// Copyright (c) 2014, 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 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
import 'package:analysis_server/src/services/completion/dart/completion_manager.dart';
import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
import 'package:analysis_server/src/utilities/extensions/ast.dart';
import 'package:analyzer/dart/analysis/features.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/token.dart';
import 'package:analyzer/dart/ast/visitor.dart';
import 'package:analyzer/src/dart/ast/token.dart';
import 'package:analyzer_plugin/src/utilities/completion/optype.dart';

const ASYNC_STAR = 'async*';
const DEFAULT_COLON = 'default:';
const DEFERRED_AS = 'deferred as';
const EXPORT_STATEMENT = "export '';";
const IMPORT_STATEMENT = "import '';";
const PART_STATEMENT = "part '';";
const SYNC_STAR = 'sync*';
const YIELD_STAR = 'yield*';

/// A contributor that produces suggestions based on the set of keywords that
/// are valid at the completion point.
class KeywordContributor extends DartCompletionContributor {
  @override
  Future<void> computeSuggestions(
      DartCompletionRequest request, SuggestionBuilder builder) async {
    // Don't suggest anything right after double or integer literals.
    if (request.target.isDoubleOrIntLiteral()) {
      return;
    }
    request.target.containingNode.accept(_KeywordVisitor(request, builder));
  }
}

/// A visitor for generating keyword suggestions.
class _KeywordVisitor extends GeneralizingAstVisitor<void> {
  final DartCompletionRequest request;

  final SuggestionBuilder builder;

  final Object entity;

  _KeywordVisitor(this.request, this.builder) : entity = request.target.entity;

  int get defaultKeyword =>
      request.useNewRelevance ? 800 : DART_RELEVANCE_KEYWORD;

  Token get droppedToken => request.target.droppedToken;

  int get highKeyword => request.useNewRelevance ? 1000 : DART_RELEVANCE_HIGH;

  int get lowKeyword =>
      request.useNewRelevance ? 400 : DART_RELEVANCE_KEYWORD - 1;

  @override
  void visitArgumentList(ArgumentList node) {
    if (request is DartCompletionRequestImpl) {
      if (request.opType.includeOnlyNamedArgumentSuggestions) {
        return;
      }
    }
    if (entity == node.rightParenthesis) {
      _addExpressionKeywords(node);
      var previous = node.findPrevious(entity as Token);
      if (previous != null && previous.isSynthetic) {
        previous = node.findPrevious(previous);
      }
      if (previous != null && previous.lexeme == ')') {
        _addSuggestion(Keyword.ASYNC);
        _addSuggestion2(ASYNC_STAR);
        _addSuggestion2(SYNC_STAR);
      }
    }
    if (entity is SimpleIdentifier && node.arguments.contains(entity)) {
      _addExpressionKeywords(node);
      var index = node.arguments.indexOf(entity);
      if (index > 0) {
        var previousArgument = node.arguments[index - 1];
        var endToken = previousArgument?.endToken;
        if (endToken?.lexeme == ')' &&
            endToken.next?.lexeme == ',' &&
            endToken.next.isSynthetic) {
          _addSuggestion(Keyword.ASYNC);
          _addSuggestion2(ASYNC_STAR);
          _addSuggestion2(SYNC_STAR);
        }
      }
    }
  }

  @override
  void visitAsExpression(AsExpression node) {
    if (identical(entity, node.asOperator) &&
        node.expression is ParenthesizedExpression) {
      _addSuggestion(Keyword.ASYNC, relevance: highKeyword);
      _addSuggestion2(ASYNC_STAR, relevance: highKeyword);
      _addSuggestion2(SYNC_STAR, relevance: highKeyword);
    }
  }

