package metricsutil

import (
	"strconv"
	"sync"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"go.uber.org/atomic"

	"github.com/milvus-io/milvus/pkg/v2/metrics"
	"github.com/milvus-io/milvus/pkg/v2/util/paramtable"
	"github.com/milvus-io/milvus/pkg/v2/util/typeutil"
)

// labeledRecord is a labeled sample point.
type labeledRecord interface {
	// Label of the access metric.
	Label() SegmentLabel

	// Finish finishes the record.
	Finish(err error)

	// getError returns the error of the record.
	// current metric system simply reject the error operation.
	getError() error
}

// globalObserver is the global resource groups observer.
var (
	once           sync.Once
	globalObserver *segmentsObserver
)

func getGlobalObserver() *segmentsObserver {
	once.Do(func() {
		globalObserver = newSegmentsObserver()
		go func() {
			d := 15 * time.Minute
			ticker := time.NewTicker(d)
			defer ticker.Stop()
			for range ticker.C {
				expireAt := time.Now().Add(-d)
				globalObserver.Expire(expireAt)
			}
		}()
	})
	return globalObserver
}

// newSegmentsObserver creates a new segmentsObserver.
// Used to check if a segment is hot or cold.
func newSegmentsObserver() *segmentsObserver {
	return &segmentsObserver{
		nodeID:   strconv.FormatInt(paramtable.GetNodeID(), 10),
		segments: typeutil.NewConcurrentMap[SegmentLabel, *segmentObserver](),
	}
}

// segmentsObserver is a observer all segments metrics.
type segmentsObserver struct {
	nodeID   string
	segments *typeutil.ConcurrentMap[SegmentLabel, *segmentObserver] // map segment id to observer.
	// one segment can be removed from one query node, for balancing or compacting.
	// no more search operation will be performed on the segment after it is removed.
	// all related metric should be expired after a while.
	// may be a huge map with 100000+ entries.
}

// Observe records a new metric
func (o *segmentsObserver) Observe(m labeledRecord) {
	if m.getError() != nil {
		return // reject error record.
		// TODO: add error as a label of metrics.
	}
	// fast path.
	label := m.Label()
	observer, ok := o.segments.Get(label)
	if !ok {
		// slow path.
		newObserver := newSegmentObserver(o.nodeID, label)
		observer, _ = o.segments.GetOrInsert(label, newObserver)
	}
	// do a observer.
	observer.Observe(m)
}

// Expire expires the observer.
func (o *segmentsObserver) Expire(expiredAt time.Time) {
	o.segments.Range(func(label SegmentLabel, value *segmentObserver) bool {
		if value.IsExpired(expiredAt) {
			o.segments.Remove(label)
			value.Clear()
			return true
		}
		return true
	})
}

// newSegmentObserver creates a new segmentObserver.
func newSegmentObserver(nodeID string, label SegmentLabel) *segmentObserver {
	now := time.Now()
	return &segmentObserver{
		label:       label,
		prom:        newPromObserver(nodeID, label),
		lastUpdates: atomic.NewPointer[time.Time](&now),
	}
}

// segmentObserver is a observer for segment metrics.
type segmentObserver struct {
	label SegmentLabel // never updates
	// observers.
	prom promMetricsObserver // prometheus metrics observer.
	// for expiration.
	lastUpdates *atomic.Pointer[time.Time] // update every access.
}

// IsExpired checks if the segment observer is expired.
func (o *segmentObserver) IsExpired(expireAt time.Time) bool {
	return o.lastUpdates.Load().Before(expireAt)
}

// Observe observe a new
func (o *segmentObserver) Observe(m labeledRecord) {
	now := time.Now()
	o.lastUpdates.Store(&now)

	switch mm := m.(type) {
	case *CacheLoadRecord:
		o.prom.ObserveCacheLoad(mm)
	case *CacheEvictRecord:
		o.prom.ObserveCacheEvict(mm)
	case QuerySegmentAccessRecord:
		o.prom.ObserveQueryAccess(mm)
	case SearchSegmentAccessRecord:
		o.prom.ObserveSearchAccess(mm)
	default:
		panic("unknown segment access metric")
	}
}

