dirTree

package main

import (
    "fmt"
    "io"
    "os"
    "sort"
)

func main() {
    out := os.Stdout
    if !(len(os.Args) == 2 || len(os.Args) == 3) {
        panic("usage go run main.go . [-f]")
    }
    path := os.Args[1]
    printFiles := len(os.Args) == 3 && os.Args[2] == "-f"
    err := dirTree(out, path, printFiles)
    if err != nil {
        panic(err.Error())
    }
}

func dirTree(out io.Writer, path string, printFiles bool) error {
    return dirLevel(out, path, printFiles, "")
}

func dirLevel(out io.Writer, path string, printFiles bool, parentPrefix string) error {
    sep := string(os.PathSeparator)

    entries, err := ReadDir(path, !printFiles)
    if err != nil {
        return err
    }
    for i, entry := range entries {

        namePrefixSymbol := '├'
        if i == len(entries)-1 {
            namePrefixSymbol = '└'
        }

        printName := fmt.Sprintf("%s%c───%s", parentPrefix, namePrefixSymbol, entry.Name())

        if entry.IsDir() {
            out.Write([]byte(printName + "\n"))

            childLvlPrefix := "\t"
            if i < len(entries)-1 {
                childLvlPrefix = "│" + childLvlPrefix
            }
            dirLevel(out, path+sep+entry.Name(), printFiles, parentPrefix+childLvlPrefix)
        }

        if !entry.IsDir() && printFiles {
            inf, err := entry.Info()
            if err != nil {
                return err
            }
            if inf.Size() > 0 {
                printName = fmt.Sprintf("%s (%db)", printName, inf.Size())
            } else {
                printName = fmt.Sprintf("%s (empty)", printName)
            }
            out.Write([]byte(printName + "\n"))
        }
    }

    return nil
}

func ReadDir(name string, filesFirst bool) ([]os.DirEntry, error) {
    f, err := os.Open(name)
    if err != nil {
        return nil, err
    }
    defer f.Close()

    dirs, err := f.ReadDir(-1)
    sort.Slice(dirs, func(i, j int) bool {
        if filesFirst && !dirs[i].IsDir() {
            return true
        }
        if filesFirst && !dirs[j].IsDir() {
            return false
        }
        return dirs[i].Name() < dirs[j].Name()
    })
    return dirs, err
}