package main

import (
	"fmt"
	"io/fs"
	"path/filepath"
	"sort"
	"syscall"
	"time"
)

type fileStats struct {
	path   string
	size   int64
	access time.Time
}

// Converts a given number of bytes into a more human-readable string.
func humanBytes(size float64) string {
	units := []string{"B", "KiB", "MiB", "GiB", "TiB", "EiB", "ZiB"}

	i := 0
	if size >= 1024 {
		for i < len(units) && size >= 1024 {
			i++
			size = size / 1024
		}
	}

	return fmt.Sprintf("%.01f %s", size, units[i])
}

func main() {
	var fileList []fileStats

	filepath.Walk("/usr", func(path string, file fs.FileInfo, err error) error {
		if err != nil {
			// Will panic if we don't handle this.
			// Ignores files we can't access (permission denied).
			return nil
		}

		if file.Mode().IsRegular() {
			stat := file.Sys().(*syscall.Stat_t)
			atime := time.Unix(int64(stat.Atim.Sec), int64(stat.Atim.Nsec))
			fs := fileStats{path, file.Size(), atime}
			fileList = append(fileList, fs)
		}
		return nil
	})

	sort.Slice(fileList, func(i, j int) bool {
		return fileList[i].size < fileList[j].size
	})

	for _, file := range fileList {
		file.access.Format("%b %d %Y")
		fmt.Printf("%s    %s    %s\n",
			file.path,
			humanBytes(float64(file.size)),
			file.access.Format("02 Jan 2006"))
	}
}