// Clear clears the observer.
func (o *segmentObserver) Clear() {
	o.prom.Clear()
}

// newPromObserver creates a new promMetrics.
func newPromObserver(nodeID string, label SegmentLabel) promMetricsObserver {
	return promMetricsObserver{
		nodeID:                               nodeID,
		label:                                label,
		DiskCacheLoadTotal:                   metrics.QueryNodeDiskCacheLoadTotal.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup),
		DiskCacheLoadDuration:                metrics.QueryNodeDiskCacheLoadDuration.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup),
		DiskCacheLoadBytes:                   metrics.QueryNodeDiskCacheLoadBytes.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup),
		DiskCacheEvictTotal:                  metrics.QueryNodeDiskCacheEvictTotal.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup),
		DiskCacheEvictDuration:               metrics.QueryNodeDiskCacheEvictDuration.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup),
		DiskCacheEvictBytes:                  metrics.QueryNodeDiskCacheEvictBytes.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup),
		QuerySegmentAccessTotal:              metrics.QueryNodeSegmentAccessTotal.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup, metrics.QueryLabel),
		QuerySegmentAccessDuration:           metrics.QueryNodeSegmentAccessDuration.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup, metrics.QueryLabel),
		QuerySegmentAccessWaitCacheTotal:     metrics.QueryNodeSegmentAccessWaitCacheTotal.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup, metrics.QueryLabel),
		QuerySegmentAccessWaitCacheDuration:  metrics.QueryNodeSegmentAccessWaitCacheDuration.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup, metrics.QueryLabel),
		SearchSegmentAccessTotal:             metrics.QueryNodeSegmentAccessTotal.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup, metrics.SearchLabel),
		SearchSegmentAccessDuration:          metrics.QueryNodeSegmentAccessDuration.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup, metrics.SearchLabel),
		SearchSegmentAccessWaitCacheTotal:    metrics.QueryNodeSegmentAccessWaitCacheTotal.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup, metrics.SearchLabel),
		SearchSegmentAccessWaitCacheDuration: metrics.QueryNodeSegmentAccessWaitCacheDuration.WithLabelValues(nodeID, label.DatabaseName, label.ResourceGroup, metrics.SearchLabel),

		DiskCacheLoadGlobalDuration:                metrics.QueryNodeDiskCacheLoadGlobalDuration.WithLabelValues(nodeID),
		DiskCacheEvictGlobalDuration:               metrics.QueryNodeDiskCacheEvictGlobalDuration.WithLabelValues(nodeID),
		QuerySegmentAccessGlobalDuration:           metrics.QueryNodeSegmentAccessGlobalDuration.WithLabelValues(nodeID, metrics.QueryLabel),
		SearchSegmentAccessGlobalDuration:          metrics.QueryNodeSegmentAccessGlobalDuration.WithLabelValues(nodeID, metrics.SearchLabel),
		QuerySegmentAccessWaitCacheGlobalDuration:  metrics.QueryNodeSegmentAccessWaitCacheGlobalDuration.WithLabelValues(nodeID, metrics.QueryLabel),
		SearchSegmentAccessWaitCacheGlobalDuration: metrics.QueryNodeSegmentAccessWaitCacheGlobalDuration.WithLabelValues(nodeID, metrics.SearchLabel),
	}
}

// promMetricsObserver is a observer for prometheus metrics.
type promMetricsObserver struct {
	nodeID string
	label  SegmentLabel // never updates

	DiskCacheLoadTotal                   prometheus.Counter
	DiskCacheLoadDuration                prometheus.Counter
	DiskCacheLoadBytes                   prometheus.Counter
	DiskCacheEvictTotal                  prometheus.Counter
	DiskCacheEvictBytes                  prometheus.Counter
	DiskCacheEvictDuration               prometheus.Counter
	QuerySegmentAccessTotal              prometheus.Counter
	QuerySegmentAccessDuration           prometheus.Counter
	QuerySegmentAccessWaitCacheTotal     prometheus.Counter
	QuerySegmentAccessWaitCacheDuration  prometheus.Counter
	SearchSegmentAccessTotal             prometheus.Counter
	SearchSegmentAccessDuration          prometheus.Counter
	SearchSegmentAccessWaitCacheTotal    prometheus.Counter
	SearchSegmentAccessWaitCacheDuration prometheus.Counter

