/.mvn/wrapper/maven-wrapper.properties"
+    if [ "$MVNW_VERBOSE" = true ]; then
+      echo "Downloading from: $jarUrl"
+    fi
+    wrapperJarPath="$BASE_DIR/.mvn/wrapper/maven-wrapper.jar"
+    if $cygwin; then
+      wrapperJarPath=`cygpath --path --windows "$wrapperJarPath"`
+    fi
+
+    if command -v wget > /dev/null; then
+        if [ "$MVNW_VERBOSE" = true ]; then
+          echo "Found wget ... using wget"
+        fi
+        if [ -z "$MVNW_USERNAME" ] || [ -z "$MVNW_PASSWORD" ]; then
+            wget "$jarUrl" -O "$wrapperJarPath"
+        else
+            wget --http-user=$MVNW_USERNAME --http-password=$MVNW_PASSWORD "$jarUrl" -O "$wrapperJarPath"
+        fi
+    elif command -v curl > /dev/null; then
+        if [ "$MVNW_VERBOSE" = true ]; then
+          echo "Found curl ... using curl"
+        fi
+        if [ -z "$MVNW_USERNAME" ] || [ -z "$MVNW_PASSWORD" ]; then
+            curl -o "$wrapperJarPath" "$jarUrl" -f
+        else
+            curl --user $MVNW_USERNAME:$MVNW_PASSWORD -o "$wrapperJarPath" "$jarUrl" -f
+        fi
+
+    else
+        if [ "$MVNW_VERBOSE" = true ]; then
+          echo "Falling back to using Java to download"
+        fi
+        javaClass="$BASE_DIR/.mvn/wrapper/MavenWrapperDownloader.java"
+        # For Cygwin, switch paths to Windows format before running javac
+        if $cygwin; then
+          javaClass=`cygpath --path --windows "$javaClass"`
+        fi
+        if [ -e "$javaClass" ]; then
+            if [ ! -e "$BASE_DIR/.mvn/wrapper/MavenWrapperDownloader.class" ]; then
+                if [ "$MVNW_VERBOSE" = true ]; then
+                  echo " - Compiling MavenWrapperDownloader.java ..."
+                fi
+                # Compiling the Java class
+                ("$JAVA_HOME/bin/javac" "$javaClass")
+            fi
+            if [ -e "$BASE_DIR/.mvn/wrapper/MavenWrapperDownloader.class" ]; then
+                # Running the downloader
+                if [ "$MVNW_VERBOSE" = true ]; then
+                  echo " - Running MavenWrapperDownloader.java ..."
+                fi
+                ("$JAVA_HOME/bin/java" -cp .mvn/wrapper MavenWrapperDownloader "$MAVEN_PROJECTBASEDIR")
+            fi
+        fi
+    fi
+fi
+##########################################################################################
+# End of extension
+##########################################################################################
+
+export MAVEN_PROJECTBASEDIR=${MAVEN_BASEDIR:-"$BASE_DIR"}
+if [ "$MVNW_VERBOSE" = true ]; then
+  echo $MAVEN_PROJECTBASEDIR
+fi
+MAVEN_OPTS="$(concat_lines "$MAVEN_PROJECTBASEDIR/.mvn/jvm.config") $MAVEN_OPTS"
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin; then
+  [ -n "$M2_HOME" ] &&
+    M2_HOME=`cygpath --path --windows "$M2_HOME"`
+  [ -n "$JAVA_HOME" ] &&
+    JAVA_HOME=`cygpath --path --windows "$JAVA_HOME"`
+  [ -n "$CLASSPATH" ] &&
+    CLASSPATH=`cygpath --path --windows "$CLASSPATH"`
+  [ -n "$MAVEN_PROJECTBASEDIR" ] &&
+    MAVEN_PROJECTBASEDIR=`cygpath --path --windows "$MAVEN_PROJECTBASEDIR"`
+fi
+
+# Provide a "standardized" way to retrieve the CLI args that will
+# work with both Windows and non-Windows executions.
+MAVEN_CMD_LINE_ARGS="$MAVEN_CONFIG $@"
+export MAVEN_CMD_LINE_ARGS
+
+WRAPPER_LAUNCHER=org.apache.maven.wrapper.MavenWrapperMain
+
+exec "$JAVACMD" \
+  $MAVEN_OPTS \
+  -classpath "$MAVEN_PROJECTBASEDIR/.mvn/wrapper/maven-wrapper.jar" \
+  "-Dmaven.home=${M2_HOME}" "-Dmaven.multiModuleProjectDirectory=${MAVEN_PROJECTBASEDIR}" \
+  ${WRAPPER_LAUNCHER} $MAVEN_CONFIG "$@"

