// Copyright 2021 Molecula Corp. All rights reserved.
package pilosa

// util.go: a place for generic, reusable utilities.

import (
	"reflect"
	"time"
)

// LeftShifted16MaxContainerKey is 0xffffffffffff0000. It is similar
// to the roaring.maxContainerKey  0x0000ffffffffffff, but
// shifted 16 bits to the left so its domain is the full [0, 2^64) bit space.
// It is used to match the semantics of the roaring.OffsetRange() API.
// This is the maximum endx value for Tx.OffsetRange(), because the lowbits,
// as in the roaring.OffsetRange(), are not allowed to be set.
// It is used in Tx.RoaringBitamp() to obtain the full contents of a fragment
// from a call from tx.OffsetRange() by requesting [0, LeftShifted16MaxContainerKey)
// with an offset of 0.
const LeftShifted16MaxContainerKey = uint64(0xffffffffffff0000) // or math.MaxUint64 - (1<<16 - 1), or 18446744073709486080

// NilInside checks if the provided iface is nil or
// contains a nil pointer, slice, array, map, or channel.
func NilInside(iface interface{}) bool {
	if iface == nil {
		return true
	}
	switch reflect.TypeOf(iface).Kind() {
	case reflect.Ptr, reflect.Slice, reflect.Array, reflect.Map, reflect.Chan:
		return reflect.ValueOf(iface).IsNil()
	}
	return false
}

//////////////////////////////////
// helper utility functions

func highbits(v uint64) uint64 { return v >> 16 }
func lowbits(v uint64) uint16  { return uint16(v & 0xFFFF) }

// GetLoopProgress returns the estimated remaining time to iterate through some
// items as well as the loop completion percentage with the following
// parameters:
// the start time, the current time, the iteration, and the number of items
func GetLoopProgress(start time.Time, now time.Time, iteration uint, total uint) (remaining time.Duration, pctDone float64) {
	itemsLeft := total - (iteration + 1)
	avgItemTime := float64(now.Sub(start)) / float64(iteration+1)
	pctDone = (float64(iteration+1) / float64(total)) * 100
	return time.Duration(avgItemTime * float64(itemsLeft)), pctDone
}

// FormatTimestampNano returns the string representation of a timestamp given:
// an epoch value, base, and time unit
func FormatTimestampNano(value, base int64, timeUnit string) string {
	return time.Unix(0, (value+base)*TimeUnitNanos(timeUnit)).UTC().Format(time.RFC3339Nano)
}