// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

// Package netlog provides a logger that monitors a TUN device and
// periodically records any traffic into a log stream.
package netlog

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"net/netip"
	"sync"
	"time"

	"tailscale.com/health"
	"tailscale.com/logpolicy"
	"tailscale.com/logtail"
	"tailscale.com/net/connstats"
	"tailscale.com/net/netmon"
	"tailscale.com/net/sockstats"
	"tailscale.com/net/tsaddr"
	"tailscale.com/tailcfg"
	"tailscale.com/types/logid"
	"tailscale.com/types/netlogtype"
	"tailscale.com/util/multierr"
	"tailscale.com/wgengine/router"
)

// pollPeriod specifies how often to poll for network traffic.
const pollPeriod = 5 * time.Second

// Device is an abstraction over a tunnel device or a magic socket.
// Both *tstun.Wrapper and *magicsock.Conn implement this interface.
type Device interface {
	SetStatistics(*connstats.Statistics)
}

type noopDevice struct{}

func (noopDevice) SetStatistics(*connstats.Statistics) {}

// Logger logs statistics about every connection.
// At present, it only logs connections within a tailscale network.
// Exit node traffic is not logged for privacy reasons.
// The zero value is ready for use.
type Logger struct {
	mu sync.Mutex // protects all fields below

	logger *logtail.Logger
	stats  *connstats.Statistics
	tun    Device
	sock   Device

	addrs    map[netip.Addr]bool
	prefixes map[netip.Prefix]bool
}

// Running reports whether the logger is running.
func (nl *Logger) Running() bool {
	nl.mu.Lock()
	defer nl.mu.Unlock()
	return nl.logger != nil
}

var testClient *http.Client

// Startup starts an asynchronous network logger that monitors
// statistics for the provided tun and/or sock device.
//
// The tun Device captures packets within the tailscale network,
// where at least one address is a tailscale IP address.
// The source is always from the perspective of the current node.
// If one of the other endpoint is not a tailscale IP address,
// then it suggests the use of a subnet router or exit node.
// For example, when using a subnet router, the source address is
// the tailscale IP address of the current node, and
// the destination address is an IP address within the subnet range.
// In contrast, when acting as a subnet router, the source address is
// an IP address within the subnet range, and the destination is a
// tailscale IP address that initiated the subnet proxy connection.
// In this case, the node acting as a subnet router is acting on behalf
// of some remote endpoint within the subnet range.
// The tun is used to populate the VirtualTraffic, SubnetTraffic,
// and ExitTraffic fields in Message.
//
// The sock Device captures packets at the magicsock layer.
// The source is always a tailscale IP address and the destination
// is a non-tailscale IP address to contact for that particular tailscale node.
// The IP protocol and source port are always zero.
// The sock is used to populated the PhysicalTraffic field in Message.
// The netMon parameter is optional; if non-nil it's used to do faster interface lookups.
func (nl *Logger) Startup(nodeID tailcfg.StableNodeID, nodeLogID, domainLogID logid.PrivateID, tun, sock Device, netMon *netmon.Monitor, health *health.Tracker) error {
	nl.mu.Lock()
	defer nl.mu.Unlock()
	if nl.logger != nil {
		return fmt.Errorf("network logger already running for %v", nl.logger.PrivateID().Public())
	}

	// Startup a log stream to Tailscale's logging service.
	logf := log.Printf
	httpc := &http.Client{Transport: logpolicy.NewLogtailTransport(logtail.DefaultHost, netMon, health, logf)}
	if testClient != nil {
		httpc = testClient
	}
	nl.logger = logtail.NewLogger(logtail.Config{
		Collection:    "tailtraffic.log.tailscale.io",
		PrivateID:     nodeLogID,
		CopyPrivateID: domainLogID,
		Stderr:        io.Discard,
		CompressLogs:  true,
		HTTPC:         httpc,
		// TODO(joetsai): Set Buffer? Use an in-memory buffer for now.

		// Include process sequence numbers to identify missing samples.
		IncludeProcID:       true,
		IncludeProcSequence: true,
	}, logf)
	nl.logger.SetSockstatsLabel(sockstats.LabelNetlogLogger)

	// Startup a data structure to track per-connection statistics.
	// There is a maximum size for individual log messages that logtail
	// can upload to the Tailscale log service, so stay below this limit.
	const maxLogSize = 256 << 10
	const maxConns = (maxLogSize - netlogtype.MaxMessageJSONSize) / netlogtype.MaxConnectionCountsJSONSize
	nl.stats = connstats.NewStatistics(pollPeriod, maxConns, func(start, end time.Time, virtual, physical map[netlogtype.Connection]netlogtype.Counts) {
		nl.mu.Lock()
		addrs := nl.addrs
		prefixes := nl.prefixes
		nl.mu.Unlock()
		recordStatistics(nl.logger, nodeID, start, end, virtual, physical, addrs, prefixes)
	})

	// Register the connection tracker into the TUN device.
	if tun == nil {
		tun = noopDevice{}
	}
	nl.tun = tun
	nl.tun.SetStatistics(nl.stats)

