// Copyright Simcord LLC
// This file is part of the Bitbon System Blockchain Node library.
// This file has been modified, you can find the original version by following the link
// <https://github.com/ethereum/go-ethereum>
//
// The Bitbon System Blockchain Node 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 Bitbon System Blockchain Node 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 Bitbon System Blockchain Node library. If not, see <http://www.gnu.org/licenses/>.

package rpc

import (
	"context"
	"encoding/base64"
	"fmt"
	"net/http"
	"net/url"
	"os"
	"strings"
	"sync"
	"time"

	mapset "github.com/deckarep/golang-set"
	"github.com/gorilla/websocket"
	"github.com/simcord-llc/bitbon-system-blockchain/log"
)

const (
	wsReadBuffer       = 1024
	wsWriteBuffer      = 1024
	wsPingInterval     = 60 * time.Second
	wsPingWriteTimeout = 5 * time.Second
)

var wsBufferPool = new(sync.Pool)

// 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 {
	var upgrader = websocket.Upgrader{
		ReadBufferSize:  wsReadBuffer,
		WriteBufferSize: wsWriteBuffer,
		WriteBufferPool: wsBufferPool,
		CheckOrigin:     wsHandshakeValidator(allowedOrigins),
	}
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		conn, err := upgrader.Upgrade(w, r, nil)
		if err != nil {
			log.Debug("WebSocket upgrade failed", "err", err)
			return
		}
		codec := newWebsocketCodec(conn)
		s.ServeCodec(codec, 0)
	})
}

// 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(*http.Request) bool {
	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(req *http.Request) bool {
		// 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 true
		}
		// Verify origin against whitelist.
		origin := strings.ToLower(req.Header.Get("Origin"))
		if allowAllOrigins || origins.Contains(origin) {
			return true
		}
		log.Warn("Rejected WebSocket connection", "origin", origin)
		return false
	}

	return f
}

type wsHandshakeError struct {
	err    error
	status string
}

func (e wsHandshakeError) Error() string {
	s := e.err.Error()
	if e.status != "" {
		s += " (HTTP status " + e.status + ")"
	}
	return s
}

// DialWebsocketWithDialer creates a new RPC client that communicates with a JSON-RPC server
// that is listening on the given endpoint using the provided dialer.
func DialWebsocketWithDialer(ctx context.Context, endpoint, origin string, dialer websocket.Dialer) (*Client, error) {
	endpoint, header, err := wsClientHeaders(endpoint, origin)
	if err != nil {
		return nil, err
	}
	return newClient(ctx, func(ctx context.Context) (ServerCodec, error) {
		conn, resp, err := dialer.DialContext(ctx, endpoint, header)
		if err != nil {
			hErr := wsHandshakeError{err: err}
			if resp != nil {
				hErr.status = resp.Status
			}
			return nil, hErr
		}
		return newWebsocketCodec(conn), 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) {
	dialer := websocket.Dialer{
		ReadBufferSize:  wsReadBuffer,
		WriteBufferSize: wsWriteBuffer,
		WriteBufferPool: wsBufferPool,
	}
	return DialWebsocketWithDialer(ctx, endpoint, origin, dialer)
}

func wsClientHeaders(endpoint, origin string) (string, http.Header, error) {
	endpointURL, err := url.Parse(endpoint)
	if err != nil {
		return endpoint, nil, err
	}
	header := make(http.Header)
	if origin != "" {
		header.Add("origin", origin)
	}
	if endpointURL.User != nil {
		b64auth := base64.StdEncoding.EncodeToString([]byte(endpointURL.User.String()))
		header.Add("authorization", "Basic "+b64auth)
		endpointURL.User = nil
	}
	return endpointURL.String(), header, nil
}

type websocketCodec struct {
	*jsonCodec
	conn *websocket.Conn

	wg        sync.WaitGroup
	pingReset chan struct{}
}

func newWebsocketCodec(conn *websocket.Conn) ServerCodec {
	conn.SetReadLimit(maxRequestContentLength)
	wc := &websocketCodec{
		jsonCodec: NewFuncCodec(conn, conn.WriteJSON, conn.ReadJSON).(*jsonCodec),
		conn:      conn,
		pingReset: make(chan struct{}, 1),
	}
	wc.wg.Add(1)
	go wc.pingLoop()
	return wc
}

func (wc *websocketCodec) close() {
	wc.jsonCodec.close()
	wc.wg.Wait()
}

func (wc *websocketCodec) writeJSON(ctx context.Context, v interface{}) error {
	err := wc.jsonCodec.writeJSON(ctx, v)
	if err == nil {
		// Notify pingLoop to delay the next idle ping.
		select {
		case wc.pingReset <- struct{}{}:
		default:
		}
	}
	return err
}

// pingLoop sends periodic ping frames when the connection is idle.
func (wc *websocketCodec) pingLoop() {
	var timer = time.NewTimer(wsPingInterval)
	defer wc.wg.Done()
	defer timer.Stop()

	for {
		select {
		case <-wc.closed():
			return
		case <-wc.pingReset:
			if !timer.Stop() {
				<-timer.C
			}
			timer.Reset(wsPingInterval)
		case <-timer.C:
			wc.jsonCodec.encMu.Lock()
			wc.conn.SetWriteDeadline(time.Now().Add(wsPingWriteTimeout))
			wc.conn.WriteMessage(websocket.PingMessage, nil)
			wc.jsonCodec.encMu.Unlock()
			timer.Reset(wsPingInterval)
		}
	}
}
