/*
 * This file is part of Go Responsiveness.
 *
 * Go Responsiveness is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software Foundation,
 * either version 2 of the License, or (at your option) any later version.
 * Go Responsiveness 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with Go Responsiveness. If not, see <https://www.gnu.org/licenses/>.
 */

package lgc

import (
	"context"
	"crypto/tls"
	"fmt"
	"io"
	"net/http"
	"net/http/httptrace"
	"os"
	"sync"
	"sync/atomic"
	"time"

	"github.com/network-quality/goresponsiveness/debug"
	"github.com/network-quality/goresponsiveness/l4s"
	"github.com/network-quality/goresponsiveness/stats"
	"github.com/network-quality/goresponsiveness/traceable"
	"github.com/network-quality/goresponsiveness/utilities"
)

// TODO: All 64-bit fields that are accessed atomically must
// appear at the top of this struct.
type LoadGeneratingConnectionDownload struct {
	downloaded         uint64
	lastIntervalEnd    int64
	ConnectToAddr      string
	URL                string
	downloadStartTime  time.Time
	client             *http.Client
	debug              debug.DebugLevel
	InsecureSkipVerify bool
	KeyLogger          io.Writer
	clientId           uint64
	tracer             *httptrace.ClientTrace
	stats              stats.TraceStats
	status             LgcStatus
	congestionControl  *string
	statusLock         *sync.Mutex
	statusWaiter       *sync.Cond
}

func NewLoadGeneratingConnectionDownload(url string, keyLogger io.Writer, connectToAddr string, insecureSkipVerify bool, congestionControl *string) LoadGeneratingConnectionDownload {
	lgd := LoadGeneratingConnectionDownload{
		URL:                url,
		KeyLogger:          keyLogger,
		ConnectToAddr:      connectToAddr,
		InsecureSkipVerify: insecureSkipVerify,
		congestionControl:  congestionControl,
		statusLock:         &sync.Mutex{},
	}
	lgd.statusWaiter = sync.NewCond(lgd.statusLock)
	return lgd
}

func (lgd *LoadGeneratingConnectionDownload) Direction() LgcDirection {
	return LGC_DOWN
}

func (lgd *LoadGeneratingConnectionDownload) WaitUntilStarted(ctxt context.Context) bool {
	conditional := func() bool { return lgd.status != LGC_STATUS_NOT_STARTED }
	go utilities.ContextSignaler(ctxt, 500*time.Millisecond, &conditional, lgd.statusWaiter)
	return utilities.WaitWithContext(ctxt, &conditional, lgd.statusLock, lgd.statusWaiter)
}

func (lgd *LoadGeneratingConnectionDownload) SetDnsStartTimeInfo(
	now time.Time,
	dnsStartInfo httptrace.DNSStartInfo,
) {
	lgd.stats.DnsStartTime = now
	lgd.stats.DnsStart = dnsStartInfo
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"DNS Start for %v: %v\n",
			lgd.ClientId(),
			dnsStartInfo,
		)
	}
}

func (lgd *LoadGeneratingConnectionDownload) SetDnsDoneTimeInfo(
	now time.Time,
	dnsDoneInfo httptrace.DNSDoneInfo,
) {
	lgd.stats.DnsDoneTime = now
	lgd.stats.DnsDone = dnsDoneInfo
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"DNS Done for %v: %v\n",
			lgd.ClientId(),
			lgd.stats.DnsDone,
		)
	}
}

func (lgd *LoadGeneratingConnectionDownload) SetConnectStartTime(
	now time.Time,
) {
	lgd.stats.ConnectStartTime = now
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"TCP Start for %v at %v\n",
			lgd.ClientId(),
			lgd.stats.ConnectStartTime,
		)
	}
}

func (lgd *LoadGeneratingConnectionDownload) SetConnectDoneTimeError(
	now time.Time,
	err error,
) {
	lgd.stats.ConnectDoneTime = now
	lgd.stats.ConnectDoneError = err
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"TCP Done for %v (with error %v) @ %v\n",
			lgd.ClientId(),
			lgd.stats.ConnectDoneError,
			lgd.stats.ConnectDoneTime,
		)
	}
}

func (lgd *LoadGeneratingConnectionDownload) SetGetConnTime(now time.Time) {
	lgd.stats.GetConnectionStartTime = now
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"Started getting connection for %v @ %v\n",
			lgd.ClientId(),
			lgd.stats.GetConnectionStartTime,
		)
	}
}