mvnw.cmd

@@ -0,0 +1,182 @@
+@REM ----------------------------------------------------------------------------
+@REM Licensed to the Apache Software Foundation (ASF) under one
+@REM or more contributor license agreements.  See the NOTICE file
+@REM distributed with this work for additional information
+@REM regarding copyright ownership.  The ASF licenses this file
+@REM to you under the Apache License, Version 2.0 (the
+@REM "License"); you may not use this file except in compliance
+@REM with the License.  You may obtain a copy of the License at
+@REM
+@REM    https://www.apache.org/licenses/LICENSE-2.0
+@REM
+@REM Unless required by applicable law or agreed to in writing,
+@REM software distributed under the License is distributed on an
+@REM "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+@REM KIND, either express or implied.  See the License for the
+@REM specific language governing permissions and limitations
+@REM under the License.
+@REM ----------------------------------------------------------------------------
+
+@REM ----------------------------------------------------------------------------
+@REM Maven Start Up Batch script
+@REM
+@REM Required ENV vars:
+@REM JAVA_HOME - location of a JDK home dir
+@REM
+@REM Optional ENV vars
+@REM M2_HOME - location of maven2's installed home dir
+@REM MAVEN_BATCH_ECHO - set to 'on' to enable the echoing of the batch commands
+@REM MAVEN_BATCH_PAUSE - set to 'on' to wait for a keystroke before ending
+@REM MAVEN_OPTS - parameters passed to the Java VM when running Maven
+@REM     e.g. to debug Maven itself, use
+@REM set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000
+@REM MAVEN_SKIP_RC - flag to disable loading of mavenrc files
+@REM ----------------------------------------------------------------------------
+
+@REM Begin all REM lines with '@' in case MAVEN_BATCH_ECHO is 'on'
+@echo off
+@REM set title of command window
+title %0
+@REM enable echoing by setting MAVEN_BATCH_ECHO to 'on'
+@if "%MAVEN_BATCH_ECHO%" == "on"  echo %MAVEN_BATCH_ECHO%
+
+@REM set %HOME% to equivalent of $HOME
+if "%HOME%" == "" (set "HOME=%HOMEDRIVE%%HOMEPATH%")
+
+@REM Execute a user defined script before this one
+if not "%MAVEN_SKIP_RC%" == "" goto skipRcPre
+@REM check for pre script, once with legacy .bat ending and once with .cmd ending
+if exist "%HOME%\mavenrc_pre.bat" call "%HOME%\mavenrc_pre.bat"
+if exist "%HOME%\mavenrc_pre.cmd" call "%HOME%\mavenrc_pre.cmd"
+:skipRcPre
+
+@setlocal
+
+set ERROR_CODE=0
+
+@REM To isolate internal variables from possible post scripts, we use another setlocal
+@setlocal
+
+@REM ==== START VALIDATION ====
+if not "%JAVA_HOME%" == "" goto OkJHome
+
+echo.
+echo Error: JAVA_HOME not found in your environment. >&2
+echo Please set the JAVA_HOME variable in your environment to match the >&2
+echo location of your Java installation. >&2
+echo.
+goto error
+
+:OkJHome
+if exist "%JAVA_HOME%\bin\java.exe" goto init
+
+echo.
+echo Error: JAVA_HOME is set to an invalid directory. >&2
+echo JAVA_HOME = "%JAVA_HOME%" >&2
+echo Please set the JAVA_HOME variable in your environment to match the >&2
+echo location of your Java installation. >&2
+echo.
+goto error
+
+@REM ==== END VALIDATION ====
+
+:init
+
+@REM Find the project base dir, i.e. the directory that contains the folder ".mvn".
+@REM Fallback to current working directory if not found.
+
+set MAVEN_PROJECTBASEDIR=%MAVEN_BASEDIR%
+IF NOT "%MAVEN_PROJECTBASEDIR%"=="" goto endDetectBaseDir
+
+set EXEC_DIR=%CD%
+set WDIR=%EXEC_DIR%
+:findBaseDir
+IF EXIST "%WDIR%"\.mvn goto baseDirFound
+cd ..
+IF "%WDIR%"=="%CD%" goto baseDirNotFound
+set WDIR=%CD%
+goto findBaseDir
+
+:baseDirFound
+set MAVEN_PROJECTBASEDIR=%WDIR%
+cd "%EXEC_DIR%"
+goto endDetectBaseDir
+
+:baseDirNotFound
+set MAVEN_PROJECTBASEDIR=%EXEC_DIR%
+cd "%EXEC_DIR%"
+
+:endDetectBaseDir
+
+IF NOT EXIST "%MAVEN_PROJECTBASEDIR%\.mvn\jvm.config" goto endReadAdditionalConfig
+
+@setlocal EnableExtensions EnableDelayedExpansion
+for /F "usebackq delims=" %%a in ("%MAVEN_PROJECTBASEDIR%\.mvn\jvm.config") do set JVM_CONFIG_MAVEN_PROPS=!JVM_CONFIG_MAVEN_PROPS! %%a
+@endlocal & set JVM_CONFIG_MAVEN_PROPS=%JVM_CONFIG_MAVEN_PROPS%
+
+:endReadAdditionalConfig
+
+SET MAVEN_JAVA_EXE="%JAVA_HOME%\bin\java.exe"
+set WRAPPER_JAR="%MAVEN_PROJECTBASEDIR%\.mvn\wrapper\maven-wrapper.jar"
+set WRAPPER_LAUNCHER=org.apache.maven.wrapper.MavenWrapperMain
+
+set DOWNLOAD_URL="https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+
+FOR /F "tokens=1,2 delims==" %%A IN ("%MAVEN_PROJECTBASEDIR%\.mvn\wrapper\maven-wrapper.properties") DO (
+    IF "%%A"=="wrapperUrl" SET DOWNLOAD_URL=%%B
+)
+
+@REM Extension to allow automatically downloading the maven-wrapper.jar from Maven-central
+@REM This allows using the maven wrapper in projects that prohibit checking in binary data.
+if exist %WRAPPER_JAR% (
+    if "%MVNW_VERBOSE%" == "true" (
+        echo Found %WRAPPER_JAR%
+    )
+) else (
+    if not "%MVNW_REPOURL%" == "" (
+        SET DOWNLOAD_URL="%MVNW_REPOURL%/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+    )
+    if "%MVNW_VERBOSE%" == "true" (
+        echo Couldn't find %WRAPPER_JAR%, downloading it ...
+        echo Downloading from: %DOWNLOAD_URL%
+    )
+
+    powershell -Command "&{"^
+		"$webclient = new-object System.Net.WebClient;"^
+		"if (-not ([string]::IsNullOrEmpty('%MVNW_USERNAME%') -and [string]::IsNullOrEmpty('%MVNW_PASSWORD%'))) {"^
+		"$webclient.Credentials = new-object System.Net.NetworkCredential('%MVNW_USERNAME%', '%MVNW_PASSWORD%');"^
+		"}"^
+		"[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; $webclient.DownloadFile('%DOWNLOAD_URL%', '%WRAPPER_JAR%')"^
+		"}"
+    if "%MVNW_VERBOSE%" == "true" (
+        echo Finished downloading %WRAPPER_JAR%
+    )
+)
+@REM End of extension
+
+@REM Provide a "standardized" way to retrieve the CLI args that will
+@REM work with both Windows and non-Windows executions.
+set MAVEN_CMD_LINE_ARGS=%*
+
+%MAVEN_JAVA_EXE% %JVM_CONFIG_MAVEN_PROPS% %MAVEN_OPTS% %MAVEN_DEBUG_OPTS% -classpath %WRAPPER_JAR% "-Dmaven.multiModuleProjectDirectory=%MAVEN_PROJECTBASEDIR%" %WRAPPER_LAUNCHER% %MAVEN_CONFIG% %*
+if ERRORLEVEL 1 goto error
+goto end
+
+:error
+set ERROR_CODE=1
+
+:end
+@endlocal & set ERROR_CODE=%ERROR_CODE%
+
+if not "%MAVEN_SKIP_RC%" == "" goto skipRcPost
+@REM check for post script, once with legacy .bat ending and once with .cmd ending
+if exist "%HOME%\mavenrc_post.bat" call "%HOME%\mavenrc_post.bat"
+if exist "%HOME%\mavenrc_post.cmd" call "%HOME%\mavenrc_post.cmd"
+:skipRcPost
+
+@REM pause the script if MAVEN_BATCH_PAUSE is set to 'on'
+if "%MAVEN_BATCH_PAUSE%" == "on" pause
+
+if "%MAVEN_TERMINATE_CMD%" == "on" exit %ERROR_CODE%
+
+exit /B %ERROR_CODE%

