// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:typed_data';

import 'package:_fe_analyzer_shared/src/types/shared_type.dart';
import 'package:analyzer/dart/analysis/features.dart';
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/nullability_suffix.dart';
import 'package:analyzer/source/line_info.dart';
import 'package:analyzer/source/source.dart';
import 'package:analyzer/source/source_range.dart';
import 'package:analyzer/src/binary/binary_reader.dart';
import 'package:analyzer/src/dart/analysis/experiments.dart';
import 'package:analyzer/src/dart/ast/ast.dart';
import 'package:analyzer/src/dart/element/element.dart';
import 'package:analyzer/src/dart/element/field_name_non_promotability_info.dart';
import 'package:analyzer/src/dart/element/name_union.dart';
import 'package:analyzer/src/dart/element/type.dart';
import 'package:analyzer/src/dart/element/type_algebra.dart';
import 'package:analyzer/src/error/inference_error.dart';
import 'package:analyzer/src/fine/library_manifest.dart';
import 'package:analyzer/src/generated/utilities_dart.dart';
import 'package:analyzer/src/summary2/ast_binary_reader.dart';
import 'package:analyzer/src/summary2/ast_binary_tag.dart';
import 'package:analyzer/src/summary2/export.dart';
import 'package:analyzer/src/summary2/informative_data.dart';
import 'package:analyzer/src/summary2/linked_element_factory.dart';
import 'package:analyzer/src/summary2/reference.dart';
import 'package:analyzer/src/utilities/extensions/element.dart';
import 'package:analyzer/src/utilities/uri_cache.dart';
import 'package:pub_semver/pub_semver.dart';

class BundleReader {
  final BinaryReader _reader;
  final Map<Uri, Uint8List> _unitsInformativeBytes;

  final Map<Uri, LibraryReader> libraryMap = {};

  BundleReader({
    required LinkedElementFactory elementFactory,
    required Uint8List resolutionBytes,
    Map<Uri, Uint8List> unitsInformativeBytes = const {},
    required Map<Uri, LibraryManifestHandle> libraryManifests,
  }) : _reader = BinaryReader(resolutionBytes),
       _unitsInformativeBytes = unitsInformativeBytes {
    const bytesOfU32 = 4;
    const countOfU32 = 4;
    _reader.offset = _reader.bytes.length - bytesOfU32 * countOfU32;
    var baseResolutionOffset = _reader.readUint32();
    var librariesOffset = _reader.readUint32();
    var referencesOffset = _reader.readUint32();
    var stringsOffset = _reader.readUint32();
    _reader.initStringTableAt(stringsOffset);

    _reader.offset = referencesOffset;
    var referenceReader = ReferenceTableReader(
      reader: _reader,
      rootReference: elementFactory.rootReference,
    );

    _reader.offset = librariesOffset;
    var libraryHeaderList = _reader.readTypedList(() {
      return _LibraryHeader(
        uri: uriCache.parse(_reader.readStringReference()),
        offset: _reader.readUint30(),
      );
    });

    for (var libraryHeader in libraryHeaderList) {
      var uri = libraryHeader.uri;
      var reference = elementFactory.rootReference.getOrCreateLibrary(uri);
      libraryMap[uri] = LibraryReader._(
        elementFactory: elementFactory,
        reader: _reader,
        uri: uri,
        unitsInformativeBytes: _unitsInformativeBytes,
        baseResolutionOffset: baseResolutionOffset,
        referenceReader: referenceReader,
        reference: reference,
        offset: libraryHeader.offset,
        manifest: libraryManifests[uri],
      );
    }
  }
}

class LibraryReader {
  final LinkedElementFactory _elementFactory;
  final BinaryReader _reader;
  final Uri uri;
  final Map<Uri, Uint8List> _unitsInformativeBytes;
  final int _baseResolutionOffset;
  final ReferenceTableReader _referenceReader;
  final LibraryReference _reference;
  final int _offset;
  final LibraryManifestHandle? manifest;

  late final LibraryElementImpl _libraryElement;

  /// Map of unique (in the bundle) IDs to fragments.
  final Map<int, FragmentImpl> idFragmentMap = {};

  LibraryReader._({
    required LinkedElementFactory elementFactory,
    required BinaryReader reader,
    required this.uri,
    required Map<Uri, Uint8List> unitsInformativeBytes,
    required int baseResolutionOffset,
    required ReferenceTableReader referenceReader,
    required LibraryReference reference,
    required int offset,
    required this.manifest,
  }) : _elementFactory = elementFactory,
       _reader = reader,
       _unitsInformativeBytes = unitsInformativeBytes,
       _baseResolutionOffset = baseResolutionOffset,
       _referenceReader = referenceReader,
       _reference = reference,
       _offset = offset;

  LibraryElementImpl readElement({required Source librarySource}) {
    var analysisContext = _elementFactory.analysisContext;
    var analysisSession = _elementFactory.analysisSession;

    _reader.offset = _offset;

    // Read enough data to create the library.
    var name = _reader.readStringReference();
    var featureSet = _readFeatureSet();

    // Create the library, link to the reference.
    _libraryElement = LibraryElementImpl(
      analysisContext,
      analysisSession,
      name,
      -1,
      0,
      featureSet,
    );
    _reference.element = _libraryElement;
    _libraryElement.reference = _reference;

    // Read the rest of non-resolution data for the library.
    _libraryElement.readFlags(_reader);
    _libraryElement.languageVersion = _readLanguageVersion();

    _libraryElement.exportEntries = _reader.readTypedList(_readExportEntry);

    _libraryElement.nameUnion = ElementNameUnion.read(_reader.readUint30List());

    _libraryElement.manifest = manifest;

    _libraryElement.loadLibraryProvider = LoadLibraryFunctionProvider(
      elementReference: _referenceReader.readTopLevelReference(_reader),
    );

    // Read the library units.
    _libraryElement.firstFragment = _readLibraryFragment(source: librarySource);

    _readClassElements();
    _readEnumElements();
    _readExtensionElements();
    _readExtensionTypeElements();
    _readTopLevelFunctionElements();
    _readMixinElements();
    _readTypeAliasElements();
    _readTopLevelVariableElements();
    _libraryElement.getters = _readGetterElements();
    _libraryElement.setters = _readSetterElements();
    _readVariableGetterSetterLinking();

    var resolutionOffset = _baseResolutionOffset + _reader.readUint30();
    _libraryElement.deferReadResolution(() {
      var libraryFragment = _libraryElement.internal.firstFragment;
      var reader = ResolutionReader(
        _elementFactory,
        _referenceReader,
        _reader.fork(resolutionOffset),
      );
      reader.currentLibraryFragment = libraryFragment;

      _libraryElement.metadata = reader._readMetadata();

      _libraryElement.entryPoint =
          reader.readElement() as TopLevelFunctionElementImpl?;