  @override
  void visitBlock(Block node) {
    var prevStmt = OpType.getPreviousStatement(node, entity);
    if (prevStmt is TryStatement) {
      if (prevStmt.finallyBlock == null) {
        _addSuggestion(Keyword.ON);
        _addSuggestion(Keyword.CATCH);
        _addSuggestion(Keyword.FINALLY);
        if (prevStmt.catchClauses.isEmpty) {
          // If try statement with no catch, on, or finally
          // then only suggest these keywords
          return;
        }
      }
    }

    if (entity is ExpressionStatement) {
      var expression = (entity as ExpressionStatement).expression;
      if (expression is SimpleIdentifier) {
        var token = expression.token;
        var previous = node.findPrevious(token);
        if (previous != null && previous.isSynthetic) {
          previous = node.findPrevious(previous);
        }
        var next = token.next;
        if (next.isSynthetic) {
          next = next.next;
        }
        if (previous != null &&
            previous.type == TokenType.CLOSE_PAREN &&
            next.type == TokenType.OPEN_CURLY_BRACKET) {
          _addSuggestion(Keyword.ASYNC);
          _addSuggestion2(ASYNC_STAR);
          _addSuggestion2(SYNC_STAR);
        }
      }
    }
    _addStatementKeywords(node);
    if (node.inCatchClause) {
      _addSuggestion(Keyword.RETHROW, relevance: lowKeyword);
    }
  }

  @override
  void visitClassDeclaration(ClassDeclaration node) {
    // Don't suggest class name
    if (entity == node.name) {
      return;
    }
    if (entity == node.rightBracket) {
      _addClassBodyKeywords();
    } else if (entity is ClassMember) {
      _addClassBodyKeywords();
      var index = node.members.indexOf(entity);
      var previous = index > 0 ? node.members[index - 1] : null;
      if (previous is MethodDeclaration && previous.body.isEmpty) {
        _addSuggestion(Keyword.ASYNC);
        _addSuggestion2(ASYNC_STAR);
        _addSuggestion2(SYNC_STAR);
      }
    } else {
      _addClassDeclarationKeywords(node);
    }
  }

  @override
  void visitCompilationUnit(CompilationUnit node) {
    var previousMember;
    for (var member in node.childEntities) {
      if (entity == member) {
        break;
      }
      previousMember = member;
    }
    if (previousMember is ClassDeclaration) {
      if (previousMember.leftBracket == null ||
          previousMember.leftBracket.isSynthetic) {
        // If the prior member is an unfinished class declaration
        // then the user is probably finishing that.
        _addClassDeclarationKeywords(previousMember);
        return;
      }
    }
    if (previousMember is ExtensionDeclaration) {
      if (previousMember.leftBracket == null ||
          previousMember.leftBracket.isSynthetic) {
        // If the prior member is an unfinished extension declaration then the
        // user is probably finishing that.
        _addExtensionDeclarationKeywords(previousMember);
        return;
      }
    }
    if (previousMember is MixinDeclaration) {
      if (previousMember.leftBracket == null ||
          previousMember.leftBracket.isSynthetic) {
        // If the prior member is an unfinished mixin declaration
        // then the user is probably finishing that.
        _addMixinDeclarationKeywords(previousMember);
        return;
      }
    }
    if (previousMember is ImportDirective) {
      if (previousMember.semicolon == null ||
          previousMember.semicolon.isSynthetic) {
        // If the prior member is an unfinished import directive
        // then the user is probably finishing that
        _addImportDirectiveKeywords(previousMember);
        return;
      }
    }
    if (previousMember == null || previousMember is Directive) {
      if (previousMember == null &&
          !node.directives.any((d) => d is LibraryDirective)) {
        _addSuggestions([Keyword.LIBRARY], relevance: highKeyword);
      }
      _addSuggestion2(IMPORT_STATEMENT, offset: 8, relevance: highKeyword);
      _addSuggestion2(EXPORT_STATEMENT, offset: 8, relevance: highKeyword);
      _addSuggestion2(PART_STATEMENT, offset: 6, relevance: highKeyword);
    }
    if (entity == null || entity is Declaration) {
      if (previousMember is FunctionDeclaration &&
          previousMember.functionExpression is FunctionExpression &&
          previousMember.functionExpression.body.isEmpty) {
        _addSuggestion(Keyword.ASYNC, relevance: highKeyword);
        _addSuggestion2(ASYNC_STAR, relevance: highKeyword);
        _addSuggestion2(SYNC_STAR, relevance: highKeyword);
      }
      _addCompilationUnitKeywords();
    }
  }

