// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'ast.dart';
import 'functional.dart';
import 'generator.dart';
import 'generator_tools.dart';
import 'pigeon_lib.dart' show TaskQueueType;

/// Documentation open symbol.
const String _docCommentPrefix = '/**';

/// Documentation continuation symbol.
const String _docCommentContinuation = ' *';

/// Documentation close symbol.
const String _docCommentSuffix = ' */';

/// Documentation comment spec.
const DocumentCommentSpecification _docCommentSpec =
    DocumentCommentSpecification(
  _docCommentPrefix,
  closeCommentToken: _docCommentSuffix,
  blockContinuationToken: _docCommentContinuation,
);

/// The standard codec for Flutter, used for any non custom codecs and extended for custom codecs.
const String _standardMessageCodec = 'StandardMessageCodec';

/// Options that control how Java code will be generated.
class JavaOptions {
  /// Creates a [JavaOptions] object
  const JavaOptions({
    this.className,
    this.package,
    this.copyrightHeader,
    this.useGeneratedAnnotation,
  });

  /// The name of the class that will house all the generated classes.
  final String? className;

  /// The package where the generated class will live.
  final String? package;

  /// A copyright header that will get prepended to generated code.
  final Iterable<String>? copyrightHeader;

  /// Determines if the `javax.annotation.Generated` is used in the output. This
  /// is false by default since that dependency isn't available in plugins by
  /// default .
  final bool? useGeneratedAnnotation;

  /// Creates a [JavaOptions] from a Map representation where:
  /// `x = JavaOptions.fromMap(x.toMap())`.
  static JavaOptions fromMap(Map<String, Object> map) {
    final Iterable<dynamic>? copyrightHeader =
        map['copyrightHeader'] as Iterable<dynamic>?;
    return JavaOptions(
      className: map['className'] as String?,
      package: map['package'] as String?,
      copyrightHeader: copyrightHeader?.cast<String>(),
      useGeneratedAnnotation: map['useGeneratedAnnotation'] as bool?,
    );
  }

  /// Converts a [JavaOptions] to a Map representation where:
  /// `x = JavaOptions.fromMap(x.toMap())`.
  Map<String, Object> toMap() {
    final Map<String, Object> result = <String, Object>{
      if (className != null) 'className': className!,
      if (package != null) 'package': package!,
      if (copyrightHeader != null) 'copyrightHeader': copyrightHeader!,
      if (useGeneratedAnnotation != null)
        'useGeneratedAnnotation': useGeneratedAnnotation!,
    };
    return result;
  }

  /// Overrides any non-null parameters from [options] into this to make a new
  /// [JavaOptions].
  JavaOptions merge(JavaOptions options) {
    return JavaOptions.fromMap(mergeMaps(toMap(), options.toMap()));
  }
}

/// Class that manages all Java code generation.
class JavaGenerator extends StructuredGenerator<JavaOptions> {
  /// Instantiates a Java Generator.
  const JavaGenerator();

  @override
  void writeFilePrologue(
      JavaOptions generatorOptions, Root root, Indent indent) {
    if (generatorOptions.copyrightHeader != null) {
      addLines(indent, generatorOptions.copyrightHeader!, linePrefix: '// ');
    }
    indent.writeln('// $generatedCodeWarning');
    indent.writeln('// $seeAlsoWarning');
    indent.newln();
  }

  @override
  void writeFileImports(
      JavaOptions generatorOptions, Root root, Indent indent) {
    if (generatorOptions.package != null) {
      indent.writeln('package ${generatorOptions.package};');
      indent.newln();
    }
    indent.writeln('import android.util.Log;');
    indent.writeln('import androidx.annotation.NonNull;');
    indent.writeln('import androidx.annotation.Nullable;');
    indent.writeln('import io.flutter.plugin.common.BasicMessageChannel;');
    indent.writeln('import io.flutter.plugin.common.BinaryMessenger;');
    indent.writeln('import io.flutter.plugin.common.MessageCodec;');
    indent.writeln('import io.flutter.plugin.common.StandardMessageCodec;');
    indent.writeln('import java.io.ByteArrayOutputStream;');
    indent.writeln('import java.nio.ByteBuffer;');
    indent.writeln('import java.util.ArrayList;');
    indent.writeln('import java.util.Arrays;');
    indent.writeln('import java.util.Collections;');
    indent.writeln('import java.util.HashMap;');
    indent.writeln('import java.util.List;');
    indent.writeln('import java.util.Map;');
    indent.newln();
  }

