package gateway

import (
	"net"
	"net/http"
	"net/http/httputil"
	"net/url"
	"strings"
)

// servePluginProxy forwards a plugin-owned prefix to an explicit loopback
// origin. No destination or path may be supplied by the client. Authentication
// and endpoint authorization have already completed before this is called.
func (g *Gateway) servePluginProxy(w http.ResponseWriter, r *http.Request, target, prefix string) {
	u, err := url.Parse(target)
	if err != nil || u.Scheme != "http" || u.User != nil || u.RawQuery != "" || u.Fragment != "" || (u.Path != "" && u.Path != "/") {
		writeError(w, http.StatusBadGateway, "plugin_proxy", "proxy must name a loopback HTTP origin")
		return
	}
	ip := net.ParseIP(u.Hostname())
	if ip == nil || !ip.IsLoopback() || u.Port() == "" {
		writeError(w, http.StatusBadGateway, "plugin_proxy", "proxy requires a literal loopback address and port")
		return
	}
	// WebSocket requests are browser-initiated and carry ambient cookies. Do not
	// allow a foreign website to use an administrator's session to open a tunnel.
	if origin := r.Header.Get("Origin"); origin != "" {
		o, e := url.Parse(origin)
		if e != nil || !strings.EqualFold(o.Host, r.Host) {
			writeError(w, http.StatusForbidden, "forbidden", "cross-origin proxy request refused")
			return
		}
	}
	proxy := httputil.NewSingleHostReverseProxy(u)
	director := proxy.Director
	proxy.Director = func(out *http.Request) {
		director(out)
		out.URL.Path = strings.TrimPrefix(r.URL.Path, prefix)
		if out.URL.Path == "" {
			out.URL.Path = "/"
		}
		out.URL.RawPath = ""
		out.Host = u.Host
		out.Header.Del("Authorization")
		out.Header.Del("Cookie")
		q := out.URL.Query()
		q.Del("api_key")
		out.URL.RawQuery = q.Encode()
	}
	proxy.ErrorHandler = func(w http.ResponseWriter, r *http.Request, err error) {
		writeError(w, http.StatusBadGateway, "plugin_proxy", "plugin service unavailable")
	}
	proxy.ServeHTTP(w, r)
}