  @override
  void visitConstructorDeclaration(ConstructorDeclaration node) {
    if (node.initializers.isNotEmpty) {
      if (entity is ConstructorInitializer) {
        _addSuggestion(Keyword.ASSERT);
      }
      var last = node.initializers.last;
      if (last == entity) {
        var previous = node.findPrevious(last.beginToken);
        if (previous != null && previous.end <= request.offset) {
          _addSuggestion(Keyword.SUPER);
          _addSuggestion(Keyword.THIS);
        }
      }
    } else {
      var separator = node.separator;
      if (separator != null) {
        var offset = request.offset;
        if (separator.end <= offset && offset <= separator.next.offset) {
          _addSuggestion(Keyword.ASSERT);
          _addSuggestion(Keyword.SUPER);
          _addSuggestion(Keyword.THIS);
        }
      }
    }
  }

  @override
  void visitDefaultFormalParameter(DefaultFormalParameter node) {
    if (entity == node.defaultValue) {
      _addExpressionKeywords(node);
    }
  }

  @override
  void visitExpression(Expression node) {
    _addExpressionKeywords(node);
  }

  @override
  void visitExpressionFunctionBody(ExpressionFunctionBody node) {
    if (entity == node.expression) {
      _addExpressionKeywords(node);
    }
  }

  @override
  void visitExtensionDeclaration(ExtensionDeclaration node) {
    // Don't suggest extension name
    if (entity == node.name) {
      return;
    }
    if (entity == node.rightBracket) {
      _addExtensionBodyKeywords();
    } else if (entity is ClassMember) {
      _addExtensionBodyKeywords();
    } else {
      _addExtensionDeclarationKeywords(node);
    }
  }

  @override
  void visitFieldDeclaration(FieldDeclaration node) {
    var fields = node.fields;
    if (entity != fields) {
      return;
    }
    var variables = fields.variables;
    if (variables.isEmpty || request.offset > variables.first.beginToken.end) {
      return;
    }
    if (node.abstractKeyword == null) {
      _addSuggestion(Keyword.ABSTRACT);
    }
    if (node.covariantKeyword == null) {
      _addSuggestion(Keyword.COVARIANT);
    }
    if (node.externalKeyword == null) {
      _addSuggestion(Keyword.EXTERNAL);
    }
    if (node.fields.lateKeyword == null &&
        request.featureSet.isEnabled(Feature.non_nullable)) {
      _addSuggestion(Keyword.LATE);
    }
    if (!node.isStatic) {
      _addSuggestion(Keyword.STATIC);
    }
    if (!variables.first.isConst) {
      _addSuggestion(Keyword.CONST);
    }
    if (!variables.first.isFinal) {
      _addSuggestion(Keyword.FINAL);
    }
  }

  @override
  void visitForEachParts(ForEachParts node) {
    if (entity == node.inKeyword) {
      var previous = node.findPrevious(node.inKeyword);
      if (previous is SyntheticStringToken && previous.lexeme == 'in') {
        previous = node.findPrevious(previous);
      }
      if (previous != null && previous.type == TokenType.EQ) {
        _addSuggestions(
            [Keyword.CONST, Keyword.FALSE, Keyword.NULL, Keyword.TRUE]);
      } else {
        _addSuggestion(Keyword.IN, relevance: highKeyword);
      }
    }
  }

  @override
  void visitForElement(ForElement node) {
    _addCollectionElementKeywords();
    _addExpressionKeywords(node);
    return super.visitForElement(node);
  }

