package main

import (
	"bytes"
	"errors"
	"flag"
	"html/template"
	"io"
	"log"
	"net"
	"net/http"
	"net/url"
	"path"
	"sort"
	"strconv"
	"strings"
	"time"

	"github.com/kballard/go-shellquote"

	"contnet.org/lib/cnm-go"
	"contnet.org/lib/cnm-go/cnmfmt"
	"contnet.org/lib/cnp-go"
)

var (
	listen      = flag.String("listen", "localhost:8080", "address for HTTP server to listen on")
	cnphost     = flag.String("cnp-host", "", "the CNP host to proxy (disables browser mode)")
	nohighlight = flag.Bool("no-highlight", false, "do not include highlight.js scripts and stylesheets")
	nostatic    = flag.Bool("no-static", false, "do not serve static files on /static")

	templates = template.Must(template.New("").Funcs(map[string]interface{}{
		"inc":     func(s string) string { return "" },
		"dec":     func() string { return "" },
		"rst":     func() string { return "" },
		"depth":   func() int { return 0 },
		"sanchor": func() template.URL { return "" },
		"lanchor": func() template.URL { return "" },
		"ianchor": func() template.URL { return "" },
		"anchor":  func() template.URL { return "" },
		"lang": func(s string) string {
			return strings.Map(func(r rune) rune {
				if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '_' || r == '-' {
					return r
				}
				return '_'
			}, s)
		},
		"href": func(s string) template.HTMLAttr {
			return "href=\"" + template.HTMLAttr(template.HTMLEscapeString(s)) + "\""
		},
		"cnmfmt": (func(cnmfmt.Text) template.HTML)(nil),
		"tourl":  (func(string) string)(nil),
	}).ParseGlob("templates/*.html"))
)

const (
	anchorCNPSchema  = "cnp://"
	anchorHTTPSchema = "http://"
	anchorPrefix     = `<a href="`
	anchorSuffix     = `">`
)

var (
	anchorTemplate = template.Must(template.New("").Parse(anchorPrefix + "{{.}}" + anchorSuffix))
)

func escapeURL(urlStr string) string {
	isCNP := len(urlStr) >= len(anchorCNPSchema) && strings.EqualFold(urlStr[:len(anchorCNPSchema)], anchorCNPSchema)
	if isCNP {
		urlStr = anchorHTTPSchema + urlStr[len(anchorCNPSchema):]
	}
	var buf bytes.Buffer
	_ = anchorTemplate.Execute(&buf, urlStr)
	urlStr = buf.String()
	urlStr = urlStr[len(anchorPrefix) : len(urlStr)-len(anchorSuffix)]
	if isCNP {
		urlStr = anchorCNPSchema + urlStr[len(anchorHTTPSchema):]
	}
	return urlStr
}

type server struct {
	host         string
	highlighting bool
}

func newServer(host string, highlighting bool) *server {
	return &server{host, highlighting}
}

func (srv *server) handleError(w http.ResponseWriter, err error) {
	code := http.StatusInternalServerError
	switch err.(type) {
	case cnp.ErrorDenied:
		code = http.StatusForbidden
	case cnp.ErrorInvalid:
		code = http.StatusInternalServerError
	case cnp.ErrorNotFound:
		code = http.StatusNotFound
	case cnp.ErrorNotSupported:
		code = http.StatusInternalServerError
	case cnp.ErrorRejected:
		code = http.StatusUnprocessableEntity
	case cnp.ErrorServerError:
		code = http.StatusBadGateway
	case cnp.ErrorSyntax:
		code = http.StatusInternalServerError
	case cnp.ErrorTooLarge:
		code = http.StatusRequestEntityTooLarge
	case cnp.ErrorVersion:
		code = http.StatusInternalServerError
	}
	log.Printf("error: %T %v", err, err)
	http.Error(w, http.StatusText(code), code)
}

func (srv *server) handleIndex(w http.ResponseWriter, r *http.Request) {
	req, _ := cnp.NewRequest("", "/", nil)
	resp, _ := cnp.NewResponse(cnp.IntentOK, []byte{})
	srv.cnpCNMToHTML(w, r, req, resp)
}