  @override
  void writeOpenNamespace(
      JavaOptions generatorOptions, Root root, Indent indent) {
    indent.writeln(
        '$_docCommentPrefix Generated class from Pigeon.$_docCommentSuffix');
    indent.writeln(
        '@SuppressWarnings({"unused", "unchecked", "CodeBlock2Expr", "RedundantSuppression"})');
    if (generatorOptions.useGeneratedAnnotation ?? false) {
      indent.writeln('@javax.annotation.Generated("dev.flutter.pigeon")');
    }
    indent.writeln('public class ${generatorOptions.className!} {');
    indent.inc();
  }

  @override
  void writeEnum(
      JavaOptions generatorOptions, Root root, Indent indent, Enum anEnum) {
    String camelToSnake(String camelCase) {
      final RegExp regex = RegExp('([a-z])([A-Z]+)');
      return camelCase
          .replaceAllMapped(regex, (Match m) => '${m[1]}_${m[2]}')
          .toUpperCase();
    }

    indent.newln();
    addDocumentationComments(
        indent, anEnum.documentationComments, _docCommentSpec);

    indent.write('public enum ${anEnum.name} ');
    indent.addScoped('{', '}', () {
      enumerate(anEnum.members, (int index, final EnumMember member) {
        addDocumentationComments(
            indent, member.documentationComments, _docCommentSpec);
        indent.writeln(
            '${camelToSnake(member.name)}($index)${index == anEnum.members.length - 1 ? ';' : ','}');
      });
      indent.newln();
      indent.writeln('private final int index;');
      indent.newln();
      indent.write('private ${anEnum.name}(final int index) ');
      indent.addScoped('{', '}', () {
        indent.writeln('this.index = index;');
      });
    });
  }

  @override
  void writeDataClass(
      JavaOptions generatorOptions, Root root, Indent indent, Class klass) {
    final Set<String> customClassNames =
        root.classes.map((Class x) => x.name).toSet();
    final Set<String> customEnumNames =
        root.enums.map((Enum x) => x.name).toSet();

    const List<String> generatedMessages = <String>[
      ' Generated class from Pigeon that represents data sent in messages.'
    ];
    indent.newln();
    addDocumentationComments(
        indent, klass.documentationComments, _docCommentSpec,
        generatorComments: generatedMessages);

    indent.write('public static final class ${klass.name} ');
    indent.addScoped('{', '}', () {
      for (final NamedType field in getFieldsInSerializationOrder(klass)) {
        _writeClassField(generatorOptions, root, indent, field);
        indent.newln();
      }

      if (getFieldsInSerializationOrder(klass)
          .map((NamedType e) => !e.type.isNullable)
          .any((bool e) => e)) {
        indent.writeln(
            '$_docCommentPrefix Constructor is private to enforce null safety; use Builder.$_docCommentSuffix');
        indent.writeln('private ${klass.name}() {}');
        indent.newln();
      }

      _writeClassBuilder(generatorOptions, root, indent, klass);
      writeClassEncode(generatorOptions, root, indent, klass, customClassNames,
          customEnumNames);
      writeClassDecode(generatorOptions, root, indent, klass, customClassNames,
          customEnumNames);
    });
  }

  void _writeClassField(
      JavaOptions generatorOptions, Root root, Indent indent, NamedType field) {
    final HostDatatype hostDatatype = getFieldHostDatatype(field, root.classes,
        root.enums, (TypeDeclaration x) => _javaTypeForBuiltinDartType(x));
    final String nullability = field.type.isNullable ? '@Nullable' : '@NonNull';
    addDocumentationComments(
        indent, field.documentationComments, _docCommentSpec);

