package main

import (
	"embed"
	"io"
	"io/fs"
	// "fmt"
	"log"
	// "os"
	// "path/filepath"
	"text/template"
	// "github.com/davecgh/go-spew/spew"
)

var (
	//go:embed "tplfiles"
	tplfiles embed.FS

	tpl *template.Template = template.New("")

	tw *TplWalker = new(TplWalker)
)

type (
	TplWalker struct {
		tpl *template.Template
		fs  fs.FS
	}
)

func (t *TplWalker) walkFunc(fpath string, d fs.DirEntry, inErr error) (err error) {

	var b []byte
	var f fs.File

	if inErr != nil {
		err = inErr
		return
	}

	if d.IsDir() {
		return
	}

	if f, err = t.fs.Open(fpath); err != nil {
		return
	}
	defer func() {
		var ok bool
		var c io.Closer
		if f != nil {
			if c, ok = f.(io.Closer); ok {
				if err = c.Close(); err != nil {
					return
				}
			}
		}
	}()

	if b, err = io.ReadAll(f); err != nil {
		return
	}

	if _, err = t.tpl.New(fpath).Parse(string(b)); err != nil {
		return
	}

	return
}

func (t *TplWalker) Walk() (err error) {

	if err = fs.WalkDir(t.fs, ".", t.walkFunc); err != nil {
		return
	}

	return
}

func init() {
	var err error

	tw.tpl = tpl
	tw.fs = tplfiles

	if err = tw.Walk(); err != nil {
		log.Panicln(err)
	}
}

func main() {
	var idx int
	var sub *template.Template

	log.Printf("Root template name is %q", tpl.Name())
	for idx, sub = range tpl.Templates() {
		log.Printf("Sub template %d: %q", idx, sub.Name())
	}
}