func (srv *server) handleCNP(w http.ResponseWriter, r *http.Request, path string) {
	host := srv.host
	if host == "" {
		ss := strings.SplitN(strings.TrimLeft(path, "/"), "/", 2)
		if len(ss) != 2 {
			if len(ss[0]) > 0 {
				http.Redirect(w, r, path+"/", http.StatusFound)
				return
			}
			srv.handleIndex(w, r)
			return
		}
		host = ss[0]
		path = "/" + ss[1]
	}

	req, err := cnp.NewRequest(host, path, nil)
	if err != nil {
		srv.handleError(w, err)
		return
	}

	err = r.ParseForm()
	if err != nil {
		srv.handleError(w, err)
	}

	if sel := r.FormValue("select"); sel != "" {
		req.SetSelect("cnm", sel)
	}

	if ims := r.Header.Get("If-Modified-Since"); ims != "" {
		var t time.Time
		t, err = http.ParseTime(ims)
		if err == nil && !t.IsZero() {
			req.SetIfModified(t)
		}
	}

	resp, err := cnp.Send(req)
	intent := "n/a"
	if resp != nil {
		intent = resp.Intent()
	}
	log.Printf("req: %q -> %q", req.Intent(), intent)
	if err != nil {
		if e, ok := err.(*net.OpError); ok && e.Op == "dial" {
			err = cnp.NewError(cnp.ReasonServerError)
		}
		srv.handleError(w, err)
		return
	}

	_, preq := r.Form["req"]
	_, phdr := r.Form["hdr"]
	_, presp := r.Form["resp"]
	_, praw := r.Form["raw"]

	if preq || phdr || presp {
		srv.cnpParamsToHTTP(w, resp)
		w.Header().Set("Content-Type", "text/plain")
		w.Header().Del("Content-Length")

		if preq {
			req.Write(w)
		}
		if presp {
			resp.Write(w)
		} else if phdr {
			resp.Header.Write(w)
		}
	} else {
		srv.cnpToWeb(w, r, req, resp, praw)
	}
}

func (srv *server) cnpToWeb(w http.ResponseWriter, r *http.Request, req *cnp.Request, resp *cnp.Response, raw bool) {
	if err := resp.Validate(); err != nil {
		srv.handleError(w, err)
		return
	}

	switch resp.ResponseIntent() {
	case cnp.IntentOK:
		srv.cnpParamsToHTTP(w, resp)
		if !raw && resp.Type() == "text/cnm" {
			srv.cnpCNMToHTML(w, r, req, resp)
		} else {
			if resp.Type() == "text/cnm" {
				w.Header().Set("Content-Type", "text/plain")
			}
			_, _ = io.Copy(w, resp.Body)
		}
	case cnp.IntentNotModified:
		w.WriteHeader(http.StatusNotModified)
	case cnp.IntentRedirect:
		host, pth, _ := resp.Location() // already validated
		loc, err := srv.cnpRedirectToHTTP(req, host, pth)
		if err != nil {
			srv.handleError(w, err)
			return
		}
		log.Println("redirecting to", loc)
		http.Redirect(w, r, loc, http.StatusFound)
	case cnp.IntentError:
		srv.handleError(w, cnp.NewError(resp.Reason()))
	default:
		srv.handleError(w, errors.New("unknown CNP response intent: "+resp.ResponseIntent()))
	}
}

func (srv *server) cnpRedirectToHTTP(req *cnp.Request, host, pth string) (string, error) {
	var loc string
	if host == "" || host == "." || host == srv.host {
		loc = pth
		if host == "." {
			loc = path.Join(path.Dir(req.Path()), loc)
		}
		if srv.host == "" {
			loc = path.Join("/", req.Host(), loc)
		}
	} else {
		rr, err := cnp.NewRequest(host, pth, nil)
		if err != nil {
			return "", err
		}
		if srv.host == "" {
			loc = path.Join("?", rr.Host(), rr.Path())
		} else {
			loc = rr.URL().String()
		}
	}
	if strings.HasSuffix(pth, "/") {
		loc = loc + "/"
	}
	return loc, nil
}

