/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import * as ts from 'typescript';

import {ClassDeclaration, ClassMember, ClassMemberKind, Declaration, Decorator, FunctionDefinition, KnownDeclaration, Parameter, reflectObjectLiteral} from '../../../src/ngtsc/reflection';
import {getTsHelperFnFromDeclaration, getTsHelperFnFromIdentifier, hasNameIdentifier} from '../utils';

import {Esm2015ReflectionHost, getClassDeclarationFromInnerDeclaration, getPropertyValueFromSymbol, isAssignmentStatement, ParamInfo} from './esm2015_host';
import {NgccClassSymbol} from './ngcc_host';


/**
 * ESM5 packages contain ECMAScript IIFE functions that act like classes. For example:
 *
 * ```
 * var CommonModule = (function () {
 *  function CommonModule() {
 *  }
 *  CommonModule.decorators = [ ... ];
 *  return CommonModule;
 * ```
 *
 * * "Classes" are decorated if they have a static property called `decorators`.
 * * Members are decorated if there is a matching key on a static property
 *   called `propDecorators`.
 * * Constructor parameters decorators are found on an object returned from
 *   a static method called `ctorParameters`.
 *
 */
export class Esm5ReflectionHost extends Esm2015ReflectionHost {
  getBaseClassExpression(clazz: ClassDeclaration): ts.Expression|null {
    const superBaseClassExpression = super.getBaseClassExpression(clazz);
    if (superBaseClassExpression !== null) {
      return superBaseClassExpression;
    }

    const iife = getIifeFn(this.getClassSymbol(clazz));
    if (iife === null) return null;

    if (iife.parameters.length !== 1 || !isSuperIdentifier(iife.parameters[0].name)) {
      return null;
    }

    if (!ts.isCallExpression(iife.parent)) {
      return null;
    }

    return iife.parent.arguments[0];
  }

  /**
   * Trace an identifier to its declaration, if possible.
   *
   * This method attempts to resolve the declaration of the given identifier, tracing back through
   * imports and re-exports until the original declaration statement is found. A `Declaration`
   * object is returned if the original declaration is found, or `null` is returned otherwise.
   *
   * In ES5, the implementation of a class is a function expression that is hidden inside an IIFE.
   * If we are looking for the declaration of the identifier of the inner function expression, we
   * will get hold of the outer "class" variable declaration and return its identifier instead. See
   * `getClassDeclarationFromInnerFunctionDeclaration()` for more info.
   *
   * @param id a TypeScript `ts.Identifier` to trace back to a declaration.
   *
   * @returns metadata about the `Declaration` if the original declaration is found, or `null`
   * otherwise.
   */
  getDeclarationOfIdentifier(id: ts.Identifier): Declaration|null {
    const declaration = super.getDeclarationOfIdentifier(id);

    if (declaration === null) {
      const nonEmittedNorImportedTsHelperDeclaration = getTsHelperFnFromIdentifier(id);
      if (nonEmittedNorImportedTsHelperDeclaration !== null) {
        // No declaration could be found for this identifier and its name matches a known TS helper
        // function. This can happen if a package is compiled with `noEmitHelpers: true` and
        // `importHelpers: false` (the default). This is, for example, the case with
        // `@nativescript/angular@9.0.0-next-2019-11-12-155500-01`.
        return {
          expression: id,
          known: nonEmittedNorImportedTsHelperDeclaration,
          node: null,
          viaModule: null,
        };
      }
    }

    if (declaration === null || declaration.node === null || declaration.known !== null) {
      return declaration;
    }

    if (!ts.isVariableDeclaration(declaration.node) || declaration.node.initializer !== undefined ||
        // VariableDeclaration => VariableDeclarationList => VariableStatement => IIFE Block
        !ts.isBlock(declaration.node.parent.parent.parent)) {
      return declaration;
    }

