date.go

package main

// This code is copy-paste from https://github.com/lomik/carbon-clickhouse/blob/f659eb147017213f22de8ba12657abc0a6e3a07d/receiver/days.go
// Copyright (c) 2016 Roman Lomonosov
// License: MIT (https://github.com/lomik/carbon-clickhouse/blob/f659eb147017213f22de8ba12657abc0a6e3a07d/LICENSE)

import "time"

// Helper for fast calculate days count from 1970-01-01 in local timezone
// Not thread-safe!
type DaysFrom1970 struct {
	todayStartTimestamp uint32
	todayEndTimestamp   uint32
	todayDays           uint16
}

func (dd *DaysFrom1970) fromTimestamp(timestamp uint32) uint16 {
	t := time.Unix(int64(timestamp), 0)
	return uint16(time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, time.UTC).Unix() / 86400)
}

func (dd *DaysFrom1970) Timestamp(timestamp uint32) uint16 {
	if timestamp >= dd.todayStartTimestamp && timestamp <= dd.todayEndTimestamp {
		return dd.todayDays
	}

	return dd.fromTimestamp(timestamp)
}

func (dd *DaysFrom1970) TimestampWithNow(timestamp uint32, now uint32) uint16 {
	if timestamp < dd.todayStartTimestamp {
		return dd.fromTimestamp(timestamp)
	}

	// timestamp >= pp.todayStartTimestamp
	if timestamp <= dd.todayEndTimestamp {
		return dd.todayDays
	}

	// timestamp > dd.todayEndTimestamp
	// check now date
	if now > dd.todayEndTimestamp {
		// update "today" required
		d := time.Unix(int64(now), 0)
		dd.todayStartTimestamp = uint32(time.Date(d.Year(), d.Month(), d.Day(), 0, 0, 0, 0, time.Local).Unix())
		dd.todayEndTimestamp = uint32(time.Date(d.Year(), d.Month(), d.Day(), 23, 59, 59, 0, time.Local).Unix())
		dd.todayDays = dd.fromTimestamp(now)
	}

	return dd.Timestamp(timestamp)
}