package store

import (
	"sync"
	"time"
)

const MaxHistoryPoints = 10000

type Sample struct {
	At    time.Time
	Value int
}

type Store struct {
	mu        sync.RWMutex
	value     int
	updatedAt time.Time
	history   []Sample
}

func (s *Store) Get() int {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.value
}

func (s *Store) Set(v int) {
	s.mu.Lock()
	s.value = v
	now := time.Now()
	s.updatedAt = now
	s.history = append(s.history, Sample{At: now, Value: v})
	s.trimHistoryLocked(now)
	s.mu.Unlock()
}

func (s *Store) trimHistoryLocked(now time.Time) {
	cutoff := now.Add(-12 * time.Hour)
	keep := s.history[:0]
	for _, point := range s.history {
		if point.At.After(cutoff) {
			keep = append(keep, point)
		}
	}
	if len(keep) > MaxHistoryPoints {
		keep = keep[len(keep)-MaxHistoryPoints:]
	}
	s.history = keep
}

func (s *Store) Snapshot() (int, time.Time, []Sample) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	history := append([]Sample(nil), s.history...)
	return s.value, s.updatedAt, history
}