src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/parser/MissingParameterException.java

@@ -0,0 +1,26 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.network.parser;
+
+/** Exception thrown when a required parameter key is not found. */
+public class MissingParameterException extends RuntimeException {
+    private final String parameterKey;
+
+    /**
+     * Creates a new exception for a missing required parameter.
+     *
+     * @param message human-readable description of the missing parameter
+     * @param parameterKey key of the parameter that could not be found
+     */
+    public MissingParameterException(String message, String parameterKey) {
+        super(message);
+        this.parameterKey = parameterKey;
+    }
+
+    /**
+     * Returns the missing parameter key.
+     *
+     * @return key of the parameter that could not be found
+     */
+    public String getParameterKey() {
+        return parameterKey;
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/parser/ParameterParseException.java

@@ -0,0 +1,27 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.network.parser;
+
+/** Exception thrown when a parameter value cannot be converted to the requested type. */
+public class ParameterParseException extends RuntimeException {
+    private final String parameterKey;
+
+    /**
+     * Creates a new parse exception with a root cause.
+     *
+     * @param message human-readable description of the parsing failure
+     * @param parameterKey key for whose value the error occured
+     * @param cause original exception thrown during parsing
+     */
+    public ParameterParseException(String message, String parameterKey, Throwable cause) {
+        super(message, cause);
+        this.parameterKey = parameterKey;
+    }
+
+    /**
+     * Returns the missing parameter key.
+     *
+     * @return key for whose value the error occured
+     */
+    public String getParameterKey() {
+        return parameterKey;
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/parser/RequestParameterAccessor.java

@@ -0,0 +1,111 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.network.parser;
+
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Provides typed access to a request's parameters by indexing them by key.
+ *
+ * <p>Supports required and optional lookups, with optional conversion from {@link String} values to
+ * domain-specific types via parser functions.
+ */
+public class RequestParameterAccessor {
+    private final Map<String, String> index;
+
+    /**
+     * Creates an accessor
+     *
+     * @param parameters to use
+     */
+    public RequestParameterAccessor(List<Parameter> parameters) {
+        this.index =
+                parameters.stream()
+                        .collect(Collectors.toUnmodifiableMap(Parameter::key, Parameter::value));
+    }
+
+    /**
+     * Returns the raw value for a required parameter key.
+     *
+     * @param key parameter key to look up
+     * @return raw parameter value
+     * @throws MissingParameterException if no parameter with the given key exists
+     */
+    public String require(String key) throws MissingParameterException {
+        String value = index.get(key);
+        if (value == null) {
+            throw new MissingParameterException(
+                    "Required parameter with key '" + key + "' is missing.", key);
+        }
+        return value;
+    }
+
+    /**
+     * Returns a parsed value for a required parameter key.
+     *
+     * @param key parameter key to look up
+     * @param parser parser used to convert the raw value
+     * @param <T> target type returned by the parser
+     * @return parsed parameter value
+     * @throws MissingParameterException if no parameter with the given key exists
+     * @throws ParameterParseException if parsing the raw value fails
+     */
+    public <T> T require(String key, ThrowingParser<T> parser)
+            throws MissingParameterException, ParameterParseException {
+        String value = require(key);
+        try {
+            return parser.parse(value);
+        } catch (Exception e) {
+            throw new ParameterParseException("Error while parsing '" + key + "' with specified parser", key, e);
+        }
+    }
+
+    /**
+     * Returns the raw value for a parameter key or the provided default value if missing.
+     *
+     * @param key parameter key to look up
+     * @param defaultValue value returned when the key does not exist
+     * @return found parameter value or {@code defaultValue} if absent
+     */
+    public String optional(String key, String defaultValue) {
+        String value = index.get(key);
+        if (value == null) {
+            return defaultValue;
+        }
+        return value;
+    }
+
+    /**
+     * Returns a parsed value for a parameter key or the provided default value if missing.
+     *
+     * @param key parameter key to look up
+     * @param defaultValue value returned when the key does not exist
+     * @param parser parser used to convert the raw value
+     * @param <T> target type returned by the parser
+     * @return parsed parameter value or {@code defaultValue} if absent
+     * @throws ParameterParseException if parsing the raw value fails
+     */
+    public <T> T optional(String key, T defaultValue, ThrowingParser<T> parser)
+            throws ParameterParseException {
+        String value = index.get(key);
+        if (value == null) {
+            return defaultValue;
+        }
+
+        try {
+            return parser.parse(value);
+        } catch (Exception e) {
+            throw new ParameterParseException("Error while parsing '" + key + "' with specified parser", key, e);
+        }
+    }
+
+    /**
+     * Checks whether a parameter with the given key exists.
+     *
+     * @param key parameter key to check
+     * @return {@code true} if the key exists, otherwise {@code false}
+     */
+    public boolean containsKey(String key) {
+        return index.containsKey(key);
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/parser/ThrowingParser.java

@@ -0,0 +1,18 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.network.parser;
+
+/**
+ * Functional parser interface used to convert a raw string parameter into a target type.
+ *
+ * @param <T> target type produced by the parser
+ */
+@FunctionalInterface
+interface ThrowingParser<T> {
+    /**
+     * Parses the provided raw parameter value.
+     *
+     * @param value raw parameter value
+     * @return parsed value
+     * @throws Exception if the value cannot be parsed
+     */
+    T parse(String value) throws Exception;
+}