    // We might have an alias to another variable declaration.
    // Search the containing iife body for it.
    const block = declaration.node.parent.parent.parent;
    const aliasSymbol = this.checker.getSymbolAtLocation(declaration.node.name);
    for (let i = 0; i < block.statements.length; i++) {
      const statement = block.statements[i];
      // Looking for statement that looks like: `AliasedVariable = OriginalVariable;`
      if (isAssignmentStatement(statement) && ts.isIdentifier(statement.expression.left) &&
          ts.isIdentifier(statement.expression.right) &&
          this.checker.getSymbolAtLocation(statement.expression.left) === aliasSymbol) {
        return this.getDeclarationOfIdentifier(statement.expression.right);
      }
    }

    return declaration;
  }

  /**
   * Parse a function declaration to find the relevant metadata about it.
   *
   * In ESM5 we need to do special work with optional arguments to the function, since they get
   * their own initializer statement that needs to be parsed and then not included in the "body"
   * statements of the function.
   *
   * @param node the function declaration to parse.
   * @returns an object containing the node, statements and parameters of the function.
   */
  getDefinitionOfFunction(node: ts.Node): FunctionDefinition|null {
    const definition = super.getDefinitionOfFunction(node);
    if (definition === null) {
      return null;
    }

    // Filter out and capture parameter initializers
    if (definition.body !== null) {
      let lookingForInitializers = true;
      const statements = definition.body.filter(s => {
        lookingForInitializers =
            lookingForInitializers && captureParamInitializer(s, definition.parameters);
        // If we are no longer looking for parameter initializers then we include this statement
        return !lookingForInitializers;
      });
      definition.body = statements;
    }

    return definition;
  }

  /**
   * Check whether a `Declaration` corresponds with a known declaration, such as a TypeScript helper
   * function, and set its `known` property to the appropriate `KnownDeclaration`.
   *
   * @param decl The `Declaration` to check.
   * @return The passed in `Declaration` (potentially enhanced with a `KnownDeclaration`).
   */
  detectKnownDeclaration<T extends Declaration>(decl: T): T {
    decl = super.detectKnownDeclaration(decl);

    // Also check for TS helpers
    if (decl.known === null && decl.node !== null) {
      decl.known = getTsHelperFnFromDeclaration(decl.node);
    }

    return decl;
  }


  ///////////// Protected Helpers /////////////

  /**
   * In ES5, the implementation of a class is a function expression that is hidden inside an IIFE,
   * whose value is assigned to a variable (which represents the class to the rest of the program).
   * So we might need to dig around to get hold of the "class" declaration.
   *
   * This method extracts a `NgccClassSymbol` if `declaration` is the function declaration inside
   * the IIFE. Otherwise, undefined is returned.
   *
   * @param declaration the declaration whose symbol we are finding.
   * @returns the symbol for the node or `undefined` if it is not a "class" or has no symbol.
   */
  protected getClassSymbolFromInnerDeclaration(declaration: ts.Node): NgccClassSymbol|undefined {
    const classSymbol = super.getClassSymbolFromInnerDeclaration(declaration);
    if (classSymbol !== undefined) {
      return classSymbol;
    }

    if (!ts.isFunctionDeclaration(declaration) || !hasNameIdentifier(declaration)) {
      return undefined;
    }

    const outerDeclaration = getClassDeclarationFromInnerDeclaration(declaration);
    if (outerDeclaration === null || !hasNameIdentifier(outerDeclaration)) {
      return undefined;
    }

    return this.createClassSymbol(outerDeclaration, declaration);
  }

  /**
   * Find the declarations of the constructor parameters of a class identified by its symbol.
   *
   * In ESM5, there is no "class" so the constructor that we want is actually the inner function
   * declaration inside the IIFE, whose return value is assigned to the outer variable declaration
   * (that represents the class to the rest of the program).
   *
   * @param classSymbol the symbol of the class (i.e. the outer variable declaration) whose
   * parameters we want to find.
   * @returns an array of `ts.ParameterDeclaration` objects representing each of the parameters in
   * the class's constructor or `null` if there is no constructor.
   */
  protected getConstructorParameterDeclarations(classSymbol: NgccClassSymbol):
      ts.ParameterDeclaration[]|null {
    const constructor = classSymbol.implementation.valueDeclaration;
    if (!ts.isFunctionDeclaration(constructor)) return null;

