const fs = require('fs')
const path = require('path')
const commander = require('commander')
const deepmerge = require('deepmerge')

const my = { secretKeys:[] }

module.exports = {
  mergeConfig({rawConfig={}, envarFiles=['./envar-base-basic.js', './envar-base-custom.js', './envar-base-secret.js']} = {}) {
    if (!global.envar) {
      global.envar = rawConfig
      // 不知为何，必须定义成全局变量，才能保证多次require只执行一次。

      console.info('<<<<<<<< Collecting Environment Configuration <<<<<<<<')

      console.info('- Loading Configuration Files (读取配置文件)')
      
      for (let configFile of envarFiles){
        if (fs.existsSync(path.resolve(configFile))) {
          global.envar = deepmerge(global.envar, require(path.resolve(configFile)))
          console.info(`  - ${configFile} is loaded.`)
        } else {
          console.warn(`  - ${configFile} is missing.`)
        }
      }
      
      global.envar.prodev = global.envar.prodev || process.env.NODE_ENV || 'development' // server = require('express')(); server.get('env') === server.settings.env === process.env.NODE_ENV
      if (global.envar.prodev === 'production' && global.envar.ENV_PRODUCTION) {
        console.info('- Applying Production Configuration (加载生产环境配置)')
        global.envar = deepmerge(global.envar, global.envar.ENV_PRODUCTION) // 注意，objectMerge后，产生了一个新的对象，而不是在原来的Config里添加
        delete global.envar.ENV_PRODUCTION
      }

      console.info('- Loading Command Line Parameters (载入命令行参数)')
      commander.version(global.envar.Base_Version || '0.0.1', '-v, --version') // 默认是 -V。如果要 -v，就要加 '-v --version'
      for (let [key, param, desc] of global.envar.Commander_Option_List || []) {
        commander.option(param, `${desc} Default = "${global.envar[key]}"`)
      }
      commander.parse(process.argv)
      delete global.envar.Commander_Option_List // do not print Commander_Option_List to console

      console.log('- Merging Command Line Parameters into Configuration (把命令行参数值合并入配置)')
      for (let key in commander) {
        if (!/^_/.test(key) && typeof commander[key] === 'string') { // commander 自带了一批 _开头的属性，过滤掉
          global.envar[key] = commander[key]
        }
      }
    }

    console.log('>>>>>>>> Collected Environment Configuration >>>>>>>>')
    return global.envar
  },

  getDynamicConfig(dynamicConfigFile='envar-base-dynamic.js') { // dynamicConfigFile should be absolute or relative to the node process's dir.
    const fullpath = path.resolve(dynamicConfigFile)
    if (fs.existsSync(fullpath)) {
      delete require.cache[require.resolve(fullpath)] // delete require.cache[fullpath] 不起作用
      return require(fullpath)
    } else {
      return {}
    }
  },

  maskSecret() {
    let envar = JSON.parse(JSON.stringify(global.envar)) // 复制一份，避免污染
    for (let key in envar) {
      if (/^SECRET_/.test(key)) {
        envar[key] = '*** confidentical ***'
      }
    }
    return envar
  }
}