  @override
  void visitFormalParameterList(FormalParameterList node) {
    var constructorDeclaration =
        node.thisOrAncestorOfType<ConstructorDeclaration>();
    if (constructorDeclaration != null) {
      _addSuggestion(Keyword.THIS);
    }
    if (entity is Token && (entity as Token).type == TokenType.CLOSE_PAREN) {
      _addSuggestion(Keyword.COVARIANT);
      _addSuggestion(Keyword.DYNAMIC);
      _addSuggestion(Keyword.VOID);
      if (request.featureSet.isEnabled(Feature.non_nullable)) {
        _addSuggestion(Keyword.REQUIRED);
      }
    } else if (entity is FormalParameter) {
      var beginToken = (entity as FormalParameter).beginToken;
      if (beginToken != null && request.target.offset == beginToken.end) {
        _addSuggestion(Keyword.COVARIANT);
        _addSuggestion(Keyword.DYNAMIC);
        _addSuggestion(Keyword.VOID);
        if (request.featureSet.isEnabled(Feature.non_nullable)) {
          _addSuggestion(Keyword.REQUIRED);
        }
      } else if (entity is FunctionTypedFormalParameter) {
        _addSuggestion(Keyword.COVARIANT);
        _addSuggestion(Keyword.DYNAMIC);
        _addSuggestion(Keyword.VOID);
        if (request.featureSet.isEnabled(Feature.non_nullable)) {
          _addSuggestion(Keyword.REQUIRED);
        }
      }
    }
  }

  @override
  void visitForParts(ForParts node) {
    // Actual: for (int x i^)
    // Parsed: for (int x; i^;)
    // Handle the degenerate case while typing - for (int x i^)
    if (node.condition == entity &&
        entity is SimpleIdentifier &&
        node is ForPartsWithDeclarations &&
        node.variables != null) {
      if (_isPreviousTokenSynthetic(entity, TokenType.SEMICOLON)) {
        _addSuggestion(Keyword.IN, relevance: highKeyword);
      }
    }
  }

  @override
  void visitForStatement(ForStatement node) {
    // Actual: for (va^)
    // Parsed: for (va^; ;)
    if (node.forLoopParts == entity) {
      _addSuggestion(Keyword.VAR, relevance: highKeyword);
    }
  }

  @override
  void visitFunctionDeclaration(FunctionDeclaration node) {
    // If the cursor is at the beginning of the declaration, include the
    // compilation unit keywords.  See dartbug.com/41039.
    if (entity == node.returnType || entity == node.name) {
      _addSuggestion(Keyword.DYNAMIC);
      _addSuggestion(Keyword.VOID);
    }
  }

  @override
  void visitFunctionExpression(FunctionExpression node) {
    if (entity == node.body) {
      var body = node.body;
      if (!body.isAsynchronous) {
        _addSuggestion(Keyword.ASYNC, relevance: highKeyword);
        if (body is! ExpressionFunctionBody) {
          _addSuggestion2(ASYNC_STAR, relevance: highKeyword);
          _addSuggestion2(SYNC_STAR, relevance: highKeyword);
        }
      }
      if (body is EmptyFunctionBody &&
          node.parent is FunctionDeclaration &&
          node.parent.parent is CompilationUnit) {
        _addCompilationUnitKeywords();
      }
    }
  }

  @override
  void visitIfElement(IfElement node) {
    _addCollectionElementKeywords();
    _addExpressionKeywords(node);
    return super.visitIfElement(node);
  }

  @override
  void visitIfStatement(IfStatement node) {
    if (_isPreviousTokenSynthetic(entity, TokenType.CLOSE_PAREN)) {
      // analyzer parser
      // Actual: if (x i^)
      // Parsed: if (x) i^
      _addSuggestion(Keyword.IS, relevance: highKeyword);
    } else if (entity == node.rightParenthesis) {
      if (node.condition.endToken.next == droppedToken) {
        // fasta parser
        // Actual: if (x i^)
        // Parsed: if (x)
        //    where "i" is in the token stream but not part of the AST
        _addSuggestion(Keyword.IS, relevance: highKeyword);
      }
    } else if (entity == node.thenStatement || entity == node.elseStatement) {
      _addStatementKeywords(node);
    } else if (entity == node.condition) {
      _addExpressionKeywords(node);
    }
  }

