package main

import (
	"html/template"
	"io"
	"os"
	"path/filepath"
	"sync"
)

type TemplateRenderer struct {
	dir       string
	templates map[string]*template.Template
	mu        sync.RWMutex
}

func NewTemplateRenderer(dir string) (*TemplateRenderer, error) {
	tr := &TemplateRenderer{
		dir:       dir,
		templates: make(map[string]*template.Template),
	}
	if err := tr.loadAll(); err != nil {
		return nil, err
	}
	return tr, nil
}

func (tr *TemplateRenderer) loadAll() error {
	entries, err := os.ReadDir(tr.dir)
	if err != nil {
		return err
	}
	for _, e := range entries {
		if e.IsDir() || filepath.Ext(e.Name()) != ".html" {
			continue
		}
		path := filepath.Join(tr.dir, e.Name())
		tmpl, err := template.ParseFiles(path)
		if err != nil {
			return err
		}
		tr.templates[e.Name()] = tmpl
	}
	return nil
}

func (tr *TemplateRenderer) Render(w io.Writer, name string, data any) error {
	tr.mu.RLock()
	tmpl, ok := tr.templates[name]
	tr.mu.RUnlock()
	if !ok {
		return os.ErrNotExist
	}
	return tmpl.Execute(w, data)
}