config/config.go

/*
 * Copyright (C) 2017 eschao <esc.chao@gmail.com>
 *
 * 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 config

import (
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"os"
	"path/filepath"
	"reflect"

	"gopkg.in/yaml.v3"
)

// Default configuration file
const (
	DefaultJSONConfig = "config.json"
	DefaultYamlConfig = "config.yaml"
	DefaultPropConfig = "config.properties"
)

const (
	JSONConfigType = "json"
	YamlConfigType = "yaml"
	PropConfigType = "properties"
)

var (
	errExpectStructPointerInsteadOf = errors.New("expect a structure pointer type instead of")
	errFileNotFound                 = errors.New("file not found")
	errNotImplemented               = errors.New("not implemented")
	errUnsupportedConfigFile        = errors.New("unsupported config file")
	errUnsupportedType              = errors.New("unsupported type")
	errValueCannotBeChanged         = errors.New("value cannot be changed")
)

// ParseDefault parses the given structure, extract default value from its tag
// and set structure with these values.
// Normally, ParseDefault should be called before any other parsing functions
// to set default values for structure.
func ParseDefault(i interface{}) error {
	ptrRef := reflect.ValueOf(i)

	if ptrRef.IsNil() || ptrRef.Kind() != reflect.Ptr {
		return fmt.Errorf("%w: %s",
			errExpectStructPointerInsteadOf, ptrRef.Kind().String())
	}

	valueOfStruct := ptrRef.Elem()
	if valueOfStruct.Kind() != reflect.Struct {
		return fmt.Errorf("%w: %s",
			errExpectStructPointerInsteadOf, valueOfStruct.Kind().String())
	}

	return parseValue(valueOfStruct)
}

func parseValue(value reflect.Value) error {
	var err error

	typeOfStruct := value.Type()

	for i := 0; i < value.NumField() && err == nil; i++ {
		valueOfField := value.Field(i)
		kindOfField := valueOfField.Kind()
		structOfField := typeOfStruct.Field(i)

		if kindOfField == reflect.Ptr {
			if !valueOfField.IsNil() && valueOfField.CanSet() {
				err = ParseDefault(valueOfField.Interface())
			} else {
				continue
			}
		} else if kindOfField == reflect.Struct {
			err = parseValue(valueOfField)
		}

		defValue, ok := structOfField.Tag.Lookup("default")
		if !ok {
			continue
		}

		err = setValue(valueOfField, defValue, structOfField)
	}

	return err
}

func setValue(value reflect.Value, defValue string, field reflect.StructField) error {
	if setUnmarshalTextValue(value, defValue) {
		return nil
	}

	if ok, err := setDurationValue(value, defValue); ok {
		return err
	}

	var err error

	switch value.Kind() {
	case reflect.Bool:
		err = setValueWithBool(value, defValue)
	case reflect.String:
		value.SetString(defValue)
	case reflect.Int8:
		err = setValueWithIntX(value, defValue, Int8Size)
	case reflect.Int16:
		err = setValueWithIntX(value, defValue, Int16Size)
	case reflect.Int, reflect.Int32:
		err = setValueWithIntX(value, defValue, Int32Size)
	case reflect.Int64:
		err = setValueWithIntX(value, defValue, Int64Size)
	case reflect.Uint8:
		err = setValueWithUintX(value, defValue, Uint8Size)
	case reflect.Uint16:
		err = setValueWithUintX(value, defValue, Uint16Size)
	case reflect.Uint, reflect.Uint32:
		err = setValueWithUintX(value, defValue, Uint32Size)
	case reflect.Uint64:
		err = setValueWithUintX(value, defValue, Uint64Size)
	case reflect.Float32:
		err = setValueWithFloatX(value, defValue, Float32Size)
	case reflect.Float64:
		err = setValueWithFloatX(value, defValue, Float64Size)
	case reflect.Slice:
		sp, ok := field.Tag.Lookup("separator")
		if !ok {
			sp = ":"
		}

