import * as path from 'path';
import {
	existsSync,
	readFileSync
} from 'fs';

export function getDefaultOptions () {
	return {
		noEmitHelpers: true,
		module: 'es2015',
		sourceMap: true
	};
}

// Gratefully lifted from 'look-up', due to problems using it directly:
//   https://github.com/jonschlinkert/look-up/blob/master/index.js
//   MIT Licenced
function findFile(cwd: string, filename: string) {
	let fp = cwd ? `${cwd}/${filename}` : filename;
	if (existsSync(fp)) {
		return fp;
	}

	const segs = cwd.split(path.sep);
	let len = segs.length;

	while (len--) {
		cwd = segs.slice(0, len).join('/');
		fp = cwd + '/' + filename;
		if (existsSync(fp)) {
			return fp;
		}
	}

	return null;
}

export function compilerOptionsFromTsConfig(typescript: typeof import('typescript')) {
	const cwd = process.cwd();
	const filePath = findFile(cwd, 'tsconfig.json');

	const tsconfig = filePath && typescript.readConfigFile(
		filePath,
		path => readFileSync(path, 'utf8')
	);

	if (!tsconfig || !tsconfig.config || !tsconfig.config.compilerOptions) return {};

	return tsconfig.config.compilerOptions;
}

export function adjustCompilerOptions ( typescript, options ) {
	// Set `sourceMap` to `inlineSourceMap` if it's a boolean
	// under the assumption that both are never specified simultaneously.
	if ( typeof options.inlineSourceMap === 'boolean' ) {
		options.sourceMap = options.inlineSourceMap;
		delete options.inlineSourceMap;
	}

	// Delete the `declaration` option to prevent compilation error.
	// See: https://github.com/rollup/rollup-plugin-typescript/issues/45
	delete options.declaration;

	// Use importHelpers from TypeScript.
	options.importHelpers = true;
}