func (srv *server) cnpParamsToHTTP(w http.ResponseWriter, resp *cnp.Response) {
	if l := resp.Length(); l > 0 {
		w.Header().Set("Content-Length", strconv.FormatInt(l, 10))
	}
	if t := resp.Type(); t != "" {
		w.Header().Set("Content-Type", t)
	}
	if m := resp.Modified(); !m.IsZero() {
		w.Header().Set("Last-Modified", m.Format(http.TimeFormat))
	}
	if t := resp.Time(); !t.IsZero() {
		w.Header().Set("Date", t.Format(http.TimeFormat))
	}
	if n := resp.Name(); n != "" {
		w.Header().Set("Content-Disposition", "inline; filename=\""+strings.Map(func(r rune) rune {
			if r < ' ' || r == ' ' || r == '\'' { // filter out nulls, control codes, newlines and quotes
				return -1
			}
			return r
		}, n)+"\"")
	}
}

type cnmPage struct {
	URL       string
	Req       string
	Resp      string
	Doc       *cnm.Document
	Site      []site
	Netcat    string
	Toc       tocSection
	Highlight bool
	Browser   bool
	depth     int
}

type tocSection struct {
	Title    string
	Children []tocSection
}

type site struct {
	Path     string
	Name     string
	Children []site
}

func genToc(b cnm.Block) []tocSection {
	var res []tocSection
	if v, ok := b.(*cnm.SectionBlock); ok && v != nil {
		if t := v.Title(); t != "" {
			var ch []tocSection
			for _, c := range v.Children() {
				ch = append(ch, genToc(c)...)
			}
			res = append(res, tocSection{
				Title:    v.Title(),
				Children: ch,
			})
		} else {
			for _, bl := range v.Children() {
				res = append(res, genToc(bl)...)
			}
		}
	} else if v, ok := b.(cnm.ContainerBlock); ok {
		for _, bl := range v.Children() {
			res = append(res, genToc(bl)...)
		}
	}
	return res
}

func cnmSite(prefix string, s cnm.Site) (st site) {
	if ss := strings.Split(path.Clean(s.Path), "/"); len(ss) > 1 {
		s.Path = strings.Join(ss[1:], "/")
		return site{
			Path: path.Join(prefix, ss[0]),
			Name: ss[0],
			Children: []site{
				cnmSite(path.Join(prefix, ss[0]), s),
			},
		}
	}

	st.Path = path.Join(prefix, s.Path)
	if s.Name == "" {
		st.Name = s.Path
	} else {
		st.Name = s.Name
	}
	if len(s.Children) > 0 {
		chs := make(map[string]site)
		for _, ch := range s.Children {
			chs[ch.Name] = cnmSite(st.Path, ch)
		}
		keys := make([]string, len(chs))
		i := 0
		for k := range chs {
			keys[i] = k
			i++
		}
		sort.Slice(keys, func(i, j int) bool {
			a, b := chs[keys[i]], chs[keys[j]]
			da, db := strings.HasSuffix(a.Name, "/"), strings.HasSuffix(b.Name, "/")
			if da && !db {
				return true
			}
			if !da && db {
				return false
			}
			return a.Name < b.Name
		})
		st.Children = make([]site, len(keys))
		for i := range keys {
			st.Children[i] = chs[keys[i]]
		}
	}
	return
}

func (srv *server) cnpCNMToHTML(w http.ResponseWriter, r *http.Request, req *cnp.Request, resp *cnp.Response) {
	doc, err := cnm.ParseDocument(resp.Body)
	if err != nil {
		srv.handleError(w, err)
		return
	}

	w.Header().Set("Content-Type", "text/html")
	w.Header().Del("Content-Length")

	var breq, bresp, buf bytes.Buffer
	req.Header.Write(&breq)
	resp.Header.Write(&bresp)
	var st []site
	if len(doc.Site.Children) > 0 {
		st = []site{
			site{"/", "/", cnmSite("/", doc.Site).Children},
		}
	}

