package vfs

import (
    "path"
    "strings"
    "fmt"
)

// Find implements "$ find . -type f" for PWD=((fsys)).
func Find(fsys FS, allowhidden bool, allowdirname, allowfilename func(string) bool) ([]string, error) {
    var filenames []string

    var dirnames []string
    dirnames = append(dirnames, ".")
    for len(dirnames) > 0 {
        dirname := dirnames[len(dirnames)-1]
        dirnames = dirnames[:len(dirnames)-1]

        entries, err := fsys.ReadDir(dirname)
        if err != nil {
            return nil, err
        }

        for _, entry := range entries {
            if strings.Contains(entry.Name(), "/") {
                return nil, fmt.Errorf("crooked entry in %q: %q", dirname, entry.Name())
            }
            entryname := path.Join(dirname, entry.Name())

            // entryname is clean, relative and not ".", so this checks precisely for hidden files
            if strings.HasPrefix(path.Base(entryname), ".") && !allowhidden {
                continue
            }

            info, err := entry.Info()
            if err != nil {
                return nil, fmt.Errorf("crooked entry %q: %v", entryname, err)
            }

            switch mode := info.Mode(); true {
            case mode.IsDir() && allowdirname(entryname):
                dirnames = append(dirnames, entryname)
            case mode.IsRegular() && allowfilename(entryname):
                filenames = append(filenames, entryname)
            }
        }
    }

    return filenames, nil
}