var path = require('path');
var autoprefixer = require('autoprefixer');
var webpack = require('webpack');
var HtmlWebpackPlugin = require('html-webpack-plugin');
var ExtractTextPlugin = require('extract-text-webpack-plugin');
var ManifestPlugin = require('webpack-manifest-plugin');
var InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
var url = require('url');
var paths = require('./paths');
var getClientEnvironment = require('./env');

function ensureSlash(path, needsSlash) {
  var hasSlash = path.endsWith('/');
  if (hasSlash && !needsSlash) {
    return path.substr(path, path.length - 1);
  } else if (!hasSlash && needsSlash) {
    return path + '/';
  } else {
    return path;
  }
}

// We use "homepage" field to infer "public path" at which the app is served.
// Webpack needs to know it to put the right <script> hrefs into HTML even in
// single-page apps that may serve index.html for nested URLs like /todos/42.
// We can't use a relative path in HTML because we don't want to load something
// like /todos/42/static/js/bundle.7289d.js. We have to know the root.
var homepagePath = require(paths.appPackageJson).homepage;
var homepagePathname = homepagePath ? url.parse(homepagePath).pathname : '/';
// Webpack uses `publicPath` to determine where the app is being served from.
// It requires a trailing slash, or the file assets will get an incorrect path.
var publicPath = ensureSlash(homepagePathname, true);
// `publicUrl` is just like `publicPath`, but we will provide it to our app
// as %PUBLIC_URL% in `index.html` and `process.env.PUBLIC_URL` in JavaScript.
// Omit trailing slash as %PUBLIC_PATH%/xyz looks better than %PUBLIC_PATH%xyz.
var publicUrl = ensureSlash(homepagePathname, false);
// Get environment variables to inject into our app.
var env = getClientEnvironment(publicUrl);

// Assert this just to be safe.
// Development builds of React are slow and not intended for production.
if (env['process.env'].NODE_ENV !== '"production"') {
  throw new Error('Production builds must have NODE_ENV=production.');
}

// This is the production configuration.
// It compiles slowly and is focused on producing a fast and minimal bundle.
// The development configuration is different and lives in a separate file.
module.exports = {
  // Don't attempt to continue if there are any errors.
  bail: true,
  // We generate sourcemaps in production. This is slow but gives good results.
  // You can exclude the *.map files from the build during deployment.
  devtool: 'source-map',
  // In production, we only want to load the polyfills and the app code.
  entry: [
    require.resolve('./polyfills'),
    paths.appIndexJs
  ],
  output: {
    // The build folder.
    path: paths.appBuild,
    // Generated JS file names (with nested folders).
    // There will be one main bundle, and one file per asynchronous chunk.
    // We don't currently advertise code splitting but Webpack supports it.
    filename: 'static/js/[name].[chunkhash:8].js',
    chunkFilename: 'static/js/[name].[chunkhash:8].chunk.js',
    // We inferred the "public path" (such as / or /my-project) from homepage.
    publicPath: publicPath
  },
  resolve: {
    // This allows you to set a fallback for where Webpack should look for modules.
    // We read `NODE_PATH` environment variable in `paths.js` and pass paths here.
    // We use `fallback` instead of `root` because we want `node_modules` to "win"
    // if there any conflicts. This matches Node resolution mechanism.
    // https://github.com/facebookincubator/create-react-app/issues/253
    fallback: paths.nodePaths,
    // These are the reasonable defaults supported by the Node ecosystem.
    // We also include JSX as a common component filename extension to support
    // some tools, although we do not recommend using it, see:
    // https://github.com/facebookincubator/create-react-app/issues/290
    extensions: ['.js', '.json', '.jsx', ''],
    alias: {
      // Support React Native Web
      // https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
      'react-native': 'react-native-web'
    }
  },

  module: {
    // First, run the linter.
    // It's important to do this before Babel processes the JS.
    preLoaders: [
      {
        test: /\.(js|jsx)$/,
        loader: 'eslint',
        include: paths.appSrc
      }
    ],
    loaders: [
      // Process JS with Babel.
      {
        test: /\.(js|jsx)$/,
        include: paths.appSrc,
        loader: 'babel',

