package smtp

import (
	"html/template"
	"io/fs"
	"strings"

	"code.nochebuena.dev/einherjar/core/xerrors"
)

// Template wraps stdlib html/template for HTML email rendering.
// Rendering is intentionally separate from [Sender.Send] — callers render
// a template to a string and assign it to [Message.Body].
type Template struct{ t *template.Template }

// ParseFS parses the named pattern files from fsys into a Template.
// Returns an error if any pattern matches no files or a file fails to parse.
func ParseFS(fsys fs.FS, patterns ...string) (*Template, error) {
	t, err := template.ParseFS(fsys, patterns...)
	if err != nil {
		return nil, xerrors.New(xerrors.ErrInvalidInput, "smtp: parse template").WithError(err)
	}
	return &Template{t: t}, nil
}

// Render executes the named template with data and returns the rendered string.
func (t *Template) Render(name string, data any) (string, error) {
	var buf strings.Builder
	if err := t.t.ExecuteTemplate(&buf, name, data); err != nil {
		return "", xerrors.New(xerrors.ErrInternal, "smtp: render template").WithError(err)
	}
	return buf.String(), nil
}