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config.go
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config.go
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// Copyright (c) 2023 Z5Labs and Contributors
//
// This software is released under the MIT License.
// https://opensource.org/licenses/MIT
package config
import (
"bytes"
"encoding"
"errors"
"io"
"reflect"
"strings"
"text/template"
"time"
"github.com/mitchellh/mapstructure"
"github.com/spf13/viper"
)
// Manager stores config values and provides helpers for
// bridging the raw config values into Go types.
type Manager struct {
*viper.Viper
}
// ReadOption configures different properties of the reader.
type ReadOption func(*reader)
// LanguageType configures the expected language the source is encoded in.
type LanguageType string
const (
YAML LanguageType = "yaml"
JSON LanguageType = "json"
TOML LanguageType = "toml"
)
// Language sets which language the config source uses.
func Language(lang LanguageType) ReadOption {
return func(r *reader) {
r.lang = lang
}
}
// TemplateFunc allows you to register template functions which
// can be used in the config source template.
func TemplateFunc(name string, f any) ReadOption {
return func(r *reader) {
r.tmplFuncs[name] = f
}
}
type reader struct {
lang LanguageType
tmplFuncs template.FuncMap
}
// Read parses the data from r and stores the config values in the returned Manager.
func Read(r io.Reader, opts ...ReadOption) (Manager, error) {
rd := reader{
lang: YAML,
tmplFuncs: make(template.FuncMap),
}
for _, opt := range opts {
opt(&rd)
}
v := viper.New()
v.SetConfigType(string(rd.lang))
err := rd.read(v, r)
if err != nil {
return Manager{}, err
}
return Manager{Viper: v}, nil
}
// Merge allows you to merge another config into an already existing one.
func Merge(m Manager, r io.Reader, opts ...ReadOption) (Manager, error) {
if m.Viper == nil {
return Read(r, opts...)
}
rd := reader{
lang: YAML,
tmplFuncs: make(template.FuncMap),
}
for _, opt := range opts {
opt(&rd)
}
var buf bytes.Buffer
err := rd.renderTemplate(&buf, r)
if err != nil {
return m, err
}
return m, m.MergeConfig(&buf)
}
// Unmarshal unmarshals the config into the value pointed to by v.
func (m Manager) Unmarshal(v interface{}) error {
dec, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
TagName: "config",
Result: v,
DecodeHook: composeDecodeHooks(
textUnmarshalerHookFunc(),
timeDurationHookFunc(),
),
})
if err != nil {
return err
}
return dec.Decode(m.AllSettings())
}
var errInvalidDecodeCondition = errors.New("invalid decode condition")
type multiError struct {
errors []error
}
func (e multiError) Error() string {
ss := make([]string, len(e.errors))
for i, e := range e.errors {
ss[i] = e.Error()
}
return strings.Join(ss, "\n")
}
func composeDecodeHooks(hs ...mapstructure.DecodeHookFunc) mapstructure.DecodeHookFuncValue {
return func(f, t reflect.Value) (any, error) {
var errs []error
for _, h := range hs {
v, err := mapstructure.DecodeHookExec(h, f, t)
if err == nil {
return v, nil
}
if err == errInvalidDecodeCondition {
continue
}
errs = append(errs, err)
}
if len(errs) == 0 {
return f.Interface(), nil
}
return nil, multiError{errors: errs}
}
}
func textUnmarshalerHookFunc() mapstructure.DecodeHookFuncType {
return func(f reflect.Type, t reflect.Type, data any) (any, error) {
if f.Kind() != reflect.String {
return nil, errInvalidDecodeCondition
}
result := reflect.New(t).Interface()
u, ok := result.(encoding.TextUnmarshaler)
if !ok {
return nil, errInvalidDecodeCondition
}
err := u.UnmarshalText([]byte(data.(string)))
if err != nil {
return nil, err
}
return result, nil
}
}
func timeDurationHookFunc() mapstructure.DecodeHookFuncType {
return func(f reflect.Type, t reflect.Type, data any) (any, error) {
if t != reflect.TypeOf(time.Duration(0)) {
return nil, errInvalidDecodeCondition
}
switch f.Kind() {
case reflect.String:
return time.ParseDuration(data.(string))
case reflect.Int:
return time.Duration(int64(data.(int))), nil
default:
return nil, errInvalidDecodeCondition
}
}
}
func (rd reader) renderTemplate(dst io.Writer, src io.Reader) error {
var sb strings.Builder
_, err := io.Copy(&sb, src)
if err != nil {
return err
}
s := sb.String()
tmpl, err := template.New("config").Funcs(rd.tmplFuncs).Parse(s)
if err != nil {
return err
}
return tmpl.Execute(dst, struct{}{})
}
func (rd reader) read(v *viper.Viper, r io.Reader) error {
var buf bytes.Buffer
err := rd.renderTemplate(&buf, r)
if err != nil {
return err
}
v.SetConfigType(string(rd.lang))
err = v.ReadConfig(&buf)
if err != nil {
return err
}
return nil
}