/**
 * @license
 * Copyright (c) 2018 The Polymer Project Authors. All rights reserved. This
 * code may only be used under the BSD style license found at
 * http://polymer.github.io/LICENSE.txt The complete set of authors may be
 * found at http://polymer.github.io/AUTHORS.txt The complete set of
 * contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt Code
 * distributed by Google as part of the polymer project is also subject to an
 * additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 */

import * as ts from 'typescript';

/**
 * The result of calling verifyTypings.
 */
export interface VerifyTypingsResult {
  success: boolean;
  errorLog: string;
}

const compilerOptions = {
  target: ts.ScriptTarget.ES2015,
  module: ts.ModuleKind.ES2015,
  moduleResolution: ts.ModuleResolutionKind.NodeJs,
  strict: true,
  noUnusedLocals: true,
  noUnusedParameters: true,
  declaration: true,
  lib: [
    'lib.dom.d.ts',
    'lib.esnext.d.ts',
  ],
};

const diagnosticsHost = {
  getNewLine: () => '\n',
  getCurrentDirectory: () => process.cwd(),
  getCanonicalFileName: (fileName: string) => fileName,
};

/**
 * Compile the given declaration file paths with TypeScript and return whether
 * compilation succeeded or failed, and a "pretty" formatted error log string.
 *
 * Uses a TypeScript compiler configuration suitable for web development, and
 * strict type checking.
 */
export function verifyTypings(filePaths: string[]): VerifyTypingsResult {
  const program = ts.createProgram(filePaths, compilerOptions);
  const emitResult = program.emit();
  const diagnostics =
      ts.getPreEmitDiagnostics(program).concat(emitResult.diagnostics);
  if (diagnostics.length > 0) {
    return {
      success: false,
      errorLog:
          ts.formatDiagnosticsWithColorAndContext(diagnostics, diagnosticsHost)
    };
  }
  return {success: true, errorLog: ''};
}