package grpc

import (
	"git.frostfs.info/TrueCloudLab/frostfs-observability/metrics"
	grpcprom "github.com/grpc-ecosystem/go-grpc-middleware/providers/prometheus"
	"github.com/prometheus/client_golang/prometheus"
	dto "github.com/prometheus/client_model/go"
	"google.golang.org/grpc"
)

var serverMetrics = grpcprom.NewServerMetrics(
	grpcprom.WithServerHandlingTimeHistogram(
		grpcprom.WithHistogramBuckets(prometheus.DefBuckets),
	),
)

func init() {
	// Description copied from grpc-ecosystem:
	// https://github.com/grpc-ecosystem/go-grpc-middleware/blob/71d7422112b1d7fadd4b8bf12a6f33ba6d22e98e/providers/prometheus/server_metrics.go#L26
	descs := []metrics.Description{
		{
			Name:           "grpc_server_started_total",
			Type:           dto.MetricType_COUNTER.String(),
			Help:           "Total number of RPCs started on the server.",
			VariableLabels: []string{"grpc_type", "grpc_service", "grpc_method"},
		},
		{
			Name:           "grpc_server_handled_total",
			Type:           dto.MetricType_COUNTER.String(),
			Help:           "Total number of RPCs completed on the server, regardless of success or failure.",
			VariableLabels: []string{"grpc_type", "grpc_service", "grpc_method", "grpc_code"},
		},
		{
			Name:           "grpc_server_msg_received_total",
			Type:           dto.MetricType_COUNTER.String(),
			Help:           "Total number of RPC stream messages received on the server.",
			VariableLabels: []string{"grpc_type", "grpc_service", "grpc_method"},
		},
		{
			Name:           "grpc_server_msg_sent_total",
			Type:           dto.MetricType_COUNTER.String(),
			Help:           "Total number of gRPC stream messages sent by the server.",
			VariableLabels: []string{"grpc_type", "grpc_service", "grpc_method"},
		},
		{
			Name:           "grpc_server_handling_seconds",
			Type:           dto.MetricType_HISTOGRAM.String(),
			Help:           "Histogram of response latency (seconds) of gRPC that had been application-level handled by the server.",
			VariableLabels: []string{"grpc_type", "grpc_service", "grpc_method"},
		},
	}
	metrics.MustRegister(serverMetrics, descs...)
}

// NewUnaryServerInterceptor returns server interceptor to collect metrics from unary RPCs.
func NewUnaryServerInterceptor() grpc.UnaryServerInterceptor {
	return serverMetrics.UnaryServerInterceptor()
}

// NewStreamServerInterceptor returns server interceptor to collect metrics from stream RPCs.
func NewStreamServerInterceptor() grpc.StreamServerInterceptor {
	return serverMetrics.StreamServerInterceptor()
}