package encoding

import (
	"encoding"
	"errors"
	"reflect"
	"strings"
)

var (
	// ErrNotAPointer .
	ErrNotAPointer = errors.New("v argument must be a pointer")
)

// Codec defines the interface gRPC uses to encode and decode messages.  Note
// that implementations of this interface must be thread safe; a Codec's
// methods can be called from concurrent goroutines.
type Codec interface {
	// Marshal returns the wire format of v.
	Marshal(v interface{}) ([]byte, error)
	// Unmarshal parses the wire format into v.
	Unmarshal(data []byte, v interface{}) error
	// Name returns the name of the Codec implementation. The returned string
	// will be used as part of content type in transmission.  The result must be
	// static; the result cannot change between calls.
	Name() string
}

var registeredCodecs = make(map[string]Codec)

// RegisterCodec registers the provided Codec for use with all transport clients and
// servers.
//
// The Codec will be stored and looked up by result of its Name() method, which
// should match the content-subtype of the encoding handled by the Codec.  This
// is case-insensitive, and is stored and looked up as lowercase.  If the
// result of calling Name() is an empty string, RegisterCodec will panic. See
// Content-Type on
// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests for
// more details.
//
// NOTE: this function must only be called during initialization time (i.e. in
// an init() function), and is not thread-safe.  If multiple Compressors are
// registered with the same name, the one registered last will take effect.
func RegisterCodec(codec Codec) {
	if codec == nil {
		panic("cannot register a nil Codec")
	}
	if codec.Name() == "" {
		panic("cannot register Codec with empty string result for Name()")
	}
	contentSubtype := strings.ToLower(codec.Name())
	registeredCodecs[contentSubtype] = codec
}

// GetCodec gets a registered Codec by content-subtype, or nil if no Codec is
// registered for the content-subtype.
//
// The content-subtype is expected to be lowercase.
func GetCodec(contentSubtype string) Codec {
	return registeredCodecs[contentSubtype]
}

// Encoding 编码接口定义
type Encoding interface {
	Marshal(v interface{}) ([]byte, error)
	Unmarshal(data []byte, v interface{}) error
}

// Marshal encode data
func Marshal(e Encoding, v interface{}) (data []byte, err error) {
	if !isPointer(v) {
		return data, ErrNotAPointer
	}
	bm, ok := v.(encoding.BinaryMarshaler)
	if ok && e == nil {
		data, err = bm.MarshalBinary()
		return
	}

	data, err = e.Marshal(v)
	if err == nil {
		return
	}
	if ok {
		data, err = bm.MarshalBinary()
	}

	return
}

// Unmarshal decode data
func Unmarshal(e Encoding, data []byte, v interface{}) (err error) {
	if !isPointer(v) {
		return ErrNotAPointer
	}
	bm, ok := v.(encoding.BinaryUnmarshaler)
	if ok && e == nil {
		err = bm.UnmarshalBinary(data)
		return err
	}
	err = e.Unmarshal(data, v)
	if err == nil {
		return
	}
	if ok {
		return bm.UnmarshalBinary(data)
	}
	return
}

func isPointer(data interface{}) bool {
	switch reflect.ValueOf(data).Kind() {
	case reflect.Ptr, reflect.Interface:
		return true
	default:
		return false
	}
}