package nnet

import (
	"context"
	"fmt"

	protocolpkg "github.com/noahlann/nnet/pkg/protocol"
)

// NNetVersionIdentifier NNet协议版本识别器
// 从协议帧头中读取版本字段（偏移4的位置，1字节）
type NNetVersionIdentifier struct {
	// versionMapping 版本映射：byte值 -> 版本字符串
	// 例如：{1: "1.0", 2: "2.0"}
	versionMapping map[byte]string
}

// NewNNetVersionIdentifier 创建NNet协议版本识别器
func NewNNetVersionIdentifier(versionMapping map[byte]string) protocolpkg.VersionIdentifier {
	if versionMapping == nil {
		// 默认映射
		versionMapping = map[byte]string{
			1: "1.0",
			2: "2.0",
		}
	}
	return &NNetVersionIdentifier{
		versionMapping: versionMapping,
	}
}

// Identify 识别协议版本
func (i *NNetVersionIdentifier) Identify(data []byte, ctx context.Context) (string, error) {
	// NNet协议格式：[Magic(4)][Version(1)][Length(4)][Data(N)][Checksum(2)]
	// 版本字段在偏移4的位置（Magic 4字节之后）
	versionOffset := 4
	minRequiredBytes := versionOffset + 1

	// 检查数据长度
	if len(data) < minRequiredBytes {
		return "", protocolpkg.NewError(fmt.Sprintf("data too short: need at least %d bytes, got %d", minRequiredBytes, len(data)))
	}

	// 检查Magic
	magic := string(data[0:4])
	if magic != "NNET" {
		return "", protocolpkg.NewError(fmt.Sprintf("invalid magic: %s", magic))
	}

	// 读取版本字段
	versionByte := data[versionOffset]

	// 查找版本映射
	version, ok := i.versionMapping[versionByte]
	if !ok {
		return "", protocolpkg.NewError(fmt.Sprintf("unknown version byte: %d", versionByte))
	}

	return version, nil
}