The Engine: A Web Theme Engine for Go

This library provides tools for managing themes (a collection of templates and supporting files) for Go. It allows theme chaining and overriding.

This library is oriented toward Web theming using html/template and text/template.

With this library, you can:

• Support numerous themes in one app
• Cascade and override themes
• Provide easy support for re-theming an existing app

Usage

Say you have the following theme directories, with the following files:

themes/
    |
    |- pretty/
    |    |
    |    |- main.tpl
    |
    |- ugly/
    |    |
    |    |- duckling.tpl
    |    |
    |    |- main.css
    |
    |- default/
         |
         |- main.tpl
         |
         |- duckling.tpl
         |
         |- main.css

There are three themes here: themes/pretty, themes/ugly, and themes/default.

There are two types of file: templates (end in .tpl) and assets (don't end in .tpl).

Say we want to apply the pretty theme, but with a backup to the default theme. We never want any ugly theme content.

package main

import "github.com/Masterminds/engine"

func main() {
    engine, err := New("themes/pretty", "themes/default")
    if err != nil {
        // ... handle the error
    }

    // Render the main.tpl, passing the template the data 42.
    // Because of the order of directories passed into New, this will
    // render to `pretty/main.tpl`.
    out, err := e.Render("main.tpl", 42)
    // ... out will have the rendered data.

    // This will use `themes/default/duckling.tpl` because there is no
    // duckling.tpl in the `themes/pretty` directory.
    out, err = e.Render("duckling.tpl", 42)

    // This will find the `main.css` in the `themes/default` folder,
    // since none exists in `themes/pretty`
    path, err := e.Asset("main.css")
}

In the example above, not that we load two of the three available templates. Engine's primary roll, then, is to negotiate which theme should be used for each individual render call.