    if (constructor.parameters.length > 0) {
      return Array.from(constructor.parameters);
    }

    if (this.isSynthesizedConstructor(constructor)) {
      return null;
    }

    return [];
  }

  /**
   * Get the parameter type and decorators for the constructor of a class,
   * where the information is stored on a static method of the class.
   *
   * In this case the decorators are stored in the body of a method
   * (`ctorParatemers`) attached to the constructor function.
   *
   * Note that unlike ESM2015 this is a function expression rather than an arrow
   * function:
   *
   * ```
   * SomeDirective.ctorParameters = function() { return [
   *   { type: ViewContainerRef, },
   *   { type: TemplateRef, },
   *   { type: IterableDiffers, },
   *   { type: undefined, decorators: [{ type: Inject, args: [INJECTED_TOKEN,] },] },
   * ]; };
   * ```
   *
   * @param paramDecoratorsProperty the property that holds the parameter info we want to get.
   * @returns an array of objects containing the type and decorators for each parameter.
   */
  protected getParamInfoFromStaticProperty(paramDecoratorsProperty: ts.Symbol): ParamInfo[]|null {
    const paramDecorators = getPropertyValueFromSymbol(paramDecoratorsProperty);
    // The decorators array may be wrapped in a function. If so unwrap it.
    const returnStatement = getReturnStatement(paramDecorators);
    const expression = returnStatement ? returnStatement.expression : paramDecorators;
    if (expression && ts.isArrayLiteralExpression(expression)) {
      const elements = expression.elements;
      return elements.map(reflectArrayElement).map(paramInfo => {
        const typeExpression = paramInfo && paramInfo.has('type') ? paramInfo.get('type')! : null;
        const decoratorInfo =
            paramInfo && paramInfo.has('decorators') ? paramInfo.get('decorators')! : null;
        const decorators = decoratorInfo && this.reflectDecorators(decoratorInfo);
        return {typeExpression, decorators};
      });
    } else if (paramDecorators !== undefined) {
      this.logger.warn(
          'Invalid constructor parameter decorator in ' + paramDecorators.getSourceFile().fileName +
              ':\n',
          paramDecorators.getText());
    }
    return null;
  }

  /**
   * Reflect over a symbol and extract the member information, combining it with the
   * provided decorator information, and whether it is a static member.
   *
   * If a class member uses accessors (e.g getters and/or setters) then it gets downleveled
   * in ES5 to a single `Object.defineProperty()` call. In that case we must parse this
   * call to extract the one or two ClassMember objects that represent the accessors.
   *
   * @param symbol the symbol for the member to reflect over.
   * @param decorators an array of decorators associated with the member.
   * @param isStatic true if this member is static, false if it is an instance property.
   * @returns the reflected member information, or null if the symbol is not a member.
   */
  protected reflectMembers(symbol: ts.Symbol, decorators?: Decorator[], isStatic?: boolean):
      ClassMember[]|null {
    const node = symbol.valueDeclaration || symbol.declarations && symbol.declarations[0];
    const propertyDefinition = node && getPropertyDefinition(node);
    if (propertyDefinition) {
      const members: ClassMember[] = [];
      if (propertyDefinition.setter) {
        members.push({
          node,
          implementation: propertyDefinition.setter,
          kind: ClassMemberKind.Setter,
          type: null,
          name: symbol.name,
          nameNode: null,
          value: null,
          isStatic: isStatic || false,
          decorators: decorators || [],
        });

        // Prevent attaching the decorators to a potential getter. In ES5, we can't tell where the
        // decorators were originally attached to, however we only want to attach them to a single
        // `ClassMember` as otherwise ngtsc would handle the same decorators twice.
        decorators = undefined;
      }
      if (propertyDefinition.getter) {
        members.push({
          node,
          implementation: propertyDefinition.getter,
          kind: ClassMemberKind.Getter,
          type: null,
          name: symbol.name,
          nameNode: null,
          value: null,
          isStatic: isStatic || false,
          decorators: decorators || [],
        });
      }
      return members;
    }

    const members = super.reflectMembers(symbol, decorators, isStatic);
    members && members.forEach(member => {
      if (member && member.kind === ClassMemberKind.Method && member.isStatic && member.node &&
          ts.isPropertyAccessExpression(member.node) && member.node.parent &&
          ts.isBinaryExpression(member.node.parent) &&
          ts.isFunctionExpression(member.node.parent.right)) {
        // Recompute the implementation for this member:
        // ES5 static methods are variable declarations so the declaration is actually the
        // initializer of the variable assignment
        member.implementation = member.node.parent.right;
      }
    });
    return members;
  }