      _libraryElement.fieldNameNonPromotabilityInfo = reader.readOptionalObject(
        () {
          return reader.readMap(
            readKey: () => reader.readStringReference(),
            readValue: () {
              return FieldNameNonPromotabilityInfo(
                conflictingFields: reader.readElementList(),
                conflictingGetters: reader.readElementList(),
                conflictingNsmClasses: reader.readElementList(),
              );
            },
          );
        },
      );

      _libraryElement.exportNamespace = _elementFactory.buildExportNamespace(
        _libraryElement.uri,
        _libraryElement.exportEntries,
      );
    });

    _declareDartCoreDynamicNever();

    InformativeDataApplier().applyToLibrary(
      _elementFactory,
      _libraryElement,
      _unitsInformativeBytes,
    );

    return _libraryElement;
  }

  void Function() _createDeferredReadResolutionCallback(
    void Function(ResolutionReader reader) callback,
  ) {
    var offset = _baseResolutionOffset + _reader.readUint30();
    return () {
      var reader = ResolutionReader(
        _elementFactory,
        _referenceReader,
        _reader.fork(offset),
      );
      callback(reader);
    };
  }

  /// These elements are implicitly declared in `dart:core`.
  void _declareDartCoreDynamicNever() {
    if (_reference.uriString == 'dart:core') {
      _reference.dynamicRef.element = DynamicElementImpl.instance;
      _reference.neverRef.element = NeverElementImpl.instance;
    }
  }

  /// Configures to read lazy data with [operation].
  ///
  /// Expected state of the reader:
  ///   - length of data to read lazily
  ///   - data to read lazily
  ///   - data to continue reading eagerly
  void _lazyRead(void Function(int offset) operation) {
    var length = _reader.readUint30();
    var offset = _reader.offset;
    _reader.offset += length;
    operation(offset);
  }

  void _readClassElements() {
    _libraryElement.classes = _reader.readTypedList(() {
      var reference = _referenceReader.readMemberContainerReference(_reader);
      var fragments = _readFragmentsById<ClassFragmentImpl>();
      var element = ClassElementImpl(reference, fragments.first);
      element.linkFragments(fragments);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();

      element.readFlags(_reader);
      element.hasNonFinalField = _reader.readBool();

      _lazyRead((offset) {
        element.deferReadMembers(() {
          _reader.runAtOffset(offset, () {
            element.ensureReadMembersForFragments();
            element.fields = _readFieldElements();
            element.getters = _readGetterElements();
            element.setters = _readSetterElements();
            _readVariableGetterSetterLinking();
            element.methods = _readMethodElements();
            if (element.isMixinApplication) {
              // Create synthetic constructors and associate with references.
              element.constructors;
            } else {
              element.constructors = _readConstructorElements();
            }
          });
        });
      });

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          reader._addTypeParameterElements(element.typeParameters);
          _readTypeParameterElementResolutions(reader, element.typeParameters);
          element.supertype = reader._readOptionalInterfaceType();
          element.mixins = reader._readInterfaceTypeList();
          element.interfaces = reader._readInterfaceTypeList();
          element.interfaceCycle = reader.readOptionalElementList();
        }),
      );

      return element;
    });
  }

  List<ClassFragmentImpl> _readClassFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = ClassFragmentImpl(name: name);
          fragment.readFlags(_reader);
          fragment.typeParameters = _readTypeParameterFragments();

          _lazyRead((membersOffset) {
            fragment.deferReadMembers(() {
              _reader.runAtOffset(membersOffset, () {
                fragment.fields = _readFieldFragments();
                fragment.getters = _readGetterFragments();
                fragment.setters = _readSetterFragments();
                fragment.methods = _readMethodFragments();
                if (!fragment.isMixinApplication) {
                  fragment.constructors = _readConstructorFragments();
                }
              });
            });
          });
          return fragment;
        },
        readResolution: (fragment, reader) {
          _readTypeParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.typeParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  List<ConstructorElementImpl> _readConstructorElements() {
    return _reader.readTypedList(() {
      var reference = _referenceReader.readMemberReference(_reader);
      var fragments = _readFragmentsById<ConstructorFragmentImpl>();
      var element = ConstructorElementImpl(
        name: fragments.first.name,
        reference: reference,
        firstFragment: fragments.first,
      );
      element.linkFragments(fragments);
      _readFormalParameterElementFlags(element);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          var enclosingElement = element.enclosingElement;
          reader._addTypeParameterElements(enclosingElement.typeParameters);
          _readFormalParameterElementResolutions(reader, element);
          element.returnType = reader.readRequiredType();
          element.superConstructor = reader.readConstructorElementMixin();
          element.redirectedConstructor = reader.readConstructorElementMixin();
        }),
      );

      return element;
    });
  }

  List<ConstructorFragmentImpl> _readConstructorFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = ConstructorFragmentImpl(name: name!);

          fragment.readFlags(_reader);
          fragment.typeName = _reader.readOptionalStringReference();
          fragment.formalParameters = _readFormalParameterFragments();

          return fragment;
        },
        readResolution: (fragment, reader) {
          var enclosingElement = fragment.element.enclosingElement;
          reader._addTypeParameterElements(enclosingElement.typeParameters);

          _readFormalParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.formalParameters,
          );
          fragment.metadata = reader._readMetadata();
          fragment.constantInitializers = reader.readNodeList();
        },
      );
    });
  }

  DirectiveUriImpl _readDirectiveUri() {
    DirectiveUriWithRelativeUriStringImpl readWithRelativeUriString() {
      var relativeUriString = _reader.readStringReference();
      return DirectiveUriWithRelativeUriStringImpl(
        relativeUriString: relativeUriString,
      );
    }

    DirectiveUriWithRelativeUriImpl readWithRelativeUri() {
      var parent = readWithRelativeUriString();
      var relativeUri = uriCache.parse(_reader.readStringReference());
      return DirectiveUriWithRelativeUriImpl(
        relativeUriString: parent.relativeUriString,
        relativeUri: relativeUri,
      );
    }