pom.xml

@@ -0,0 +1,71 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>org.springframework.boot</groupId>
+		<artifactId>spring-boot-starter-parent</artifactId>
+		<version>2.6.0</version>
+		<relativePath/> <!-- lookup parent from repository -->
+	</parent>
+	<groupId>nl.andrewl</groupId>
+	<artifactId>rail-signal-api</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<name>rail-signal-api</name>
+	<description>A simple API for tracking rail traffic in signalled blocks.</description>
+	<properties>
+		<java.version>17</java.version>
+	</properties>
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-data-jpa</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-web</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-websocket</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>com.h2database</groupId>
+			<artifactId>h2</artifactId>
+		</dependency>
+
+		<dependency>
+			<groupId>org.projectlombok</groupId>
+			<artifactId>lombok</artifactId>
+			<optional>true</optional>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>io.projectreactor</groupId>
+			<artifactId>reactor-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.springframework.boot</groupId>
+				<artifactId>spring-boot-maven-plugin</artifactId>
+				<configuration>
+					<excludes>
+						<exclude>
+							<groupId>org.projectlombok</groupId>
+							<artifactId>lombok</artifactId>
+						</exclude>
+					</excludes>
+				</configuration>
+			</plugin>
+		</plugins>
+	</build>
+
+</project>