func (lgd *LoadGeneratingConnectionDownload) SetGotConnTimeInfo(
	now time.Time,
	gotConnInfo httptrace.GotConnInfo,
) {
	if gotConnInfo.Reused {
		fmt.Printf("Unexpectedly reusing a connection!\n")
		panic(!gotConnInfo.Reused)
	}
	lgd.stats.GetConnectionDoneTime = now
	lgd.stats.ConnInfo = gotConnInfo
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"Got connection for %v at %v with info %v\n",
			lgd.ClientId(),
			lgd.stats.GetConnectionDoneTime,
			lgd.stats.ConnInfo,
		)
	}

	if lgd.congestionControl != nil {
		if debug.IsDebug(lgd.debug) {
			fmt.Printf(
				"Attempting to set congestion control algorithm to %v for connection %v at %v with info %v\n",
				*lgd.congestionControl,
				lgd.ClientId(),
				lgd.stats.GetConnectionDoneTime,
				lgd.stats.ConnInfo,
			)
		}
		if err := l4s.SetL4S(lgd.stats.ConnInfo.Conn, lgd.congestionControl); err != nil {
			fmt.Fprintf(
				os.Stderr,
				"Error setting L4S for %v at %v: %v\n",
				lgd.ClientId(),
				lgd.stats.GetConnectionDoneTime,
				err.Error(),
			)
		}
	}
}

func (lgd *LoadGeneratingConnectionDownload) SetTLSHandshakeStartTime(
	now time.Time,
) {
	lgd.stats.TLSStartTime = utilities.Some(now)
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"Started TLS Handshake for %v @ %v\n",
			lgd.ClientId(),
			lgd.stats.TLSStartTime,
		)
	}
}

func (lgd *LoadGeneratingConnectionDownload) SetTLSHandshakeDoneTimeState(
	now time.Time,
	connectionState tls.ConnectionState,
) {
	lgd.stats.TLSDoneTime = utilities.Some(now)
	lgd.stats.TLSConnInfo = connectionState
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"Completed TLS handshake for %v at %v with info %v\n",
			lgd.ClientId(),
			lgd.stats.TLSDoneTime,
			lgd.stats.TLSConnInfo,
		)
	}
}

func (lgd *LoadGeneratingConnectionDownload) SetHttpWroteRequestTimeInfo(
	now time.Time,
	info httptrace.WroteRequestInfo,
) {
	lgd.stats.HttpWroteRequestTime = now
	lgd.stats.HttpInfo = info
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"(lgd) Http finished writing request for %v at %v with info %v\n",
			lgd.ClientId(),
			lgd.stats.HttpWroteRequestTime,
			lgd.stats.HttpInfo,
		)
	}
}

func (lgd *LoadGeneratingConnectionDownload) SetHttpResponseReadyTime(
	now time.Time,
) {
	lgd.stats.HttpResponseReadyTime = now
	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"Got the first byte of HTTP response headers for %v at %v\n",
			lgd.ClientId(),
			lgd.stats.HttpResponseReadyTime,
		)
	}
}

func (lgd *LoadGeneratingConnectionDownload) ClientId() uint64 {
	return lgd.clientId
}

func (lgd *LoadGeneratingConnectionDownload) TransferredInInterval() (uint64, time.Duration) {
	transferred := atomic.SwapUint64(&lgd.downloaded, 0)
	newIntervalEnd := (time.Now().Sub(lgd.downloadStartTime)).Nanoseconds()
	previousIntervalEnd := atomic.SwapInt64(&lgd.lastIntervalEnd, newIntervalEnd)
	intervalLength := time.Duration(newIntervalEnd - previousIntervalEnd)
	if debug.IsDebug(lgd.debug) {
		fmt.Printf("download: Transferred: %v bytes in %v.\n", transferred, intervalLength)
	}
	return transferred, intervalLength
}

func (lgd *LoadGeneratingConnectionDownload) Client() *http.Client {
	return lgd.client
}

type loadGeneratingConnectionDownloadReader struct {
	n        *uint64
	ctx      context.Context
	readable io.Reader
	lgd      *LoadGeneratingConnectionDownload
}

func (cr *loadGeneratingConnectionDownloadReader) Read(p []byte) (n int, err error) {
	if cr.ctx.Err() != nil {
		return 0, io.EOF
	}