    indent.writeln(
        'private $nullability ${hostDatatype.datatype} ${field.name};');
    indent.newln();
    indent.write(
        'public $nullability ${hostDatatype.datatype} ${_makeGetter(field)}() ');
    indent.addScoped('{', '}', () {
      indent.writeln('return ${field.name};');
    });
    indent.newln();
    indent.writeScoped(
        'public void ${_makeSetter(field)}($nullability ${hostDatatype.datatype} setterArg) {',
        '}', () {
      if (!field.type.isNullable) {
        indent.writeScoped('if (setterArg == null) {', '}', () {
          indent.writeln(
              'throw new IllegalStateException("Nonnull field \\"${field.name}\\" is null.");');
        });
      }
      indent.writeln('this.${field.name} = setterArg;');
    });
  }

  void _writeClassBuilder(
    JavaOptions generatorOptions,
    Root root,
    Indent indent,
    Class klass,
  ) {
    indent.write('public static final class Builder ');
    indent.addScoped('{', '}', () {
      for (final NamedType field in getFieldsInSerializationOrder(klass)) {
        final HostDatatype hostDatatype = getFieldHostDatatype(
            field,
            root.classes,
            root.enums,
            (TypeDeclaration x) => _javaTypeForBuiltinDartType(x));
        final String nullability =
            field.type.isNullable ? '@Nullable' : '@NonNull';
        indent.newln();
        indent.writeln(
            'private @Nullable ${hostDatatype.datatype} ${field.name};');
        indent.newln();
        indent.writeScoped(
            'public @NonNull Builder ${_makeSetter(field)}($nullability ${hostDatatype.datatype} setterArg) {',
            '}', () {
          indent.writeln('this.${field.name} = setterArg;');
          indent.writeln('return this;');
        });
      }
      indent.newln();
      indent.write('public @NonNull ${klass.name} build() ');
      indent.addScoped('{', '}', () {
        const String returnVal = 'pigeonReturn';
        indent.writeln('${klass.name} $returnVal = new ${klass.name}();');
        for (final NamedType field in getFieldsInSerializationOrder(klass)) {
          indent.writeln('$returnVal.${_makeSetter(field)}(${field.name});');
        }
        indent.writeln('return $returnVal;');
      });
    });
  }

  @override
  void writeClassEncode(
    JavaOptions generatorOptions,
    Root root,
    Indent indent,
    Class klass,
    Set<String> customClassNames,
    Set<String> customEnumNames,
  ) {
    indent.newln();
    indent.writeln('@NonNull');
    indent.write('ArrayList<Object> toList() ');
    indent.addScoped('{', '}', () {
      indent.writeln(
          'ArrayList<Object> toListResult = new ArrayList<Object>(${klass.fields.length});');
      for (final NamedType field in getFieldsInSerializationOrder(klass)) {
        final HostDatatype hostDatatype = getFieldHostDatatype(
            field,
            root.classes,
            root.enums,
            (TypeDeclaration x) => _javaTypeForBuiltinDartType(x));
        String toWriteValue = '';
        final String fieldName = field.name;
        if (!hostDatatype.isBuiltin &&
            customClassNames.contains(field.type.baseName)) {
          toWriteValue = '($fieldName == null) ? null : $fieldName.toList()';
        } else if (!hostDatatype.isBuiltin &&
            customEnumNames.contains(field.type.baseName)) {
          toWriteValue = '$fieldName == null ? null : $fieldName.index';
        } else {
          toWriteValue = field.name;
        }
        indent.writeln('toListResult.add($toWriteValue);');
      }
      indent.writeln('return toListResult;');
    });
  }

