Make it possible to add custom API documentation based on the deployment location

application/src/ext/resources/org/opentripplanner/ext/apis/transmodel/custom-documentation-entur.properties

@@ -0,0 +1,27 @@
+# Use:
+#   <TypeName>[.<FieldName>].(description|deprecated)[.append]
+#
+# Examples
+#  // Replace the existing type description
+#  Quay.description=The place for boarding/alighting a vehicle
+#
+#  // Append to the existing type description
+#  Quay.description.append=Append
+#
+#  // Replace the existing field description
+#  Quay.name.description=The public name
+#
+#  // Append to the existing field description
+#  Quay.name.description.append=(Source NSR)
+#
+#  // Insert deprecated reason. Due to a bug in the Java GraphQL lib, an existing deprecated
+#  // reason cannot be updated. Deleting the reason from the schema, and adding it back using
+#  // the "default" TransmodelApiDocumentationProfile is a workaround.
+#  Quay.name.deprecated=This field is deprecated ...
+
+
+TariffZone.description=A **zone** used to define a zonal fare structure in a zone-counting or \
+  zone-matrix system. This includes TariffZone, as well as the specialised FareZone elements. \
+  TariffZones are deprecated, please use FareZones. \
+  \
+  **TariffZone data will not be maintained from 1. MAY 2025 (Entur).**

application/src/main/java/org/opentripplanner/apis/support/graphql/injectdoc/ApiDocumentationProfile.java

@@ -0,0 +1,30 @@
+package org.opentripplanner.apis.support.graphql.injectdoc;
+
+import org.opentripplanner.framework.doc.DocumentedEnum;
+
+public enum ApiDocumentationProfile implements DocumentedEnum<ApiDocumentationProfile> {
+  DEFAULT,
+  ENTUR;
+
+  private static final String TYPE_DOC =
+    """
+    List of available custom documentation profiles. A profile is used to inject custom
+    documentation like type and field description or a deprecated reason.
+
+    Currently, ONLY the Transmodel API supports this feature.
+    """;
+
+  @Override
+  public String typeDescription() {
+    return TYPE_DOC;
+  }
+
+  @Override
+  public String enumValueDescription() {
+    return switch (this) {
+      case DEFAULT -> "Default documentation is used.";
+      case ENTUR -> "Entur specific documentation. This deprecate features not supported at Entur," +
+      " Norway.";
+    };
+  }
+}

application/src/main/java/org/opentripplanner/apis/support/graphql/injectdoc/CustomDocumentation.java