src/main/java/nl/andrewl/railsignalapi/RailSignalApiApplication.java

@@ -0,0 +1,13 @@
+package nl.andrewl.railsignalapi;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class RailSignalApiApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(RailSignalApiApplication.class, args);
+	}
+
+}

src/main/java/nl/andrewl/railsignalapi/dao/BranchRepository.java

@@ -0,0 +1,16 @@
+package nl.andrewl.railsignalapi.dao;
+
+import nl.andrewl.railsignalapi.model.Branch;
+import nl.andrewl.railsignalapi.model.RailSystem;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+import java.util.List;
+import java.util.Optional;
+
+@Repository
+public interface BranchRepository extends JpaRepository<Branch, Long> {
+	Optional<Branch> findByIdAndRailSystem(long id, RailSystem railSystem);
+	Optional<Branch> findByNameAndRailSystem(String name, RailSystem railSystem);
+	List<Branch> findAllByNameAndRailSystem(String name, RailSystem railSystem);
+}

src/main/java/nl/andrewl/railsignalapi/dao/RailSystemRepository.java

@@ -0,0 +1,10 @@
+package nl.andrewl.railsignalapi.dao;
+
+import nl.andrewl.railsignalapi.model.RailSystem;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface RailSystemRepository extends JpaRepository<RailSystem, Long> {
+	boolean existsByName(String name);
+}

src/main/java/nl/andrewl/railsignalapi/dao/SignalRepository.java

@@ -0,0 +1,22 @@
+package nl.andrewl.railsignalapi.dao;
+
+import nl.andrewl.railsignalapi.model.Branch;
+import nl.andrewl.railsignalapi.model.RailSystem;
+import nl.andrewl.railsignalapi.model.Signal;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.stereotype.Repository;
+
+import java.util.List;
+import java.util.Optional;
+
+@Repository
+public interface SignalRepository extends JpaRepository<Signal, Long> {
+	Optional<Signal> findByIdAndRailSystem(long id, RailSystem railSystem);
+	boolean existsByNameAndRailSystem(String name, RailSystem railSystem);
+
+	@Query("SELECT DISTINCT s FROM Signal s " +
+			"LEFT JOIN s.branchConnections bc " +
+			"WHERE bc.branch = :branch")
+	List<Signal> findAllConnectedToBranch(Branch branch);
+}

src/main/java/nl/andrewl/railsignalapi/dao/TrainRepository.java

@@ -0,0 +1,9 @@
+package nl.andrewl.railsignalapi.dao;
+
+import nl.andrewl.railsignalapi.model.Train;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface TrainRepository extends JpaRepository<Train, Long> {
+}

src/main/java/nl/andrewl/railsignalapi/model/Branch.java

@@ -0,0 +1,38 @@
+package nl.andrewl.railsignalapi.model;
+
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+import javax.persistence.*;
+import java.util.HashSet;
+import java.util.Set;
+
+@Entity
+@NoArgsConstructor
+@Getter
+public class Branch {
+	@Id
+	@GeneratedValue
+	private Long id;
+
+	@ManyToOne(optional = false, fetch = FetchType.LAZY)
+	private RailSystem railSystem;
+
+	@Column(nullable = false)
+	private String name;
+
+	@Enumerated(EnumType.STRING)
+	@Setter
+	private BranchStatus status;
+
+	@OneToMany(mappedBy = "branch", orphanRemoval = true)
+	private Set<SignalBranchConnection> signalConnections;
+
+	public Branch(RailSystem railSystem, String name, BranchStatus status) {
+		this.railSystem = railSystem;
+		this.name = name;
+		this.status = status;
+		this.signalConnections = new HashSet<>();
+	}
+}

src/main/java/nl/andrewl/railsignalapi/model/BranchStatus.java

@@ -0,0 +1,6 @@
+package nl.andrewl.railsignalapi.model;
+
+public enum BranchStatus {
+	FREE,
+	OCCUPIED
+}

src/main/java/nl/andrewl/railsignalapi/model/Direction.java

@@ -0,0 +1,12 @@
+package nl.andrewl.railsignalapi.model;
+
+public enum Direction {
+	NORTH,
+	SOUTH,
+	EAST,
+	WEST,
+	NORTH_WEST,
+	NORTH_EAST,
+	SOUTH_WEST,
+	SOUTH_EAST
+}

src/main/java/nl/andrewl/railsignalapi/model/Position.java

@@ -0,0 +1,17 @@
+package nl.andrewl.railsignalapi.model;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import javax.persistence.Embeddable;
+
+@Embeddable
+@Data
+@AllArgsConstructor
+@NoArgsConstructor
+public class Position {
+	private double x;
+	private double y;
+	private double z;
+}