	if *cr.n == 0 {
		cr.lgd.statusLock.Lock()
		cr.lgd.status = LGC_STATUS_RUNNING
		cr.lgd.statusWaiter.Broadcast()
		cr.lgd.statusLock.Unlock()
	}

	n, err = cr.readable.Read(p)
	atomic.AddUint64(cr.n, uint64(n))
	return
}

func (lgd *LoadGeneratingConnectionDownload) Start(
	parentCtx context.Context,
	debugLevel debug.DebugLevel,
) bool {
	lgd.downloaded = 0
	lgd.debug = debugLevel
	lgd.clientId = utilities.GenerateUniqueId()

	transport := &http.Transport{
		Proxy: http.ProxyFromEnvironment,
		TLSClientConfig: &tls.Config{
			InsecureSkipVerify: lgd.InsecureSkipVerify,
		},
	}

	if !utilities.IsInterfaceNil(lgd.KeyLogger) {
		if debug.IsDebug(lgd.debug) {
			fmt.Printf(
				"Using an SSL Key Logger for this load-generating download.\n",
			)
		}

		// The presence of a custom TLSClientConfig in a *generic* `transport`
		// means that go will default to HTTP/1.1 and cowardly avoid HTTP/2:
		// https://github.com/golang/go/blob/7ca6902c171b336d98adbb103d701a013229c806/src/net/http/transport.go#L278
		// Also, it would appear that the API's choice of HTTP vs HTTP2 can
		// depend on whether the url contains
		// https:// or http://:
		// https://github.com/golang/go/blob/7ca6902c171b336d98adbb103d701a013229c806/src/net/http/transport.go#L74
		transport.TLSClientConfig.KeyLogWriter = lgd.KeyLogger
	}
	transport.TLSClientConfig.InsecureSkipVerify = lgd.InsecureSkipVerify

	utilities.OverrideHostTransport(transport, lgd.ConnectToAddr)

	lgd.client = &http.Client{Transport: transport}
	lgd.tracer = traceable.GenerateHttpTimingTracer(lgd, lgd.debug)

	if debug.IsDebug(lgd.debug) {
		fmt.Printf(
			"Started a load-generating download (id: %v).\n",
			lgd.clientId,
		)
	}

	go lgd.doDownload(parentCtx)
	return true
}

func (lgd *LoadGeneratingConnectionDownload) Status() LgcStatus {
	return lgd.status
}

func (lgd *LoadGeneratingConnectionDownload) Stats() *stats.TraceStats {
	return &lgd.stats
}

func (lgd *LoadGeneratingConnectionDownload) doDownload(ctx context.Context) error {
	var request *http.Request = nil
	var get *http.Response = nil
	var err error = nil

	if request, err = http.NewRequestWithContext(
		httptrace.WithClientTrace(ctx, lgd.tracer),
		"GET",
		lgd.URL,
		nil,
	); err != nil {
		lgd.statusLock.Lock()
		lgd.status = LGC_STATUS_ERROR
		lgd.statusWaiter.Broadcast()
		lgd.statusLock.Unlock()
		return err
	}

	// Used to disable compression
	request.Header.Set("Accept-Encoding", "identity")
	request.Header.Set("User-Agent", utilities.UserAgent())

	lgd.downloadStartTime = time.Now()
	lgd.lastIntervalEnd = 0

	if get, err = lgd.client.Do(request); err != nil {
		lgd.statusLock.Lock()
		lgd.status = LGC_STATUS_ERROR
		lgd.statusWaiter.Broadcast()
		lgd.statusLock.Unlock()
		return err
	}

	// Header.Get returns "" when not set
	if get.Header.Get("Content-Encoding") != "" {
		lgd.statusLock.Lock()
		lgd.status = LGC_STATUS_ERROR
		lgd.statusWaiter.Broadcast()
		lgd.statusLock.Unlock()
		fmt.Printf("Content-Encoding header was set (compression not allowed)")
		return fmt.Errorf("Content-Encoding header was set (compression not allowed)")
	}
	cr := &loadGeneratingConnectionDownloadReader{n: &lgd.downloaded, ctx: ctx, lgd: lgd, readable: get.Body}
	_, _ = io.Copy(io.Discard, cr)

	lgd.statusLock.Lock()
	lgd.status = LGC_STATUS_DONE
	lgd.statusWaiter.Broadcast()
	lgd.statusLock.Unlock()

	get.Body.Close()
	if debug.IsDebug(lgd.debug) {
		fmt.Printf("Ending a load-generating download.\n")
	}

	return nil
}