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// Copyright © 2019 Bjørn Erik Pedersen <bjorn.erik.pedersen@gmail.com>.
//
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
package tmc
import (
"encoding"
"fmt"
"math/big"
"reflect"
"strconv"
"time"
)
// Adapter wraps a type to preserve type information when encoding and decoding
// a map.
//
// The simples way to create new adapters is via the NewAdapter function.
type Adapter interface {
FromString(s string) (interface{}, error)
MarshalText() (text []byte, err error)
Type() reflect.Type
Wrap(v interface{}) Adapter
}
var (
// DefaultTypeAdapters contains the default set of type adapters.
DefaultTypeAdapters = []Adapter{
// Time
NewAdapter(time.Now(), nil, nil),
NewAdapter(
3*time.Hour,
func(s string) (interface{}, error) { return time.ParseDuration(s) },
func(v interface{}) (string, error) { return v.(time.Duration).String(), nil },
),
// Numbers
NewAdapter(big.NewRat(1, 2), nil, nil),
NewAdapter(
int(32),
func(s string) (interface{}, error) {
return strconv.Atoi(s)
},
func(v interface{}) (string, error) {
return strconv.Itoa(v.(int)), nil
},
),
}
)
// NewAdapter creates a new adapter that wraps the target type.
//
// fromString can be omitted if target implements encoding.TextUnmarshaler.
// toString can be omitted if target implements encoding.TextMarshaler.
//
// It will panic if it can not be created.
func NewAdapter(
target interface{},
fromString func(s string) (interface{}, error),
toString func(v interface{}) (string, error)) Adapter {
targetValue := reflect.ValueOf(target)
targetType := targetValue.Type()
wasPointer := targetType.Kind() == reflect.Ptr
if !wasPointer {
// Need the pointer to see the TextUnmarshaler implementation.
v := targetValue
targetValue = reflect.New(targetType)
targetValue.Elem().Set(v)
}
if fromString == nil {
if _, ok := targetValue.Interface().(encoding.TextUnmarshaler); ok {
fromString = func(s string) (interface{}, error) {
typ := targetType
if typ.Kind() == reflect.Ptr {
typ = typ.Elem()
}
v := reflect.New(typ)
err := v.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(s))
if err != nil {
return nil, err
}
if !wasPointer {
v = v.Elem()
}
return v.Interface(), nil
}
} else {
panic(fmt.Sprintf("%T can not be unmarshaled", target))
}
}
var marshalText func(v interface{}) ([]byte, error)
if toString != nil {
marshalText = func(v interface{}) ([]byte, error) {
s, err := toString(v)
return []byte(s), err
}
} else if _, ok := target.(encoding.TextMarshaler); ok {
marshalText = func(v interface{}) ([]byte, error) {
return v.(encoding.TextMarshaler).MarshalText()
}
} else {
panic(fmt.Sprintf("%T can not be marshaled", target))
}
return &adapter{
targetType: targetType,
fromString: fromString,
marshalText: marshalText,
}
}
var _ Adapter = (*adapter)(nil)
type adapter struct {
fromString func(s string) (interface{}, error)
marshalText func(v interface{}) (text []byte, err error)
targetType reflect.Type
target interface{}
}
func (a *adapter) FromString(s string) (interface{}, error) {
return a.fromString(s)
}
func (a *adapter) MarshalText() (text []byte, err error) {
return a.marshalText(a.target)
}
func (a adapter) Type() reflect.Type {
return a.targetType
}
func (a adapter) Wrap(v interface{}) Adapter {
a.target = v
return &a
}
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