package webserver

import (
	"fmt"
	"html/template"
	"io"
	"io/ioutil"
	"mime"
	"net"
	"net/http"
	nurl "net/url"
	"os"
	fp "path/filepath"
	"regexp"
	"strings"
	"syscall"
)

var (
	rxRepeatedStrip = regexp.MustCompile(`(?i)-+`)

	presetMimeTypes = map[string]string{
		".css":  "text/css; charset=utf-8",
		".html": "text/html; charset=utf-8",
		".js":   "application/javascript",
		".png":  "image/png",
	}
)

func guessTypeByExtension(ext string) string {
	ext = strings.ToLower(ext)

	if v, ok := presetMimeTypes[ext]; ok {
		return v
	}

	return mime.TypeByExtension(ext)
}

func serveFile(w http.ResponseWriter, filePath string, cache bool) error {
	// Open file
	src, err := assets.Open(filePath)
	if err != nil {
		return err
	}
	defer src.Close()

	// Cache this file if needed
	if cache {
		info, err := src.Stat()
		if err != nil {
			return err
		}

		etag := fmt.Sprintf(`W/"%x-%x"`, info.ModTime().Unix(), info.Size())
		w.Header().Set("ETag", etag)
		w.Header().Set("Cache-Control", "max-age=86400")
	} else {
		w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
	}

	// Set content type
	ext := fp.Ext(filePath)
	mimeType := guessTypeByExtension(ext)
	if mimeType != "" {
		w.Header().Set("Content-Type", mimeType)
		w.Header().Set("X-Content-Type-Options", "nosniff")
	}

	// Serve file
	_, err = io.Copy(w, src)
	return err
}

func createRedirectURL(newPath, previousPath string) string {
	urlQueries := nurl.Values{}
	urlQueries.Set("dst", previousPath)

	redirectURL, _ := nurl.Parse(newPath)
	redirectURL.RawQuery = urlQueries.Encode()
	return redirectURL.String()
}

func redirectPage(w http.ResponseWriter, r *http.Request, url string) {
	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
	w.Header().Set("Pragma", "no-cache")
	w.Header().Set("Expires", "0")
	http.Redirect(w, r, url, 301)
}

func assetExists(filePath string) bool {
	f, err := assets.Open(filePath)
	if f != nil {
		f.Close()
	}
	return err == nil || !os.IsNotExist(err)
}

func fileExists(filePath string) bool {
	info, err := os.Stat(filePath)
	return !os.IsNotExist(err) && !info.IsDir()
}

func createTemplate(filename string, funcMap template.FuncMap) (*template.Template, error) {
	// Open file
	src, err := assets.Open(filename)
	if err != nil {
		return nil, err
	}
	defer src.Close()

	// Read file content
	srcContent, err := ioutil.ReadAll(src)
	if err != nil {
		return nil, err
	}

	// Create template
	return template.New(filename).Delims("$$", "$$").Funcs(funcMap).Parse(string(srcContent))
}

// getArchivalName converts an URL into an archival name.
func getArchivalName(src string) string {
	archivalURL := src

	// Some URL have its query or path escaped, e.g. Wikipedia and Dev.to.
	// For example, Wikipedia's stylesheet looks like this :
	//   load.php?lang=en&modules=ext.3d.styles%7Cext.cite.styles%7Cext.uls.interlanguage
	// However, when browser download it, it will be registered as unescaped query :
	//   load.php?lang=en&modules=ext.3d.styles|ext.cite.styles|ext.uls.interlanguage
	// So, for archival URL, we need to unescape the query and path first.
	tmp, err := nurl.Parse(src)
	if err == nil {
		unescapedQuery, _ := nurl.QueryUnescape(tmp.RawQuery)
		if unescapedQuery != "" {
			tmp.RawQuery = unescapedQuery
		}

		archivalURL = tmp.String()
		archivalURL = strings.Replace(archivalURL, tmp.EscapedPath(), tmp.Path, 1)
	}

	archivalURL = strings.ReplaceAll(archivalURL, "://", "/")
	archivalURL = strings.ReplaceAll(archivalURL, "?", "-")
	archivalURL = strings.ReplaceAll(archivalURL, "#", "-")
	archivalURL = strings.ReplaceAll(archivalURL, "/", "-")
	archivalURL = strings.ReplaceAll(archivalURL, " ", "-")
	archivalURL = rxRepeatedStrip.ReplaceAllString(archivalURL, "-")

	return archivalURL
}

func checkError(err error) {
	if err == nil {
		return
	}

	// Check for a broken connection, as it is not really a
	// condition that warrants a panic stack trace.
	if ne, ok := err.(*net.OpError); ok {
		if se, ok := ne.Err.(*os.SyscallError); ok {
			if se.Err == syscall.EPIPE || se.Err == syscall.ECONNRESET {
				return
			}
		}
	}

	panic(err)
}