// This file is part of MinIO Console Server
// Copyright (c) 2020 MinIO, Inc.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program 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 Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package restapi

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"net"
	"net/http"
	"strings"
	"sync"

	"github.com/gorilla/websocket"
	"github.com/minio/minio/pkg/madmin"
)

// shortTraceMsg Short trace record
type shortTraceMsg struct {
	Host       string    `json:"host"`
	Time       string    `json:"time"`
	Client     string    `json:"client"`
	CallStats  callStats `json:"callStats"`
	FuncName   string    `json:"api"`
	Path       string    `json:"path"`
	Query      string    `json:"query"`
	StatusCode int       `json:"statusCode"`
	StatusMsg  string    `json:"statusMsg"`
}

type callStats struct {
	Rx       int    `json:"rx"`
	Tx       int    `json:"tx"`
	Duration string `json:"duration"`
	Ttfb     string `json:"timeToFirstByte"`
}

// trace serves madmin.ServiceTraceInfo
// on a Websocket connection.
func (wsc *wsClient) trace() {
	defer func() {
		log.Println("trace stopped")
		// close connection after return
		wsc.conn.close()
	}()
	log.Println("trace started")

	err := startTraceInfo(wsc.conn, wsc.madmin)
	// Send Connection Close Message indicating the Status Code
	// see https://tools.ietf.org/html/rfc6455#page-45
	if err != nil {
		// If connection exceeded read deadline send Close
		// Message Policy Violation code since we don't want
		// to let the receiver figure out the read deadline.
		// This is a generic code designed if there is a
		// need to hide specific details about the policy.
		if nErr, ok := err.(net.Error); ok && nErr.Timeout() {
			wsc.conn.writeMessage(websocket.CloseMessage, websocket.FormatCloseMessage(websocket.ClosePolicyViolation, ""))
			return
		}
		// else, internal server error
		wsc.conn.writeMessage(websocket.CloseMessage, websocket.FormatCloseMessage(websocket.CloseInternalServerErr, err.Error()))
		return
	}
	// normal closure
	wsc.conn.writeMessage(websocket.CloseMessage, websocket.FormatCloseMessage(websocket.CloseNormalClosure, ""))
}

// startTraceInfo starts trace of the servers
// by first setting a websocket reader that will
// check for a heartbeat.
//
// A WaitGroup is used to handle goroutines and to ensure
// all finish in the proper order. If any, sendTraceInfo()
// or wsReadCheck() returns, trace should end.
func startTraceInfo(conn WSConn, client MinioAdmin) (mError error) {
	// a WaitGroup waits for a collection of goroutines to finish
	wg := sync.WaitGroup{}
	// a cancel context is needed to end all goroutines used
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	// Set number of goroutines to wait. wg.Wait()
	// waitsuntil counter is zero (all are done)
	wg.Add(3)
	// start go routine for reading websocket heartbeat
	readErr := wsReadCheck(ctx, &wg, conn)
	// send Stream of Trace Info to the ws c.connection
	traceCh := sendTraceInfo(ctx, &wg, conn, client)
	// If wsReadCheck returns it means that it is not possible to check
	// ws heartbeat anymore so we stop from doing trace, cancel context
	// for all goroutines.
	go func(wg *sync.WaitGroup) {
		defer wg.Done()
		if err := <-readErr; err != nil {
			log.Println("error on wsReadCheck:", err)
			mError = err
		}
		// cancel context for all goroutines.
		cancel()
	}(&wg)

	// wait for traceCh to finish
	if err := <-traceCh; err != nil {
		mError = err
	}

	// if traceCh closes for any reason,
	// cancel context for all goroutines
	cancel()
	// wait all goroutines to finish
	wg.Wait()
	return mError
}

// sendTraceInfo sends stream of Trace Info to the ws connection
func sendTraceInfo(ctx context.Context, wg *sync.WaitGroup, conn WSConn, client MinioAdmin) <-chan error {
	// decrements the WaitGroup counter
	// by one when the function returns
	defer wg.Done()
	ch := make(chan error)
	go func(ch chan<- error) {
		defer close(ch)

		// trace all traffic
		allTraffic := true
		// Trace failed requests only
		errOnly := false
		// Start listening on all trace activity.
		traceCh := client.serviceTrace(ctx, allTraffic, errOnly)

		for traceInfo := range traceCh {
			if traceInfo.Err != nil {
				log.Println("error on serviceTrace:", traceInfo.Err)
				ch <- traceInfo.Err
				return
			}
			// Serialize message to be sent
			traceInfoBytes, err := json.Marshal(shortTrace(&traceInfo))
			if err != nil {
				fmt.Println("error on json.Marshal:", err)
				ch <- err
				return
			}
			// Send Message through websocket connection
			err = conn.writeMessage(websocket.TextMessage, traceInfoBytes)
			if err != nil {
				log.Println("error writeMessage:", err)
				ch <- err
				return
			}
		}
		// TODO: verbose
	}(ch)

	return ch
}

// shortTrace creates a shorter Trace Info message.
//   Same implementation as github/minio/mc/cmd/admin-trace.go
func shortTrace(info *madmin.ServiceTraceInfo) shortTraceMsg {
	t := info.Trace
	s := shortTraceMsg{}

	s.Time = t.ReqInfo.Time.String()
	s.Path = t.ReqInfo.Path
	s.Query = t.ReqInfo.RawQuery
	s.FuncName = t.FuncName
	s.StatusCode = t.RespInfo.StatusCode
	s.StatusMsg = http.StatusText(t.RespInfo.StatusCode)
	s.CallStats.Duration = t.CallStats.Latency.String()
	s.CallStats.Rx = t.CallStats.InputBytes
	s.CallStats.Tx = t.CallStats.OutputBytes

	if host, ok := t.ReqInfo.Headers["Host"]; ok {
		s.Host = strings.Join(host, "")
	}
	cSlice := strings.Split(t.ReqInfo.Client, ":")
	s.Client = cSlice[0]
	return s
}