src/main/java/nl/andrewl/railsignalapi/model/RailSystem.java

@@ -0,0 +1,25 @@
+package nl.andrewl.railsignalapi.model;
+
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+import javax.persistence.Column;
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+
+@Entity
+@Getter
+@NoArgsConstructor
+public class RailSystem {
+	@Id
+	@GeneratedValue
+	private Long id;
+
+	@Column(nullable = false, unique = true)
+	private String name;
+
+	public RailSystem(String name) {
+		this.name = name;
+	}
+}

src/main/java/nl/andrewl/railsignalapi/model/Signal.java

@@ -0,0 +1,31 @@
+package nl.andrewl.railsignalapi.model;
+
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+import javax.persistence.*;
+import java.util.Set;
+
+@Entity
+@Getter
+@NoArgsConstructor
+public class Signal {
+	@Id
+	@GeneratedValue
+	private Long id;
+
+	@ManyToOne(optional = false, fetch = FetchType.LAZY)
+	private RailSystem railSystem;
+
+	@Column(nullable = false)
+	private String name;
+
+	@OneToMany(mappedBy = "signal", orphanRemoval = true, cascade = CascadeType.ALL)
+	private Set<SignalBranchConnection> branchConnections;
+
+	public Signal(RailSystem railSystem, String name, Set<SignalBranchConnection> branchConnections) {
+		this.railSystem = railSystem;
+		this.name = name;
+		this.branchConnections = branchConnections;
+	}
+}

src/main/java/nl/andrewl/railsignalapi/model/SignalBranchConnection.java

@@ -0,0 +1,30 @@
+package nl.andrewl.railsignalapi.model;
+
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+import javax.persistence.*;
+
+@Entity
+@NoArgsConstructor
+@Getter
+public class SignalBranchConnection {
+	@Id
+	@GeneratedValue
+	private Long id;
+
+	@ManyToOne(optional = false)
+	private Signal signal;
+
+	@ManyToOne(optional = false, cascade = CascadeType.PERSIST)
+	private Branch branch;
+
+	@Enumerated(EnumType.STRING)
+	private Direction direction;
+
+	public SignalBranchConnection(Signal signal, Branch branch, Direction direction) {
+		this.signal = signal;
+		this.branch = branch;
+		this.direction = direction;
+	}
+}

src/main/java/nl/andrewl/railsignalapi/model/Train.java

@@ -0,0 +1,20 @@
+package nl.andrewl.railsignalapi.model;
+
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+import javax.persistence.*;
+
+@Entity
+@NoArgsConstructor
+@Getter
+public class Train {
+	@Id
+	@GeneratedValue
+	private Long id;
+
+	private String name;
+
+	@ManyToOne(fetch = FetchType.LAZY)
+	private Branch currentBranch;
+}

src/main/java/nl/andrewl/railsignalapi/rest/RailSystemsApiController.java

@@ -0,0 +1,26 @@
+package nl.andrewl.railsignalapi.rest;
+
+import lombok.RequiredArgsConstructor;
+import nl.andrewl.railsignalapi.rest.dto.RailSystemCreationPayload;
+import nl.andrewl.railsignalapi.rest.dto.RailSystemResponse;
+import nl.andrewl.railsignalapi.service.RailSystemService;
+import org.springframework.web.bind.annotation.*;
+
+import java.util.List;
+
+@RestController
+@RequestMapping(path = "/api/railSystems")
+@RequiredArgsConstructor
+public class RailSystemsApiController {
+	private final RailSystemService railSystemService;
+
+	@GetMapping
+	public List<RailSystemResponse> getRailSystems() {
+		return railSystemService.getRailSystems();
+	}
+
+	@PostMapping
+	public RailSystemResponse createRailSystem(@RequestBody RailSystemCreationPayload payload) {
+		return railSystemService.createRailSystem(payload);
+	}
+}

src/main/java/nl/andrewl/railsignalapi/rest/SignalsApiController.java

@@ -0,0 +1,19 @@
+package nl.andrewl.railsignalapi.rest;
+
+import lombok.RequiredArgsConstructor;
+import nl.andrewl.railsignalapi.rest.dto.SignalCreationPayload;
+import nl.andrewl.railsignalapi.rest.dto.SignalResponse;
+import nl.andrewl.railsignalapi.service.SignalService;
+import org.springframework.web.bind.annotation.*;
+
+@RestController
+@RequestMapping(path = "/api/railSystems/{rsId}/signals")
+@RequiredArgsConstructor
+public class SignalsApiController {
+	private final SignalService signalService;
+
+	@PostMapping
+	public SignalResponse createSignal(@PathVariable long rsId, @RequestBody SignalCreationPayload payload) {
+		return signalService.createSignal(rsId, payload);
+	}
+}

