// Copyright 2023 LiveKit, Inc.
//
// 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 service

import (
	"errors"
	"fmt"
	"io"
	"strings"
	"sync"
	"time"

	"github.com/frostbyte73/core"
	"github.com/gorilla/websocket"
	"google.golang.org/protobuf/proto"

	"github.com/livekit/protocol/livekit"
	"github.com/livekit/protocol/logger"
	"github.com/livekit/protocol/utils/protojson"

	"github.com/livekit/livekit-server/pkg/rtc/types"
)

const (
	pingFrequency     = 10 * time.Second
	pingTimeout       = 2 * time.Second
	closeWriteTimeout = 5 * time.Second
)

type WSSignalConnection struct {
	conn    types.WebsocketClient
	mu      sync.Mutex
	useJSON bool

	// maximum size (in bytes) of a single decompressed message; 0 disables the limit
	messageSizeLimit int64

	closed core.Fuse
}

func NewWSSignalConnection(conn types.WebsocketClient, messageSizeLimit int64) *WSSignalConnection {
	wsc := &WSSignalConnection{
		conn:             conn,
		mu:               sync.Mutex{},
		useJSON:          false,
		messageSizeLimit: messageSizeLimit,
	}
	go wsc.pingWorker()
	return wsc
}

// readMessage reads a single websocket message, bounding the size of the
// decompressed payload. The transport-level read limit (SetReadLimit) only
// accounts for the compressed bytes read off the wire, so a small compressed
// frame can still expand into a much larger buffer once inflated. Reading through
// an io.LimitReader caps the decompressed size at the same limit.
func (c *WSSignalConnection) readMessage() (int, []byte, error) {
	messageType, r, err := c.conn.NextReader()
	if err != nil {
		return messageType, nil, err
	}

	if c.messageSizeLimit > 0 {
		// read one byte past the limit so an exactly-at-limit message is accepted
		// while anything larger is detected and rejected
		limited := io.LimitReader(r, c.messageSizeLimit+1)
		payload, err := io.ReadAll(limited)
		if err != nil {
			return messageType, nil, err
		}
		if int64(len(payload)) > c.messageSizeLimit {
			return messageType, nil, fmt.Errorf("signal message exceeds size limit of %d bytes", c.messageSizeLimit)
		}
		return messageType, payload, nil
	}

	payload, err := io.ReadAll(r)
	return messageType, payload, err
}

func (c *WSSignalConnection) Close() error {
	c.closed.Break()

	return c.conn.Close()
}

func (c *WSSignalConnection) CloseWithReason(reason string) error {
	c.closed.Break()

	msg := websocket.FormatCloseMessage(websocket.CloseNormalClosure, reason)
	_ = c.conn.WriteControl(websocket.CloseMessage, msg, time.Now().Add(closeWriteTimeout))
	return c.conn.Close()
}

func (c *WSSignalConnection) SetReadDeadline(deadline time.Time) error {
	return c.conn.SetReadDeadline(deadline)
}

func (c *WSSignalConnection) ReadRequest() (*livekit.SignalRequest, int, error) {
	// handle special messages and pass on the rest
	messageType, payload, err := c.readMessage()
	if err != nil {
		return nil, 0, err
	}

	msg := &livekit.SignalRequest{}
	switch messageType {
	case websocket.BinaryMessage:
		if c.useJSON {
			c.mu.Lock()
			// switch to protobuf if client supports it
			c.useJSON = false
			c.mu.Unlock()
		}
		// protobuf encoded
		err := proto.Unmarshal(payload, msg)
		return msg, len(payload), err
	case websocket.TextMessage:
		c.mu.Lock()
		// json encoded, also write back JSON
		c.useJSON = true
		c.mu.Unlock()
		err := protojson.Unmarshal(payload, msg)
		return msg, len(payload), err
	default:
		logger.Debugw("unsupported message", "message", messageType)
		return nil, len(payload), nil
	}
}

func (c *WSSignalConnection) ReadWorkerMessage() (*livekit.WorkerMessage, int, error) {
	// handle special messages and pass on the rest
	messageType, payload, err := c.readMessage()
	if err != nil {
		return nil, 0, err
	}

	msg := &livekit.WorkerMessage{}
	switch messageType {
	case websocket.BinaryMessage:
		if c.useJSON {
			c.mu.Lock()
			// switch to protobuf if client supports it
			c.useJSON = false
			c.mu.Unlock()
		}
		// protobuf encoded
		err := proto.Unmarshal(payload, msg)
		return msg, len(payload), err
	case websocket.TextMessage:
		c.mu.Lock()
		// json encoded, also write back JSON
		c.useJSON = true
		c.mu.Unlock()
		err := protojson.Unmarshal(payload, msg)
		return msg, len(payload), err
	default:
		logger.Debugw("unsupported message", "message", messageType)
		return nil, len(payload), nil
	}
}

func (c *WSSignalConnection) WriteResponse(msg *livekit.SignalResponse) (int, error) {
	var msgType int
	var payload []byte
	var err error

	c.mu.Lock()
	defer c.mu.Unlock()

	if c.useJSON {
		msgType = websocket.TextMessage
		payload, err = protojson.Marshal(msg)
	} else {
		msgType = websocket.BinaryMessage
		payload, err = proto.Marshal(msg)
	}
	if err != nil {
		return 0, err
	}

	return len(payload), c.conn.WriteMessage(msgType, payload)
}

func (c *WSSignalConnection) WriteServerMessage(msg *livekit.ServerMessage) (int, error) {
	var msgType int
	var payload []byte
	var err error

	c.mu.Lock()
	defer c.mu.Unlock()

	if c.useJSON {
		msgType = websocket.TextMessage
		payload, err = protojson.Marshal(msg)
	} else {
		msgType = websocket.BinaryMessage
		payload, err = proto.Marshal(msg)
	}
	if err != nil {
		return 0, err
	}

	return len(payload), c.conn.WriteMessage(msgType, payload)
}

func (c *WSSignalConnection) pingWorker() {
	ticker := time.NewTicker(pingFrequency)
	defer ticker.Stop()

	for {
		select {
		case <-c.closed.Watch():
			return

		case <-ticker.C:
			err := c.conn.WriteControl(websocket.PingMessage, []byte(""), time.Now().Add(pingTimeout))
			if err != nil {
				return
			}
		}
	}
}

// IsWebSocketCloseError checks that error is normal/expected closure
func IsWebSocketCloseError(err error) bool {
	return errors.Is(err, io.EOF) ||
		strings.HasSuffix(err.Error(), "use of closed network connection") ||
		strings.HasSuffix(err.Error(), "connection reset by peer") ||
		websocket.IsCloseError(
			err,
			websocket.CloseAbnormalClosure,
			websocket.CloseGoingAway,
			websocket.CloseNormalClosure,
			websocket.CloseNoStatusReceived,
		)
}