// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package rpc

import (
	"bytes"
	"context"
	"crypto/tls"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	mapset "github.com/deckarep/golang-set"
	"github.com/ethereum/go-ethereum/log"
	"golang.org/x/net/websocket"
)

// websocketJSONCodec is a custom JSON codec with payload size enforcement and
// special number parsing.
var websocketJSONCodec = websocket.Codec{
	// Marshal is the stock JSON marshaller used by the websocket library too.
	Marshal: func(v interface{}) ([]byte, byte, error) {
		msg, err := json.Marshal(v)
		return msg, websocket.TextFrame, err
	},
	// Unmarshal is a specialized unmarshaller to properly convert numbers.
	Unmarshal: func(msg []byte, payloadType byte, v interface{}) error {
		dec := json.NewDecoder(bytes.NewReader(msg))
		dec.UseNumber()

		return dec.Decode(v)
	},
}

// WebsocketHandler returns a handler that serves JSON-RPC to WebSocket connections.
//
// allowedOrigins should be a comma-separated list of allowed origin URLs.
// To allow connections with any origin, pass "*".
func (s *Server) WebsocketHandler(allowedOrigins []string) http.Handler {
	return websocket.Server{
		Handshake: wsHandshakeValidator(allowedOrigins),
		Handler: func(conn *websocket.Conn) {
			codec := newWebsocketCodec(conn)
			s.ServeCodec(codec, OptionMethodInvocation|OptionSubscriptions)
		},
	}
}

func newWebsocketCodec(conn *websocket.Conn) ServerCodec {
	// Create a custom encode/decode pair to enforce payload size and number encoding
	conn.MaxPayloadBytes = maxRequestContentLength
	encoder := func(v interface{}) error {
		return websocketJSONCodec.Send(conn, v)
	}
	decoder := func(v interface{}) error {
		return websocketJSONCodec.Receive(conn, v)
	}
	rpcconn := Conn(conn)
	if conn.IsServerConn() {
		// Override remote address with the actual socket address because
		// package websocket crashes if there is no request origin.
		addr := conn.Request().RemoteAddr
		if wsaddr := conn.RemoteAddr().(*websocket.Addr); wsaddr.URL != nil {
			// Add origin if present.
			addr += "(" + wsaddr.URL.String() + ")"
		}
		rpcconn = connWithRemoteAddr{conn, addr}
	}
	return NewCodec(rpcconn, encoder, decoder)
}

// NewWSServer creates a new websocket RPC server around an API provider.
//
// Deprecated: use Server.WebsocketHandler
func NewWSServer(allowedOrigins []string, srv *Server) *http.Server {
	return &http.Server{Handler: srv.WebsocketHandler(allowedOrigins)}
}

// wsHandshakeValidator returns a handler that verifies the origin during the
// websocket upgrade process. When a '*' is specified as an allowed origins all
// connections are accepted.
func wsHandshakeValidator(allowedOrigins []string) func(*websocket.Config, *http.Request) error {
	origins := mapset.NewSet()
	allowAllOrigins := false

	for _, origin := range allowedOrigins {
		if origin == "*" {
			allowAllOrigins = true
		}
		if origin != "" {
			origins.Add(strings.ToLower(origin))
		}
	}

	// allow localhost if no allowedOrigins are specified.
	if len(origins.ToSlice()) == 0 {
		origins.Add("http://localhost")
		if hostname, err := os.Hostname(); err == nil {
			origins.Add("http://" + strings.ToLower(hostname))
		}
	}

	log.Debug(fmt.Sprintf("Allowed origin(s) for WS RPC interface %v", origins.ToSlice()))

	f := func(cfg *websocket.Config, req *http.Request) error {
		// Skip origin verification if no Origin header is present. The origin check
		// is supposed to protect against browser based attacks. Browsers always set
		// Origin. Non-browser software can put anything in origin and checking it doesn't
		// provide additional security.
		if _, ok := req.Header["Origin"]; !ok {
			return
		}
		// Verify origin against whitelist.
		origin := strings.ToLower(req.Header.Get("Origin"))
		if allowAllOrigins || origins.Contains(origin) {
			return nil
		}
		log.Warn("Rejected WebSocket connection", "origin", origin)
		return errors.New("origin not allowed")
	}

	return f
}

func wsGetConfig(endpoint, origin string) (*websocket.Config, error) {
	if origin == "" {
		var err error
		if origin, err = os.Hostname(); err != nil {
			return nil, err
		}
		if strings.HasPrefix(endpoint, "wss") {
			origin = "https://" + strings.ToLower(origin)
		} else {
			origin = "http://" + strings.ToLower(origin)
		}
	}
	config, err := websocket.NewConfig(endpoint, origin)
	if err != nil {
		return nil, err
	}

	if config.Location.User != nil {
		b64auth := base64.StdEncoding.EncodeToString([]byte(config.Location.User.String()))
		config.Header.Add("Authorization", "Basic "+b64auth)
		config.Location.User = nil
	}
	return config, nil
}

// DialWebsocket creates a new RPC client that communicates with a JSON-RPC server
// that is listening on the given endpoint.
//
// The context is used for the initial connection establishment. It does not
// affect subsequent interactions with the client.
func DialWebsocket(ctx context.Context, endpoint, origin string) (*Client, error) {
	config, err := wsGetConfig(endpoint, origin)
	if err != nil {
		return nil, err
	}

	return newClient(ctx, func(ctx context.Context) (ServerCodec, error) {
		conn, err := wsDialContext(ctx, config)
		if err != nil {
			return nil, err
		}
		return newWebsocketCodec(conn), nil
	})
}

func wsDialContext(ctx context.Context, config *websocket.Config) (*websocket.Conn, error) {
	var conn net.Conn
	var err error
	switch config.Location.Scheme {
	case "ws":
		conn, err = dialContext(ctx, "tcp", wsDialAddress(config.Location))
	case "wss":
		dialer := contextDialer(ctx)
		conn, err = tls.DialWithDialer(dialer, "tcp", wsDialAddress(config.Location), config.TlsConfig)
	default:
		err = websocket.ErrBadScheme
	}
	if err != nil {
		return nil, err
	}
	ws, err := websocket.NewClient(config, conn)
	if err != nil {
		conn.Close()
		return nil, err
	}
	return ws, err
}

var wsPortMap = map[string]string{"ws": "80", "wss": "443"}

func wsDialAddress(location *url.URL) string {
	if _, ok := wsPortMap[location.Scheme]; ok {
		if _, _, err := net.SplitHostPort(location.Host); err != nil {
			return net.JoinHostPort(location.Host, wsPortMap[location.Scheme])
		}
	}
	return location.Host
}

func dialContext(ctx context.Context, network, addr string) (net.Conn, error) {
	d := &net.Dialer{KeepAlive: tcpKeepAliveInterval}
	return d.DialContext(ctx, network, addr)
}

func contextDialer(ctx context.Context) *net.Dialer {
	dialer := &net.Dialer{Cancel: ctx.Done(), KeepAlive: tcpKeepAliveInterval}
	if deadline, ok := ctx.Deadline(); ok {
		dialer.Deadline = deadline
	} else {
		dialer.Deadline = time.Now().Add(defaultDialTimeout)
	}
	return dialer
}