	u := req.URL()
	port := u.Port()
	if port == "" {
		port = strconv.Itoa(cnp.DefaultPort)
	}
	hdrs := req.Header.String()
	hdrs = hdrs[:len(hdrs)-1]

	tmpl, err := templates.Clone()
	if err != nil {
		srv.handleError(w, err)
		return
	}

	var toc []tocSection
	if doc.Content != nil {
		toc = genToc(doc.Content)
	}
	err = srv.addTemplateFuncs(tmpl, req, resp).ExecuteTemplate(&buf, "page.html", cnmPage{
		URL:       u.String(),
		Req:       breq.String(),
		Resp:      bresp.String(),
		Doc:       doc,
		Netcat:    shellquote.Join("echo", hdrs) + " | " + shellquote.Join("nc", req.Host(), port),
		Site:      st,
		Toc:       tocSection{Children: toc},
		Highlight: srv.highlighting,
		Browser:   srv.host == "",
	})
	if err != nil {
		srv.handleError(w, err)
		return
	}

	_, _ = io.Copy(w, &buf)
}

func (srv *server) addTemplateFuncs(tmpl *template.Template, req *cnp.Request, resp *cnp.Response) *template.Template {
	sections := []string{}
	indices := []int{1}
	sanchors := map[string]bool{}
	lanchors := map[string]bool{}
	anchor := func() template.URL {
		var secs []string
		for _, s := range sections {
			if s = url.PathEscape(s); s != "" {
				secs = append(secs, s)
			}
		}
		return template.URL(strings.Join(secs, "/"))
	}
	return tmpl.Funcs(map[string]interface{}{
		"inc": func(s string) string {
			sections = append(sections, s)
			indices = append(indices, 1)
			return ""
		},
		"dec": func() string {
			sections = sections[:len(sections)-1]
			indices = indices[:len(indices)-1]
			indices[len(indices)-1]++
			return ""
		},
		"rst": func() string {
			sections = []string{}
			indices = []int{1}
			sanchors = map[string]bool{}
			lanchors = map[string]bool{}
			return ""
		},
		"depth": func() int {
			d := len(sections) + 1
			if d > 6 {
				return 6
			}
			return d
		},
		"anchor": anchor,
		"ianchor": func() template.URL {
			var buf bytes.Buffer
			for i, n := range indices[:len(indices)-1] {
				if i != 0 {
					buf.WriteByte('.')
				}
				buf.WriteString(strconv.Itoa(n))
			}
			return template.URL(buf.String())
		},
		"sanchor": func() template.URL {
			s := url.PathEscape(sections[len(sections)-1])
			if sanchors[s] {
				return ""
			}
			sanchors[s] = true
			return template.URL(s)
		},
		"lanchor": func() template.URL {
			s := string(anchor())
			if lanchors[s] {
				return ""
			}
			lanchors[s] = true
			return template.URL(s)
		},
		"cnmfmt": func(txt cnmfmt.Text) template.HTML {
			return srv.fmtToHTML(req, txt)
		},
		"tourl": func(s string) string {
			u, _ := srv.linkToURL(req, s)
			return u
		},
	})
}

func (srv *server) fmtToHTML(req *cnp.Request, text cnmfmt.Text) template.HTML {
	if len(text.Spans) == 0 {
		return ""
	}

	var last cnmfmt.Span
	var buf bytes.Buffer
	hadText := true

	spans := make([]cnmfmt.Span, len(text.Spans)+1)
	copy(spans, text.Spans)
	spans[len(spans)-1] = cnmfmt.Span{} // end all formats

	var tags []string
	for _, span := range spans {
		if last.Format.Link != span.Format.Link {
			if !hadText && last.Format.Link != "" { // no text in link
				template.HTMLEscape(&buf, []byte(last.Format.Link))
			}
			hadText = false
		}
		srv.handleTags(req, &buf, &tags, last.Format, span.Format)
		if span.Text != "" {
			hadText = true
			template.HTMLEscape(&buf, []byte(span.Text))
		}
		last = span
	}

