package main

import (
	"cmp"
	_ "embed"
	"fmt"
	"html/template"
	"io"
	"mime"
	"net/http"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strings"
	"time"
)

//go:embed assets/index.html
var indexHTML string

//go:embed assets/about.html
var aboutHTML []byte

//go:embed assets/favicon.ico
var faviconICO []byte

type server struct {
	root     string // as configured, used for display paths
	rootReal string // symlink-resolved root, used for containment checks
	hidden   bool
	footer   string
	follow   bool // serve symlinks even when they point outside root
	tpl      *template.Template
}

func newServer(cfg *Config) *server {
	rootReal, err := filepath.EvalSymlinks(cfg.Root)
	if err != nil {
		rootReal = cfg.Root
	}
	return &server{
		root:     cfg.Root,
		rootReal: rootReal,
		hidden:   cfg.Hidden,
		footer:   cfg.Footer,
		follow:   cfg.FollowSymlinks,
		tpl:      template.Must(template.New("index").Parse(indexHTML)),
	}
}

type row struct {
	Name    string
	URL     string
	IsDir   bool
	Size    int64
	ModTime time.Time
	Type    string
}

func (r row) SizeS() string { return humanSize(r.Size) }
func (r row) ModS() string  { return r.ModTime.Format("2006-01-02 15:04") }

type headerCol struct {
	Label  string
	Class  string
	URL    string
	Active bool
	Desc   bool
}

type crumb struct{ Name, URL string }

type listData struct {
	Path      string
	Crumbs    []crumb
	Headers   []headerCol
	Rows      []row
	HasParent bool
	Wget      string
	Footer    string
}

var sortKeys = map[string]bool{"name": true, "size": true, "modified": true, "type": true}

func (s *server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet && r.Method != http.MethodHead {
		w.Header().Set("Allow", "GET, HEAD")
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}

	upath := r.URL.Path
	if !strings.HasPrefix(upath, "/") {
		upath = "/" + upath
	}
	clean := path.Clean(upath)
	switch clean {
	case "/about":
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		w.Write(aboutHTML)
		return
	case "/favicon.ico":
		w.Header().Set("Content-Type", "image/x-icon")
		w.Header().Set("Cache-Control", "max-age=604800")
		w.Write(faviconICO)
		return
	}

	fsPath := filepath.Join(s.rootReal, filepath.FromSlash(strings.TrimPrefix(clean, "/")))
	realPath, err := filepath.EvalSymlinks(fsPath)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	if !s.follow && realPath != s.rootReal && !strings.HasPrefix(realPath, s.rootReal+string(os.PathSeparator)) {
		http.NotFound(w, r) // symlink escaping the served root
		return
	}

	info, err := os.Stat(realPath)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	if info.IsDir() && !strings.HasSuffix(upath, "/") {
		localRedirect(w, r, path.Base(upath)+"/")
		return
	}
	if !info.IsDir() {
		s.serveFile(w, r, realPath, filepath.Base(clean), info)
		return
	}
	s.serveListing(w, r, realPath, clean)
}

func localRedirect(w http.ResponseWriter, r *http.Request, newPath string) {
	if q := r.URL.RawQuery; q != "" {
		newPath += "?" + q
	}
	w.Header().Set("Location", newPath)
	w.WriteHeader(http.StatusMovedPermanently)
}

func (s *server) serveFile(w http.ResponseWriter, r *http.Request, path, name string, info os.FileInfo) {
	f, err := os.Open(path)
	if err != nil {
		http.Error(w, "cannot open file", http.StatusInternalServerError)
		return
	}
	defer f.Close()
	disp := "attachment"
	if inlineFile(f, name) {
		disp = "inline"
	}
	w.Header().Set("Content-Disposition",
		mime.FormatMediaType(disp, map[string]string{"filename": name}))
	http.ServeContent(w, r, name, info.ModTime(), f)
}

func inlineFile(f *os.File, name string) bool {
	if ct := mime.TypeByExtension(strings.ToLower(filepath.Ext(name))); ct != "" {
		return inlineMIME(ct)
	}
	buf := make([]byte, 512)
	n, err := f.Read(buf)
	if _, serr := f.Seek(0, io.SeekStart); serr != nil {
		return false
	}
	if err != nil && err != io.EOF {
		return false
	}
	return inlineMIME(http.DetectContentType(buf[:n]))
}

func inlineMIME(ct string) bool {
	if i := strings.IndexByte(ct, ';'); i >= 0 {
		ct = strings.TrimSpace(ct[:i])
	}
	switch {
	case strings.HasPrefix(ct, "image/"),
		strings.HasPrefix(ct, "audio/"),
		strings.HasPrefix(ct, "video/"),
		strings.HasPrefix(ct, "text/"):
		return ct != "text/html"
	case ct == "application/pdf",
		ct == "application/xml",
		ct == "application/json":
		return true
	}
	return false
}