  @override
  void visitImportDirective(ImportDirective node) {
    if (entity == node.asKeyword) {
      if (node.deferredKeyword == null) {
        _addSuggestion(Keyword.DEFERRED, relevance: highKeyword);
      }
    }
    // Handle degenerate case where import statement does not have a semicolon
    // and the cursor is in the uri string
    if ((entity == node.semicolon &&
            node.uri != null &&
            node.uri.offset + 1 != request.offset) ||
        node.combinators.contains(entity)) {
      _addImportDirectiveKeywords(node);
    }
  }

  @override
  void visitInstanceCreationExpression(InstanceCreationExpression node) {
    if (entity == node.constructorName) {
      // no keywords in 'new ^' expression
    } else {
      super.visitInstanceCreationExpression(node);
    }
  }

  @override
  void visitIsExpression(IsExpression node) {
    if (entity == node.isOperator) {
      _addSuggestion(Keyword.IS, relevance: highKeyword);
    } else {
      _addExpressionKeywords(node);
    }
  }

  @override
  void visitLibraryIdentifier(LibraryIdentifier node) {
    // no suggestions
  }

  @override
  void visitListLiteral(ListLiteral node) {
    _addCollectionElementKeywords();
    super.visitListLiteral(node);
  }

  @override
  void visitMethodDeclaration(MethodDeclaration node) {
    if (entity == node.body) {
      if (node.body.isEmpty) {
        _addClassBodyKeywords();
        _addSuggestion(Keyword.ASYNC);
        _addSuggestion2(ASYNC_STAR);
        _addSuggestion2(SYNC_STAR);
      } else {
        _addSuggestion(Keyword.ASYNC, relevance: highKeyword);
        if (node.body is! ExpressionFunctionBody) {
          _addSuggestion2(ASYNC_STAR, relevance: highKeyword);
          _addSuggestion2(SYNC_STAR, relevance: highKeyword);
        }
      }
    } else if (entity == node.returnType || entity == node.name) {
      // If the cursor is at the beginning of the declaration, include the class
      // body keywords.  See dartbug.com/41039.
      _addClassBodyKeywords();
    }
  }

  @override
  void visitMethodInvocation(MethodInvocation node) {
    if (entity == node.methodName) {
      // no keywords in '.' expressions
    } else if (entity == node.argumentList) {
      // Note that we're checking the argumentList rather than the typeArgumentList
      // as you'd expect. For some reason, when the cursor is in a type argument
      // list (f<^>()), the entity is the invocation's argumentList...
      // See similar logic in `imported_reference_contributor`.

      _addSuggestion(Keyword.DYNAMIC);
      _addSuggestion(Keyword.VOID);
    } else {
      super.visitMethodInvocation(node);
    }
  }

  @override
  void visitMixinDeclaration(MixinDeclaration node) {
    // Don't suggest mixin name
    if (entity == node.name) {
      return;
    }
    if (entity == node.rightBracket) {
      _addClassBodyKeywords();
    } else if (entity is ClassMember) {
      _addClassBodyKeywords();
      var index = node.members.indexOf(entity);
      var previous = index > 0 ? node.members[index - 1] : null;
      if (previous is MethodDeclaration && previous.body.isEmpty) {
        _addSuggestion(Keyword.ASYNC);
        _addSuggestion2(ASYNC_STAR);
        _addSuggestion2(SYNC_STAR);
      }
    } else {
      _addMixinDeclarationKeywords(node);
    }
  }

  @override
  void visitNamedExpression(NamedExpression node) {
    if (entity is SimpleIdentifier && entity == node.expression) {
      _addExpressionKeywords(node);
    }
  }