src/main/java/nl/andrewl/railsignalapi/rest/WebConfig.java

@@ -0,0 +1,11 @@
+package nl.andrewl.railsignalapi.rest;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.servlet.config.annotation.EnableWebMvc;
+import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
+
+@Configuration
+@EnableWebMvc
+public class WebConfig implements WebMvcConfigurer {
+
+}

src/main/java/nl/andrewl/railsignalapi/rest/dto/BranchResponse.java

@@ -0,0 +1,13 @@
+package nl.andrewl.railsignalapi.rest.dto;
+
+import nl.andrewl.railsignalapi.model.Branch;
+
+public record BranchResponse(
+		long id,
+		String name,
+		String status
+) {
+	public BranchResponse(Branch branch) {
+		this(branch.getId(), branch.getName(), branch.getStatus().name());
+	}
+}

src/main/java/nl/andrewl/railsignalapi/rest/dto/RailSystemCreationPayload.java

@@ -0,0 +1,4 @@
+package nl.andrewl.railsignalapi.rest.dto;
+
+public record RailSystemCreationPayload(String name) {
+}

src/main/java/nl/andrewl/railsignalapi/rest/dto/RailSystemResponse.java

@@ -0,0 +1,9 @@
+package nl.andrewl.railsignalapi.rest.dto;
+
+import nl.andrewl.railsignalapi.model.RailSystem;
+
+public record RailSystemResponse(long id, String name) {
+	public RailSystemResponse(RailSystem rs) {
+		this(rs.getId(), rs.getName());
+	}
+}

src/main/java/nl/andrewl/railsignalapi/rest/dto/SignalCreationPayload.java

@@ -0,0 +1,10 @@
+package nl.andrewl.railsignalapi.rest.dto;
+
+import java.util.List;
+
+public record SignalCreationPayload(
+		String name,
+		List<BranchData> branchConnections
+) {
+	public static record BranchData(String direction, String name, Long id) {}
+}

src/main/java/nl/andrewl/railsignalapi/rest/dto/SignalResponse.java

@@ -0,0 +1,31 @@
+package nl.andrewl.railsignalapi.rest.dto;
+
+import nl.andrewl.railsignalapi.model.Signal;
+import nl.andrewl.railsignalapi.model.SignalBranchConnection;
+
+import java.util.List;
+
+public record SignalResponse(
+		long id,
+		String name,
+		List<ConnectionData> branchConnections
+) {
+	public SignalResponse(Signal signal) {
+		this(
+				signal.getId(),
+				signal.getName(),
+				signal.getBranchConnections().stream()
+						.map(ConnectionData::new)
+						.toList()
+		);
+	}
+
+	public static record ConnectionData(
+			String direction,
+			BranchResponse branch
+	) {
+		public ConnectionData(SignalBranchConnection c) {
+			this(c.getDirection().name(), new BranchResponse(c.getBranch()));
+		}
+	}
+}

src/main/java/nl/andrewl/railsignalapi/service/RailSystemService.java

@@ -0,0 +1,34 @@
+package nl.andrewl.railsignalapi.service;
+
+import lombok.RequiredArgsConstructor;
+import nl.andrewl.railsignalapi.dao.RailSystemRepository;
+import nl.andrewl.railsignalapi.model.RailSystem;
+import nl.andrewl.railsignalapi.rest.dto.RailSystemCreationPayload;
+import nl.andrewl.railsignalapi.rest.dto.RailSystemResponse;
+import org.springframework.data.domain.Sort;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+import org.springframework.web.server.ResponseStatusException;
+
+import java.util.List;
+
+@Service
+@RequiredArgsConstructor
+public class RailSystemService {
+	private final RailSystemRepository railSystemRepository;
+
+	@Transactional
+	public List<RailSystemResponse> getRailSystems() {
+		return railSystemRepository.findAll(Sort.by("name")).stream().map(RailSystemResponse::new).toList();
+	}
+
+	@Transactional
+	public RailSystemResponse createRailSystem(RailSystemCreationPayload payload) {
+		if (railSystemRepository.existsByName(payload.name())) {
+			throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "A rail system with that name already exists.");
+		}
+		RailSystem rs = new RailSystem(payload.name());
+		return new RailSystemResponse(railSystemRepository.save(rs));
+	}
+}