  @override
  void writeClassDecode(
    JavaOptions generatorOptions,
    Root root,
    Indent indent,
    Class klass,
    Set<String> customClassNames,
    Set<String> customEnumNames,
  ) {
    indent.newln();
    indent.write(
        'static @NonNull ${klass.name} fromList(@NonNull ArrayList<Object> list) ');
    indent.addScoped('{', '}', () {
      const String result = 'pigeonResult';
      indent.writeln('${klass.name} $result = new ${klass.name}();');
      enumerate(getFieldsInSerializationOrder(klass),
          (int index, final NamedType field) {
        final String fieldVariable = field.name;
        final String setter = _makeSetter(field);
        indent.writeln('Object $fieldVariable = list.get($index);');
        if (customEnumNames.contains(field.type.baseName)) {
          indent.writeln(
              '$result.$setter(${_intToEnum(fieldVariable, field.type.baseName)});');
        } else {
          indent.writeln(
              '$result.$setter(${_castObject(field, root.classes, root.enums, fieldVariable)});');
        }
      });
      indent.writeln('return $result;');
    });
  }

  /// Writes the code for a flutter [Api], [api].
  /// Example:
  /// public static final class Foo {
  ///   public Foo(BinaryMessenger argBinaryMessenger) {...}
  ///   public interface Reply<T> {
  ///     void reply(T reply);
  ///   }
  ///   public int add(int x, int y, Reply<int> callback) {...}
  /// }
  @override
  void writeFlutterApi(
    JavaOptions generatorOptions,
    Root root,
    Indent indent,
    Api api,
  ) {
    assert(api.location == ApiLocation.flutter);
    if (getCodecClasses(api, root).isNotEmpty) {
      _writeCodec(indent, api, root);
    }
    const List<String> generatedMessages = <String>[
      ' Generated class from Pigeon that represents Flutter messages that can be called from Java.'
    ];
    addDocumentationComments(indent, api.documentationComments, _docCommentSpec,
        generatorComments: generatedMessages);

    indent.write('public static final class ${api.name} ');
    indent.addScoped('{', '}', () {
      indent.writeln('private final BinaryMessenger binaryMessenger;');
      indent.newln();
      indent.write('public ${api.name}(BinaryMessenger argBinaryMessenger) ');
      indent.addScoped('{', '}', () {
        indent.writeln('this.binaryMessenger = argBinaryMessenger;');
      });
      indent.newln();
      indent.write('/** Public interface for sending reply. */ ');
      indent.write('public interface Reply<T> ');
      indent.addScoped('{', '}', () {
        indent.writeln('void reply(T reply);');
      });
      final String codecName = _getCodecName(api);
      indent.writeln('/** The codec used by ${api.name}. */');
      indent.write('static MessageCodec<Object> getCodec() ');
      indent.addScoped('{', '}', () {
        indent.write('return ');
        if (getCodecClasses(api, root).isNotEmpty) {
          indent.addln('$codecName.INSTANCE;');
        } else {
          indent.addln('new $_standardMessageCodec();');
        }
      });

      for (final Method func in api.methods) {
        final String channelName = makeChannelName(api, func);
        final String returnType = func.returnType.isVoid
            ? 'Void'
            : _javaTypeForDartType(func.returnType);
        String sendArgument;
        addDocumentationComments(
            indent, func.documentationComments, _docCommentSpec);
        if (func.arguments.isEmpty) {
          indent
              .write('public void ${func.name}(Reply<$returnType> callback) ');
          sendArgument = 'null';
        } else {
          final Iterable<String> argTypes = func.arguments
              .map((NamedType e) => _nullsafeJavaTypeForDartType(e.type));
          final Iterable<String> argNames =
              indexMap(func.arguments, _getSafeArgumentName);
          if (func.arguments.length == 1) {
            sendArgument =
                'new ArrayList<Object>(Collections.singletonList(${argNames.first}))';
          } else {
            sendArgument =
                'new ArrayList<Object>(Arrays.asList(${argNames.join(', ')}))';
          }
          final String argsSignature =
              map2(argTypes, argNames, (String x, String y) => '$x $y')
                  .join(', ');
          indent.write(
              'public void ${func.name}($argsSignature, Reply<$returnType> callback) ');
        }
        indent.addScoped('{', '}', () {
          const String channel = 'channel';
          indent.writeln('BasicMessageChannel<Object> $channel =');
          indent.nest(2, () {
            indent.writeln('new BasicMessageChannel<>(');
            indent.nest(2, () {
              indent.writeln('binaryMessenger, "$channelName", getCodec());');
            });
          });
          indent.writeln('$channel.send(');
          indent.nest(2, () {
            indent.writeln('$sendArgument,');
            indent.write('channelReply -> ');
            if (func.returnType.isVoid) {
              indent.addln('callback.reply(null));');
            } else {
              indent.addScoped('{', '});', () {
                const String output = 'output';
                indent.writeln('@SuppressWarnings("ConstantConditions")');
                if (func.returnType.baseName == 'int') {
                  indent.writeln(
                      '$returnType $output = channelReply == null ? null : ((Number) channelReply).longValue();');
                } else {
                  indent.writeln(
                      '$returnType $output = ($returnType) channelReply;');
                }
                indent.writeln('callback.reply($output);');
              });
            }
          });
        });
      }
    });
  }