    DirectiveUriWithSourceImpl readWithSource() {
      var parent = readWithRelativeUri();

      var analysisContext = _elementFactory.analysisContext;
      var sourceFactory = analysisContext.sourceFactory;

      var sourceUriStr = _reader.readStringReference();
      var sourceUri = uriCache.parse(sourceUriStr);
      var source = sourceFactory.forUri2(sourceUri)!;

      return DirectiveUriWithSourceImpl(
        relativeUriString: parent.relativeUriString,
        relativeUri: parent.relativeUri,
        source: source,
      );
    }

    var kindIndex = _reader.readByte();
    var kind = DirectiveUriKind.values[kindIndex];
    switch (kind) {
      case DirectiveUriKind.withLibrary:
        var parent = readWithSource();
        return DirectiveUriWithLibraryImpl.read(
          relativeUriString: parent.relativeUriString,
          relativeUri: parent.relativeUri,
          source: parent.source,
        );
      case DirectiveUriKind.withUnit:
        var parent = readWithSource();
        var libraryFragment = _readLibraryFragment(source: parent.source);
        return DirectiveUriWithUnitImpl(
          relativeUriString: parent.relativeUriString,
          relativeUri: parent.relativeUri,
          libraryFragment: libraryFragment,
        );
      case DirectiveUriKind.withSource:
        return readWithSource();
      case DirectiveUriKind.withRelativeUri:
        return readWithRelativeUri();
      case DirectiveUriKind.withRelativeUriString:
        return readWithRelativeUriString();
      case DirectiveUriKind.withNothing:
        return DirectiveUriImpl();
    }
  }

  void _readEnumElements() {
    _libraryElement.enums = _reader.readTypedList(() {
      var reference = _referenceReader.readMemberContainerReference(_reader);
      var fragments = _readFragmentsById<EnumFragmentImpl>();
      var element = EnumElementImpl(reference, fragments.first);
      element.linkFragments(fragments);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);
      element.hasNonFinalField = _reader.readBool();

      _lazyRead((offset) {
        element.deferReadMembers(() {
          _reader.runAtOffset(offset, () {
            element.ensureReadMembersForFragments();
            element.fields = _readFieldElements();
            element.getters = _readGetterElements();
            element.setters = _readSetterElements();
            _readVariableGetterSetterLinking();
            element.constructors = _readConstructorElements();
            element.methods = _readMethodElements();
          });
        });
      });
      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          reader._addTypeParameterElements(element.typeParameters);
          _readTypeParameterElementResolutions(reader, element.typeParameters);
          element.supertype = reader._readOptionalInterfaceType();
          element.mixins = reader._readInterfaceTypeList();
          element.interfaces = reader._readInterfaceTypeList();
          element.interfaceCycle = reader.readOptionalElementList();
        }),
      );

      return element;
    });
  }

  List<EnumFragmentImpl> _readEnumFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = EnumFragmentImpl(name: name);
          fragment.readFlags(_reader);
          fragment.typeParameters = _readTypeParameterFragments();

          _lazyRead((offset) {
            fragment.deferReadMembers(() {
              _reader.runAtOffset(offset, () {
                fragment.fields = _readFieldFragments();
                fragment.getters = _readGetterFragments();
                fragment.setters = _readSetterFragments();
                fragment.constructors = _readConstructorFragments();
                fragment.methods = _readMethodFragments();
              });
            });
          });
          return fragment;
        },
        readResolution: (fragment, reader) {
          _readTypeParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.typeParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  ExportEntry _readExportEntry() {
    return ExportEntry(
      name: _reader.readStringReference(),
      reference: _referenceReader.readExportableReference(_reader),
      locations: _reader.readTypedList(_readExportLocation),
    );
  }

  ExportLocation _readExportLocation() {
    return ExportLocation(
      fragmentIndex: _reader.readUint30(),
      exportIndex: _reader.readUint30(),
    );
  }

  void _readExtensionElements() {
    _libraryElement.extensions = _reader.readTypedList(() {
      var reference = _referenceReader.readMemberContainerReference(_reader);
      var fragments = _readFragmentsById<ExtensionFragmentImpl>();
      var element = ExtensionElementImpl(reference, fragments.first);
      element.linkFragments(fragments);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);

      _lazyRead((offset) {
        element.deferReadMembers(() {
          _reader.runAtOffset(offset, () {
            element.ensureReadMembersForFragments();
            element.fields = _readFieldElements();
            element.getters = _readGetterElements();
            element.setters = _readSetterElements();
            _readVariableGetterSetterLinking();
            element.methods = _readMethodElements();
          });
        });
      });

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          reader._addTypeParameterElements(element.typeParameters);
          _readTypeParameterElementResolutions(reader, element.typeParameters);
          element.extendedType = reader.readRequiredType();
          // TODO(scheglov): read resolution information
        }),
      );

      return element;
    });
  }

  List<ExtensionFragmentImpl> _readExtensionFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = ExtensionFragmentImpl(name: name);
          fragment.readFlags(_reader);
          fragment.typeParameters = _readTypeParameterFragments();

          _lazyRead((offset) {
            fragment.deferReadMembers(() {
              _reader.runAtOffset(offset, () {
                fragment.fields = _readFieldFragments();
                fragment.getters = _readGetterFragments();
                fragment.setters = _readSetterFragments();
                fragment.methods = _readMethodFragments();
              });
            });
          });
          return fragment;
        },
        readResolution: (fragment, reader) {
          _readTypeParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.typeParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  void _readExtensionTypeElements() {
    _libraryElement.extensionTypes = _reader.readTypedList(() {
      var reference = _referenceReader.readMemberContainerReference(_reader);
      var fragments = _readFragmentsById<ExtensionTypeFragmentImpl>();
      var element = ExtensionTypeElementImpl(reference, fragments.first);
      element.linkFragments(fragments);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);

      element.hasRepresentationSelfReference = _reader.readBool();
      element.hasImplementsSelfReference = _reader.readBool();

      _lazyRead((offset) {
        element.deferReadMembers(() {
          _reader.runAtOffset(offset, () {
            element.ensureReadMembersForFragments();
            element.fields = _readFieldElements();
            element.getters = _readGetterElements();
            element.setters = _readSetterElements();
            _readVariableGetterSetterLinking();
            element.constructors = _readConstructorElements();
            element.methods = _readMethodElements();
          });
        });
      });

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          reader._addTypeParameterElements(element.typeParameters);
          _readTypeParameterElementResolutions(reader, element.typeParameters);
          element.typeErasure = reader.readRequiredType();
          element.interfaces = reader._readInterfaceTypeList();
          element.interfaceCycle = reader.readOptionalElementList();
        }),
      );

      return element;
    });
  }

  List<ExtensionTypeFragmentImpl> _readExtensionTypeFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = ExtensionTypeFragmentImpl(name: name);
          fragment.readFlags(_reader);
          fragment.typeParameters = _readTypeParameterFragments();

          _lazyRead((offset) {
            fragment.deferReadMembers(() {
              _reader.runAtOffset(offset, () {
                fragment.fields = _readFieldFragments();
                fragment.getters = _readGetterFragments();
                fragment.setters = _readSetterFragments();
                fragment.constructors = _readConstructorFragments();
                fragment.methods = _readMethodFragments();
              });
            });
          });
          return fragment;
        },
        readResolution: (fragment, reader) {
          _readTypeParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.typeParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  FeatureSet _readFeatureSet() {
    var featureSetEncoded = _reader.readUint8List();
    return ExperimentStatus.fromStorage(featureSetEncoded);
  }

