// Template rendering
//
// Abstracts the rendering of static HTML templates.
// Render(...) handles rendering the provided template with the
// default partial templates (header, footer, general base...), handles
// getting the paths to those template files and feeding the data (including
// some internally-generated context) when hydrating the template.
package main

import (
	"fmt"
	"io"
	"path/filepath"
	"text/template"
	"time"
)

type RenderMeta struct {
	RenderStart time.Time
}

type RenderContext struct {
	Data interface{}
	Meta RenderMeta
}

func getRenderDuration(start time.Time) time.Duration {
	return time.Now().Sub(start)
}

func Render(w io.Writer, templateName string, data interface{}) error {
	asTemplatePath := func(templateName string) string {
		return filepath.Join("templates", fmt.Sprintf("%s.html.tmpl", templateName))
	}

	templatePartials := []string{
		asTemplatePath(templateName),
		asTemplatePath("base"),
		asTemplatePath("footer"),
	}

	start := time.Now()

	tmpl := template.New(templateName).Funcs(template.FuncMap{
		"getRenderDuration": getRenderDuration,
	})

	tmpl, err := tmpl.ParseFiles(templatePartials...)

	if err != nil {
		return err
	}

	renderContext := RenderContext{Data: data, Meta: RenderMeta{RenderStart: start}}

	return tmpl.ExecuteTemplate(w, "base", renderContext)
}