  @override
  void writeApis(JavaOptions generatorOptions, Root root, Indent indent) {
    if (root.apis.any((Api api) =>
        api.location == ApiLocation.host &&
        api.methods.any((Method it) => it.isAsynchronous))) {
      indent.newln();
      _writeResultInterface(indent);
    }
    super.writeApis(generatorOptions, root, indent);
  }

  /// Write the java code that represents a host [Api], [api].
  /// Example:
  /// public interface Foo {
  ///   int add(int x, int y);
  ///   static void setup(BinaryMessenger binaryMessenger, Foo api) {...}
  /// }
  @override
  void writeHostApi(
      JavaOptions generatorOptions, Root root, Indent indent, Api api) {
    assert(api.location == ApiLocation.host);
    if (getCodecClasses(api, root).isNotEmpty) {
      _writeCodec(indent, api, root);
    }
    const List<String> generatedMessages = <String>[
      ' Generated interface from Pigeon that represents a handler of messages from Flutter.'
    ];
    addDocumentationComments(indent, api.documentationComments, _docCommentSpec,
        generatorComments: generatedMessages);

    indent.write('public interface ${api.name} ');
    indent.addScoped('{', '}', () {
      for (final Method method in api.methods) {
        _writeInterfaceMethod(generatorOptions, root, indent, api, method);
      }
      indent.newln();
      final String codecName = _getCodecName(api);
      indent.writeln('/** The codec used by ${api.name}. */');
      indent.write('static MessageCodec<Object> getCodec() ');
      indent.addScoped('{', '}', () {
        indent.write('return ');
        if (getCodecClasses(api, root).isNotEmpty) {
          indent.addln('$codecName.INSTANCE;');
        } else {
          indent.addln('new $_standardMessageCodec();');
        }
      });

      indent.writeln(
          '${_docCommentPrefix}Sets up an instance of `${api.name}` to handle messages through the `binaryMessenger`.$_docCommentSuffix');
      indent.write(
          'static void setup(BinaryMessenger binaryMessenger, ${api.name} api) ');
      indent.addScoped('{', '}', () {
        for (final Method method in api.methods) {
          _writeMethodSetup(generatorOptions, root, indent, api, method);
        }
      });
    });
  }

  /// Write a method in the interface.
  /// Example:
  ///   int add(int x, int y);
  void _writeInterfaceMethod(JavaOptions generatorOptions, Root root,
      Indent indent, Api api, final Method method) {
    final String nullableType = method.isAsynchronous
        ? ''
        : _nullabilityAnnotationFromType(method.returnType);
    final String returnType = method.isAsynchronous
        ? 'void'
        : _javaTypeForDartType(method.returnType);
    final List<String> argSignature = <String>[];
    if (method.arguments.isNotEmpty) {
      final Iterable<String> argTypes = method.arguments
          .map((NamedType e) => _nullsafeJavaTypeForDartType(e.type));
      final Iterable<String> argNames =
          method.arguments.map((NamedType e) => e.name);
      argSignature
          .addAll(map2(argTypes, argNames, (String argType, String argName) {
        return '$argType $argName';
      }));
    }
    if (method.isAsynchronous) {
      final String resultType = method.returnType.isVoid
          ? 'Void'
          : _javaTypeForDartType(method.returnType);
      argSignature.add('Result<$resultType> result');
    }
    if (method.documentationComments.isNotEmpty) {
      addDocumentationComments(
          indent, method.documentationComments, _docCommentSpec);
    } else {
      indent.newln();
    }
    if (nullableType != '') {
      indent.writeln(nullableType);
    }
    indent.writeln('$returnType ${method.name}(${argSignature.join(', ')});');
  }