	DiskCacheLoadGlobalDuration                prometheus.Observer
	DiskCacheEvictGlobalDuration               prometheus.Observer
	QuerySegmentAccessGlobalDuration           prometheus.Observer
	SearchSegmentAccessGlobalDuration          prometheus.Observer
	QuerySegmentAccessWaitCacheGlobalDuration  prometheus.Observer
	SearchSegmentAccessWaitCacheGlobalDuration prometheus.Observer
}

// ObserveLoad records a new cache load
func (o *promMetricsObserver) ObserveCacheLoad(r *CacheLoadRecord) {
	o.DiskCacheLoadTotal.Inc()
	o.DiskCacheLoadBytes.Add(r.getBytes())
	d := r.getMilliseconds()
	o.DiskCacheLoadDuration.Add(d)
	o.DiskCacheLoadGlobalDuration.Observe(d)
}

// ObserveCacheEvict records a new cache evict.
func (o *promMetricsObserver) ObserveCacheEvict(r *CacheEvictRecord) {
	o.DiskCacheEvictTotal.Inc()
	o.DiskCacheEvictBytes.Add(r.getBytes())
	d := r.getMilliseconds()
	o.DiskCacheEvictDuration.Add(d)
	o.DiskCacheEvictGlobalDuration.Observe(d)
}

// ObserveQueryAccess records a new query access.
func (o *promMetricsObserver) ObserveQueryAccess(r QuerySegmentAccessRecord) {
	o.QuerySegmentAccessTotal.Inc()
	d := r.getMilliseconds()
	o.QuerySegmentAccessDuration.Add(d)
	o.QuerySegmentAccessGlobalDuration.Observe(d)
	if r.isCacheMiss {
		o.QuerySegmentAccessWaitCacheTotal.Inc()
		d := r.getWaitLoadMilliseconds()
		o.QuerySegmentAccessWaitCacheDuration.Add(d)
		o.QuerySegmentAccessWaitCacheGlobalDuration.Observe(d)
	}
}

// ObserveSearchAccess records a new search access.
func (o *promMetricsObserver) ObserveSearchAccess(r SearchSegmentAccessRecord) {
	o.SearchSegmentAccessTotal.Inc()
	d := r.getMilliseconds()
	o.SearchSegmentAccessDuration.Add(d)
	o.SearchSegmentAccessGlobalDuration.Observe(d)
	if r.isCacheMiss {
		o.SearchSegmentAccessWaitCacheTotal.Inc()
		d := r.getWaitLoadMilliseconds()
		o.SearchSegmentAccessWaitCacheDuration.Add(d)
		o.SearchSegmentAccessWaitCacheGlobalDuration.Observe(d)
	}
}

// Clear clears the prometheus metrics.
func (o *promMetricsObserver) Clear() {
	label := o.label

	metrics.QueryNodeDiskCacheLoadTotal.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup)
	metrics.QueryNodeDiskCacheLoadBytes.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup)
	metrics.QueryNodeDiskCacheLoadDuration.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup)
	metrics.QueryNodeDiskCacheEvictTotal.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup)
	metrics.QueryNodeDiskCacheEvictBytes.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup)
	metrics.QueryNodeDiskCacheEvictDuration.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup)

	metrics.QueryNodeSegmentAccessTotal.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup, metrics.SearchLabel)
	metrics.QueryNodeSegmentAccessTotal.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup, metrics.QueryLabel)
	metrics.QueryNodeSegmentAccessDuration.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup, metrics.SearchLabel)
	metrics.QueryNodeSegmentAccessDuration.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup, metrics.QueryLabel)

	metrics.QueryNodeSegmentAccessWaitCacheTotal.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup, metrics.SearchLabel)
	metrics.QueryNodeSegmentAccessWaitCacheTotal.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup, metrics.QueryLabel)
	metrics.QueryNodeSegmentAccessWaitCacheDuration.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup, metrics.SearchLabel)
	metrics.QueryNodeSegmentAccessWaitCacheDuration.DeleteLabelValues(o.nodeID, label.DatabaseName, label.ResourceGroup, metrics.QueryLabel)
}