	return template.HTML("<p>" + buf.String() + "</p>")
}

func (srv *server) handleTags(req *cnp.Request, buf *bytes.Buffer, tags *[]string, old, new cnmfmt.Format) {
	if old == new {
		return
	}

	close := map[string]bool{
		"b":   old.Emphasized && !new.Emphasized,
		"i":    old.Alternate && !new.Alternate,
		"code": old.Code && !new.Code,
		"q":    old.Quote && !new.Quote,
		"a":    old.Link != "" && old.Link != new.Link,
	}

	open := map[string]bool{
		"b":   !old.Emphasized && new.Emphasized,
		"i":    !old.Alternate && new.Alternate,
		"code": !old.Code && new.Code,
		"q":    !old.Quote && new.Quote,
		"a":    new.Link != "" && old.Link != new.Link,
	}

	t := *tags

	pop := len(t)
	for i := len(t) - 1; i >= 0; i-- {
		if close[t[i]] {
			pop = i
		}
	}
	for i := len(t) - 1; i >= pop; i-- {
		if !close[t[i]] {
			open[t[i]] = true
		}
		buf.WriteString("</" + t[i] + ">")
	}
	*tags = t[:pop]

	tagPush(buf, tags, open, "b", "<b>")
	tagPush(buf, tags, open, "i", "<i>")
	tagPush(buf, tags, open, "code", "<code>")
	tagPush(buf, tags, open, "q", "<q>")

	link, extern := srv.linkToURL(req, new.Link)
	tagPush(buf, tags, open, "a", "<a"+extern+" href=\""+escapeURL(link)+"\">")
}

func (srv *server) linkToURL(req *cnp.Request, link string) (urlStr, extern string) {
	urlStr = "#ZcnpfmtZ"
	host := srv.host
	if host == "" {
		host = req.Host()
	}
	if u, err := url.Parse(link); err == nil {
		if u.Scheme == "cnp" && (srv.host == "" || u.Host == srv.host) {
			var lhost, lpath string
			lhost = u.Host
			lpath = u.Path
			if u.Host == srv.host {
				lhost = ""
			} else {
				extern = " class=\"cnp-external cnp-external-cnp\" data-scheme=\"cnp\""
			}
			urlStr = path.Join("/", lhost, lpath)
			if strings.HasSuffix(link, "/") {
				urlStr += "/"
			}
			if u.Fragment != "" {
				urlStr += "#" + u.Fragment
			}
		} else if u.Scheme != "" {
			hscheme := template.HTMLEscapeString(u.Scheme)
			extern = " class=\"cnp-external cnp-external-" + hscheme + "\" data-scheme=\"" + hscheme + "\""
			urlStr = u.String()
		} else {
			urlStr = u.Path
			if srv.host == "" {
				if !strings.HasPrefix(urlStr, "/") {
					urlStr = req.Path() + "/" + urlStr
				}
				urlStr = "/" + host + cnp.Clean("/"+urlStr)
			}
			if u.Fragment != "" {
				urlStr += "#" + u.Fragment
			}
		}
	}
	return
}

func tagPush(buf *bytes.Buffer, tags *[]string, ok map[string]bool, name, tag string) {
	if ok[name] {
		buf.WriteString(tag)
		*tags = append(*tags, name)
	}
}

func (srv *server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	log.Printf("access: %s %s %q", r.RemoteAddr, r.Method, r.URL)
	if r.Method == http.MethodPost {
		u := r.FormValue("url")
		req, err := cnp.NewRequestURL(u, nil)
		if err != nil {
			http.Error(w, err.Error(), http.StatusUnprocessableEntity)
			return
		}
		http.Redirect(w, r, path.Join("/", req.Host(), req.Path()), http.StatusFound)
	} else {
		srv.handleCNP(w, r, r.URL.Path)
	}
}

func main() {
	flag.Parse()

	srv := newServer(*cnphost, !*nohighlight)

	if !*nostatic {
		http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.Dir("static"))))
	}
	http.Handle("/", srv)

	log.Printf("listening on %s", *listen)
	panic(http.ListenAndServe(*listen, nil))
}