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

// util.go: a place for generic, reusable utilities.
import (
	"fmt"
	"os"
	"os/user"
	"path/filepath"
	"strings"
	"time"

	"github.com/shirou/gopsutil/v3/mem"
)

// 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

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

// 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
}

type MemoryUsage struct {
	Capacity uint64 `json:"capacity"`
	TotalUse uint64 `json:"totalUsed"`
}

// GetMemoryUsage gets the memory usage
func GetMemoryUsage() (MemoryUsage, error) {
	usage, err := mem.VirtualMemory()
	if usage == nil || err != nil {
		return MemoryUsage{}, fmt.Errorf("reading virtual memory: %v", err)
	}
	return MemoryUsage{Capacity: usage.Total, TotalUse: usage.Used}, nil
}

type DiskUsage struct {
	Usage int64 `json:"usage"`
}

// GetDiskUsage gets the disk usage of the path
func GetDiskUsage(path string) (DiskUsage, error) {
	usr, _ := user.Current()
	dir := usr.HomeDir
	if path == "~" {
		path = dir
	} else if strings.HasPrefix(path, "~/") {
		path = filepath.Join(dir, path[2:])
	}

	var size int64
	err := filepath.Walk(path, func(_ string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if !info.IsDir() {
			size += info.Size()
		}
		return err
	})
	return DiskUsage{size}, err
}

// Rev reverses a string
func Rev(input string) string {
	n := 0
	runes := make([]rune, len(input))
	for _, r := range input {
		runes[n] = r
		n++
	}
	runes = runes[0:n]

	for i := 0; i < n/2; i++ {
		runes[i], runes[n-1-i] = runes[n-1-i], runes[i]
	}

	return string(runes)
}

// ReplaceFirstFromBack replaces the first instance of toReplace from the back of
// the string s
func ReplaceFirstFromBack(s, toReplace, replacement string) string {
	return Rev(strings.Replace(Rev(s), Rev(toReplace), Rev(replacement), 1))
}