httpserver/templates/templates.go

// Package templates helps sites to manage their templates
package templates

import (
	"bytes"
	"errors"
	"io"
	"io/fs"
	"net/http"
	"path/filepath"

	"github.com/flosch/pongo2/v6"
	"github.com/gin-gonic/gin/render"
	"github.com/rs/zerolog/log"
)

var (
	_ pongo2.TemplateLoader = &FSLoader{}
	_ render.Render         = &renderer{}
	_ pongo2.TemplateLoader = &EmptyLoader{}
)

// TemplateSite is an interface that is for storing templates.
type TemplateSite interface {
	Templates() pongo2.TemplateLoader
}

// FSLoader is an interim until pongo merges the  pullrequest for fs.FS
type FSLoader struct {
	fs.FS
}

// Abs return the join of base and name
func (e *FSLoader) Abs(base, name string) string {
	return filepath.Join(filepath.Dir(base), name)
}

// Get returns an io.Reader where the template's content can be read from.
func (e *FSLoader) Get(path string) (reader io.Reader, err error) {
	f, err := e.FS.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	bt, err := io.ReadAll(f)
	if err != nil {
		return nil, err
	}

	return bytes.NewBuffer(bt), nil
}

// Pongo2Renderer is an simple wrapper for gin to use pongo2 templates
type Pongo2Renderer struct {
	ts *pongo2.TemplateSet
}

// NewPongo2Renderer creates an wrapper for gin
func NewPongo2Renderer(ts *pongo2.TemplateSet) render.HTMLRender {
	return &Pongo2Renderer{ts: ts}
}

// Instance create an new instance of an REnder object
func (p2r *Pongo2Renderer) Instance(name string, data any) render.Render {
	tmpl, err := p2r.ts.FromFile(name)
	r := &renderer{
		tmpl: tmpl,
		err:  err,
	}
	if data != nil {
		switch data.(type) {
		case pongo2.Context:
			r.data = data.(pongo2.Context)
		case map[string]any:
			r.data = data.(map[string]any)
		default:
			r.err = errors.New("Failed to detect possible format for pongo2. It needs to be map[string]any or pongo2.Context")
		}
	}
	log.Debug().Msg("Returning an instance")
	return r
}

type renderer struct {
	tmpl *pongo2.Template
	err  error
	data pongo2.Context
}

// Render renders the template
func (r *renderer) Render(rw http.ResponseWriter) error {
	if r.err != nil {
		log.Debug().Msg("rendering failed")
		return r.err
	}
	log.Debug().Msg("wirting template")
	return r.tmpl.ExecuteWriter(r.data, rw)
}

// WriteContentType is an static function that always writes text/html as the Contenttype into the response
func (*renderer) WriteContentType(rw http.ResponseWriter) {
	rw.Header().Set("Content-Type", "text/html")
}

// EmptyLoader is an Empty Loader
type EmptyLoader struct{}

// Abs return the join of base and name
func (*EmptyLoader) Abs(base, name string) string {
	return filepath.Join(filepath.Dir(base), name)
}

// Get returns always errors
func (*EmptyLoader) Get(string) (io.Reader, error) {
	return nil, errors.New("This Loader has no templates")
}