  List<FieldElementImpl> _readFieldElements() {
    return _reader.readTypedList(() {
      var reference = _referenceReader.readMemberReference(_reader);
      var fragments = _readFragmentsById<FieldFragmentImpl>();
      var element = FieldElementImpl(
        reference: reference,
        firstFragment: fragments.first,
      );
      element.linkFragments(fragments);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);
      element.typeInferenceError = _readTopLevelInferenceError();

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          var enclosingElement = element.enclosingElement;
          reader._addTypeParameterElements(enclosingElement.typeParameters);
          element.type = reader.readRequiredType();
        }),
      );

      return element;
    });
  }

  List<FieldFragmentImpl> _readFieldFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = FieldFragmentImpl(name: name);
          fragment.readFlags(_reader);
          return fragment;
        },
        readResolution: (fragment, reader) {
          var enclosingElement = fragment.element.enclosingElement;
          reader._addTypeParameterElements(enclosingElement.typeParameters);

          fragment.metadata = reader._readMetadata();
          if (reader.readOptionalExpression() case var initializer?) {
            fragment.constantInitializer = initializer;
            ConstantContextForExpressionImpl(fragment, initializer);
          }
        },
      );
    });
  }

  void _readFormalParameterElementFlags(ExecutableElementImpl executable) {
    var elements = executable.formalParametersIncludingRecovery;
    for (var element in elements) {
      element.readFlags(_reader);
    }
  }

  void _readFormalParameterElementResolutions(
    ResolutionReader reader,
    ExecutableElementImpl executable,
  ) {
    var elements = executable.formalParametersIncludingRecovery;
    for (var element in elements) {
      element.type = reader.readRequiredType();
      if (element is FieldFormalParameterElementImpl) {
        element.field = reader.readElement() as FieldElementImpl?;
      }
    }
  }

  /// Read the formal parameter list for a top-level function, method,
  /// constructor, getter, or setter declaration.
  // TODO(scheglov): Deduplicate parameter reading implementation.
  List<FormalParameterFragmentImpl> _readFormalParameterFragments() {
    return _reader.readTypedList(() {
      var id = _readFragmentId();
      var fragmentName = _readFragmentName();
      var isFieldFormalParameter = _reader.readBool();
      var isSuperParameter = _reader.readBool();

      var kindIndex = _reader.readByte();
      var kind = ResolutionReader._formalParameterKind(kindIndex);

      FormalParameterFragmentImpl fragment;
      if (isFieldFormalParameter) {
        var privateName = _reader.readOptionalStringReference();
        fragment = FieldFormalParameterFragmentImpl(
          name: fragmentName,
          nameOffset: null,
          parameterKind: kind,
          privateName: privateName,
        );
      } else if (isSuperParameter) {
        fragment = SuperFormalParameterFragmentImpl(
          name: fragmentName,
          nameOffset: null,
          parameterKind: kind,
        );
      } else {
        fragment = FormalParameterFragmentImpl(
          name: fragmentName,
          nameOffset: null,
          parameterKind: kind,
        );
      }
      idFragmentMap[id] = fragment;
      fragment.readFlags(_reader);
      return fragment;
    });
  }

  /// Read the resolution for a formal parameter list fragment for a
  /// top-level function, method, constructor, getter, or setter
  /// declaration.
  void _readFormalParameterFragmentsResolution(
    LibraryFragmentImpl libraryFragment,
    ResolutionReader reader,
    List<FormalParameterFragmentImpl> fragments,
  ) {
    for (var fragment in fragments) {
      fragment.metadata = reader._readMetadata();
      fragment.constantInitializer = reader.readOptionalExpression();
    }
  }

  T _readFragmentById<T extends FragmentImpl>() {
    var id = _readFragmentId();
    return idFragmentMap[id] as T;
  }

  int _readFragmentId() {
    return _reader.readUint30();
  }

  String? _readFragmentName() {
    return _reader.readOptionalStringReference();
  }

  List<T> _readFragmentsById<T extends FragmentImpl>() {
    return _reader.readTypedList(_readFragmentById);
  }

  List<GetterElementImpl> _readGetterElements() {
    return _reader.readTypedList(() {
      var reference = _referenceReader.readDeclarationReference(_reader);
      var fragments = _readFragmentsById<GetterFragmentImpl>();
      var element = GetterElementImpl(reference, fragments.first);
      element.linkFragments(fragments);
      _readFormalParameterElementFlags(element);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          var enclosingElement = element.enclosingElement;
          if (enclosingElement is InstanceElementImpl) {
            reader._addTypeParameterElements(enclosingElement.typeParameters);
          }

          _readFormalParameterElementResolutions(reader, element);
          element.returnType = reader.readRequiredType();
        }),
      );

      return element;
    });
  }

  List<GetterFragmentImpl> _readGetterFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = GetterFragmentImpl(name: name);

          fragment.readFlags(_reader);
          fragment.formalParameters = _readFormalParameterFragments();
          return fragment;
        },
        readResolution: (fragment, reader) {
          var enclosingElement = fragment.element.enclosingElement;
          if (enclosingElement is InstanceElementImpl) {
            reader._addTypeParameterElements(enclosingElement.typeParameters);
          }

          _readFormalParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.formalParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  LibraryLanguageVersion _readLanguageVersion() {
    var packageMajor = _reader.readUint30();
    var packageMinor = _reader.readUint30();
    var package = Version(packageMajor, packageMinor, 0);

    Version? override;
    if (_reader.readBool()) {
      var overrideMajor = _reader.readUint30();
      var overrideMinor = _reader.readUint30();
      override = Version(overrideMajor, overrideMinor, 0);
    }

    return LibraryLanguageVersion(package: package, override: override);
  }

  List<LibraryExportImpl> _readLibraryExports() {
    return _reader.readTypedList(() {
      return LibraryExportImpl(
        combinators: _reader.readTypedList(_readNamespaceCombinator),
        exportKeywordOffset: -1,
        uri: _readDirectiveUri(),
      );
    });
  }