  @override
  void visitNode(AstNode node) {
    // ignored
  }

  @override
  void visitParenthesizedExpression(ParenthesizedExpression node) {
    var expression = node.expression;
    if (expression is Identifier || expression is PropertyAccess) {
      if (entity == node.rightParenthesis) {
        var next = expression.endToken.next;
        if (next == entity || next == droppedToken) {
          // Fasta parses `if (x i^)` as `if (x ^) where the `i` is in the token
          // stream but not part of the ParenthesizedExpression.
          _addSuggestion(Keyword.IS, relevance: highKeyword);
          return;
        }
      }
    }
    _addExpressionKeywords(node);
  }

  @override
  void visitPrefixedIdentifier(PrefixedIdentifier node) {
    if (entity != node.identifier) {
      _addExpressionKeywords(node);
    }
  }

  @override
  void visitPropertyAccess(PropertyAccess node) {
    // suggestions before '.' but not after
    if (entity != node.propertyName) {
      super.visitPropertyAccess(node);
    }
  }

  @override
  void visitReturnStatement(ReturnStatement node) {
    if (entity == node.expression) {
      _addExpressionKeywords(node);
    }
  }

  @override
  void visitSetOrMapLiteral(SetOrMapLiteral node) {
    _addCollectionElementKeywords();
    super.visitSetOrMapLiteral(node);
  }

  @override
  void visitSpreadElement(SpreadElement node) {
    _addExpressionKeywords(node);
    return super.visitSpreadElement(node);
  }

  @override
  void visitStringLiteral(StringLiteral node) {
    // ignored
  }

  @override
  void visitSwitchCase(SwitchCase node) {
    _addStatementKeywords(node);
    return super.visitSwitchCase(node);
  }

  @override
  void visitSwitchStatement(SwitchStatement node) {
    if (entity == node.expression) {
      _addExpressionKeywords(node);
    } else if (entity == node.rightBracket) {
      if (node.members.isEmpty) {
        _addSuggestion(Keyword.CASE, relevance: highKeyword);
        _addSuggestion2(DEFAULT_COLON, relevance: highKeyword);
      } else {
        _addSuggestion(Keyword.CASE);
        _addSuggestion2(DEFAULT_COLON);
        _addStatementKeywords(node);
      }
    }
    if (node.members.contains(entity)) {
      if (entity == node.members.first) {
        _addSuggestion(Keyword.CASE, relevance: highKeyword);
        _addSuggestion2(DEFAULT_COLON, relevance: highKeyword);
      } else {
        _addSuggestion(Keyword.CASE);
        _addSuggestion2(DEFAULT_COLON);
        _addStatementKeywords(node);
      }
    }
  }

  @override
  void visitTopLevelVariableDeclaration(TopLevelVariableDeclaration node) {
    var variableDeclarationList = node.variables;
    if (entity != variableDeclarationList) return;
    var variables = variableDeclarationList.variables;
    if (variables.isEmpty || request.offset > variables.first.beginToken.end) {
      return;
    }
    if (node.externalKeyword == null) {
      _addSuggestion(Keyword.EXTERNAL);
    }
    if (variableDeclarationList.lateKeyword == null &&
        request.featureSet.isEnabled(Feature.non_nullable)) {
      _addSuggestion(Keyword.LATE);
    }
    if (!variables.first.isConst) {
      _addSuggestion(Keyword.CONST);
    }
    if (!variables.first.isFinal) {
      _addSuggestion(Keyword.FINAL);
    }
  }

  @override
  void visitTryStatement(TryStatement node) {
    var obj = entity;
    if (obj is CatchClause ||
        (obj is KeywordToken && obj.value() == Keyword.FINALLY)) {
      _addSuggestion(Keyword.ON);
      _addSuggestion(Keyword.CATCH);
      return null;
    }
    return visitStatement(node);
  }