src/main/java/nl/andrewl/railsignalapi/service/SignalService.java

@@ -0,0 +1,128 @@
+package nl.andrewl.railsignalapi.service;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import nl.andrewl.railsignalapi.dao.BranchRepository;
+import nl.andrewl.railsignalapi.dao.RailSystemRepository;
+import nl.andrewl.railsignalapi.dao.SignalRepository;
+import nl.andrewl.railsignalapi.model.*;
+import nl.andrewl.railsignalapi.rest.dto.SignalCreationPayload;
+import nl.andrewl.railsignalapi.rest.dto.SignalResponse;
+import nl.andrewl.railsignalapi.websocket.BranchUpdateMessage;
+import nl.andrewl.railsignalapi.websocket.SignalUpdateMessage;
+import nl.andrewl.railsignalapi.websocket.SignalUpdateType;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+import org.springframework.web.server.ResponseStatusException;
+import org.springframework.web.socket.TextMessage;
+import org.springframework.web.socket.WebSocketMessage;
+import org.springframework.web.socket.WebSocketSession;
+
+import java.io.IOException;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+
+@Service
+@RequiredArgsConstructor
+@Slf4j
+public class SignalService {
+	private final RailSystemRepository railSystemRepository;
+	private final SignalRepository signalRepository;
+	private final BranchRepository branchRepository;
+
+	private final Map<Long, WebSocketSession> signalWebSocketSessions = new ConcurrentHashMap<>();
+
+	@Transactional
+	public SignalResponse createSignal(long rsId, SignalCreationPayload payload) {
+		var rs = railSystemRepository.findById(rsId)
+				.orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "Rail system not found."));
+		if (signalRepository.existsByNameAndRailSystem(payload.name(), rs)) {
+			throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "Signal " + payload.name() + " already exists.");
+		}
+		Set<SignalBranchConnection> branchConnections = new HashSet<>();
+		Signal signal = new Signal(rs, payload.name(), branchConnections);
+		for (var branchData : payload.branchConnections()) {
+			Branch branch;
+			if (branchData.id() != null) {
+				branch = this.branchRepository.findByIdAndRailSystem(branchData.id(), rs)
+						.orElseThrow(() -> new ResponseStatusException(HttpStatus.BAD_REQUEST, "Branch id " + branchData.id() + " is invalid."));
+			} else {
+				branch = this.branchRepository.findByNameAndRailSystem(branchData.name(), rs)
+						.orElse(new Branch(rs, branchData.name(), BranchStatus.FREE));
+			}
+			Direction dir = Direction.valueOf(branchData.direction().trim().toUpperCase());
+			branchConnections.add(new SignalBranchConnection(signal, branch, dir));
+		}
+		signal = signalRepository.save(signal);
+		return new SignalResponse(signal);
+	}
+
+	public void registerSignalWebSocketSession(long signalId, WebSocketSession session) {
+		this.signalWebSocketSessions.put(signalId, session);
+	}
+
+	public void deregisterSignalWebSocketSession(long signalId) {
+		this.signalWebSocketSessions.remove(signalId);
+	}
+
+	@Transactional
+	public void handleSignalUpdate(long signalId, SignalUpdateMessage updateMessage) {
+		var signal = signalRepository.findById(signalId)
+				.orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND));
+		Branch fromBranch = null;
+		Branch toBranch = null;
+		for (var con : signal.getBranchConnections()) {
+			if (con.getBranch().getId() == updateMessage.fromBranchId()) {
+				fromBranch = con.getBranch();
+			}
+			if (con.getBranch().getId() == updateMessage.toBranchId()) {
+				toBranch = con.getBranch();
+			}
+		}
+		if (fromBranch == null || toBranch == null) {
+			throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "Invalid branches.");
+		}
+		SignalUpdateType updateType = SignalUpdateType.valueOf(updateMessage.type().trim().toUpperCase());
+		if (updateType == SignalUpdateType.BEGIN && toBranch.getStatus() != BranchStatus.FREE) {
+			log.warn("Warning! Train is entering a non-free branch {}.", toBranch.getName());
+		}
+		if (toBranch.getStatus() != BranchStatus.OCCUPIED) {
+			toBranch.setStatus(BranchStatus.OCCUPIED);
+			branchRepository.save(toBranch);
+			broadcastToConnectedSignals(toBranch);
+		}
+		if (updateType == SignalUpdateType.END) {
+			if (fromBranch.getStatus() != BranchStatus.FREE) {
+				fromBranch.setStatus(BranchStatus.FREE);
+				branchRepository.save(fromBranch);
+				broadcastToConnectedSignals(fromBranch);
+			}
+		}
+	}
+
+	private void broadcastToConnectedSignals(Branch branch) {
+		ObjectMapper mapper = new ObjectMapper();
+		try {
+			WebSocketMessage<String> msg = new TextMessage(mapper.writeValueAsString(new BranchUpdateMessage(branch.getId(), branch.getStatus().name())));
+			signalRepository.findAllConnectedToBranch(branch).stream()
+					.map(s -> signalWebSocketSessions.get(s.getId()))
+					.filter(Objects::nonNull)
+					.forEach(session -> {
+						try {
+							session.sendMessage(msg);
+						} catch (IOException e) {
+							e.printStackTrace();
+						}
+					});
+		} catch (JsonProcessingException e) {
+			e.printStackTrace();
+		}
+
+	}
+}

