// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.

package utils

import (
	"bytes"
	"errors"
	"html/template"
	"io"
	"path/filepath"
	"sync/atomic"

	"github.com/fsnotify/fsnotify"

	"github.com/mattermost/mattermost-server/v5/mlog"
	"github.com/mattermost/mattermost-server/v5/utils/fileutils"
)

type HTMLTemplateWatcher struct {
	templates atomic.Value
	stop      chan struct{}
	stopped   chan struct{}
}

func NewHTMLTemplateWatcher(directory string) (*HTMLTemplateWatcher, error) {
	templatesDir, _ := fileutils.FindDir(directory)
	mlog.Debug("Parsing server templates", mlog.String("templates_directory", templatesDir))

	ret := &HTMLTemplateWatcher{
		stop:    make(chan struct{}),
		stopped: make(chan struct{}),
	}

	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return nil, err
	}

	if err = watcher.Add(templatesDir); err != nil {
		return nil, err
	}

	htmlTemplates, err := template.ParseGlob(filepath.Join(templatesDir, "*.html"))
	if err != nil {
		return nil, err
	}
	ret.templates.Store(htmlTemplates)

	go func() {
		defer close(ret.stopped)
		defer watcher.Close()

		for {
			select {
			case <-ret.stop:
				return
			case event := <-watcher.Events:
				if event.Op&fsnotify.Write == fsnotify.Write {
					mlog.Info("Re-parsing templates because of modified file", mlog.String("file_name", event.Name))
					if htmlTemplates, err := template.ParseGlob(filepath.Join(templatesDir, "*.html")); err != nil {
						mlog.Error("Failed to parse templates.", mlog.Err(err))
					} else {
						ret.templates.Store(htmlTemplates)
					}
				}
			case err := <-watcher.Errors:
				mlog.Error("Failed in directory watcher", mlog.Err(err))
			}
		}
	}()

	return ret, nil
}

func (w *HTMLTemplateWatcher) Templates() *template.Template {
	return w.templates.Load().(*template.Template)
}

func (w *HTMLTemplateWatcher) Close() {
	close(w.stop)
	<-w.stopped
}

type HTMLTemplate struct {
	Templates    *template.Template
	TemplateName string
	Props        map[string]interface{}
	HTML         map[string]template.HTML
}

func NewHTMLTemplate(templates *template.Template, templateName string) *HTMLTemplate {
	return &HTMLTemplate{
		Templates:    templates,
		TemplateName: templateName,
		Props:        make(map[string]interface{}),
		HTML:         make(map[string]template.HTML),
	}
}

func (t *HTMLTemplate) Render() string {
	var text bytes.Buffer
	t.RenderToWriter(&text)
	return text.String()
}

func (t *HTMLTemplate) RenderToWriter(w io.Writer) error {
	if t.Templates == nil {
		return errors.New("no html templates")
	}

	if err := t.Templates.ExecuteTemplate(w, t.TemplateName, t); err != nil {
		mlog.Warn("Error rendering template", mlog.String("template_name", t.TemplateName), mlog.Err(err))
		return err
	}

	return nil
}