package record

import (
	"errors"
	"reflect"
)

var (
	// ErrPayloadTypeNotRegistered is returned from ConsumeEnvelope when the Envelope's
	// PayloadType does not match any registered Record types.
	ErrPayloadTypeNotRegistered = errors.New("payload type is not registered")

	payloadTypeRegistry = make(map[string]Record)
)

// Record represents a data type that can be used as the payload of an Envelope.
// The Record interface defines the methods used to marshal and unmarshal a Record
// type to a byte slice.
//
// Record types may be "registered" as the default for a given Envelope.PayloadType
// using the RegisterPayloadType function. Once a Record type has been registered,
// an instance of that type will be created and used to unmarshal the payload of
// any Envelope with the registered PayloadType when the Envelope is opened using
// the ConsumeEnvelope function.
//
// To use an unregistered Record type instead, use ConsumeTypedEnvelope and pass in
// an instance of the Record type that you'd like the Envelope's payload to be
// unmarshaled into.
type Record interface {
	MarshalRecord() ([]byte, error)

	UnmarshalRecord([]byte) error
}

// RegisterPayloadType associates a binary payload type identifier with a concrete
// Record type. This is used to automatically unmarshal Record payloads from Envelopes
// when using ConsumeEnvelope, and to automatically marshal Records and determine the
// correct PayloadType when calling MakeEnvelopeWithRecord.
//
// Callers must provide an instance of the record type to be registered, which must be
// a pointer type. Registration should be done in the init function of the package
// where the Record type is defined:
//
//    package hello_record
//
//    var HelloRecordPayloadType = []byte("/libp2p/hello-record")
//
//    func init() {
//        RegisterPayloadType(HelloRecordPayloadType, &HelloRecord{})
//    }
//
//    type HelloRecord struct { } // etc..
//
func RegisterPayloadType(payloadType []byte, prototype Record) {
	payloadTypeRegistry[string(payloadType)] = prototype
}

func unmarshalRecordPayload(payloadType []byte, payloadBytes []byte) (Record, error) {
	rec, err := blankRecordForPayloadType(payloadType)
	if err != nil {
		return nil, err
	}
	err = rec.UnmarshalRecord(payloadBytes)
	if err != nil {
		return nil, err
	}
	return rec, nil
}

func blankRecordForPayloadType(payloadType []byte) (Record, error) {
	prototype, ok := payloadTypeRegistry[string(payloadType)]
	if !ok {
		return nil, ErrPayloadTypeNotRegistered
	}

	valueType := getValueType(prototype)
	val := reflect.New(valueType)
	asRecord := val.Interface().(Record)
	return asRecord, nil
}

func payloadTypeForRecord(rec Record) ([]byte, bool) {
	valueType := getValueType(rec)

	for k, v := range payloadTypeRegistry {
		t := getValueType(v)
		if t.AssignableTo(valueType) {
			return []byte(k), true
		}
	}
	return []byte{}, false
}

func getValueType(i interface{}) reflect.Type {
	valueType := reflect.TypeOf(i)
	if valueType.Kind() == reflect.Ptr {
		valueType = valueType.Elem()
	}
	return valueType
}