src/main/java/nl/andrewl/railsignalapi/websocket/BranchUpdateMessage.java

@@ -0,0 +1,4 @@
+package nl.andrewl.railsignalapi.websocket;
+
+public record BranchUpdateMessage(long branchId, String status) {
+}

src/main/java/nl/andrewl/railsignalapi/websocket/SignalUpdateMessage.java

@@ -0,0 +1,7 @@
+package nl.andrewl.railsignalapi.websocket;
+
+public record SignalUpdateMessage(
+		long fromBranchId,
+		long toBranchId,
+		String type
+) {}

src/main/java/nl/andrewl/railsignalapi/websocket/SignalUpdateType.java

@@ -0,0 +1,15 @@
+package nl.andrewl.railsignalapi.websocket;
+
+public enum SignalUpdateType {
+	/**
+	 * Indicates the beginning of a train's transition between two signalled
+	 * sections of rail.
+	 */
+	BEGIN,
+
+	/**
+	 * Indicates the end of a train's transition between two signalled sections
+	 * of rail.
+	 */
+	END
+}

src/main/java/nl/andrewl/railsignalapi/websocket/SignalWebSocketHandler.java

@@ -0,0 +1,50 @@
+package nl.andrewl.railsignalapi.websocket;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import nl.andrewl.railsignalapi.service.SignalService;
+import org.springframework.stereotype.Component;
+import org.springframework.web.socket.CloseStatus;
+import org.springframework.web.socket.TextMessage;
+import org.springframework.web.socket.WebSocketSession;
+import org.springframework.web.socket.handler.TextWebSocketHandler;
+
+@Component
+@RequiredArgsConstructor
+@Slf4j
+public class SignalWebSocketHandler extends TextWebSocketHandler {
+	private final ObjectMapper mapper = new ObjectMapper();
+	private final SignalService signalService;
+
+	@Override
+	public void afterConnectionEstablished(WebSocketSession session) throws Exception {
+		String signalIdHeader = session.getHandshakeHeaders().getFirst("X-RailSignal-SignalId");
+		if (signalIdHeader == null || signalIdHeader.isBlank()) {
+			session.close(CloseStatus.PROTOCOL_ERROR);
+			return;
+		}
+		long signalId = Long.parseLong(signalIdHeader);
+		session.getAttributes().put("signalId", signalId);
+		signalService.registerSignalWebSocketSession(signalId, session);
+		log.info("Connection established with signal {}.", signalId);
+	}
+
+	@Override
+	protected void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
+		var msg = mapper.readValue(message.getPayload(), SignalUpdateMessage.class);
+		Long signalId = (Long) session.getAttributes().get("signalId");
+		if (signalId == null) {
+			log.warn("Got text message from a websocket session that did not establish a signalId session attribute.");
+		} else {
+			log.info("Received update from signal {}.", signalId);
+			signalService.handleSignalUpdate(signalId, msg);
+		}
+	}
+
+	@Override
+	public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
+		signalService.deregisterSignalWebSocketSession((Long) session.getAttributes().get("signalId"));
+		log.info("Closed connection to signal {}. Status: {}", session.getAttributes().get("signalId"), status.toString());
+	}
+}

src/main/java/nl/andrewl/railsignalapi/websocket/WebSocketConfig.java

@@ -0,0 +1,19 @@
+package nl.andrewl.railsignalapi.websocket;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.socket.config.annotation.EnableWebSocket;
+import org.springframework.web.socket.config.annotation.WebSocketConfigurer;
+import org.springframework.web.socket.config.annotation.WebSocketHandlerRegistry;
+
+@Configuration
+@EnableWebSocket
+@RequiredArgsConstructor
+public class WebSocketConfig implements WebSocketConfigurer {
+	private final SignalWebSocketHandler webSocketHandler;
+
+	@Override
+	public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
+		registry.addHandler(webSocketHandler, "/api/ws-signal");
+	}
+}

src/main/resources/application.properties

@@ -0,0 +1,11 @@
+spring.datasource.url=jdbc:h2:file:./rail-signal-api-db
+spring.jpa.hibernate.ddl-auto=update
+spring.jpa.open-in-view=false
+
+spring.datasource.hikari.maximum-pool-size=5
+spring.datasource.hikari.minimum-idle=1
+
+server.port=8080
+server.tomcat.threads.max=10
+server.tomcat.threads.min-spare=2
+server.tomcat.processor-cache=50

src/test/java/nl/andrewl/railsignalapi/RailSignalApiApplicationTests.java

@@ -0,0 +1,13 @@
+package nl.andrewl.railsignalapi;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+
+@SpringBootTest
+class RailSignalApiApplicationTests {
+
+	@Test
+	void contextLoads() {
+	}
+
+}