  LibraryFragmentImpl _readLibraryFragment({required Source source}) {
    var resolutionOffset = _baseResolutionOffset + _reader.readUint30();

    var libraryFragment = LibraryFragmentImpl(
      library: _libraryElement,
      source: source,
      lineInfo: LineInfo([0]),
    );

    libraryFragment.deferReadResolution(() {
      var reader = ResolutionReader(
        _elementFactory,
        _referenceReader,
        _reader.fork(resolutionOffset),
      );

      reader.currentLibraryFragment = libraryFragment;

      for (var import in libraryFragment.libraryImports) {
        import.metadata = reader._readMetadata();
        var uri = import.uri;
        if (uri is DirectiveUriWithLibraryImpl) {
          uri.library = reader.libraryOfUri(uri.source.uri);
        }
      }

      for (var export in libraryFragment.libraryExports) {
        export.metadata = reader._readMetadata();
        var uri = export.uri;
        if (uri is DirectiveUriWithLibraryImpl) {
          uri.library = reader.libraryOfUri(uri.source.uri);
        }
      }

      for (var part in libraryFragment.parts) {
        part.metadata = reader._readMetadata();
      }
    });

    libraryFragment.readFlags(_reader);

    libraryFragment.libraryImports = _readLibraryImports(libraryFragment);
    libraryFragment.libraryExports = _readLibraryExports();

    libraryFragment.classes = _readClassFragments();
    libraryFragment.enums = _readEnumFragments();
    libraryFragment.extensions = _readExtensionFragments();
    libraryFragment.extensionTypes = _readExtensionTypeFragments();
    libraryFragment.functions = _readTopLevelFunctionFragments();
    libraryFragment.mixins = _readMixinFragments();
    libraryFragment.typeAliases = _readTypeAliasFragments(libraryFragment);

    libraryFragment.topLevelVariables = _readTopLevelVariableFragments();
    libraryFragment.getters = _readGetterFragments();
    libraryFragment.setters = _readSetterFragments();

    libraryFragment.parts = _readPartIncludes();

    return libraryFragment;
  }

  PrefixFragmentImpl? _readLibraryImportPrefixFragment(
    LibraryFragmentImpl libraryFragment,
  ) {
    return _reader.readOptionalObject(() {
      var fragmentName = _readFragmentName();
      var id = _reader.readStringReference();
      var isDeferred = _reader.readBool();
      var fragment = PrefixFragmentImpl(
        name: fragmentName,
        firstTokenOffset: null,
        nameOffset: null,
        isDeferred: isDeferred,
      );
      libraryFragment.bindLibraryImportPrefixElement(
        id: id,
        fragment: fragment,
      );
      return fragment;
    });
  }

  List<LibraryImportImpl> _readLibraryImports(
    LibraryFragmentImpl libraryFragment,
  ) {
    return _reader.readTypedList(() {
      return LibraryImportImpl(
        isSynthetic: _reader.readBool(),
        combinators: _reader.readTypedList(_readNamespaceCombinator),
        importKeywordOffset: -1,
        prefix: _readLibraryImportPrefixFragment(libraryFragment),
        uri: _readDirectiveUri(),
      );
    });
  }

  List<MethodElementImpl> _readMethodElements() {
    return _reader.readTypedList(() {
      var reference = _referenceReader.readMemberReference(_reader);
      var fragments = _readFragmentsById<MethodFragmentImpl>();
      var element = MethodElementImpl(
        name: fragments.first.name,
        reference: reference,
        firstFragment: fragments.first,
      );
      element.linkFragments(fragments);
      _readFormalParameterElementFlags(element);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);
      element.typeInferenceError = _readTopLevelInferenceError();

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          var enclosingElement = element.enclosingElement;
          reader._addTypeParameterElements(enclosingElement.typeParameters);

          reader._addTypeParameterElements(element.typeParameters);
          _readTypeParameterElementResolutions(reader, element.typeParameters);

          _readFormalParameterElementResolutions(reader, element);
          element.returnType = reader.readRequiredType();
        }),
      );

      return element;
    });
  }

  List<MethodFragmentImpl> _readMethodFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = MethodFragmentImpl(name: name);

          fragment.readFlags(_reader);
          fragment.typeParameters = _readTypeParameterFragments();
          fragment.formalParameters = _readFormalParameterFragments();
          return fragment;
        },
        readResolution: (fragment, reader) {
          var enclosingElement = fragment.element.enclosingElement;
          reader._addTypeParameterElements(enclosingElement.typeParameters);

          _readTypeParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.typeParameters,
          );
          _readFormalParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.formalParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  void _readMixinElements() {
    _libraryElement.mixins = _reader.readTypedList(() {
      var reference = _referenceReader.readMemberContainerReference(_reader);
      var fragments = _readFragmentsById<MixinFragmentImpl>();
      var element = MixinElementImpl(reference, fragments.first);
      element.linkFragments(fragments);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();

      element.readFlags(_reader);
      element.hasNonFinalField = _reader.readBool();

      _lazyRead((offset) {
        element.deferReadMembers(() {
          _reader.runAtOffset(offset, () {
            element.ensureReadMembersForFragments();
            element.fields = _readFieldElements();
            element.getters = _readGetterElements();
            element.setters = _readSetterElements();
            _readVariableGetterSetterLinking();
            element.constructors = _readConstructorElements();
            element.methods = _readMethodElements();
          });
        });
      });

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          reader._addTypeParameterElements(element.typeParameters);
          _readTypeParameterElementResolutions(reader, element.typeParameters);
          element.superclassConstraints = reader._readInterfaceTypeList();
          element.interfaces = reader._readInterfaceTypeList();
          element.interfaceCycle = reader.readOptionalElementList();
        }),
      );

      return element;
    });
  }

  List<MixinFragmentImpl> _readMixinFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = MixinFragmentImpl(name: name);
          fragment.readFlags(_reader);
          fragment.superInvokedNames = _reader.readStringReferenceList();
          fragment.typeParameters = _readTypeParameterFragments();

          _lazyRead((offset) {
            fragment.deferReadMembers(() {
              _reader.runAtOffset(offset, () {
                fragment.fields = _readFieldFragments();
                fragment.getters = _readGetterFragments();
                fragment.setters = _readSetterFragments();
                fragment.constructors = _readConstructorFragments();
                fragment.methods = _readMethodFragments();
              });
            });
          });
          return fragment;
        },
        readResolution: (fragment, reader) {
          _readTypeParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.typeParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  NamespaceCombinator _readNamespaceCombinator() {
    var tag = _reader.readByte();
    if (tag == Tag.HideCombinator) {
      var combinator = HideElementCombinatorImpl();
      combinator.hiddenNames = _reader.readStringReferenceList();
      return combinator;
    } else if (tag == Tag.ShowCombinator) {
      var combinator = ShowElementCombinatorImpl();
      combinator.shownNames = _reader.readStringReferenceList();
      return combinator;
    } else {
      throw UnimplementedError('tag: $tag');
    }
  }

  FragmentImpl? _readOptionalFragmentById() {
    return _reader.readOptionalObject(_readFragmentById);
  }

  /// Read the reference of a non-local element.
  Reference? _readOptionalReference() {
    return _reader.readOptionalObject(
      () => _referenceReader.readReference(_reader),
    );
  }

  List<PartIncludeImpl> _readPartIncludes() {
    return _reader.readTypedList(() {
      var uri = _readDirectiveUri();
      return PartIncludeImpl(partKeywordOffset: -1, uri: uri);
    });
  }

