package messenger

import (
	"bytes"
	_ "embed"
	"html/template"

	"github.com/vanng822/go-premailer/premailer"
	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
)

//go:embed base.gohtml
var mailTmpl string

var engine *template.Template
var app App

func init() {
	md := goldmark.New(
		goldmark.WithExtensions(extension.GFM),
	)
	engine = template.Must(template.New("email").Funcs(template.FuncMap{
		"ToHTML": func(mdtext string) (string, error) {
			var buf bytes.Buffer
			if err := md.Convert([]byte(mdtext), &buf); err != nil {
				return "", err
			}
			return buf.String(), nil
		},
	}).Parse(mailTmpl))
}

func Parse(b *Base) (string, error) {
	b.App = app
	buf := &bytes.Buffer{}
	err := engine.Execute(buf, b)
	if err != nil {
		return "", err
	}
	pre, err := premailer.NewPremailerFromString(buf.String(), premailer.NewOptions())
	if err != nil {
		return "", err
	}
	html, err := pre.Transform()
	return html, err
}