package axon

import (
	"fmt"

	"github.com/vmihailenco/msgpack/v5"
)

// MarshalEvent encodes an Event to MessagePack. Fields are encoded in the
// canonical struct order using the msgpack struct tags. Binary fields (id,
// pubkey, sig, content) are encoded as msgpack bin type ([]byte).
func MarshalEvent(e *Event) ([]byte, error) {
	b, err := msgpack.Marshal(e)
	if err != nil {
		return nil, fmt.Errorf("axon: marshal event: %w", err)
	}
	return b, nil
}

// UnmarshalEvent decodes a MessagePack blob into an Event.
func UnmarshalEvent(data []byte) (*Event, error) {
	var e Event
	if err := msgpack.Unmarshal(data, &e); err != nil {
		return nil, fmt.Errorf("axon: unmarshal event: %w", err)
	}
	return &e, nil
}

// MarshalMessage encodes a wire message as a msgpack array: [type, payload].
// messageType is a uint16; payload is any msgpack-serializable value.
func MarshalMessage(messageType uint16, payload interface{}) ([]byte, error) {
	b, err := msgpack.Marshal([]interface{}{messageType, payload})
	if err != nil {
		return nil, fmt.Errorf("axon: marshal message: %w", err)
	}
	return b, nil
}

// UnmarshalMessageType reads only the first element of a [type, payload]
// msgpack array, returning the message type without decoding the payload.
func UnmarshalMessageType(data []byte) (uint16, error) {
	var arr []msgpack.RawMessage
	if err := msgpack.Unmarshal(data, &arr); err != nil {
		return 0, fmt.Errorf("axon: unmarshal message: %w", err)
	}
	if len(arr) < 1 {
		return 0, fmt.Errorf("axon: message array is empty")
	}
	var t uint16
	if err := msgpack.Unmarshal(arr[0], &t); err != nil {
		return 0, fmt.Errorf("axon: unmarshal message type: %w", err)
	}
	return t, nil
}