  /// Write a static setup function in the interface.
  /// Example:
  ///   static void setup(BinaryMessenger binaryMessenger, Foo api) {...}
  void _writeMethodSetup(JavaOptions generatorOptions, Root root, Indent indent,
      Api api, final Method method) {
    final String channelName = makeChannelName(api, method);
    indent.write('');
    indent.addScoped('{', '}', () {
      String? taskQueue;
      if (method.taskQueueType != TaskQueueType.serial) {
        taskQueue = 'taskQueue';
        indent.writeln(
            'BinaryMessenger.TaskQueue taskQueue = binaryMessenger.makeBackgroundTaskQueue();');
      }
      indent.writeln('BasicMessageChannel<Object> channel =');
      indent.nest(2, () {
        indent.writeln('new BasicMessageChannel<>(');
        indent.nest(2, () {
          indent.write('binaryMessenger, "$channelName", getCodec()');
          if (taskQueue != null) {
            indent.addln(', $taskQueue);');
          } else {
            indent.addln(');');
          }
        });
      });
      indent.write('if (api != null) ');
      indent.addScoped('{', '} else {', () {
        indent.writeln('channel.setMessageHandler(');
        indent.nest(2, () {
          indent.write('(message, reply) -> ');
          indent.addScoped('{', '});', () {
            final String returnType = method.returnType.isVoid
                ? 'Void'
                : _javaTypeForDartType(method.returnType);
            indent.writeln('ArrayList wrapped = new ArrayList<>();');
            indent.write('try ');
            indent.addScoped('{', '}', () {
              final List<String> methodArgument = <String>[];
              if (method.arguments.isNotEmpty) {
                indent.writeln(
                    'ArrayList<Object> args = (ArrayList<Object>) message;');
                indent.writeln('assert args != null;');
                enumerate(method.arguments, (int index, NamedType arg) {
                  // The StandardMessageCodec can give us [Integer, Long] for
                  // a Dart 'int'.  To keep things simple we just use 64bit
                  // longs in Pigeon with Java.
                  final bool isInt = arg.type.baseName == 'int';
                  final String argType =
                      isInt ? 'Number' : _javaTypeForDartType(arg.type);
                  final String argName = _getSafeArgumentName(index, arg);
                  final String argExpression = isInt
                      ? '($argName == null) ? null : $argName.longValue()'
                      : argName;
                  String accessor = 'args.get($index)';
                  if (isEnum(root, arg.type)) {
                    accessor = _intToEnum(accessor, arg.type.baseName);
                  } else if (argType != 'Object') {
                    accessor = '($argType) $accessor';
                  }
                  indent.writeln('$argType $argName = $accessor;');
                  if (!arg.type.isNullable) {
                    indent.write('if ($argName == null) ');
                    indent.addScoped('{', '}', () {
                      indent.writeln(
                          'throw new NullPointerException("$argName unexpectedly null.");');
                    });
                  }
                  methodArgument.add(argExpression);
                });
              }
              if (method.isAsynchronous) {
                final String resultValue =
                    method.returnType.isVoid ? 'null' : 'result';
                const String resultName = 'resultCallback';
                indent.format('''
Result<$returnType> $resultName = 
\t\tnew Result<$returnType>() {
\t\t\tpublic void success($returnType result) {
\t\t\t\twrapped.add(0, $resultValue);
\t\t\t\treply.reply(wrapped);
\t\t\t}