  List<SetterElementImpl> _readSetterElements() {
    return _reader.readTypedList(() {
      var reference = _referenceReader.readDeclarationReference(_reader);
      var fragments = _readFragmentsById<SetterFragmentImpl>();
      var element = SetterElementImpl(reference, fragments.first);
      element.linkFragments(fragments);
      _readFormalParameterElementFlags(element);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          var enclosingElement = element.enclosingElement;
          if (enclosingElement is InstanceElementImpl) {
            reader._addTypeParameterElements(enclosingElement.typeParameters);
          }

          _readFormalParameterElementResolutions(reader, element);
          element.returnType = reader.readRequiredType();
        }),
      );

      return element;
    });
  }

  List<SetterFragmentImpl> _readSetterFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = SetterFragmentImpl(name: name);

          fragment.readFlags(_reader);
          fragment.formalParameters = _readFormalParameterFragments();
          return fragment;
        },
        readResolution: (fragment, reader) {
          var enclosingElement = fragment.element.enclosingElement;
          if (enclosingElement is InstanceElementImpl) {
            reader._addTypeParameterElements(enclosingElement.typeParameters);
          }

          _readFormalParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.formalParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  /// [T] must also implement [DeferredResolutionReadingMixin], we configure
  /// it with [readResolution].
  T _readTemplateFragment<T extends FragmentImpl>({
    required T Function(String? name) create,
    required void Function(T fragment, ResolutionReader reader) readResolution,
  }) {
    var id = _readFragmentId();
    var name = _readFragmentName();
    var resolutionOffset = _baseResolutionOffset + _reader.readUint30();
    var fragment = create(name);
    idFragmentMap[id] = fragment;

    if (fragment case DeferredResolutionReadingMixin deferred) {
      deferred.deferReadResolution(() {
        var reader = ResolutionReader(
          _elementFactory,
          _referenceReader,
          _reader.fork(resolutionOffset),
        );

        // TODO(scheglov): type casts are not good :-(
        reader.currentLibraryFragment =
            fragment.libraryFragment as LibraryFragmentImpl;

        readResolution(fragment, reader);
      });
    }

    return fragment;
  }

  void _readTopLevelFunctionElements() {
    _libraryElement.topLevelFunctions = _reader.readTypedList(() {
      var reference = _referenceReader.readTopLevelReference(_reader);
      var fragments = _readFragmentsById<TopLevelFunctionFragmentImpl>();
      var element = TopLevelFunctionElementImpl(reference, fragments.first);
      element.linkFragments(fragments);
      _readFormalParameterElementFlags(element);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          reader._addTypeParameterElements(element.typeParameters);
          _readTypeParameterElementResolutions(reader, element.typeParameters);

          _readFormalParameterElementResolutions(reader, element);
          element.returnType = reader.readRequiredType();
        }),
      );

      return element;
    });
  }

  List<TopLevelFunctionFragmentImpl> _readTopLevelFunctionFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = TopLevelFunctionFragmentImpl(name: name);

          fragment.readFlags(_reader);
          fragment.typeParameters = _readTypeParameterFragments();
          fragment.formalParameters = _readFormalParameterFragments();
          return fragment;
        },
        readResolution: (fragment, reader) {
          _readTypeParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.typeParameters,
          );
          _readFormalParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.formalParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  TopLevelInferenceError? _readTopLevelInferenceError() {
    return TopLevelInferenceError.readOptional(_reader);
  }

  void _readTopLevelVariableElements() {
    _libraryElement.topLevelVariables = _reader.readTypedList(() {
      var reference = _referenceReader.readTopLevelReference(_reader);
      var fragments = _readFragmentsById<TopLevelVariableFragmentImpl>();
      var element = TopLevelVariableElementImpl(reference, fragments.first);
      element.linkFragments(fragments);
      element.previousFragmentOfDifferentKind = _readOptionalFragmentById();
      element.readFlags(_reader);
      element.typeInferenceError = _readTopLevelInferenceError();

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          element.type = reader.readRequiredType();
        }),
      );

      return element;
    });
  }

  List<TopLevelVariableFragmentImpl> _readTopLevelVariableFragments() {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = TopLevelVariableFragmentImpl(name: name);
          fragment.readFlags(_reader);
          return fragment;
        },
        readResolution: (fragment, reader) {
          reader.currentLibraryFragment = fragment.libraryFragment;
          fragment.metadata = reader._readMetadata();
          if (reader.readOptionalExpression() case var initializer?) {
            fragment.constantInitializer = initializer;
            ConstantContextForExpressionImpl(fragment, initializer);
          }
        },
      );
    });
  }

  void _readTypeAliasElements() {
    _libraryElement.typeAliases = _reader.readTypedList(() {
      var reference = _referenceReader.readTopLevelReference(_reader);
      var fragment = _readFragmentById<TypeAliasFragmentImpl>();
      var element = TypeAliasElementImpl(reference, fragment);
      element.readFlags(_reader);

      element.deferReadResolution(
        _createDeferredReadResolutionCallback((reader) {
          reader._addTypeParameterElements(element.typeParameters);
          _readTypeParameterElementResolutions(reader, element.typeParameters);
          element.aliasedType = reader.readRequiredType();
        }),
      );

      return element;
    });
  }

  List<TypeAliasFragmentImpl> _readTypeAliasFragments(
    LibraryFragmentImpl libraryFragment,
  ) {
    return _reader.readTypedList(() {
      return _readTemplateFragment(
        create: (name) {
          var fragment = TypeAliasFragmentImpl(
            name: name,
            firstTokenOffset: null,
          );

          fragment.readFlags(_reader);
          fragment.typeParameters = _readTypeParameterFragments();
          return fragment;
        },
        readResolution: (fragment, reader) {
          _readTypeParameterFragmentsResolution(
            fragment.libraryFragment,
            reader,
            fragment.typeParameters,
          );
          fragment.metadata = reader._readMetadata();
        },
      );
    });
  }

  void _readTypeParameterElementResolutions(
    ResolutionReader reader,
    List<TypeParameterElementImpl> elements,
  ) {
    for (var element in elements) {
      var varianceEncoding = reader.readByte();
      element.variance = _decodeVariance(varianceEncoding);
      element.bound = reader.readType();
      element.defaultType = reader.readType();
    }
  }

