conf/settings.go

package conf

import (
	"errors"
	"strconv"
	"strings"
)

var (
	ErrNotFound        = errors.New("conf: key not found")
	ErrCouldNotConvert = errors.New("conf: could not cast one or more values to required type")
)

const valuesSeparator = ","

// Setting represents key-value pair read from config file.
// It's Value field holds the value of key parsed from the configuration
type Setting struct {
	Name  string
	Value string
}

// Int converts Setting Value to int. Returned error
// will be non nil if convesion failed.
func (s Setting) Int() (int, error) {
	return parseValue(s.Value, strconv.Atoi)
}

// IntSlice splits Setting Value (separator is ",") and adds
// each of resulting values to []int if possible.
// If one or more values can not be converted to float64 those will be dropped
// and method will return conf.ErrCouldNotConvert.
// Check error to be sure that all required values were parsed.
func (s Setting) IntSlice() ([]int, error) {
	return parseSlice(s.Value, strconv.Atoi)
}

// Float64 converts Setting Value to float64. Returned error
// will be non nil if convesion failed.
func (s Setting) Float64() (float64, error) {
	return parseValue(s.Value, parseFloat64)
}

// Float64Slice splits Setting Value (separator is ",") and adds
// each of resulting values to []float64 if possible.
// If one or more values can not be converted to float64 those will be dropped
// and method will return conf.ErrCouldNotConvert.
// Check error to be sure that all required values were parsed.
func (s Setting) Float64Slice() ([]float64, error) {
	return parseSlice(s.Value, parseFloat64)
}

// String returns option Value as string
// This method also implements Stringer interface from fmt module
func (s Setting) String() string {
	return s.Value
}

// StringSlice splits Setting's Value (separator is ",") and adds
// each of resulting values to []string trimming leading and trailing spaces
// from each string.
func (s Setting) StringSlice() []string {
	return tidySplit(s.Value)
}

// Bool tries to interpret Setting's Value as bool
// "1", "t", "T", true", "True", "TRUE" yields true
// "0", "f", "F, "false", "False", "FALSE" yields false
// If nothing matches will return false and conf.ErrCouldNotConvert.
func (s Setting) Bool() (bool, error) {
	return parseValue(s.Value, strconv.ParseBool)
}

func parseSlice[T any](s string, f func(string) (T, error)) ([]T, error) {
	split := tidySplit(s)

	list := make([]T, 0, len(split))
	for _, str := range split {
		v, err := parseValue(str, f)
		if err != nil {
			return list, err
		}

		list = append(list, v)
	}

	return list, nil
}

func parseValue[T any](s string, f func(string) (T, error)) (T, error) {
	v, err := f(s)
	if err != nil {
		return v, errors.Join(ErrCouldNotConvert, err)
	}

	return v, err
}

func tidySplit(s string) []string {
	splitted := strings.Split(s, valuesSeparator)
	for i, str := range splitted {
		splitted[i] = strings.TrimSpace(str)
	}
	return splitted
}

func parseFloat64(s string) (float64, error) {
	return strconv.ParseFloat(s, 64)
}