	// Register the connection tracker into magicsock.
	if sock == nil {
		sock = noopDevice{}
	}
	nl.sock = sock
	nl.sock.SetStatistics(nl.stats)

	return nil
}

func recordStatistics(logger *logtail.Logger, nodeID tailcfg.StableNodeID, start, end time.Time, connstats, sockStats map[netlogtype.Connection]netlogtype.Counts, addrs map[netip.Addr]bool, prefixes map[netip.Prefix]bool) {
	m := netlogtype.Message{NodeID: nodeID, Start: start.UTC(), End: end.UTC()}

	classifyAddr := func(a netip.Addr) (isTailscale, withinRoute bool) {
		// NOTE: There could be mis-classifications where an address is treated
		// as a Tailscale IP address because the subnet range overlaps with
		// the subnet range that Tailscale IP addresses are allocated from.
		// This should never happen for IPv6, but could happen for IPv4.
		withinRoute = addrs[a]
		for p := range prefixes {
			if p.Contains(a) && p.Bits() > 0 {
				withinRoute = true
				break
			}
		}
		return withinRoute && tsaddr.IsTailscaleIP(a), withinRoute && !tsaddr.IsTailscaleIP(a)
	}

	exitTraffic := make(map[netlogtype.Connection]netlogtype.Counts)
	for conn, cnts := range connstats {
		srcIsTailscaleIP, srcWithinSubnet := classifyAddr(conn.Src.Addr())
		dstIsTailscaleIP, dstWithinSubnet := classifyAddr(conn.Dst.Addr())
		switch {
		case srcIsTailscaleIP && dstIsTailscaleIP:
			m.VirtualTraffic = append(m.VirtualTraffic, netlogtype.ConnectionCounts{Connection: conn, Counts: cnts})
		case srcWithinSubnet || dstWithinSubnet:
			m.SubnetTraffic = append(m.SubnetTraffic, netlogtype.ConnectionCounts{Connection: conn, Counts: cnts})
		default:
			const anonymize = true
			if anonymize {
				// Only preserve the address if it is a Tailscale IP address.
				srcOrig, dstOrig := conn.Src, conn.Dst
				conn = netlogtype.Connection{} // scrub everything by default
				if srcIsTailscaleIP {
					conn.Src = netip.AddrPortFrom(srcOrig.Addr(), 0)
				}
				if dstIsTailscaleIP {
					conn.Dst = netip.AddrPortFrom(dstOrig.Addr(), 0)
				}
			}
			exitTraffic[conn] = exitTraffic[conn].Add(cnts)
		}
	}
	for conn, cnts := range exitTraffic {
		m.ExitTraffic = append(m.ExitTraffic, netlogtype.ConnectionCounts{Connection: conn, Counts: cnts})
	}
	for conn, cnts := range sockStats {
		m.PhysicalTraffic = append(m.PhysicalTraffic, netlogtype.ConnectionCounts{Connection: conn, Counts: cnts})
	}

	if len(m.VirtualTraffic)+len(m.SubnetTraffic)+len(m.ExitTraffic)+len(m.PhysicalTraffic) > 0 {
		if b, err := json.Marshal(m); err != nil {
			logger.Logf("json.Marshal error: %v", err)
		} else {
			logger.Logf("%s", b)
		}
	}
}

func makeRouteMaps(cfg *router.Config) (addrs map[netip.Addr]bool, prefixes map[netip.Prefix]bool) {
	addrs = make(map[netip.Addr]bool)
	for _, p := range cfg.LocalAddrs {
		if p.IsSingleIP() {
			addrs[p.Addr()] = true
		}
	}
	prefixes = make(map[netip.Prefix]bool)
	insertPrefixes := func(rs []netip.Prefix) {
		for _, p := range rs {
			if p.IsSingleIP() {
				addrs[p.Addr()] = true
			} else {
				prefixes[p] = true
			}
		}
	}
	insertPrefixes(cfg.Routes)
	insertPrefixes(cfg.SubnetRoutes)
	return addrs, prefixes
}

// ReconfigRoutes configures the network logger with updated routes.
// The cfg is used to classify the types of connections captured by
// the tun Device passed to Startup.
func (nl *Logger) ReconfigRoutes(cfg *router.Config) {
	nl.mu.Lock()
	defer nl.mu.Unlock()
	// TODO(joetsai): There is a race where deleted routes are not known at
	// the time of extraction. We need to keep old routes around for a bit.
	nl.addrs, nl.prefixes = makeRouteMaps(cfg)
}

// Shutdown shuts down the network logger.
// This attempts to flush out all pending log messages.
// Even if an error is returned, the logger is still shut down.
func (nl *Logger) Shutdown(ctx context.Context) error {
	nl.mu.Lock()
	defer nl.mu.Unlock()
	if nl.logger == nil {
		return nil
	}

	// Shutdown in reverse order of Startup.
	// Do not hold lock while shutting down since this may flush one last time.
	nl.mu.Unlock()
	nl.sock.SetStatistics(nil)
	nl.tun.SetStatistics(nil)
	err1 := nl.stats.Shutdown(ctx)
	err2 := nl.logger.Shutdown(ctx)
	nl.mu.Lock()

	// Purge state.
	nl.logger = nil
	nl.stats = nil
	nl.tun = nil
	nl.sock = nil
	nl.addrs = nil
	nl.prefixes = nil

	return multierr.New(err1, err2)
}