\t\t\tpublic void error(Throwable error) {
\t\t\t\tArrayList<Object> wrappedError = wrapError(error);
\t\t\t\treply.reply(wrappedError);
\t\t\t}
\t\t};
''');
                methodArgument.add(resultName);
              }
              final String call =
                  'api.${method.name}(${methodArgument.join(', ')})';
              if (method.isAsynchronous) {
                indent.writeln('$call;');
              } else if (method.returnType.isVoid) {
                indent.writeln('$call;');
                indent.writeln('wrapped.add(0, null);');
              } else {
                indent.writeln('$returnType output = $call;');
                indent.writeln('wrapped.add(0, output);');
              }
            }, addTrailingNewline: false);
            indent.add(' catch (Error | RuntimeException exception) ');
            indent.addScoped('{', '}', () {
              indent.writeln(
                  'ArrayList<Object> wrappedError = wrapError(exception);');
              if (method.isAsynchronous) {
                indent.writeln('reply.reply(wrappedError);');
              } else {
                indent.writeln('wrapped = wrappedError;');
              }
            });
            if (!method.isAsynchronous) {
              indent.writeln('reply.reply(wrapped);');
            }
          });
        });
      });
      indent.addScoped(null, '}', () {
        indent.writeln('channel.setMessageHandler(null);');
      });
    });
  }

  /// Writes the codec class that will be used by [api].
  /// Example:
  /// private static class FooCodec extends StandardMessageCodec {...}
  void _writeCodec(Indent indent, Api api, Root root) {
    assert(getCodecClasses(api, root).isNotEmpty);
    final Iterable<EnumeratedClass> codecClasses = getCodecClasses(api, root);
    final String codecName = _getCodecName(api);
    indent.newln();
    indent.write(
        'private static class $codecName extends $_standardMessageCodec ');
    indent.addScoped('{', '}', () {
      indent.writeln(
          'public static final $codecName INSTANCE = new $codecName();');
      indent.newln();
      indent.writeln('private $codecName() {}');
      indent.newln();
      indent.writeln('@Override');
      indent.write(
          'protected Object readValueOfType(byte type, @NonNull ByteBuffer buffer) ');
      indent.addScoped('{', '}', () {
        indent.write('switch (type) ');
        indent.addScoped('{', '}', () {
          for (final EnumeratedClass customClass in codecClasses) {
            indent.writeln('case (byte) ${customClass.enumeration}:');
            indent.nest(1, () {
              indent.writeln(
                  'return ${customClass.name}.fromList((ArrayList<Object>) readValue(buffer));');
            });
          }
          indent.writeln('default:');
          indent.nest(1, () {
            indent.writeln('return super.readValueOfType(type, buffer);');
          });
        });
      });
      indent.newln();
      indent.writeln('@Override');
      indent.write(
          'protected void writeValue(@NonNull ByteArrayOutputStream stream, Object value) ');
      indent.addScoped('{', '}', () {
        bool firstClass = true;
        for (final EnumeratedClass customClass in codecClasses) {
          if (firstClass) {
            indent.write('');
            firstClass = false;
          }
          indent.add('if (value instanceof ${customClass.name}) ');
          indent.addScoped('{', '} else ', () {
            indent.writeln('stream.write(${customClass.enumeration});');
            indent.writeln(
                'writeValue(stream, ((${customClass.name}) value).toList());');
          }, addTrailingNewline: false);
        }
        indent.addScoped('{', '}', () {
          indent.writeln('super.writeValue(stream, value);');
        });
      });
    });
    indent.newln();
  }

  void _writeResultInterface(Indent indent) {
    indent.write('public interface Result<T> ');
    indent.addScoped('{', '}', () {
      indent.writeln('void success(T result);');
      indent.newln();
      indent.writeln('void error(Throwable error);');
    });
  }

  void _writeWrapError(Indent indent) {
    indent.format('''
@NonNull
private static ArrayList<Object> wrapError(@NonNull Throwable exception) {
\tArrayList<Object> errorList = new ArrayList<>(3);
\terrorList.add(exception.toString());
\terrorList.add(exception.getClass().getSimpleName());
\terrorList.add(
\t\t"Cause: " + exception.getCause() + ", Stacktrace: " + Log.getStackTraceString(exception));
\treturn errorList;
}''');
  }

  @override
  void writeGeneralUtilities(
      JavaOptions generatorOptions, Root root, Indent indent) {
    _writeWrapError(indent);
  }

