package store

import (
	"sync"
	"time"
)

// uploadHistory tracks running total/count of upload durations for one device.
type uploadHistory struct {
	mu    sync.Mutex
	total time.Duration
	count int64
}

func (u *uploadHistory) add(d time.Duration) {
	u.mu.Lock()
	defer u.mu.Unlock()
	u.total += d
	u.count++
}

func (u *uploadHistory) average() time.Duration {
	u.mu.Lock()
	defer u.mu.Unlock()
	if u.count == 0 {
		return 0
	}
	// Truncating integer division — same idea as C# BigInteger total / count.
	return u.total / time.Duration(u.count)
}

func (s *Store) uploadFor(id DeviceID) *uploadHistory {
	s.mu.Lock()
	defer s.mu.Unlock()

	u, ok := s.uploads[id]
	if !ok {
		u = &uploadHistory{}
		s.uploads[id] = u
	}
	return u
}

// AddUpload records an upload duration (nanoseconds as time.Duration) for deviceID.
// sent_at from the API is intentionally ignored here; the HTTP layer still accepts it.
func (s *Store) AddUpload(deviceID DeviceID, uploadTime time.Duration) {
	s.uploadFor(deviceID).add(uploadTime)
}

// AverageUploadTime returns the mean upload duration for deviceID.
// Formatting for the API (duration.String()) belongs at the HTTP edge.
// Unknown / never-seen devices return 0.
func (s *Store) AverageUploadTime(deviceID DeviceID) time.Duration {
	s.mu.Lock()
	u, ok := s.uploads[deviceID]
	s.mu.Unlock()
	if !ok {
		return 0
	}
	return u.average()
}