kgpz_web/templating/engine.go

package templating

import (
	"html/template"
	"io"
	"io/fs"
	"sync"
)

type Engine struct {
	// NOTE: LayoutRegistry and TemplateRegistry have their own syncronization & cache and do not require a mutex here
	LayoutRegistry   *LayoutRegistry
	TemplateRegistry *TemplateRegistry

	mu      *sync.Mutex
	FuncMap template.FuncMap
}

func NewEngine(layouts, templates *fs.FS) *Engine {
	return &Engine{
		mu:               &sync.Mutex{},
		LayoutRegistry:   NewLayoutRegistry(*layouts),
		TemplateRegistry: NewTemplateRegistry(*templates),
		FuncMap:          template.FuncMap{},
	}
}

func (e *Engine) Load() error {
	wg := sync.WaitGroup{}
	wg.Add(2)

	go func() {
		defer wg.Done()
		e.LayoutRegistry.Load()
	}()

	go func() {
		defer wg.Done()
		e.TemplateRegistry.Load()
	}()

	wg.Wait()
	return nil
}

func (e *Engine) Render(out io.Writer, path string, data interface{}, layout ...string) error {
	// TODO: check if a reload is needed if files on disk have changed

	var l *template.Template
	if layout == nil || len(layout) == 0 {
		lay, err := e.LayoutRegistry.Default()
		if err != nil {
			return err
		}
		l = lay
	} else {
		lay, err := e.LayoutRegistry.Layout(layout[0])
		if err != nil {
			return err
		}
		l = lay
	}

	lay, err := l.Clone()
	if err != nil {
		return err
	}

	err = e.TemplateRegistry.Add(path, lay)
	if err != nil {
		return err
	}

	err = lay.Execute(out, data)
	if err != nil {
		return err
	}

	return nil
}