// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.

package api4

import (
	"net/http"
	"strconv"

	"github.com/gorilla/websocket"

	"github.com/mattermost/mattermost/server/public/model"
	"github.com/mattermost/mattermost/server/public/shared/mlog"
	"github.com/mattermost/mattermost/server/v8/channels/app/platform"
	"github.com/mattermost/mattermost/server/v8/channels/web"
)

const (
	connectionIDParam      = "connection_id"
	sequenceNumberParam    = "sequence_number"
	postedAckParam         = "posted_ack"
	disconnectErrCodeParam = "disconnect_err_code"

	clientPingTimeoutErrCode      = 4000
	clientSequenceMismatchErrCode = 4001
)

// validateDisconnectErrCode ensures the specified disconnect error code
// is a valid websocket close code
func validateDisconnectErrCode(errCode string) bool {
	if errCode == "" {
		return false
	}

	// Ensure the disconnect code is a standard close code
	code, err := strconv.Atoi(errCode)
	if err != nil {
		return false
	}

	// We only support the standard close codes between
	// 1000 and 1016, and a few custom application codes
	if (code < 1000 || code > 1016) &&
		code != clientPingTimeoutErrCode &&
		code != clientSequenceMismatchErrCode {
		return false
	}

	return true
}

func (api *API) InitWebSocket() {
	// Optionally supports a trailing slash
	api.BaseRoutes.APIRoot.Handle("/{websocket:websocket(?:\\/)?}", api.APIHandlerTrustRequester(connectWebSocket)).Methods(http.MethodGet)
}

func connectWebSocket(c *Context, w http.ResponseWriter, r *http.Request) {
	upgrader := websocket.Upgrader{
		ReadBufferSize:  model.SocketMaxMessageSizeKb,
		WriteBufferSize: model.SocketMaxMessageSizeKb,
		CheckOrigin:     c.App.OriginChecker(),
	}

	ws, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		params := map[string]any{
			"BlockedOrigin": r.Header.Get("Origin"),
		}
		c.Err = model.NewAppError("connect", "api.web_socket.connect.upgrade.app_error", params, "", http.StatusBadRequest).Wrap(err)
		return
	}

	// We initialize webconn with all the necessary data.
	// If the queues are empty, they are initialized in the constructor.
	cfg := &platform.WebConnConfig{
		WebSocket:     ws,
		Session:       *c.AppContext.Session(),
		TFunc:         c.AppContext.T,
		Locale:        "",
		Active:        true,
		PostedAck:     r.URL.Query().Get(postedAckParam) == "true",
		RemoteAddress: c.AppContext.IPAddress(),
		XForwardedFor: c.AppContext.XForwardedFor(),
	}

	disconnectErrCode := r.URL.Query().Get(disconnectErrCodeParam)
	if codeValid := validateDisconnectErrCode(disconnectErrCode); codeValid {
		cfg.DisconnectErrCode = disconnectErrCode
	}

	// The WebSocket upgrade request coming from mobile is missing the
	// user agent so we need to fallback on the session's metadata.
	if c.AppContext.Session().IsMobileApp() {
		cfg.OriginClient = "mobile"
	} else {
		cfg.OriginClient = string(web.GetOriginClient(r))
	}

	cfg.ConnectionID = r.URL.Query().Get(connectionIDParam)
	if cfg.ConnectionID == "" || c.AppContext.Session().UserId == "" {
		// If not present, we assume client is not capable yet, or it's a fresh connection.
		// We just create a new ID.
		cfg.ConnectionID = model.NewId()
		// In case of fresh connection id, sequence number is already zero.
	} else {
		cfg, err = c.App.Srv().Platform().PopulateWebConnConfig(c.AppContext.Session(), cfg, r.URL.Query().Get(sequenceNumberParam))
		if err != nil {
			c.Logger.Error("Error while populating webconn config", mlog.String("id", r.URL.Query().Get(connectionIDParam)), mlog.Err(err))
			ws.Close()
			return
		}
	}

	wc := c.App.Srv().Platform().NewWebConn(cfg, c.App, c.App.Srv().Channels())
	if c.AppContext.Session().UserId != "" {
		err = c.App.Srv().Platform().HubRegister(wc)
		if err != nil {
			c.Logger.Error("Error while registering to hub", mlog.String("id", r.URL.Query().Get(connectionIDParam)), mlog.Err(err))
			ws.Close()
			return
		}
	}

	wc.Pump()
}