  /**
   * Find statements related to the given class that may contain calls to a helper.
   *
   * In ESM5 code the helper calls are hidden inside the class's IIFE.
   *
   * @param classSymbol the class whose helper calls we are interested in. We expect this symbol
   * to reference the inner identifier inside the IIFE.
   * @returns an array of statements that may contain helper calls.
   */
  protected getStatementsForClass(classSymbol: NgccClassSymbol): ts.Statement[] {
    const classDeclarationParent = classSymbol.implementation.valueDeclaration.parent;
    return ts.isBlock(classDeclarationParent) ? Array.from(classDeclarationParent.statements) : [];
  }

  ///////////// Host Private Helpers /////////////

  /**
   * A constructor function may have been "synthesized" by TypeScript during JavaScript emit,
   * in the case no user-defined constructor exists and e.g. property initializers are used.
   * Those initializers need to be emitted into a constructor in JavaScript, so the TypeScript
   * compiler generates a synthetic constructor.
   *
   * We need to identify such constructors as ngcc needs to be able to tell if a class did
   * originally have a constructor in the TypeScript source. For ES5, we can not tell an
   * empty constructor apart from a synthesized constructor, but fortunately that does not
   * matter for the code generated by ngtsc.
   *
   * When a class has a superclass however, a synthesized constructor must not be considered
   * as a user-defined constructor as that prevents a base factory call from being created by
   * ngtsc, resulting in a factory function that does not inject the dependencies of the
   * superclass. Hence, we identify a default synthesized super call in the constructor body,
   * according to the structure that TypeScript's ES2015 to ES5 transformer generates in
   * https://github.com/Microsoft/TypeScript/blob/v3.2.2/src/compiler/transformers/es2015.ts#L1082-L1098
   *
   * Additionally, we handle synthetic delegate constructors that are emitted when TypeScript
   * downlevel's ES2015 synthetically generated to ES5. These vary slightly from the default
   * structure mentioned above because the ES2015 output uses a spread operator, for delegating
   * to the parent constructor, that is preserved through a TypeScript helper in ES5. e.g.
   *
   * ```
   * return _super.apply(this, tslib.__spread(arguments)) || this;
   * ```
   *
   * Such constructs can be still considered as synthetic delegate constructors as they are
   * the product of a common TypeScript to ES5 synthetic constructor, just being downleveled
   * to ES5 using `tsc`. See: https://github.com/angular/angular/issues/38453.
   *
   *
   * @param constructor a constructor function to test
   * @returns true if the constructor appears to have been synthesized
   */
  private isSynthesizedConstructor(constructor: ts.FunctionDeclaration): boolean {
    if (!constructor.body) return false;

    const firstStatement = constructor.body.statements[0];
    if (!firstStatement) return false;

    return this.isSynthesizedSuperThisAssignment(firstStatement) ||
        this.isSynthesizedSuperReturnStatement(firstStatement);
  }

  /**
   * Identifies synthesized super calls which pass-through function arguments directly and are
   * being assigned to a common `_this` variable. The following patterns we intend to match:
   *
   * 1. Delegate call emitted by TypeScript when it emits ES5 directly.
   *   ```
   *   var _this = _super !== null && _super.apply(this, arguments) || this;
   *   ```
   *
   * 2. Delegate call emitted by TypeScript when it downlevel's ES2015 to ES5.
   *   ```
   *   var _this = _super.apply(this, tslib.__spread(arguments)) || this;
   *   ```
   *
   *
   * @param statement a statement that may be a synthesized super call
   * @returns true if the statement looks like a synthesized super call
   */
  private isSynthesizedSuperThisAssignment(statement: ts.Statement): boolean {
    if (!ts.isVariableStatement(statement)) return false;