  @override
  void visitTypeArgumentList(TypeArgumentList node) {
    _addSuggestion(Keyword.DYNAMIC);
    _addSuggestion(Keyword.VOID);
  }

  @override
  void visitVariableDeclaration(VariableDeclaration node) {
    if (entity == node.initializer) {
      _addExpressionKeywords(node);
    }
  }

  void _addClassBodyKeywords() {
    _addSuggestions([
      Keyword.CONST,
      Keyword.COVARIANT,
      Keyword.DYNAMIC,
      Keyword.FACTORY,
      Keyword.FINAL,
      Keyword.GET,
      Keyword.OPERATOR,
      Keyword.SET,
      Keyword.STATIC,
      Keyword.VAR,
      Keyword.VOID
    ]);
    if (request.featureSet.isEnabled(Feature.non_nullable)) {
      _addSuggestion(Keyword.LATE);
    }
  }

  void _addClassDeclarationKeywords(ClassDeclaration node) {
    // Very simplistic suggestion because analyzer will warn if
    // the extends / with / implements keywords are out of order
    if (node.extendsClause == null) {
      _addSuggestion(Keyword.EXTENDS, relevance: highKeyword);
    } else if (node.withClause == null) {
      _addSuggestion(Keyword.WITH, relevance: highKeyword);
    }
    if (node.implementsClause == null) {
      _addSuggestion(Keyword.IMPLEMENTS, relevance: highKeyword);
    }
  }

  void _addCollectionElementKeywords() {
    if (request.featureSet.isEnabled(Feature.control_flow_collections)) {
      _addSuggestions([
        Keyword.FOR,
        Keyword.IF,
      ]);
    }
  }

  void _addCompilationUnitKeywords() {
    _addSuggestions([
      Keyword.ABSTRACT,
      Keyword.CLASS,
      Keyword.CONST,
      Keyword.COVARIANT,
      Keyword.DYNAMIC,
      Keyword.FINAL,
      Keyword.TYPEDEF,
      Keyword.VAR,
      Keyword.VOID
    ], relevance: highKeyword);
    if (request.featureSet.isEnabled(Feature.extension_methods)) {
      _addSuggestion(Keyword.EXTENSION, relevance: highKeyword);
    }
    if (request.featureSet.isEnabled(Feature.non_nullable)) {
      _addSuggestion(Keyword.LATE, relevance: highKeyword);
    }
  }

  void _addExpressionKeywords(AstNode node) {
    _addSuggestions([
      Keyword.FALSE,
      Keyword.NULL,
      Keyword.TRUE,
    ]);
    if (!request.inConstantContext) {
      _addSuggestions([Keyword.CONST]);
    }
    if (node.inClassMemberBody) {
      _addSuggestions([Keyword.SUPER, Keyword.THIS]);
    }
    if (node.inAsyncMethodOrFunction) {
      _addSuggestion(Keyword.AWAIT);
    }
  }

  void _addExtensionBodyKeywords() {
    _addSuggestions([
      Keyword.CONST,
      Keyword.DYNAMIC,
      Keyword.FINAL,
      Keyword.GET,
      Keyword.OPERATOR,
      Keyword.SET,
      Keyword.STATIC,
      Keyword.VAR,
      Keyword.VOID
    ]);
    if (request.featureSet.isEnabled(Feature.non_nullable)) {
      _addSuggestion(Keyword.LATE);
    }
  }

  void _addExtensionDeclarationKeywords(ExtensionDeclaration node) {
    if (node.onKeyword == null || node.onKeyword.isSynthetic) {
      _addSuggestion(Keyword.ON, relevance: highKeyword);
    }
  }