@@ -0,0 +1,173 @@
+package org.opentripplanner.apis.support.graphql.injectdoc;
+
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Properties;
+import javax.annotation.Nullable;
+import org.opentripplanner.framework.application.OtpAppException;
+import org.opentripplanner.utils.text.TextVariablesSubstitution;
+
+/**
+ * Load custom documentation from a properties file and make it available to any
+ * consumer using the {@code type-name[.field-name]} as key for lookups.
+ */
+public class CustomDocumentation {
+
+  private static final String APPEND_SUFFIX = ".append";
+  private static final String DESCRIPTION_SUFFIX = ".description";
+  private static final String DEPRECATED_SUFFIX = ".deprecated";
+
+  /** Put custom documentaion in the following sandbox package */
+  private static final String DOC_PATH = "org/opentripplanner/ext/apis/transmodel/";
+  private static final String FILE_NAME = "custom-documentation";
+  private static final String FILE_EXTENSION = ".properties";
+
+  private static final CustomDocumentation EMPTY = new CustomDocumentation(Map.of());
+
+  private final Map<String, String> textMap;
+
+  /**
+   * Package local to be unit-testable
+   */
+  CustomDocumentation(Map<String, String> textMap) {
+    this.textMap = textMap;
+  }
+
+  public static CustomDocumentation of(ApiDocumentationProfile profile) {
+    if (profile == ApiDocumentationProfile.DEFAULT) {
+      return EMPTY;
+    }
+    var map = loadCustomDocumentationFromPropertiesFile(profile);
+    return map.isEmpty() ? EMPTY : new CustomDocumentation(map);
+  }
+
+  public boolean isEmpty() {
+    return textMap.isEmpty();
+  }
+
+  /**
+   * Get documentation for a type. The given {@code typeName} is used as the key. The
+   * documentation text is resolved by:
+   * <ol>
+   *   <li>
+   *     first looking up the given {@code key} + {@code ".description"}. If a value is found, then
+   *     the value is returned.
+   *   <li>
+   *     then {@code key} + {@code ".description.append"} is used. If a value is found the
+   *     {@code originalDoc} + {@code value} is returned.
+   *   </li>
+   * </ol>
+   * @param typeName Use {@code TYPE_NAME} or {@code TYPE_NAME.FIELD_NAME} as key.
+   */
+  public Optional<String> typeDescription(String typeName, @Nullable String originalDoc) {
+    return text(typeName, DESCRIPTION_SUFFIX, originalDoc);
+  }
+
+  /**
+   * Same as {@link #typeDescription(String, String)} except the given {@code typeName} and
+   * {@code fieldName} is used as the key.
+   * <pre>
+   * key := typeName + "." fieldNAme
+   * </pre>
+   */
+  public Optional<String> fieldDescription(
+    String typeName,
+    String fieldName,
+    @Nullable String originalDoc
+  ) {
+    return text(key(typeName, fieldName), DESCRIPTION_SUFFIX, originalDoc);
+  }
+
+  /**
+   * Get <em>deprecated reason</em> for a field (types cannot be deprecated). The key
+   * ({@code key = typeName + '.' + fieldName} is used to retrieve the reason from the properties
+   * file. The deprecated documentation text is resolved by:
+   * <ol>
+   *   <li>
+   *     first looking up the given {@code key} + {@code ".deprecated"}. If a value is found, then
+   *     the value is returned.
+   *   <li>
+   *     then {@code key} + {@code ".deprecated.append"} is used. If a value is found the
+   *     {@code originalDoc} + {@code text} is returned.
+   *   </li>
+   * </ol>
+   * Any {@code null} values are excluded from the result and if both the input {@code originalDoc}
+   * and the resolved value is {@code null}, then {@code empty} is returned.
+   */
+  public Optional<String> fieldDeprecatedReason(
+    String typeName,
+    String fieldName,
+    @Nullable String originalDoc
+  ) {
+    return text(key(typeName, fieldName), DEPRECATED_SUFFIX, originalDoc);
+  }
+
+  /* private methods */
+
+  /**
+   * Create a key from the given {@code typeName} and {@code fieldName}
+   */
+  private static String key(String typeName, String fieldName) {
+    return typeName + "." + fieldName;
+  }
+
+  private Optional<String> text(String key, String suffix, @Nullable String originalText) {
+    final String k = key + suffix;
+    return text(k).or(() -> appendText(k, originalText));
+  }
+
+  private Optional<String> text(String key) {
+    return Optional.ofNullable(textMap.get(key));
+  }
+
+  private Optional<String> appendText(String key, @Nullable String originalText) {
+    String value = textMap.get(key + APPEND_SUFFIX);
+    if (value == null) {
+      return Optional.empty();
+    }
+    return originalText == null ? Optional.of(value) : Optional.of(originalText + "\n\n" + value);
+  }
+
+  /* private methods */
+
+  private static Map<String, String> loadCustomDocumentationFromPropertiesFile(
+    ApiDocumentationProfile profile
+  ) {
+    try {
+      final String resource = resourceName(profile);
+      var input = ClassLoader.getSystemResourceAsStream(resource);
+      if (input == null) {
+        throw new OtpAppException("Resource not found: %s", resource);
+      }
+      var props = new Properties();
+      props.load(new InputStreamReader(input, StandardCharsets.UTF_8));
+      Map<String, String> map = new HashMap<>();
+
+      for (String key : props.stringPropertyNames()) {
+        String value = props.getProperty(key);
+        if (value == null) {
+          value = "";
+        }
+        map.put(key, value);
+      }
+      return TextVariablesSubstitution.insertVariables(
+        map,
+        varName -> errorHandlerVariableSubstitution(varName, resource)
+      );
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  private static void errorHandlerVariableSubstitution(String name, String source) {
+    throw new OtpAppException("Variable substitution failed for '${%s}' in %s.", name, source);
+  }
+
+  private static String resourceName(ApiDocumentationProfile profile) {
+    return DOC_PATH + FILE_NAME + "-" + profile.name().toLowerCase() + FILE_EXTENSION;
+  }
+}