interval.go

package tsdb

import (
	"fmt"
	"time"
)

var (
	defaultRes  int64         = 1500
	minInterval time.Duration = 1 * time.Millisecond
	year        time.Duration = time.Hour * 24 * 365
	day         time.Duration = time.Hour * 24 * 365
)

func CalculateInterval(timerange *TimeRange) string {
	interval := time.Duration((timerange.MustGetTo().UnixNano() - timerange.MustGetFrom().UnixNano()) / defaultRes)

	if interval < minInterval {
		return formatDuration(minInterval)
	}

	return formatDuration(roundInterval(interval))
}

func formatDuration(inter time.Duration) string {
	if inter >= year {
		return fmt.Sprintf("%dy", inter/year)
	}

	if inter >= day {
		return fmt.Sprintf("%dd", inter/day)
	}

	if inter >= time.Hour {
		return fmt.Sprintf("%dh", inter/time.Hour)
	}

	if inter >= time.Minute {
		return fmt.Sprintf("%dm", inter/time.Minute)
	}

	if inter >= time.Second {
		return fmt.Sprintf("%ds", inter/time.Second)
	}

	if inter >= time.Millisecond {
		return fmt.Sprintf("%dms", inter/time.Millisecond)
	}

	return "1ms"
}

func roundInterval(interval time.Duration) time.Duration {
	switch true {
	// 0.015s
	case interval <= 15*time.Millisecond:
		return time.Millisecond * 10 // 0.01s
	// 0.035s
	case interval <= 35*time.Millisecond:
		return time.Millisecond * 20 // 0.02s
	// 0.075s
	case interval <= 75*time.Millisecond:
		return time.Millisecond * 50 // 0.05s
	// 0.15s
	case interval <= 150*time.Millisecond:
		return time.Millisecond * 100 // 0.1s
	// 0.35s
	case interval <= 350*time.Millisecond:
		return time.Millisecond * 200 // 0.2s
	// 0.75s
	case interval <= 750*time.Millisecond:
		return time.Millisecond * 500 // 0.5s
	// 1.5s
	case interval <= 1500*time.Millisecond:
		return time.Millisecond * 1000 // 1s
	// 3.5s
	case interval <= 3500*time.Millisecond:
		return time.Millisecond * 2000 // 2s
	// 7.5s
	case interval <= 7500*time.Millisecond:
		return time.Millisecond * 5000 // 5s
	// 12.5s
	case interval <= 12500*time.Millisecond:
		return time.Millisecond * 10000 // 10s
	// 17.5s
	case interval <= 17500*time.Millisecond:
		return time.Millisecond * 15000 // 15s
	// 25s
	case interval <= 25000*time.Millisecond:
		return time.Millisecond * 20000 // 20s
	// 45s
	case interval <= 45000*time.Millisecond:
		return time.Millisecond * 30000 // 30s
	// 1.5m
	case interval <= 90000*time.Millisecond:
		return time.Millisecond * 60000 // 1m
	// 3.5m
	case interval <= 210000*time.Millisecond:
		return time.Millisecond * 120000 // 2m
	// 7.5m
	case interval <= 450000*time.Millisecond:
		return time.Millisecond * 300000 // 5m
	// 12.5m
	case interval <= 750000*time.Millisecond:
		return time.Millisecond * 600000 // 10m
	// 12.5m
	case interval <= 1050000*time.Millisecond:
		return time.Millisecond * 900000 // 15m
	// 25m
	case interval <= 1500000*time.Millisecond:
		return time.Millisecond * 1200000 // 20m
	// 45m
	case interval <= 2700000*time.Millisecond:
		return time.Millisecond * 1800000 // 30m
	// 1.5h
	case interval <= 5400000*time.Millisecond:
		return time.Millisecond * 3600000 // 1h
	// 2.5h
	case interval <= 9000000*time.Millisecond:
		return time.Millisecond * 7200000 // 2h
	// 4.5h
	case interval <= 16200000*time.Millisecond:
		return time.Millisecond * 10800000 // 3h
	// 9h
	case interval <= 32400000*time.Millisecond:
		return time.Millisecond * 21600000 // 6h
	// 24h
	case interval <= 86400000*time.Millisecond:
		return time.Millisecond * 43200000 // 12h
	// 48h
	case interval <= 172800000*time.Millisecond:
		return time.Millisecond * 86400000 // 24h
	// 1w
	case interval <= 604800000*time.Millisecond:
		return time.Millisecond * 86400000 // 24h
	// 3w
	case interval <= 1814400000*time.Millisecond:
		return time.Millisecond * 604800000 // 1w
	// 2y
	case interval < 3628800000*time.Millisecond:
		return time.Millisecond * 2592000000 // 30d
	default:
		return time.Millisecond * 31536000000 // 1y
	}
}