    const variableDeclarations = statement.declarationList.declarations;
    if (variableDeclarations.length !== 1) return false;

    const variableDeclaration = variableDeclarations[0];
    if (!ts.isIdentifier(variableDeclaration.name) ||
        !variableDeclaration.name.text.startsWith('_this'))
      return false;

    const initializer = variableDeclaration.initializer;
    if (!initializer) return false;

    return this.isSynthesizedDefaultSuperCall(initializer);
  }
  /**
   * Identifies synthesized super calls which pass-through function arguments directly and
   * are being returned. The following patterns correspond to synthetic super return calls:
   *
   * 1. Delegate call emitted by TypeScript when it emits ES5 directly.
   *   ```
   *   return _super !== null && _super.apply(this, arguments) || this;
   *   ```
   *
   * 2. Delegate call emitted by TypeScript when it downlevel's ES2015 to ES5.
   *   ```
   *   return _super.apply(this, tslib.__spread(arguments)) || this;
   *   ```
   *
   * @param statement a statement that may be a synthesized super call
   * @returns true if the statement looks like a synthesized super call
   */
  private isSynthesizedSuperReturnStatement(statement: ts.Statement): boolean {
    if (!ts.isReturnStatement(statement)) return false;

    const expression = statement.expression;
    if (!expression) return false;

    return this.isSynthesizedDefaultSuperCall(expression);
  }

  /**
   * Identifies synthesized super calls which pass-through function arguments directly. The
   * synthetic delegate super call match the following patterns we intend to match:
   *
   * 1. Delegate call emitted by TypeScript when it emits ES5 directly.
   *   ```
   *   _super !== null && _super.apply(this, arguments) || this;
   *   ```
   *
   * 2. Delegate call emitted by TypeScript when it downlevel's ES2015 to ES5.
   *   ```
   *   _super.apply(this, tslib.__spread(arguments)) || this;
   *   ```
   *
   * @param expression an expression that may represent a default super call
   * @returns true if the expression corresponds with the above form
   */
  private isSynthesizedDefaultSuperCall(expression: ts.Expression): boolean {
    if (!isBinaryExpr(expression, ts.SyntaxKind.BarBarToken)) return false;
    if (expression.right.kind !== ts.SyntaxKind.ThisKeyword) return false;

    const left = expression.left;
    if (isBinaryExpr(left, ts.SyntaxKind.AmpersandAmpersandToken)) {
      return isSuperNotNull(left.left) && this.isSuperApplyCall(left.right);
    } else {
      return this.isSuperApplyCall(left);
    }
  }

  /**
   * Tests whether the expression corresponds to a `super` call passing through
   * function arguments without any modification. e.g.
   *
   * ```
   * _super !== null && _super.apply(this, arguments) || this;
   * ```
   *
   * This structure is generated by TypeScript when transforming ES2015 to ES5, see
   * https://github.com/Microsoft/TypeScript/blob/v3.2.2/src/compiler/transformers/es2015.ts#L1148-L1163
   *
   * Additionally, we also handle cases where `arguments` are wrapped by a TypeScript spread helper.
   * This can happen if ES2015 class output contain auto-generated constructors due to class
   * members. The ES2015 output will be using `super(...arguments)` to delegate to the superclass,
   * but once downleveled to ES5, the spread operator will be persisted through a TypeScript spread
   * helper. For example:
   *
   * ```
   * _super.apply(this, __spread(arguments)) || this;
   * ```
   *
   * More details can be found in: https://github.com/angular/angular/issues/38453.
   *
   * @param expression an expression that may represent a default super call
   * @returns true if the expression corresponds with the above form
   */
  private isSuperApplyCall(expression: ts.Expression): boolean {
    if (!ts.isCallExpression(expression) || expression.arguments.length !== 2) return false;

    const targetFn = expression.expression;
    if (!ts.isPropertyAccessExpression(targetFn)) return false;
    if (!isSuperIdentifier(targetFn.expression)) return false;
    if (targetFn.name.text !== 'apply') return false;

    const thisArgument = expression.arguments[0];
    if (thisArgument.kind !== ts.SyntaxKind.ThisKeyword) return false;

    const argumentsExpr = expression.arguments[1];

