package connectsrv

import (
	"context"
	"time"

	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/metric"
	"go.opentelemetry.io/otel/metric/noop"
)

// meterName scopes the gateway edge's OpenTelemetry instruments.
const meterName = "scrabble/gateway/edge"

// serverMetrics holds the edge's operational instruments. It defaults to no-ops;
// NewServer installs the real meter when one is supplied in Deps.
type serverMetrics struct {
	edge metric.Float64Histogram
}

// newServerMetrics builds the instruments on meter (nil selects a no-op meter),
// falling back to a no-op histogram on the (rare) construction error.
func newServerMetrics(meter metric.Meter) *serverMetrics {
	if meter == nil {
		meter = noop.NewMeterProvider().Meter(meterName)
	}
	h, err := meter.Float64Histogram("edge_request_duration",
		metric.WithUnit("s"),
		metric.WithDescription("Seconds to serve one Connect Execute call, by message type and result."))
	if err != nil {
		h, _ = noop.NewMeterProvider().Meter(meterName).Float64Histogram("edge_request_duration")
	}
	return &serverMetrics{edge: h}
}

// recordEdge records the duration of one Execute call labelled by message type and
// outcome (ok, domain, unauthenticated, rate_limited, unknown_type or internal).
func (m *serverMetrics) recordEdge(ctx context.Context, msgType, result string, start time.Time) {
	m.edge.Record(ctx, time.Since(start).Seconds(), metric.WithAttributes(
		attribute.String("message_type", msgType),
		attribute.String("result", result),
	))
}