/**
 * @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';

export type Import = {
  name: string,
  importModule: string,
  node: ts.ImportDeclaration
};

/** Gets import information about the specified identifier by using the type checker. */
export function getImportOfIdentifier(typeChecker: ts.TypeChecker, node: ts.Identifier): Import|
    null {
  const symbol = typeChecker.getSymbolAtLocation(node);

  if (!symbol || !symbol.declarations.length) {
    return null;
  }

  const decl = symbol.declarations[0];

  if (!ts.isImportSpecifier(decl)) {
    return null;
  }

  // Since "decl" is an import specifier, we can walk up three times to get a reference
  // to the import declaration node (NamedImports -> ImportClause -> ImportDeclaration).
  const importDecl = decl.parent.parent.parent;

  if (!ts.isStringLiteral(importDecl.moduleSpecifier)) {
    return null;
  }

  return {
    // Handles aliased imports: e.g. "import {Component as myComp} from ...";
    name: decl.propertyName ? decl.propertyName.text : decl.name.text,
    importModule: importDecl.moduleSpecifier.text,
    node: importDecl
  };
}