    // If the super is directly invoked with `arguments`, return `true`. This represents the
    // common TypeScript output where the delegate constructor super call matches the following
    // pattern: `super.apply(this, arguments)`.
    if (isArgumentsIdentifier(argumentsExpr)) {
      return true;
    }

    // The other scenario we intend to detect: The `arguments` variable might be wrapped with the
    // TypeScript spread helper (either through tslib or inlined). This can happen if an explicit
    // delegate constructor uses `super(...arguments)` in ES2015 and is downleveled to ES5 using
    // `--downlevelIteration`. The output in such cases would not directly pass the function
    // `arguments` to the `super` call, but wrap it in a TS spread helper. The output would match
    // the following pattern: `super.apply(this, tslib.__spread(arguments))`. We check for such
    // constructs below, but perform the detection of the call expression definition as last as
    // that is the most expensive operation here.
    if (!ts.isCallExpression(argumentsExpr) || argumentsExpr.arguments.length !== 1 ||
        !isArgumentsIdentifier(argumentsExpr.arguments[0])) {
      return false;
    }

    const argumentsCallExpr = argumentsExpr.expression;
    let argumentsCallDeclaration: Declaration|null = null;

    // The `__spread` helper could be globally available, or accessed through a namespaced
    // import. Hence we support a property access here as long as it resolves to the actual
    // known TypeScript spread helper.
    if (ts.isIdentifier(argumentsCallExpr)) {
      argumentsCallDeclaration = this.getDeclarationOfIdentifier(argumentsCallExpr);
    } else if (
        ts.isPropertyAccessExpression(argumentsCallExpr) &&
        ts.isIdentifier(argumentsCallExpr.name)) {
      argumentsCallDeclaration = this.getDeclarationOfIdentifier(argumentsCallExpr.name);
    }

    return argumentsCallDeclaration !== null &&
        argumentsCallDeclaration.known === KnownDeclaration.TsHelperSpread;
  }
}

///////////// Internal Helpers /////////////

/**
 * Represents the details about property definitions that were set using `Object.defineProperty`.
 */
interface PropertyDefinition {
  setter: ts.FunctionExpression|null;
  getter: ts.FunctionExpression|null;
}

/**
 * In ES5, getters and setters have been downleveled into call expressions of
 * `Object.defineProperty`, such as
 *
 * ```
 * Object.defineProperty(Clazz.prototype, "property", {
 *   get: function () {
 *       return 'value';
 *   },
 *   set: function (value) {
 *       this.value = value;
 *   },
 *   enumerable: true,
 *   configurable: true
 * });
 * ```
 *
 * This function inspects the given node to determine if it corresponds with such a call, and if so
 * extracts the `set` and `get` function expressions from the descriptor object, if they exist.
 *
 * @param node The node to obtain the property definition from.
 * @returns The property definition if the node corresponds with accessor, null otherwise.
 */
function getPropertyDefinition(node: ts.Node): PropertyDefinition|null {
  if (!ts.isCallExpression(node)) return null;

  const fn = node.expression;
  if (!ts.isPropertyAccessExpression(fn) || !ts.isIdentifier(fn.expression) ||
      fn.expression.text !== 'Object' || fn.name.text !== 'defineProperty')
    return null;

  const descriptor = node.arguments[2];
  if (!descriptor || !ts.isObjectLiteralExpression(descriptor)) return null;

  return {
    setter: readPropertyFunctionExpression(descriptor, 'set'),
    getter: readPropertyFunctionExpression(descriptor, 'get'),
  };
}

function readPropertyFunctionExpression(object: ts.ObjectLiteralExpression, name: string) {
  const property = object.properties.find(
      (p): p is ts.PropertyAssignment =>
          ts.isPropertyAssignment(p) && ts.isIdentifier(p.name) && p.name.text === name);