  List<TypeParameterFragmentImpl> _readTypeParameterFragments() {
    return _reader.readTypedList(() {
      var fragmentName = _readFragmentName();
      var fragment = TypeParameterFragmentImpl(name: fragmentName);
      fragment.readFlags(_reader);
      return fragment;
    });
  }

  void _readTypeParameterFragmentsResolution(
    LibraryFragmentImpl libraryFragment,
    ResolutionReader reader,
    List<TypeParameterFragmentImpl> fragments,
  ) {
    reader._addTypeParameterFragments(fragments);
    for (var fragment in fragments) {
      fragment.metadata = reader._readMetadata();
    }
  }

  void _readVariableGetterSetterLinking() {
    _reader.readTypedList(() {
      var variable =
          _referenceReader.readReference(_reader).element
              as PropertyInducingElementImpl;

      var optionalGetter = _readOptionalReference()?.element;
      if (optionalGetter != null) {
        var getter = optionalGetter as GetterElementImpl;
        variable.getter = getter;
        getter.variable = variable;
      }

      var optionalSetter = _readOptionalReference()?.element;
      if (optionalSetter != null) {
        var setter = optionalSetter as SetterElementImpl;
        variable.setter = setter;
        setter.variable = variable;
      }

      for (var variableFragment in variable.internal.fragments) {
        var getterFragment = _readOptionalFragmentById() as GetterFragmentImpl?;
        if (getterFragment != null) {
          variableFragment.inducedGetter = getterFragment;
        }

        var setterFragment = _readOptionalFragmentById() as SetterFragmentImpl?;
        if (setterFragment != null) {
          variableFragment.inducedSetter = setterFragment;
        }
      }
    });
  }

  static Variance? _decodeVariance(int index) {
    var tag = TypeParameterVarianceTag.values[index];
    switch (tag) {
      case TypeParameterVarianceTag.legacy:
        return null;
      case TypeParameterVarianceTag.unrelated:
        return Variance.unrelated;
      case TypeParameterVarianceTag.covariant:
        return Variance.covariant;
      case TypeParameterVarianceTag.contravariant:
        return Variance.contravariant;
      case TypeParameterVarianceTag.invariant:
        return Variance.invariant;
    }
  }
}

/// Helper for reading elements and types from their binary encoding.
class ResolutionReader {
  final LinkedElementFactory _elementFactory;
  final ReferenceTableReader _referenceReader;
  final BinaryReader _reader;

  late LibraryFragmentImpl currentLibraryFragment;

  /// The stack of [TypeParameterElementImpl]s and [FormalParameterElementImpl]s
  /// that are available in the scope of [readElement] and [readType].
  ///
  /// This stack is shared with the client of the reader, and update mostly
  /// by the client. However it is also updated during [_readFunctionType].
  final List<ElementImpl> _localElements = [];

  ResolutionReader(this._elementFactory, this._referenceReader, this._reader);

  LibraryElementImpl libraryOfUri(Uri uri) {
    return _elementFactory.libraryOfUri2(uri);
  }

  bool readBool() {
    return _reader.readBool();
  }

  int readByte() {
    return _reader.readByte();
  }

  InternalConstructorElement? readConstructorElementMixin() {
    return readElement() as InternalConstructorElement?;
  }

  double readDouble() {
    return _reader.readDouble();
  }

  Element? readElement() {
    var kind = readEnum(ElementTag.values);
    switch (kind) {
      case ElementTag.null_:
        return null;
      case ElementTag.dynamic_:
        return DynamicElementImpl.instance;
      case ElementTag.never_:
        return NeverElementImpl.instance;
      case ElementTag.multiplyDefined:
        return null;
      case ElementTag.memberWithTypeArguments:
        var elementImpl = readElement() as ElementImpl;
        var enclosing = elementImpl.enclosingElement as InstanceElementImpl;

        var typeArguments = _readTypeList();
        var substitution = Substitution.fromPairs2(
          enclosing.typeParameters,
          typeArguments,
        );

        if (elementImpl is ExecutableElementImpl) {
          return elementImpl.substitute(substitution);
        } else {
          elementImpl as FieldElementImpl;
          return elementImpl.substitute(substitution);
        }
      case ElementTag.elementImpl:
        var reference = _referenceReader.readReference(_reader);
        return _elementFactory.elementOfReference3(reference);
      case ElementTag.libraryImportPrefix:
        var fragmentUri = _reader.readUri();
        var prefixId = _reader.readStringReference();
        return currentLibraryFragment.element.fragments
            .singleWhere((fragment) => fragment.source.uri == fragmentUri)
            .libraryImportPrefixById(prefixId);
      case ElementTag.typeParameter:
        var index = _reader.readUint30();
        return _localElements[index] as TypeParameterElementImpl;
      case ElementTag.formalParameter:
        var enclosing = readElement() as ExecutableElementImpl;
        var index = _reader.readUint30();
        return enclosing.formalParametersIncludingRecovery[index];
    }
  }

  List<T> readElementList<T extends Element>() {
    return _reader.readTypedListCast<T>(readElement);
  }

  T readEnum<T extends Enum>(List<T> values) {
    return _reader.readEnum(values);
  }

  Map<K, V> readMap<K, V>({
    required K Function() readKey,
    required V Function() readValue,
  }) {
    return _reader.readMap(readKey: readKey, readValue: readValue);
  }

  MetadataImpl readMetadata() {
    return _readMetadata();
  }

  List<T> readNodeList<T>() {
    return _readNodeList();
  }

  List<T>? readOptionalElementList<T extends Element>() {
    return _reader.readOptionalObject(readElementList);
  }

  ExpressionImpl? readOptionalExpression() {
    if (_reader.readBool()) {
      return _readRequiredNode() as ExpressionImpl;
    } else {
      return null;
    }
  }

  FunctionTypeImpl? readOptionalFunctionType() {
    var type = readType();
    return type is FunctionTypeImpl ? type : null;
  }

  T? readOptionalObject<T>(T Function() read) {
    return _reader.readOptionalObject(read);
  }

  List<TypeImpl>? readOptionalTypeList() {
    if (_reader.readBool()) {
      return _readTypeList();
    } else {
      return null;
    }
  }

  TypeImpl readRequiredType() {
    return readType()!;
  }

  SourceRange readSourceRange() {
    var offset = readUint30();
    var length = readUint30();
    return SourceRange(offset, length);
  }

  String readStringReference() {
    return _reader.readStringReference();
  }

  List<String> readStringReferenceList() {
    return _reader.readStringReferenceList();
  }

  TypeImpl? readType() {
    var tag = readEnum(TypeTag.values);
    switch (tag) {
      case TypeTag.NullType:
        return null;
      case TypeTag.DynamicType:
        var type = DynamicTypeImpl.instance;
        return _readAliasElementArguments(type);
      case TypeTag.FunctionType:
        var type = _readFunctionType();
        return _readAliasElementArguments(type);
      case TypeTag.InterfaceType:
        var element = readElement() as InterfaceElementImpl;
        var typeArguments = _readTypeList();
        var nullability = _readNullability();
        var type = element.instantiateImpl(
          typeArguments: typeArguments,
          nullabilitySuffix: nullability,
        );
        return _readAliasElementArguments(type);
      case TypeTag.InterfaceType_noTypeArguments_none:
        var element = readElement() as InterfaceElementImpl;
        var type = element.instantiateImpl(
          typeArguments: const [],
          nullabilitySuffix: NullabilitySuffix.none,
        );
        return _readAliasElementArguments(type);
      case TypeTag.InterfaceType_noTypeArguments_question:
        var element = readElement() as InterfaceElementImpl;
        var type = element.instantiateImpl(
          typeArguments: const [],
          nullabilitySuffix: NullabilitySuffix.question,
        );
        return _readAliasElementArguments(type);
      case TypeTag.InvalidType:
        var type = InvalidTypeImpl.instance;
        return _readAliasElementArguments(type);
      case TypeTag.NeverType:
        var nullability = _readNullability();
        var type = NeverTypeImpl.instance.withNullability(nullability);
        return _readAliasElementArguments(type);
      case TypeTag.RecordType:
        var type = _readRecordType();
        return _readAliasElementArguments(type);
      case TypeTag.TypeParameterType:
        var element = readElement() as TypeParameterElementImpl;
        var nullability = _readNullability();
        var type = element.instantiate(nullabilitySuffix: nullability);
        return _readAliasElementArguments(type);
      case TypeTag.VoidType:
        var type = VoidTypeImpl.instance;
        return _readAliasElementArguments(type);
    }
  }

