// Copyright (c) 2016, 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:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/visitor.dart';

/**
 * Compute the set of external names referenced in the [unit].
 */
Set<String> computeReferencedNames(CompilationUnit unit) {
  _ReferencedNamesComputer computer = new _ReferencedNamesComputer();
  unit.accept(computer);
  return computer.names;
}

/**
 * Chained set of local names, that hide corresponding external names.
 */
class _LocalNameScope {
  final _LocalNameScope enclosing;
  Set<String> names;

  _LocalNameScope(this.enclosing);

  factory _LocalNameScope.forBlock(_LocalNameScope enclosing, Block node) {
    _LocalNameScope scope = new _LocalNameScope(enclosing);
    for (Statement statement in node.statements) {
      if (statement is FunctionDeclarationStatement) {
        scope.add(statement.functionDeclaration.name);
      } else if (statement is VariableDeclarationStatement) {
        scope.addVariableNames(statement.variables);
      }
    }
    return scope;
  }

  factory _LocalNameScope.forClass(
      _LocalNameScope enclosing, ClassDeclaration node) {
    _LocalNameScope scope = new _LocalNameScope(enclosing);
    scope.addTypeParameters(node.typeParameters);
    for (ClassMember member in node.members) {
      if (member is FieldDeclaration) {
        scope.addVariableNames(member.fields);
      } else if (member is MethodDeclaration) {
        scope.add(member.name);
      }
    }
    return scope;
  }

  factory _LocalNameScope.forClassTypeAlias(
      _LocalNameScope enclosing, ClassTypeAlias node) {
    _LocalNameScope scope = new _LocalNameScope(enclosing);
    scope.addTypeParameters(node.typeParameters);
    return scope;
  }

  factory _LocalNameScope.forConstructor(
      _LocalNameScope enclosing, ConstructorDeclaration node) {
    _LocalNameScope scope = new _LocalNameScope(enclosing);
    scope.addFormalParameters(node.parameters);
    return scope;
  }

  factory _LocalNameScope.forFunction(
      _LocalNameScope enclosing, FunctionDeclaration node) {
    _LocalNameScope scope = new _LocalNameScope(enclosing);
    scope.addTypeParameters(node.functionExpression.typeParameters);
    scope.addFormalParameters(node.functionExpression.parameters);
    return scope;
  }

  factory _LocalNameScope.forFunctionTypeAlias(
      _LocalNameScope enclosing, FunctionTypeAlias node) {
    _LocalNameScope scope = new _LocalNameScope(enclosing);
    scope.addTypeParameters(node.typeParameters);
    return scope;
  }

  factory _LocalNameScope.forMethod(
      _LocalNameScope enclosing, MethodDeclaration node) {
    _LocalNameScope scope = new _LocalNameScope(enclosing);
    scope.addTypeParameters(node.typeParameters);
    scope.addFormalParameters(node.parameters);
    return scope;
  }

  factory _LocalNameScope.forUnit(CompilationUnit node) {
    _LocalNameScope scope = new _LocalNameScope(null);
    for (CompilationUnitMember declaration in node.declarations) {
      if (declaration is NamedCompilationUnitMember) {
        scope.add(declaration.name);
      } else if (declaration is TopLevelVariableDeclaration) {
        scope.addVariableNames(declaration.variables);
      }
    }
    return scope;
  }

  void add(SimpleIdentifier identifier) {
    if (identifier != null) {
      names ??= new Set<String>();
      names.add(identifier.name);
    }
  }

  void addFormalParameters(FormalParameterList parameterList) {
    if (parameterList != null) {
      parameterList.parameters
          .map((p) => p is NormalFormalParameter ? p.identifier : null)
          .forEach(add);
    }
  }

  void addTypeParameters(TypeParameterList typeParameterList) {
    if (typeParameterList != null) {
      typeParameterList.typeParameters.map((p) => p.name).forEach(add);
    }
  }

  void addVariableNames(VariableDeclarationList variableList) {
    for (VariableDeclaration variable in variableList.variables) {
      add(variable.name);
    }
  }

  bool contains(String name) {
    if (names != null && names.contains(name)) {
      return true;
    }
    if (enclosing != null) {
      return enclosing.contains(name);
    }
    return false;
  }
}

class _ReferencedNamesComputer extends GeneralizingAstVisitor {
  final Set<String> names = new Set<String>();
  final Set<String> importPrefixNames = new Set<String>();