  return property && ts.isFunctionExpression(property.initializer) && property.initializer || null;
}

function getReturnStatement(declaration: ts.Expression|undefined): ts.ReturnStatement|undefined {
  return declaration && ts.isFunctionExpression(declaration) ?
      declaration.body.statements.find(ts.isReturnStatement) :
      undefined;
}

function reflectArrayElement(element: ts.Expression) {
  return ts.isObjectLiteralExpression(element) ? reflectObjectLiteral(element) : null;
}

function isArgumentsIdentifier(expression: ts.Expression): boolean {
  return ts.isIdentifier(expression) && expression.text === 'arguments';
}

function isSuperNotNull(expression: ts.Expression): boolean {
  return isBinaryExpr(expression, ts.SyntaxKind.ExclamationEqualsEqualsToken) &&
      isSuperIdentifier(expression.left);
}

function isBinaryExpr(
    expression: ts.Expression, operator: ts.BinaryOperator): expression is ts.BinaryExpression {
  return ts.isBinaryExpression(expression) && expression.operatorToken.kind === operator;
}

function isSuperIdentifier(node: ts.Node): boolean {
  // Verify that the identifier is prefixed with `_super`. We don't test for equivalence
  // as TypeScript may have suffixed the name, e.g. `_super_1` to avoid name conflicts.
  // Requiring only a prefix should be sufficiently accurate.
  return ts.isIdentifier(node) && node.text.startsWith('_super');
}

/**
 * Parse the statement to extract the ESM5 parameter initializer if there is one.
 * If one is found, add it to the appropriate parameter in the `parameters` collection.
 *
 * The form we are looking for is:
 *
 * ```
 * if (arg === void 0) { arg = initializer; }
 * ```
 *
 * @param statement a statement that may be initializing an optional parameter
 * @param parameters the collection of parameters that were found in the function definition
 * @returns true if the statement was a parameter initializer
 */
function captureParamInitializer(statement: ts.Statement, parameters: Parameter[]) {
  if (ts.isIfStatement(statement) && isUndefinedComparison(statement.expression) &&
      ts.isBlock(statement.thenStatement) && statement.thenStatement.statements.length === 1) {
    const ifStatementComparison = statement.expression;           // (arg === void 0)
    const thenStatement = statement.thenStatement.statements[0];  // arg = initializer;
    if (isAssignmentStatement(thenStatement)) {
      const comparisonName = ifStatementComparison.left.text;
      const assignmentName = thenStatement.expression.left.text;
      if (comparisonName === assignmentName) {
        const parameter = parameters.find(p => p.name === comparisonName);
        if (parameter) {
          parameter.initializer = thenStatement.expression.right;
          return true;
        }
      }
    }
  }
  return false;
}

function isUndefinedComparison(expression: ts.Expression): expression is ts.Expression&
    {left: ts.Identifier, right: ts.Expression} {
  return ts.isBinaryExpression(expression) &&
      expression.operatorToken.kind === ts.SyntaxKind.EqualsEqualsEqualsToken &&
      ts.isVoidExpression(expression.right) && ts.isIdentifier(expression.left);
}

/**
 * Parse the declaration of the given `classSymbol` to find the IIFE wrapper function.
 *
 * This function may accept a `_super` argument if there is a base class.
 *
 * ```
 * var TestClass = (function (_super) {
 *   __extends(TestClass, _super);
 *   function TestClass() {}
 *   return TestClass;
 * }(BaseClass));
 * ```
 *
 * @param classSymbol the class whose iife wrapper function we want to get.
 * @returns the IIFE function or null if it could not be parsed.
 */
function getIifeFn(classSymbol: NgccClassSymbol|undefined): ts.FunctionExpression|null {
  if (classSymbol === undefined) {
    return null;
  }

  const innerDeclaration = classSymbol.implementation.valueDeclaration;
  const iifeBody = innerDeclaration.parent;
  if (!ts.isBlock(iifeBody)) {
    return null;
  }

  const iifeWrapper = iifeBody.parent;
  return iifeWrapper && ts.isFunctionExpression(iifeWrapper) ? iifeWrapper : null;
}