  List<T> readTypedList<T>(T Function() read) {
    return _reader.readTypedList(read);
  }

  int readUint30() {
    return _reader.readUint30();
  }

  int readUint32() {
    return _reader.readUint32();
  }

  void setOffset(int offset) {
    _reader.offset = offset;
  }

  void _addTypeParameterElements(
    List<TypeParameterElementImpl> typeParameters,
  ) {
    for (var typeParameter in typeParameters) {
      _localElements.add(typeParameter);
    }
  }

  void _addTypeParameterFragments(
    List<TypeParameterFragmentImpl> typeParameters,
  ) {
    for (var typeParameter in typeParameters) {
      // TODO(scheglov): review later
      _localElements.add(typeParameter.element);
    }
  }

  TypeImpl _readAliasElementArguments(TypeImpl type) {
    var aliasElement = readElement();
    if (aliasElement != null) {
      aliasElement as TypeAliasElementImpl;
      var alias = InstantiatedTypeAliasElementImpl(
        element: aliasElement,
        typeArguments: _readTypeList(),
        nullabilitySuffix: _readNullability(),
      );
      return type.withAlias(alias);
    }
    return type;
  }

  /// Read the formal parameter list for a function type annotation or type
  /// alias of a function type.
  List<FormalParameterFragmentImpl> _readFormalParameterFragments(
    LibraryFragmentImpl? libraryFragment,
  ) {
    return readTypedList(() {
      var fragment = FormalParameterFragmentImpl(
        name: _readFragmentName(),
        nameOffset: null,
        parameterKind: _formalParameterKind(_reader.readByte()),
      );
      fragment.initElement();
      fragment.element.type = readRequiredType();
      return fragment;
    });
  }

  String? _readFragmentName() {
    return _reader.readOptionalStringReference();
  }

  // TODO(scheglov): Optimize for write/read of types without type parameters.
  FunctionTypeImpl _readFunctionType() {
    // TODO(scheglov): reuse for formal parameters
    var typeParameters = _readTypeParameterFragments(null);
    var returnType = readRequiredType();
    var formalParameters = _readFormalParameterFragments(null);

    var nullability = _readNullability();

    _localElements.length -= typeParameters.length;

    return FunctionTypeImpl(
      typeParameters: typeParameters.map((f) => f.asElement2).toList(),
      formalParameters: formalParameters.map((f) => f.asElement2).toList(),
      returnType: returnType,
      nullabilitySuffix: nullability,
    );
  }

  InterfaceTypeImpl _readInterfaceType() {
    return readType() as InterfaceTypeImpl;
  }

  List<InterfaceTypeImpl> _readInterfaceTypeList() {
    return readTypedList(_readInterfaceType);
  }

  MetadataImpl _readMetadata() {
    var annotations = readTypedList(() {
      var ast = _readRequiredNode() as AnnotationImpl;
      return ElementAnnotationImpl(currentLibraryFragment, ast);
    });

    return MetadataImpl(annotations);
  }

  List<T> _readNodeList<T>() {
    return readTypedList(() {
      return _readRequiredNode() as T;
    });
  }

  NullabilitySuffix _readNullability() {
    var index = _reader.readByte();
    return NullabilitySuffix.values[index];
  }

  InterfaceTypeImpl? _readOptionalInterfaceType() {
    return readType() as InterfaceTypeImpl?;
  }

  RecordTypeImpl _readRecordType() {
    var positionalFields = readTypedList(() {
      return RecordTypePositionalFieldImpl(type: readRequiredType());
    });

    var namedFields = readTypedList(() {
      return RecordTypeNamedFieldImpl(
        name: _reader.readStringReference(),
        type: readRequiredType(),
      );
    });

    var nullabilitySuffix = _readNullability();

    return RecordTypeImpl(
      positionalFields: positionalFields,
      namedFields: namedFields,
      nullabilitySuffix: nullabilitySuffix,
    );
  }

  AstNode _readRequiredNode() {
    var astReader = AstBinaryReader(reader: this);
    return astReader.readNode();
  }

  List<TypeImpl> _readTypeList() {
    return readTypedList(() {
      return readRequiredType();
    });
  }

  List<TypeParameterFragmentImpl> _readTypeParameterFragments(
    LibraryFragmentImpl? libraryFragment,
  ) {
    var typeParameters = readTypedList(() {
      var fragmentName = _readFragmentName();
      var typeParameterFragment = TypeParameterFragmentImpl(name: fragmentName);
      var typeParameterElement = TypeParameterElementImpl(
        firstFragment: typeParameterFragment,
      );
      _localElements.add(typeParameterElement);
      // TODO(scheglov): why not element?
      return typeParameterFragment;
    });

    for (var typeParameter in typeParameters) {
      typeParameter.element.bound = readType();
      if (libraryFragment != null) {
        typeParameter.metadata = _readMetadata();
      }
    }
    return typeParameters;
  }

  static ParameterKind _formalParameterKind(int encoding) {
    if (encoding == Tag.ParameterKindRequiredPositional) {
      return ParameterKind.REQUIRED;
    } else if (encoding == Tag.ParameterKindOptionalPositional) {
      return ParameterKind.POSITIONAL;
    } else if (encoding == Tag.ParameterKindRequiredNamed) {
      return ParameterKind.NAMED_REQUIRED;
    } else if (encoding == Tag.ParameterKindOptionalNamed) {
      return ParameterKind.NAMED;
    } else {
      throw StateError('Unexpected parameter kind encoding: $encoding');
    }
  }
}

/// Information that we need to know about each library before reading it,
/// and without reading it.
///
/// Specifically, the [offset] allows us to know the location of each library,
/// so that when we need to read this library, we know where it starts without
/// reading previous libraries.
class _LibraryHeader {
  final Uri uri;
  final int offset;

  _LibraryHeader({required this.uri, required this.offset});
}