  void _addImportDirectiveKeywords(ImportDirective node) {
    var hasDeferredKeyword = node.deferredKeyword != null;
    var hasAsKeyword = node.asKeyword != null;
    if (!hasAsKeyword) {
      _addSuggestion(Keyword.AS, relevance: highKeyword);
    }
    if (!hasDeferredKeyword) {
      if (!hasAsKeyword) {
        _addSuggestion2(DEFERRED_AS, relevance: highKeyword);
      } else if (entity == node.asKeyword) {
        _addSuggestion(Keyword.DEFERRED, relevance: highKeyword);
      }
    }
    if (!hasDeferredKeyword || hasAsKeyword) {
      if (node.combinators.isEmpty) {
        _addSuggestion(Keyword.SHOW, relevance: highKeyword);
        _addSuggestion(Keyword.HIDE, relevance: highKeyword);
      }
    }
  }

  void _addMixinDeclarationKeywords(MixinDeclaration node) {
    // Very simplistic suggestion because analyzer will warn if
    // the on / implements clauses are out of order
    if (node.onClause == null) {
      _addSuggestion(Keyword.ON, relevance: highKeyword);
    }
    if (node.implementsClause == null) {
      _addSuggestion(Keyword.IMPLEMENTS, relevance: highKeyword);
    }
  }

  void _addStatementKeywords(AstNode node) {
    if (node.inClassMemberBody) {
      _addSuggestions([Keyword.SUPER, Keyword.THIS]);
    }
    if (node.inAsyncMethodOrFunction) {
      _addSuggestion(Keyword.AWAIT);
    } else if (node.inAsyncStarOrSyncStarMethodOrFunction) {
      _addSuggestion(Keyword.AWAIT);
      _addSuggestion(Keyword.YIELD);
      _addSuggestion2(YIELD_STAR);
    }
    if (node.inLoop) {
      _addSuggestions([Keyword.BREAK, Keyword.CONTINUE]);
    }
    if (node.inSwitch) {
      _addSuggestions([Keyword.BREAK]);
    }
    if (_isEntityAfterIfWithoutElse(node)) {
      _addSuggestions([Keyword.ELSE]);
    }
    _addSuggestions([
      Keyword.ASSERT,
      Keyword.CONST,
      Keyword.DO,
      Keyword.DYNAMIC,
      Keyword.FINAL,
      Keyword.FOR,
      Keyword.IF,
      Keyword.RETURN,
      Keyword.SWITCH,
      Keyword.THROW,
      Keyword.TRY,
      Keyword.VAR,
      Keyword.VOID,
      Keyword.WHILE
    ]);
    if (request.featureSet.isEnabled(Feature.non_nullable)) {
      _addSuggestion(Keyword.LATE);
    }
  }

  void _addSuggestion(Keyword keyword, {int relevance}) {
    _addSuggestion2(keyword.lexeme, relevance: relevance);
  }

  void _addSuggestion2(String keyword, {int offset, int relevance}) {
    builder.suggestKeyword(keyword,
        offset: offset, relevance: relevance ?? defaultKeyword);
  }

  void _addSuggestions(List<Keyword> keywords, {int relevance}) {
    keywords.forEach((Keyword keyword) {
      _addSuggestion(keyword, relevance: relevance);
    });
  }

  bool _isEntityAfterIfWithoutElse(AstNode node) {
    var block = node?.thisOrAncestorOfType<Block>();
    if (block == null) {
      return false;
    }
    var entity = this.entity;
    if (entity is Statement) {
      var entityIndex = block.statements.indexOf(entity);
      if (entityIndex > 0) {
        var prevStatement = block.statements[entityIndex - 1];
        return prevStatement is IfStatement &&
            prevStatement.elseStatement == null;
      }
    }
    if (entity is Token) {
      for (var statement in block.statements) {
        if (statement.endToken.next == entity) {
          return statement is IfStatement && statement.elseStatement == null;
        }
      }
    }
    return false;
  }

  static bool _isPreviousTokenSynthetic(Object entity, TokenType type) {
    if (entity is AstNode) {
      var token = entity.beginToken;
      var previousToken = entity.findPrevious(token);
      return previousToken != null &&
          previousToken.isSynthetic &&
          previousToken.type == type;
    }
    return false;
  }
}