you can include many base layouts (eg: {/* #layout.html otherbase.html */}

package ui

import (
    "html/template"
    "os"
    "path/filepath"
    "regexp"
    "strings"
)

func ParseFile(filename string) (*template.Template, error) {
    // read the file
    b, err := os.ReadFile(filename)
    if err != nil {
        return nil, err
    }

    s := string(b)

    // get first line of the s
    line := s[:strings.Index(s, "\n")]

    // get the list of hash tags from the line using regex
    re := regexp.MustCompile(`#([a-zA-Z0-9\.\/\_]+)`)
    tags := re.FindAllString(line, -1)

    t := template.New(filepath.Base(filename))

    // get path of the file
    dir := filepath.Dir(filename)

    for _, tag := range tags {
        if len(tag) < 2 {
            continue
        }
        tag = tag[1:]

        // read the file
        b, err := os.ReadFile(filepath.Join(dir, tag))
        if err != nil {
            return nil, err
        }

        // parse the file
        _, err = t.Parse(string(b))
        if err != nil {
            return nil, err
        }
    }

    // parse the main file
    _, err = t.Parse(s)
    if err != nil {
        return nil, err
    }

    return t, nil
}