package pgproto3

import (
	"encoding/binary"
	"encoding/hex"
	"encoding/json"

	"github.com/jackc/pgx/v5/internal/pgio"
)

type BackendKeyData struct {
	ProcessID uint32
	SecretKey []byte
}

// Backend identifies this message as sendable by the PostgreSQL backend.
func (*BackendKeyData) Backend() {}

// Decode decodes src into dst. src must contain the complete message with the exception of the initial 1 byte message
// type identifier and 4 byte message length.
func (dst *BackendKeyData) Decode(src []byte) error {
	if len(src) < 8 {
		return &invalidMessageLenErr{messageType: "BackendKeyData", expectedLen: 8, actualLen: len(src)}
	}

	dst.ProcessID = binary.BigEndian.Uint32(src[:4])
	dst.SecretKey = make([]byte, len(src)-4)
	copy(dst.SecretKey, src[4:])

	return nil
}

// Encode encodes src into dst. dst will include the 1 byte message type identifier and the 4 byte message length.
func (src *BackendKeyData) Encode(dst []byte) ([]byte, error) {
	dst, sp := beginMessage(dst, 'K')
	dst = pgio.AppendUint32(dst, src.ProcessID)
	dst = append(dst, src.SecretKey...)
	return finishMessage(dst, sp)
}

// MarshalJSON implements encoding/json.Marshaler.
func (src BackendKeyData) MarshalJSON() ([]byte, error) {
	return json.Marshal(struct {
		Type      string
		ProcessID uint32
		SecretKey string
	}{
		Type:      "BackendKeyData",
		ProcessID: src.ProcessID,
		SecretKey: hex.EncodeToString(src.SecretKey),
	})
}

// UnmarshalJSON implements encoding/json.Unmarshaler.
func (dst *BackendKeyData) UnmarshalJSON(data []byte) error {
	var msg struct {
		ProcessID uint32
		SecretKey string
	}
	if err := json.Unmarshal(data, &msg); err != nil {
		return err
	}

	dst.ProcessID = msg.ProcessID
	secretKey, err := hex.DecodeString(msg.SecretKey)
	if err != nil {
		return err
	}
	dst.SecretKey = secretKey
	return nil
}