package fs

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
)

type FS interface {
	isFS()
}

type DirEntry struct {
	Name string
	FS   FS
}

type Entries interface {
	Get() []DirEntry
}

type Dir struct {
	Entries
}

func (d Dir) isFS() {}

type Contents interface {
	Get() io.Reader
}

type File struct {
	Contents
}

func (f File) isFS() {}

func Realize(path string, f FS) error {
	if f == nil {
		return fmt.Errorf("cannot realize nil FS at %s", path)
	}
	switch t := f.(type) {
	case File:
		osf, err := os.Create(path)
		if err != nil {
			return fmt.Errorf("cannot create file %s: %w", path, err)
		}
		defer osf.Close()
		_, err = io.Copy(osf, t.Get())
		if err != nil {
			return fmt.Errorf("cannot write file %s: %w", path, err)
		}
	case Dir:
		err := os.Mkdir(path, 0666)
		if err != nil {
			return fmt.Errorf("cannot create dir %s: %w", path, err)
		}
		for _, child := range t.Get() {
			err := Realize(filepath.Join(path, child.Name), child.FS)
			if err != nil {
				return err
			}
		}
	default:
		panic("unknown File type")
	}
	return nil
}