  _LocalNameScope localScope = new _LocalNameScope(null);

  @override
  visitBlock(Block node) {
    _LocalNameScope outerScope = localScope;
    try {
      localScope = new _LocalNameScope.forBlock(localScope, node);
      super.visitBlock(node);
    } finally {
      localScope = outerScope;
    }
  }

  @override
  visitClassDeclaration(ClassDeclaration node) {
    _LocalNameScope outerScope = localScope;
    try {
      localScope = new _LocalNameScope.forClass(localScope, node);
      super.visitClassDeclaration(node);
    } finally {
      localScope = outerScope;
    }
  }

  @override
  visitClassTypeAlias(ClassTypeAlias node) {
    _LocalNameScope outerScope = localScope;
    try {
      localScope = new _LocalNameScope.forClassTypeAlias(localScope, node);
      super.visitClassTypeAlias(node);
    } finally {
      localScope = outerScope;
    }
  }

  @override
  visitCompilationUnit(CompilationUnit node) {
    localScope = new _LocalNameScope.forUnit(node);
    super.visitCompilationUnit(node);
  }

  @override
  visitConstructorDeclaration(ConstructorDeclaration node) {
    _LocalNameScope outerScope = localScope;
    try {
      localScope = new _LocalNameScope.forConstructor(localScope, node);
      super.visitConstructorDeclaration(node);
    } finally {
      localScope = outerScope;
    }
  }

  @override
  visitConstructorName(ConstructorName node) {
    if (node.parent is! ConstructorDeclaration) {
      super.visitConstructorName(node);
    }
  }

  @override
  visitFunctionDeclaration(FunctionDeclaration node) {
    _LocalNameScope outerScope = localScope;
    try {
      localScope = new _LocalNameScope.forFunction(localScope, node);
      super.visitFunctionDeclaration(node);
    } finally {
      localScope = outerScope;
    }
  }

  @override
  visitFunctionTypeAlias(FunctionTypeAlias node) {
    _LocalNameScope outerScope = localScope;
    try {
      localScope = new _LocalNameScope.forFunctionTypeAlias(localScope, node);
      super.visitFunctionTypeAlias(node);
    } finally {
      localScope = outerScope;
    }
  }

  @override
  visitImportDirective(ImportDirective node) {
    if (node.prefix != null) {
      importPrefixNames.add(node.prefix.name);
    }
    super.visitImportDirective(node);
  }

  @override
  visitMethodDeclaration(MethodDeclaration node) {
    _LocalNameScope outerScope = localScope;
    try {
      localScope = new _LocalNameScope.forMethod(localScope, node);
      super.visitMethodDeclaration(node);
    } finally {
      localScope = outerScope;
    }
  }

  @override
  visitSimpleIdentifier(SimpleIdentifier node) {
    // Ignore all declarations.
    if (node.inDeclarationContext()) {
      return;
    }
    // Ignore class names references from constructors.
    AstNode parent = node.parent;
    if (parent is ConstructorDeclaration && parent.returnType == node) {
      return;
    }
    // Prepare name.
    String name = node.name;
    // Ignore names shadowed by local elements.
    if (node.isQualified || _isNameExpressionLabel(parent)) {
      // Cannot be local.
    } else {
      if (localScope.contains(name)) {
        return;
      }
      if (importPrefixNames.contains(name)) {
        return;
      }
    }
    // Do add the name.
    names.add(name);
  }

  static bool _isNameExpressionLabel(AstNode parent) {
    if (parent is Label) {
      AstNode parent2 = parent?.parent;
      return parent2 is NamedExpression && parent2.name == parent;
    }
    return false;
  }
}