		err = setValueWithSlice(value, defValue, sp)
	default:
		err = fmt.Errorf("%w: %s", errUnsupportedType, value.Kind().String())
	}

	return err
}

// ParseCli parses given structure interface and set it with command line input
func ParseCli(out interface{}, name string, args []string) ([]string, error) {
	cli := NewCLI(name)
	if err := cli.Init(out); err != nil {
		return nil, err
	}

	err := cli.Parse(args)

	return cli.Args, err
}

// ParseConfig parses given structure interface and set it with default
// configuration file.
// The configFlag is a command line flag to tell where to locate configure file.
// If the config file doesn't exist, the default config fill will be searched
// under the same folder with the fixed order: config.json, config.yaml and
// config.properties
func ParseConfig(out interface{}, configFlag string) error {
	configFile := flag.String(configFlag, "", "Specify configuration file")
	flag.Parse()

	return ParseConfigFile(out, *configFile)
}

// ParseConfigFile parses given structure interface and set its value with
// the specified configuration file
func ParseConfigFile(out interface{}, configFile string) error {
	var err error
	if configFile == "" {
		configFile, err = getDefaultConfigFile()
		if err != nil {
			return err
		}
	}

	configType, err := getConfigFileType(configFile)
	if err != nil {
		return err
	}

	switch configType {
	case JSONConfigType:
		err = parseJSON(out, configFile)
	case YamlConfigType:
		err = parseYaml(out, configFile)
	case PropConfigType:
		err = parseProp(out, configFile)
	default:
		err = fmt.Errorf("%w: %s", errUnsupportedConfigFile, configFile)
	}

	return err
}

// parseJSON parses JSON file and set structure with its value
func parseJSON(out interface{}, jsonFile string) error {
	raw, err := os.ReadFile(jsonFile)
	if err != nil {
		return fmt.Errorf("open json config file: %w", err)
	}

	if err := json.Unmarshal(raw, out); err != nil {
		return fmt.Errorf("json unmarshal: %w", err)
	}

	return nil
}

// parseYaml parses Yaml file and set structure with its value
func parseYaml(out interface{}, yamlFile string) error {
	raw, err := os.ReadFile(yamlFile)
	if err != nil {
		return fmt.Errorf("open yaml config file: %w", err)
	}

	if err := yaml.Unmarshal(raw, out); err != nil {
		return fmt.Errorf("unmarshal yaml: %w", err)
	}

	return nil
}

// parseProp parses Properties file and set structure with its value
func parseProp(_ interface{}, _ /* The propFile */ string) error {
	return fmt.Errorf("%w: properties config", errNotImplemented)
}

// getDefaultConfigFile returns a existing default config file. The checking
// order is fixed with beginning from: config.json to config.yaml and
// config.properties
func getDefaultConfigFile() (string, error) {
	exe, err := os.Executable()
	if err != nil {
		return "", fmt.Errorf("%w: %w", errFileNotFound, err)
	}

	path := filepath.Dir(exe) + string(filepath.Separator)

	// Check json config
	jsonConfig := path + DefaultJSONConfig
	if _, err := os.Stat(jsonConfig); err == nil {
		return jsonConfig, nil
	}

	// Check yaml config
	yamlConfig := path + DefaultYamlConfig
	if _, err := os.Stat(yamlConfig); err == nil {
		return yamlConfig, nil
	}

	// Check prop config
	propConfig := path + DefaultPropConfig
	if _, err := os.Stat(propConfig); err == nil {
		return propConfig, nil
	}

	return "", fmt.Errorf("default config %w in path: %s", errFileNotFound, path)
}

// getConfigFileType analyzes config file extension name and return
// corresponding type: json, yaml or properties
func getConfigFileType(configFile string) (string, error) {
	ext := filepath.Ext(configFile)
	switch ext {
	case ".json":
		return JSONConfigType, nil
	case ".yaml":
		return YamlConfigType, nil
	case ".properties", ".prop":
		return PropConfigType, nil
	}

	return "", fmt.Errorf("%w: %s", errUnsupportedConfigFile, configFile)
}