package cache

import (
	"context"
	"fmt"
	"sync"

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

// CacheMetrics exposes cache-related metric instruments.
type CacheMetrics struct {
	CacheOperationsTotal metric.Int64Counter
	CacheHitsTotal       metric.Int64Counter
	CacheMissesTotal    metric.Int64Counter
}

var (
	cacheMetricsInstance *CacheMetrics
	cacheMetricsOnce     sync.Once
	cacheMetricsErr      error
)

// GetCacheMetrics lazily initializes cache metric instruments and returns a cached reference.
func GetCacheMetrics(ctx context.Context) (*CacheMetrics, error) {
	cacheMetricsOnce.Do(func() {
		cacheMetricsInstance, cacheMetricsErr = newCacheMetrics()
	})
	return cacheMetricsInstance, cacheMetricsErr
}

func newCacheMetrics() (*CacheMetrics, error) {
	meter := otel.GetMeterProvider().Meter(
		"github.com/beckn-one/beckn-onix/cache",
		metric.WithInstrumentationVersion("1.0.0"),
	)

	m := &CacheMetrics{}
	var err error

	if m.CacheOperationsTotal, err = meter.Int64Counter(
		"onix_cache_operations_total",
		metric.WithDescription("Redis cache operations"),
		metric.WithUnit("{operation}"),
	); err != nil {
		return nil, fmt.Errorf("onix_cache_operations_total: %w", err)
	}

	if m.CacheHitsTotal, err = meter.Int64Counter(
		"onix_cache_hits_total",
		metric.WithDescription("Redis cache hits"),
		metric.WithUnit("{hit}"),
	); err != nil {
		return nil, fmt.Errorf("onix_cache_hits_total: %w", err)
	}

	if m.CacheMissesTotal, err = meter.Int64Counter(
		"onix_cache_misses_total",
		metric.WithDescription("Redis cache misses"),
		metric.WithUnit("{miss}"),
	); err != nil {
		return nil, fmt.Errorf("onix_cache_misses_total: %w", err)
	}

	return m, nil
}