const del = require('del');
const mocha = require('gulp-mocha');
const sourcemaps = require('gulp-sourcemaps');
const tslint = require('gulp-tslint');
const typescript = require('gulp-typescript');
const util = require('gulp-util');
const merge2 = require('merge2');
const path = require('path');
const through = require('through2');

Error.stackTraceLimit = Infinity;

module.exports = function(gulp) {

  const jsCoreDir = __dirname;
  const tslintPath = path.resolve(jsCoreDir, 'node_modules/google-ts-style/tslint.json');
  const tsconfigPath = path.resolve(jsCoreDir, 'tsconfig.json');
  const outDir = path.resolve(jsCoreDir, 'build');
  const srcDir = path.resolve(jsCoreDir, 'src');
  const testDir = path.resolve(jsCoreDir, 'test');

  function onError() {}

  // Coalesces all specified --file parameters into a single array
  const files = !util.env.file ? [] :
        Array.isArray(util.env.file) ? util.env.file : [util.env.file];

  // If --dev is passed, override certain ts config options
  let tsDevOptions = {};
  if (util.env.dev) {
    tsDevOptions = {
      allowUnreachableCode: true,
      noUnusedParameters: false,
      noImplicitAny: false,
      noImplicitThis: false,
      noEmitOnError: false
    };
  }

  /**
   * Helper function that creates a gulp task function that opens files in a
   * directory that match a certain glob pattern, transpiles them, and writes them
   * to an output directory.
   * @param {Object} globs
   * @param {string=} globs.transpile The glob pattern for files to transpile.
   *   Defaults to match all *.ts files in baseDir (incl. subdirectories).
   * @param {string=} globs.copy The glob pattern for files to transpile.
   *   Defaults to match all but *.ts files in baseDir (incl. subdirectories).
   * @return A gulp task function.
   */
  function makeCompileFn(globs) {
    const transpileGlob = globs.transpile || `${srcDir}/**/*.ts`;
    const copyGlob = globs.copy || '!(**/*)';
    return () => {
      const tsProject = typescript.createProject(tsconfigPath, tsDevOptions)();
      const { dts, js } = gulp.src(transpileGlob, { base: jsCoreDir })
            .pipe(sourcemaps.init())
            .pipe(tsProject)
            .on('error', onError);
      const jsmap = js.pipe(sourcemaps.write(jsCoreDir, {
        includeContent: false,
        sourceRoot: path.resolve(jsCoreDir, '..')
      }));
      const copy = gulp.src(copyGlob, { base: jsCoreDir });
      return merge2([
        js.pipe(gulp.dest(`${outDir}`)),
        dts.pipe(gulp.dest(`${outDir}/types`)),
        jsmap.pipe(gulp.dest(`${outDir}`)),
        copy.pipe(gulp.dest(`${outDir}`))
      ]);
    };
  }

  /**
   * Runs tslint on files in src/, with linting rules defined in tslint.json.
   */
  gulp.task('js.core.lint', 'Emits linting errors found in src/ and test/.', () => {
    const program = require('tslint').Linter.createProgram(tsconfigPath);
    gulp.src([`${srcDir}/**/*.ts`, `${srcDir}/**/*.ts`])
        .pipe(tslint({
          configuration: tslintPath,
          formatter: 'codeFrame',
          program
        }))
        .pipe(tslint.report())
        .on('warning', onError);
  });

  gulp.task('js.core.clean', 'Deletes transpiled code.', () => {
    return del(outDir);
  });

  /**
   * Transpiles TypeScript files in src/ to JavaScript according to the settings
   * found in tsconfig.json.
   * Currently, all errors are emitted twice. This is being tracked here:
   * https://github.com/ivogabe/gulp-typescript/issues/438
   */
  gulp.task('js.core.compile', 'Transpiles src/.',
            makeCompileFn({ transpile: [`${srcDir}/**/*.ts`] }));

  /**
   * Transpiles TypeScript files in both src/ and test/.
   */
  gulp.task('js.core.test.compile', 'After dep tasks, transpiles test/.', ['js.core.compile'],
            makeCompileFn({ transpile: [`${testDir}/**/*.ts`], copy: `${testDir}/**/!(*.ts)` }));

  /**
   * Transpiles src/ and test/, and then runs all tests.
   */
  gulp.task('js.core.test', 'After dep tasks, runs all tests.',
            ['js.core.test.compile'], () => {
              return gulp.src(`${outDir}/test/**/*.js`)
                  .pipe(mocha());
            }
           );

  /**
   * Transpiles individual files, specified by the --file flag.
   */
  gulp.task('js.core.compile.single', 'Transpiles individual files specified by --file.',
            makeCompileFn({
              transpile: files.map(f => path.relative('.', f))
            })
           );

  /**
   * Run individual tests, specified by their pre-transpiled source path (as
   * supplied through the '--file' flag). This is intended to be used as part of a
   * VS Code "Gulp task" launch configuration; setting the "args" field to
   * ["test.single", "--file", "${file}"] makes it possible for one to debug the
   * currently open TS mocha test file in one step.
   */
  gulp.task('js.core.test.single', 'After dep tasks, runs individual files specified ' +
            'by --file.', ['js.core.compile', 'js.core.compile.single'], () => {
              // util.env contains CLI arguments for the gulp task.
              // Determine the path to the transpiled version of this TS file.
              const getTranspiledPath = (file) => {
                const dir = path.dirname(path.relative('.', file));
                const basename = path.basename(file, '.ts');
                return `${outDir}/${dir}/${basename}.js`;
              };
              // Construct an instance of Mocha's runner API and feed it the path to the
              // transpiled source.
              return gulp.src(files.map(getTranspiledPath))
                  .pipe(through.obj((file, enc, cb) => {
                    // Construct a new Mocha runner instance.
                    const Mocha = require('mocha');
                    const runner = new Mocha();
                    // Add the path to the test file to debug.
                    runner.addFile(file.path);
                    // Run the test suite.
                    runner.run((failures) => {
                      if (failures > 0) {
                        cb(new Error(`Mocha: ${failures} failures in ${file.path}]`));
                      } else {
                        cb(null);
                      }
                    });
                  }));
            }
           );

};