  @override
  void writeCloseNamespace(
      JavaOptions generatorOptions, Root root, Indent indent) {
    indent.dec();
    indent.addln('}');
  }
}

/// Calculates the name of the codec that will be generated for [api].
String _getCodecName(Api api) => '${api.name}Codec';

/// Converts an expression that evaluates to an nullable int to an expression
/// that evaluates to a nullable enum.
String _intToEnum(String expression, String enumName) =>
    '$expression == null ? null : $enumName.values()[(int) $expression]';

String _getArgumentName(int count, NamedType argument) =>
    argument.name.isEmpty ? 'arg$count' : argument.name;

/// Returns an argument name that can be used in a context where it is possible to collide.
String _getSafeArgumentName(int count, NamedType argument) =>
    '${_getArgumentName(count, argument)}Arg';

String _makeGetter(NamedType field) {
  final String uppercased =
      field.name.substring(0, 1).toUpperCase() + field.name.substring(1);
  return 'get$uppercased';
}

String _makeSetter(NamedType field) {
  final String uppercased =
      field.name.substring(0, 1).toUpperCase() + field.name.substring(1);
  return 'set$uppercased';
}

/// Converts a [List] of [TypeDeclaration]s to a comma separated [String] to be
/// used in Java code.
String _flattenTypeArguments(List<TypeDeclaration> args) {
  return args.map<String>(_javaTypeForDartType).join(', ');
}

String _javaTypeForBuiltinGenericDartType(
  TypeDeclaration type,
  int numberTypeArguments,
) {
  if (type.typeArguments.isEmpty) {
    return '${type.baseName}<${repeat('Object', numberTypeArguments).join(', ')}>';
  } else {
    return '${type.baseName}<${_flattenTypeArguments(type.typeArguments)}>';
  }
}

String? _javaTypeForBuiltinDartType(TypeDeclaration type) {
  const Map<String, String> javaTypeForDartTypeMap = <String, String>{
    'bool': 'Boolean',
    'int': 'Long',
    'String': 'String',
    'double': 'Double',
    'Uint8List': 'byte[]',
    'Int32List': 'int[]',
    'Int64List': 'long[]',
    'Float64List': 'double[]',
  };
  if (javaTypeForDartTypeMap.containsKey(type.baseName)) {
    return javaTypeForDartTypeMap[type.baseName];
  } else if (type.baseName == 'List') {
    return _javaTypeForBuiltinGenericDartType(type, 1);
  } else if (type.baseName == 'Map') {
    return _javaTypeForBuiltinGenericDartType(type, 2);
  } else {
    return null;
  }
}

String _javaTypeForDartType(TypeDeclaration type) {
  return _javaTypeForBuiltinDartType(type) ?? type.baseName;
}

String _nullabilityAnnotationFromType(TypeDeclaration type) {
  return type.isVoid ? '' : (type.isNullable ? '@Nullable ' : '@NonNull ');
}

String _nullsafeJavaTypeForDartType(TypeDeclaration type) {
  final String nullSafe = _nullabilityAnnotationFromType(type);
  return '$nullSafe${_javaTypeForDartType(type)}';
}

/// Casts variable named [varName] to the correct host datatype for [field].
/// This is for use in codecs where we may have a map representation of an
/// object.
String _castObject(
    NamedType field, List<Class> classes, List<Enum> enums, String varName) {
  final HostDatatype hostDatatype = getFieldHostDatatype(field, classes, enums,
      (TypeDeclaration x) => _javaTypeForBuiltinDartType(x));
  if (field.type.baseName == 'int') {
    return '($varName == null) ? null : (($varName instanceof Integer) ? (Integer) $varName : (${hostDatatype.datatype}) $varName)';
  } else if (!hostDatatype.isBuiltin &&
      classes.map((Class x) => x.name).contains(field.type.baseName)) {
    return '($varName == null) ? null : ${hostDatatype.datatype}.fromList((ArrayList<Object>) $varName)';
  } else {
    return '(${hostDatatype.datatype}) $varName';
  }
}