config.go

/*
 * Copyright 2018 InfAI (CC SES)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"os"
	"reflect"
	"regexp"
	"strconv"
	"strings"
)

type ConfigStruct struct {
	MongoUrl                   string
	MongoTable                 string
	ConnectorGatewayCollection string
	ConnectorDeviceCollection  string
	DeviceStateCollection      string
	GatewayStateCollection     string

	ServerPort     string
	LogLevel       string
	PermissionsUrl string

	AmqpUrl              string
	AmqpReconnectTimeout int64
	AmqpConsumerName     string
	AmqpMsgLogging	     string

	InfluxdbUrl     string
	InfluxdbDb      string
	InfluxdbUser    string
	InfluxdbPw      string
	InfluxdbTimeout int64

	ConnectorLogTopic string
	DeviceLogTopic    string
	GatewayLogTopic   string

	ForceUser string
	ForceAuth string
}

type ConfigType *ConfigStruct

var Config ConfigType

func LoadConfig(location string) error {
	file, error := os.Open(location)
	if error != nil {
		log.Println("error on config load: ", error)
		return error
	}
	decoder := json.NewDecoder(file)
	configuration := ConfigStruct{}
	error = decoder.Decode(&configuration)
	if error != nil {
		log.Println("invalid config json: ", error)
		return error
	}
	HandleEnvironmentVars(&configuration)
	HandleDefaultValues(&configuration)
	Config = &configuration
	return nil
}

func HandleDefaultValues(config ConfigType) {

}

var camel = regexp.MustCompile("(^[^A-Z]*|[A-Z]*)([A-Z][^A-Z]+|$)")

func fieldNameToEnvName(s string) string {
	var a []string
	for _, sub := range camel.FindAllStringSubmatch(s, -1) {
		if sub[1] != "" {
			a = append(a, sub[1])
		}
		if sub[2] != "" {
			a = append(a, sub[2])
		}
	}
	return strings.ToUpper(strings.Join(a, "_"))
}

// preparations for docker
func HandleEnvironmentVars(config ConfigType) {
	configValue := reflect.Indirect(reflect.ValueOf(config))
	configType := configValue.Type()
	for index := 0; index < configType.NumField(); index++ {
		fieldName := configType.Field(index).Name
		envName := fieldNameToEnvName(fieldName)
		envValue := os.Getenv(envName)
		if envValue != "" {
			fmt.Println("use environment variable: ", envName, " = ", envValue)
			if configValue.FieldByName(fieldName).Kind() == reflect.Int64 {
				i, _ := strconv.ParseInt(envValue, 10, 64)
				configValue.FieldByName(fieldName).SetInt(i)
			}
			if configValue.FieldByName(fieldName).Kind() == reflect.String {
				configValue.FieldByName(fieldName).SetString(envValue)
			}
			if configValue.FieldByName(fieldName).Kind() == reflect.Slice {
				val := []string{}
				for _, element := range strings.Split(envValue, ",") {
					val = append(val, strings.TrimSpace(element))
				}
				configValue.FieldByName(fieldName).Set(reflect.ValueOf(val))
			}
		}
	}
}