package builder

import (
	"encoding/xml"
	"io"
	"os"
	"path/filepath"
	"strings"
	"text/template"
	"website/internal/atom"
	"website/internal/config"
	"website/internal/content"
	"website/internal/log"

	"github.com/PuerkitoBio/goquery"
	"github.com/a-h/htmlformat"
	"github.com/antchfx/xmlquery"
	"github.com/antchfx/xpath"
	"github.com/pkg/errors"
	"golang.org/x/net/html"
)

var (
	css           string
	templateFiles = make(map[string]*os.File)
	nsMap         = map[string]string{
		"xsl":   "http://www.w3.org/1999/XSL/Transform",
		"atom":  "http://www.w3.org/2005/Atom",
		"xhtml": "http://www.w3.org/1999/xhtml",
	}
)

func loadCSS() {
	bytes, err := os.ReadFile("templates/style.css")
	if err != nil {
		panic(err)
	}
	css = string(bytes)
}

func loadTemplate(path string) (file *os.File, err error) {
	if templateFiles[path] == nil {
		file, err = os.OpenFile(path, os.O_RDONLY, 0)
		if err != nil {
			return nil, errors.Wrapf(err, "could not load template at path %s", path)
		}
		templateFiles[path] = file
	}
	file = templateFiles[path]

	return
}

type QuerySelection struct {
	*goquery.Selection
}

type QueryDocument struct {
	*goquery.Document
}

func NewDocumentFromReader(r io.Reader) (*QueryDocument, error) {
	doc, err := goquery.NewDocumentFromReader(r)

	return &QueryDocument{doc}, errors.Wrap(err, "could not create query document")
}

func (q *QueryDocument) Find(selector string) *QuerySelection {
	return &QuerySelection{q.Document.Find(selector)}
}

func renderRobotsTXT(config config.Config) (io.Reader, error) {
	r, w := io.Pipe()
	tpl, err := template.ParseFiles("templates/robots.tmpl")
	if err != nil {
		return nil, err
	}
	go func() {
		err = tpl.Execute(w, map[string]interface{}{
			"BaseURL": config.BaseURL,
		})
		if err != nil {
			w.CloseWithError(err)
		}
		w.Close()
	}()
	return r, nil
}

func renderFeed(
	title string,
	config config.Config,
	posts []content.Post,
	specific string,
) (io.Reader, error) {
	reader, err := loadTemplate("templates/feed.xml")
	if err != nil {
		return nil, err
	}
	defer func() {
		_, err := reader.Seek(0, io.SeekStart)
		if err != nil {
			panic("could not reset reader: " + err.Error())
		}
	}()
	doc, err := xmlquery.Parse(reader)
	if err != nil {
		return nil, errors.Wrap(err, "could not parse XML")
	}
	feed := doc.SelectElement("feed")
	feed.SelectElement("title").FirstChild.Data = title
	feed.SelectElement("link").SetAttr("href", config.BaseURL.String())
	feed.SelectElement("id").FirstChild.Data = atom.MakeTagURI(config, specific)
	datetime, err := posts[0].Date.UTC().MarshalText()
	if err != nil {
		return nil, errors.Wrap(err, "could not convert post date to text")
	}
	feed.SelectElement("updated").FirstChild.Data = string(datetime)
	tpl := feed.SelectElement("entry")
	xmlquery.RemoveFromTree(tpl)

	for _, post := range posts {
		fullURL := config.BaseURL.JoinPath(post.URL).String()
		text, err := xml.MarshalIndent(&atom.FeedEntry{
			Title:   post.Title,
			Link:    atom.MakeLink(fullURL),
			ID:      atom.MakeTagURI(config, post.Basename),
			Updated: post.Date.UTC(),
			Summary: post.Description,
			Author:  config.Title,
			Content: atom.FeedContent{
				Content: post.Content,
				Type:    "html",
			},
		}, "  ", "    ")
		if err != nil {
			return nil, errors.Wrap(err, "could not marshal xml")
		}
		entry, err := xmlquery.ParseWithOptions(
			strings.NewReader(string(text)),
			xmlquery.ParserOptions{
				Decoder: &xmlquery.DecoderOptions{
					Strict:    false,
					AutoClose: xml.HTMLAutoClose,
					Entity:    xml.HTMLEntity,
				},
			},
		)
		if err != nil {
			return nil, errors.Wrap(err, "could not parse XML")
		}
		xmlquery.AddChild(feed, entry.SelectElement("entry"))
	}

	return strings.NewReader(doc.OutputXML(true)), nil
}

func renderFeedStyles() (*strings.Reader, error) {
	reader, err := loadTemplate("templates/feed-styles.xsl")
	if err != nil {
		return nil, err
	}
	defer func() {
		_, err := reader.Seek(0, io.SeekStart)
		if err != nil {
			panic("could not reset reader: " + err.Error())
		}
	}()
	doc, err := xmlquery.Parse(reader)
	if err != nil {
		return nil, errors.Wrap(err, "could not parse XML")
	}
	expr, err := xpath.CompileWithNS("//xhtml:style", nsMap)
	if err != nil {
		return nil, errors.Wrap(err, "could not parse XML")
	}
	style := xmlquery.QuerySelector(doc, expr)
	xmlquery.AddChild(style, &xmlquery.Node{
		Type: xmlquery.TextNode,
		Data: css,
	})

	return strings.NewReader(doc.OutputXML(true)), nil
}

func getFeedStylesHash(r *strings.Reader) (string, error) {
	doc, err := xmlquery.Parse(r)
	if err != nil {
		return "", err
	}
	expr, err := xpath.CompileWithNS("//xhtml:style", nsMap)
	if err != nil {
		return "", errors.Wrap(err, "could not parse XPath")
	}
	style := xmlquery.QuerySelector(doc, expr)

	return hash(style.InnerText()), nil
}

func getHTMLStyleHash(filenames ...string) (string, error) {
	fn := filepath.Join(filenames...)
	f, err := os.Open(fn)
	if err != nil {
		return "", err
	}
	defer f.Close()
	doc, err := NewDocumentFromReader(f)
	if err != nil {
		return "", err
	}
	html := doc.Find("head > style").Text()
	return hash(html), nil
}

func renderHTML(doc *goquery.Document) io.Reader {
	r, w := io.Pipe()

	go func() {
		_, err := w.Write([]byte("<!doctype html>\n"))
		if err != nil {
			log.Error("error writing doctype", "error", err)
			w.CloseWithError(err)
		}
		err = htmlformat.Nodes(w, []*html.Node{doc.Children().Get(0)})
		if err != nil {
			log.Error("error rendering html", "error", err)
			w.CloseWithError(err)

			return
		}
		defer w.Close()
	}()

	return r
}