import * as FS from 'fs';

import {
  LanguageServiceHost,
  ScriptSnapshot,
  createDocumentRegistry,
  createLanguageService,
  flattenDiagnosticMessageText,
  getDefaultLibFilePath,
} from 'typescript';

/**
 * @param object An object that can be serialized to JSON.
 */
export function checkObjectTypeErrors(
  object: any,
  typeFileName: string,
  typeName: string,
): string[] | undefined {
  let json = JSON.stringify(object);

  let typeFileContent = FS.readFileSync(typeFileName);

  let validationContent = `${typeFileContent}\nconst _: ${typeName} = ${json};`;

  return checkTypeErrors(validationContent);
}

function checkTypeErrors(content: string): string[] | undefined {
  const scriptFileName = '_.ts';

  const serviceHost: LanguageServiceHost = {
    getScriptFileNames() {
      return [scriptFileName];
    },
    getScriptVersion() {
      return '0';
    },
    getScriptSnapshot(fileName) {
      if (fileName === scriptFileName) {
        return ScriptSnapshot.fromString(content);
      } else {
        try {
          return ScriptSnapshot.fromString(FS.readFileSync(fileName, 'utf-8'));
        } catch (error) {
          return undefined;
        }
      }
    },
    getCurrentDirectory() {
      return __dirname;
    },
    getCompilationSettings() {
      return {
        strict: true,
        noEmit: true,
      };
    },
    getDefaultLibFileName(options) {
      return getDefaultLibFilePath(options);
    },
  };

  const languageService = createLanguageService(
    serviceHost,
    createDocumentRegistry(),
  );

  let diagnostics = [
    ...languageService.getSyntacticDiagnostics(scriptFileName),
    ...languageService.getSemanticDiagnostics(scriptFileName),
  ];

  if (!diagnostics.length) {
    return undefined;
  }

  return diagnostics.map(diagnostic =>
    flattenDiagnosticMessageText(diagnostic.messageText, '\n'),
  );
}