const webpack = require('webpack');
const path = require('path');


/**
 * Plugin that simplifies creation of HTML files to serve your bundles
 * npm i --save-dev html-webpack-plugin
 * @type {HtmlWebpackPlugin}
 */
const HtmlWebpackPlugin = require('html-webpack-plugin');


/**
 * A webpack plugin to remove/clean your build folder(s) before building
 * npm i clean-webpack-plugin --save-dev
 * @type {CleanWebpackPlugin}
 */
const CleanWebpackPlugin = require('clean-webpack-plugin');


/**
 * 提取css到单独文件
 * npm install --save-dev mini-css-extract-plugin
 */
const MiniCssExtractPlugin = require("mini-css-extract-plugin");
/**
 * css 压缩 会清除css中注释
 * npm install --save-dev optimize-css-assets-webpack-plugin
 */
const OptimizeCSSAssetsPlugin = require("optimize-css-assets-webpack-plugin");


/**
 * js 压缩
 * npm install uglifyjs-webpack-plugin --save-dev
 */
const UglifyJsPlugin = require("uglifyjs-webpack-plugin");


module.exports = {
    mode: 'production',
    /**
     * entry 输入文件
     */
    entry: {
        /**
         * common 自定义公共文件
         * common: ['./commons/a.js', "./commons/b.js"],
         */
        common: [],
        /**
         * app 主文件
         */
        app: './main.js',

    },
    /**
     * 打包输出
     */
    output: {
        /**
         * publicPath
         * 生成如下链接
         * <script type="text/javascript" src="/cx/tpl/Support/search/dist/build.js">
         */
        publicPath: '/cx/tpl/Support/search/dist/',

        /**
         * [name] 指向entry 的key 也就是 app
         */
        filename: '[name].js',
        path: path.resolve(__dirname, 'dist/'),
    },
    plugins: [
        /**
         * 打包HTML
         */
        new HtmlWebpackPlugin({
            title: 'Output Management',
            /**
             * template 指定要打包的原文件
             */
            template: './online.html'
        }),
        /**
         * 由 webpack 生成的文件或目录才能被 CleanWebpackPlugin 删除
         * 下面配置的是 打包前 需要被删除的目录
         */
        new CleanWebpackPlugin(['dist', 'build']),
        new MiniCssExtractPlugin({
            filename: "[name].css",
            chunkFilename: "[id].css"
        }),
        // new webpack.optimize.DedupePlugin(),

        /**
         *  提取SourceMap到独立文件
         */
        new webpack.SourceMapDevToolPlugin({
            filename: '[name].js.map',
            // exclude: ['vendor.js']
        })
    ],

    /**
     * devtool 调试工具，用来追踪被打包前源文件的错误
     * 关闭可减少打包文件的大小
     */
    // devtool: 'inline-source-map',


    module: {
        rules: [
            {
                    /**
                     *  https://www.npmjs.com/package/babel-loader
                     *  npm install -D babel-loader @babel/core @babel/preset-env webpack
                     */
                    test: /\.m?js$/,
                    exclude: /(node_modules|bower_components)/,
                    use: {
                        loader: 'babel-loader',
                        options: {
                            presets: ['@babel/preset-env', '@babel/react']
                        }
                    }
                },
            {
                test: /\.css$/,
                use: [
                    {
                        loader: MiniCssExtractPlugin.loader,
                        options: {
                            // you can specify a publicPath here
                            // by default it use publicPath in webpackOptions.output
                            publicPath: '../'
                        }
                    },
                    "css-loader"
                ]
            }
        ]
    },
    optimization: {
        /**
         * 分包
         */
        splitChunks: {
            chunks: 'all',
            minSize: 30000,
            maxSize: 0,

        },

        minimizer: [
            new UglifyJsPlugin({
                cache: true,
                parallel: true,
                /**
                 *  sourceMap 和 devtool: 'inline-source-map', 冲突
                 */
                sourceMap: false, // set to true if you want JS source maps,
                /**
                 *  extractComments 导出备注
                 */
                extractComments: 'all'
            }),
            new OptimizeCSSAssetsPlugin({})
        ]
    }
};