      },
      // Sass loader
      {
        test: /\.scss$/,
        include: paths.appSrc,
        loaders: ['style', 'css', 'sass']
      },
      // The notation here is somewhat confusing.
      // "postcss" loader applies autoprefixer to our CSS.
      // "css" loader resolves paths in CSS and adds assets as dependencies.
      // "style" loader normally turns CSS into JS modules injecting <style>,
      // but unlike in development configuration, we do something different.
      // `ExtractTextPlugin` first applies the "postcss" and "css" loaders
      // (second argument), then grabs the result CSS and puts it into a
      // separate file in our build process. This way we actually ship
      // a single CSS file in production instead of JS code injecting <style>
      // tags. If you use code splitting, however, any async bundles will still
      // use the "style" loader inside the async code so CSS from them won't be
      // in the main CSS file.
      {
        test: /\.css$/,
        // "?-autoprefixer" disables autoprefixer in css-loader itself:
        // https://github.com/webpack/css-loader/issues/281
        // We already have it thanks to postcss. We only pass this flag in
        // production because "css" loader only enables autoprefixer-powered
        // removal of unnecessary prefixes when Uglify plugin is enabled.
        // Webpack 1.x uses Uglify plugin as a signal to minify *all* the assets
        // including CSS. This is confusing and will be removed in Webpack 2:
        // https://github.com/webpack/webpack/issues/283
        loader: ExtractTextPlugin.extract('style', 'css?importLoaders=1&-autoprefixer!postcss')
        // Note: this won't work without `new ExtractTextPlugin()` in `plugins`.
      },
      // JSON is not enabled by default in Webpack but both Node and Browserify
      // allow it implicitly so we also enable it.
      {
        test: /\.json$/,
        loader: 'json'
      },
      // "file" loader makes sure those assets end up in the `build` folder.
      // When you `import` an asset, you get its filename.
      {
        test: /\.(ico|jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2)(\?.*)?$/,
        loader: 'file',
        query: {
          name: 'static/media/[name].[hash:8].[ext]'
        }
      },
      // "url" loader works just like "file" loader but it also embeds
      // assets smaller than specified size as data URLs to avoid requests.
      {
        test: /\.(mp4|webm|wav|mp3|m4a|aac|oga)(\?.*)?$/,
        loader: 'url',
        query: {
          limit: 10000,
          name: 'static/media/[name].[hash:8].[ext]'
        }
      }
    ]
  },

  // We use PostCSS for autoprefixing only.
  postcss: function() {
    return [
      autoprefixer({
        browsers: [
          '>1%',
          'last 4 versions',
          'Firefox ESR',
          'not ie < 9', // React doesn't support IE8 anyway
        ]
      }),
    ];
  },
  plugins: [
    // Makes the public URL available as %PUBLIC_URL% in index.html, e.g.:
    // <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
    // In production, it will be an empty string unless you specify "homepage"
    // in `package.json`, in which case it will be the pathname of that URL.
    new InterpolateHtmlPlugin({
      PUBLIC_URL: publicUrl
    }),
    // Generates an `index.html` file with the <script> injected.
    new HtmlWebpackPlugin({
      inject: true,
      template: paths.appHtml,
      minify: {
        removeComments: true,
        collapseWhitespace: true,
        removeRedundantAttributes: true,
        useShortDoctype: true,
        removeEmptyAttributes: true,
        removeStyleLinkTypeAttributes: true,
        keepClosingSlash: true,
        minifyJS: true,
        minifyCSS: true,
        minifyURLs: true
      }
    }),
    // Makes some environment variables available to the JS code, for example:
    // if (process.env.NODE_ENV === 'production') { ... }. See `./env.js`.
    // It is absolutely essential that NODE_ENV was set to production here.
    // Otherwise React will be compiled in the very slow development mode.
    new webpack.DefinePlugin(env),
    // This helps ensure the builds are consistent if source hasn't changed:
    new webpack.optimize.OccurrenceOrderPlugin(),
    // Try to dedupe duplicated modules, if any:
    new webpack.optimize.DedupePlugin(),
    // Minify the code.
    new webpack.optimize.UglifyJsPlugin({
      compress: {
        screw_ie8: true, // React doesn't support IE8
        warnings: false
      },
      mangle: {
        screw_ie8: true
      },
      output: {
        comments: false,
        screw_ie8: true
      }
    }),
    // Note: this won't work without ExtractTextPlugin.extract(..) in `loaders`.
    new ExtractTextPlugin('static/css/[name].[contenthash:8].css'),
    // Generate a manifest file which contains a mapping of all asset filenames
    // to their corresponding output file so that tools can pick it up without
    // having to parse `index.html`.
    new ManifestPlugin({
      fileName: 'asset-manifest.json'
    })
  ],
  // Some libraries import Node modules but don't use them in the browser.
  // Tell Webpack to provide empty mocks for them so importing them works.
  node: {
    fs: 'empty',
    net: 'empty',
    tls: 'empty'
  }
};
