package metrics

import (
	"fmt"
	"io"
)

// PrometheusExporter 将内部指标导出为 Prometheus 文本格式。
type PrometheusExporter struct {
	metrics Metrics
}

// NewPrometheusExporter 创建 Prometheus 导出器。
func NewPrometheusExporter(m Metrics) *PrometheusExporter {
	return &PrometheusExporter{
		metrics: m,
	}
}

// Export 将指标写入指定的 io.Writer。
func (e *PrometheusExporter) Export(w io.Writer) error {
	// 连接数
	fmt.Fprintf(w, "# HELP nnet_connections Current number of connections\n")
	fmt.Fprintf(w, "# TYPE nnet_connections gauge\n")
	fmt.Fprintf(w, "nnet_connections %d\n", e.metrics.GetConnections())

	// 请求数
	fmt.Fprintf(w, "# HELP nnet_requests Total number of requests\n")
	fmt.Fprintf(w, "# TYPE nnet_requests counter\n")
	fmt.Fprintf(w, "nnet_requests %d\n", e.metrics.GetRequests())

	// 错误数
	fmt.Fprintf(w, "# HELP nnet_errors Total number of errors\n")
	fmt.Fprintf(w, "# TYPE nnet_errors counter\n")
	fmt.Fprintf(w, "nnet_errors %d\n", e.metrics.GetErrors())

	// 接收字节数
	fmt.Fprintf(w, "# HELP nnet_bytes_received Total bytes received\n")
	fmt.Fprintf(w, "# TYPE nnet_bytes_received counter\n")
	fmt.Fprintf(w, "nnet_bytes_received %d\n", e.metrics.GetBytesReceived())

	// 发送字节数
	fmt.Fprintf(w, "# HELP nnet_bytes_sent Total bytes sent\n")
	fmt.Fprintf(w, "# TYPE nnet_bytes_sent counter\n")
	fmt.Fprintf(w, "nnet_bytes_sent %d\n", e.metrics.GetBytesSent())

	return nil
}