func (s *server) serveListing(w http.ResponseWriter, r *http.Request, dirPath, urlPath string) {
	entries, err := os.ReadDir(dirPath)
	if err != nil {
		http.Error(w, "cannot read directory", http.StatusInternalServerError)
		return
	}

	sortKey := r.URL.Query().Get("sort")
	if !sortKeys[sortKey] {
		sortKey = "name"
	}
	desc := r.URL.Query().Get("dir") == "desc"

	dirURL := urlPath
	if !strings.HasSuffix(dirURL, "/") {
		dirURL += "/"
	}
	rows := make([]row, 0, len(entries))
	for _, e := range entries {
		name := e.Name()
		if !s.hidden && strings.HasPrefix(name, ".") {
			continue
		}
		isDir := e.IsDir()
		var size int64
		var mod time.Time
		if info, err := e.Info(); err == nil { // lstat: does not follow symlinks
			mod = info.ModTime()
			if !isDir {
				size = info.Size()
			}
		}
		if e.Type()&os.ModeSymlink != 0 {
			if ti, err := os.Stat(filepath.Join(dirPath, name)); err == nil {
				isDir = ti.IsDir()
				mod = ti.ModTime()
				if isDir {
					size = 0
				} else {
					size = ti.Size()
				}
			}
		}
		typ := "-"
		if isDir {
			typ = "dir"
		} else if ext := strings.TrimPrefix(filepath.Ext(name), "."); ext != "" {
			typ = strings.ToLower(ext)
		}
		rows = append(rows, row{
			Name:    name,
			URL:     dirURL + url.PathEscape(name),
			IsDir:   isDir,
			Size:    size,
			ModTime: mod,
			Type:    typ,
		})
	}

	sort.SliceStable(rows, func(i, j int) bool {
		a, b := rows[i], rows[j]
		if a.IsDir != b.IsDir {
			return a.IsDir
		}
		var c int
		switch sortKey {
		case "size":
			c = cmp.Compare(a.Size, b.Size)
		case "modified":
			c = a.ModTime.Compare(b.ModTime)
		case "type":
			if c = strings.Compare(a.Type, b.Type); c == 0 {
				c = strings.Compare(strings.ToLower(a.Name), strings.ToLower(b.Name))
			}
		default:
			c = strings.Compare(strings.ToLower(a.Name), strings.ToLower(b.Name))
		}
		if desc {
			return c > 0
		}
		return c < 0
	})

	headers := []struct {
		Label string
		Key   string
		Class string
	}{
		{"Name", "name", ""},
		{"Type", "type", "ty"},
		{"Size", "size", "sz"},
		{"Modified", "modified", "mod"},
	}
	cols := make([]headerCol, len(headers))
	for i, h := range headers {
		cols[i] = headerCol{
			Label:  h.Label,
			Class:  h.Class,
			Active: h.Key == sortKey,
			Desc:   h.Key == sortKey && desc,
		}
		d := "asc"
		if h.Key == sortKey && !desc {
			d = "desc"
		}
		cols[i].URL = dirURL + "?sort=" + h.Key + "&dir=" + d
	}

	crumbs := []crumb{{Name: "root", URL: "/"}}
	cur := ""
	for _, seg := range segments(urlPath) {
		cur += "/" + seg
		crumbs = append(crumbs, crumb{Name: seg, URL: cur + "/"})
	}

	s.tpl.Execute(w, listData{
		Path:      dirURL,
		Crumbs:    crumbs,
		Headers:   cols,
		Rows:      rows,
		HasParent: urlPath != "/",
		Wget:      wgetCmd(r, dirURL),
		Footer:    s.footer,
	})
}

func wgetCmd(r *http.Request, dirURL string) string {
	cmd := "wget -r -np -nH"
	if n := len(segments(dirURL)); n > 0 {
		cmd += fmt.Sprintf(" --cut-dirs=%d", n)
	}
	return cmd + ` -R "index.html*" -e robots=off ` + shellQuote(baseURL(r)+dirURL)
}

// shellQuote quotes s so it is treated as a single literal argument by POSIX shells.
func shellQuote(s string) string {
	return "'" + strings.ReplaceAll(s, "'", `'\''`) + "'"
}

func baseURL(r *http.Request) string {
	scheme := "http"
	if r.TLS != nil || r.Header.Get("X-Forwarded-Proto") == "https" {
		scheme = "https"
	}
	return scheme + "://" + r.Host
}

func segments(p string) []string {
	p = strings.Trim(p, "/")
	if p == "" {
		return nil
	}
	return strings.Split(p, "/")
}

func humanSize(n int64) string {
	const unit = 1024
	if n < unit {
		return fmt.Sprintf("%d B", n)
	}
	div, exp := int64(unit), 0
	for m := n / unit; m >= unit; m /= unit {
		div *= unit
		exp++
	}
	return fmt.Sprintf("%.1f %ciB", float64(n)/float64(div), "KMGTPE"[exp])
}