/*
Copyright 2014 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package kubectl

import (
	"fmt"
	"net"
	"net/http"
	"net/http/httputil"
	"net/url"
	"os"
	"regexp"
	"strings"
	"time"

	"github.com/golang/glog"
	restclient "k8s.io/client-go/rest"
	"k8s.io/kubernetes/pkg/util"
)

const (
	DefaultHostAcceptRE   = "^localhost$,^127\\.0\\.0\\.1$,^\\[::1\\]$"
	DefaultPathAcceptRE   = "^.*"
	DefaultPathRejectRE   = "^/api/.*/pods/.*/exec,^/api/.*/pods/.*/attach"
	DefaultMethodRejectRE = "^$"
)

var (
	// The reverse proxy will periodically flush the io writer at this frequency.
	// Only matters for long poll connections like the one used to watch. With an
	// interval of 0 the reverse proxy will buffer content sent on any connection
	// with transfer-encoding=chunked.
	// TODO: Flush after each chunk so the client doesn't suffer a 100ms latency per
	// watch event.
	ReverseProxyFlushInterval = 100 * time.Millisecond
)

// FilterServer rejects requests which don't match one of the specified regular expressions
type FilterServer struct {
	// Only paths that match this regexp will be accepted
	AcceptPaths []*regexp.Regexp
	// Paths that match this regexp will be rejected, even if they match the above
	RejectPaths []*regexp.Regexp
	// Hosts are required to match this list of regexp
	AcceptHosts []*regexp.Regexp
	// Methods that match this regexp are rejected
	RejectMethods []*regexp.Regexp
	// The delegate to call to handle accepted requests.
	delegate http.Handler
}

// Splits a comma separated list of regexps into an array of Regexp objects.
func MakeRegexpArray(str string) ([]*regexp.Regexp, error) {
	parts := strings.Split(str, ",")
	result := make([]*regexp.Regexp, len(parts))
	for ix := range parts {
		re, err := regexp.Compile(parts[ix])
		if err != nil {
			return nil, err
		}
		result[ix] = re
	}
	return result, nil
}

func MakeRegexpArrayOrDie(str string) []*regexp.Regexp {
	result, err := MakeRegexpArray(str)
	if err != nil {
		glog.Fatalf("Error compiling re: %v", err)
	}
	return result
}

func matchesRegexp(str string, regexps []*regexp.Regexp) bool {
	for _, re := range regexps {
		if re.MatchString(str) {
			glog.V(6).Infof("%v matched %s", str, re)
			return true
		}
	}
	return false
}

func (f *FilterServer) accept(method, path, host string) bool {
	if matchesRegexp(path, f.RejectPaths) {
		return false
	}
	if matchesRegexp(method, f.RejectMethods) {
		return false
	}
	if matchesRegexp(path, f.AcceptPaths) && matchesRegexp(host, f.AcceptHosts) {
		return true
	}
	return false
}

// Make a copy of f which passes requests along to the new delegate.
func (f *FilterServer) HandlerFor(delegate http.Handler) *FilterServer {
	f2 := *f
	f2.delegate = delegate
	return &f2
}

// Get host from a host header value like "localhost" or "localhost:8080"
func extractHost(header string) (host string) {
	host, _, err := net.SplitHostPort(header)
	if err != nil {
		host = header
	}
	return host
}

func (f *FilterServer) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
	host := extractHost(req.Host)
	if f.accept(req.Method, req.URL.Path, host) {
		glog.V(3).Infof("Filter accepting %v %v %v", req.Method, req.URL.Path, host)
		f.delegate.ServeHTTP(rw, req)
		return
	}
	glog.V(3).Infof("Filter rejecting %v %v %v", req.Method, req.URL.Path, host)
	rw.WriteHeader(http.StatusForbidden)
	rw.Write([]byte("<h3>Unauthorized</h3>"))
}

// ProxyServer is a http.Handler which proxies Kubernetes APIs to remote API server.
type ProxyServer struct {
	handler http.Handler
}

// NewProxyServer creates and installs a new ProxyServer.
// It automatically registers the created ProxyServer to http.DefaultServeMux.
// 'filter', if non-nil, protects requests to the api only.
func NewProxyServer(filebase string, apiProxyPrefix string, staticPrefix string, filter *FilterServer, cfg *restclient.Config) (*ProxyServer, error) {
	host := cfg.Host
	if !strings.HasSuffix(host, "/") {
		host = host + "/"
	}
	target, err := url.Parse(host)
	if err != nil {
		return nil, err
	}
	proxy := newProxy(target)
	if proxy.Transport, err = restclient.TransportFor(cfg); err != nil {
		return nil, err
	}
	proxyServer := http.Handler(proxy)
	if filter != nil {
		proxyServer = filter.HandlerFor(proxyServer)
	}

	if !strings.HasPrefix(apiProxyPrefix, "/api") {
		proxyServer = stripLeaveSlash(apiProxyPrefix, proxyServer)
	}

	mux := http.NewServeMux()
	mux.Handle(apiProxyPrefix, proxyServer)
	if filebase != "" {
		// Require user to explicitly request this behavior rather than
		// serving their working directory by default.
		mux.Handle(staticPrefix, newFileHandler(staticPrefix, filebase))
	}
	return &ProxyServer{handler: mux}, nil
}

// Listen is a simple wrapper around net.Listen.
func (s *ProxyServer) Listen(address string, port int) (net.Listener, error) {
	return net.Listen("tcp", fmt.Sprintf("%s:%d", address, port))
}

// ListenUnix does net.Listen for a unix socket
func (s *ProxyServer) ListenUnix(path string) (net.Listener, error) {
	// Remove any socket, stale or not, but fall through for other files
	fi, err := os.Stat(path)
	if err == nil && (fi.Mode()&os.ModeSocket) != 0 {
		os.Remove(path)
	}
	// Default to only user accessible socket, caller can open up later if desired
	oldmask, _ := util.Umask(0077)
	l, err := net.Listen("unix", path)
	util.Umask(oldmask)
	return l, err
}

// Serve starts the server using given listener, loops forever.
func (s *ProxyServer) ServeOnListener(l net.Listener) error {
	server := http.Server{
		Handler: s.handler,
	}
	return server.Serve(l)
}

func newProxy(target *url.URL) *httputil.ReverseProxy {
	director := func(req *http.Request) {
		req.URL.Scheme = target.Scheme
		req.URL.Host = target.Host
		req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
	}
	return &httputil.ReverseProxy{Director: director, FlushInterval: ReverseProxyFlushInterval}
}

func newFileHandler(prefix, base string) http.Handler {
	return http.StripPrefix(prefix, http.FileServer(http.Dir(base)))
}

func singleJoiningSlash(a, b string) string {
	aslash := strings.HasSuffix(a, "/")
	bslash := strings.HasPrefix(b, "/")
	switch {
	case aslash && bslash:
		return a + b[1:]
	case !aslash && !bslash:
		return a + "/" + b
	}
	return a + b
}

// like http.StripPrefix, but always leaves an initial slash. (so that our
// regexps will work.)
func stripLeaveSlash(prefix string, h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
		p := strings.TrimPrefix(req.URL.Path, prefix)
		if len(p) >= len(req.URL.Path) {
			http.NotFound(w, req)
			return
		}
		if len(p) > 0 && p[:1] != "/" {
			p = "/" + p
		}
		req.URL.Path = p
		h.ServeHTTP(w, req)
	})
}
