// netmon – real-time dual-interface network dashboard
// WTFPL – 2025-05-16 sneak@sneak.berlin
package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"math"
	"net"
	"os/exec"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/gdamore/tcell/v2"
)

//-----------------------------------------------------------------------------
// Configuration flags
//-----------------------------------------------------------------------------

var (
	ifaceA  = flag.String("ifaceA", "gu0", "primary network interface")
	labelA  = flag.String("labelA", "gu LAN - VPN outbound", "label for ifaceA")
	ifaceB  = flag.String("ifaceB", "backhaul0", "secondary network interface")
	labelB  = flag.String("labelB", "Cox cable direct", "label for ifaceB")

	hostCSV = flag.String("hosts",
		"1.1.1.1,8.8.8.8,8.8.4.4,google.com,github.com,console.aws.amazon.com,"+
			"console.cloud.google.com,fast.com,cloudflare.com,datavi.be",
		"comma-separated hosts for reachability checks")
)

//-----------------------------------------------------------------------------
// Constants
//-----------------------------------------------------------------------------

const (
	icmpTimeout      = 500 * time.Millisecond // per-ping timeout
	tcpTimeout       = 500 * time.Millisecond // TCP handshake timeout
	packetLossPings  = 20                     // pings per host for loss calc
	packetLossPeriod = 5 * time.Second       // how often to recalc loss
	statsHistory     = 300                    // 5 minutes of 1 Hz samples
	screenRefresh    = 500 * time.Millisecond // spinner / UI cadence
)

//-----------------------------------------------------------------------------
// Runtime data structures
//-----------------------------------------------------------------------------

type InterfaceStatus struct {
	Name  string
	Label string
	IPInfo string

	Reachable map[string]bool   // last reachability results
	Loss      map[string]float64// packet-loss %
	TCP       map[string][]float64 // rolling TCP ms samples

	LastPing time.Time

	mu sync.RWMutex
}

//-----------------------------------------------------------------------------
// Helpers – maths without external deps
//-----------------------------------------------------------------------------

func minMaxAvgStd(nums []float64) (min, max, avg, std float64) {
	if len(nums) == 0 {
		return
	}
	min, max = nums[0], nums[0]
	var sum float64
	for _, v := range nums {
		if v < min {
			min = v
		}
		if v > max {
			max = v
		}
		sum += v
	}
	avg = sum / float64(len(nums))
	var varSum float64
	for _, v := range nums {
		diff := v - avg
		varSum += diff * diff
	}
	std = math.Sqrt(varSum / float64(len(nums)))
	return
}

//-----------------------------------------------------------------------------
// External look-ups
//-----------------------------------------------------------------------------

type ipInfo struct {
	IP, Hostname, Org string
}

func fetchIPInfo(iface string) string {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()
	out, err := exec.CommandContext(ctx,
		"curl", "-s", "--interface", iface, "--max-time", "2", "ipinfo.io").Output()
	if err != nil {
		return "(ipinfo error)"
	}
	var resp ipInfo
	_ = json.Unmarshal(out, &resp)
	if resp.IP == "" {
		return "(ipinfo parse error)"
	}
	return fmt.Sprintf("%s [%s] %s", resp.IP, resp.Hostname, resp.Org)
}

//-----------------------------------------------------------------------------
// Ping helpers
//-----------------------------------------------------------------------------

func pingOnce(iface, host string) bool {
	ctx, cancel := context.WithTimeout(context.Background(), icmpTimeout)
	defer cancel()
	err := exec.CommandContext(ctx,
		"ping", "-I", iface, "-c1", "-W1", host).Run()
	return err == nil
}

func lossPercent(iface, host string) float64 {
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()

	out, err := exec.CommandContext(ctx,
		"ping", "-q", "-i", "0.05", "-c", fmt.Sprint(packetLossPings),
		"-W1", "-I", iface, host).CombinedOutput()
	if err != nil {
		return 1.0
	}
	for _, line := range strings.Split(string(out), "\n") {
		if !strings.Contains(line, "packet loss") {
			continue
		}
		for _, f := range strings.Fields(line) {
			if strings.HasSuffix(f, "%") {
				pct, _ := strconv.ParseFloat(strings.TrimSuffix(f, "%"), 64)
				return pct / 100.0
			}
		}
	}
	return 1.0
}

//-----------------------------------------------------------------------------
// TCP helpers
//-----------------------------------------------------------------------------

func localAddrFor(iface string) (net.Addr, error) {
	ni, err := net.InterfaceByName(iface)
	if err != nil {
		return nil, err
	}
	addrs, err := ni.Addrs()
	if err != nil {
		return nil, err
	}
	for _, a := range addrs {
		if ipnet, ok := a.(*net.IPNet); ok && ipnet.IP.To4() != nil {
			return &net.TCPAddr{IP: ipnet.IP}, nil
		}
	}
	return nil, fmt.Errorf("no IPv4 on %s", iface)
}

func tcpDuration(iface, hostPort string) time.Duration {
	la, err := localAddrFor(iface)
	if err != nil {
		return tcpTimeout
	}
	d := net.Dialer{Timeout: tcpTimeout, LocalAddr: la}
	start := time.Now()
	conn, err := d.Dial("tcp", hostPort)
	if err != nil {
		return tcpTimeout
	}
	conn.Close()
	return time.Since(start)
}

//-----------------------------------------------------------------------------
// Goroutines – reachability, loss, TCP stats
//-----------------------------------------------------------------------------

func reachabilityLoop(ctx context.Context, st *InterfaceStatus, hosts []string) {
	tick := time.NewTicker(time.Second)
	defer tick.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-tick.C:
			var wg sync.WaitGroup
			results := make(map[string]bool, len(hosts))
			mu := sync.Mutex{}

			for _, h := range hosts {
				wg.Add(1)
				go func(host string) {
					defer wg.Done()
					ok := pingOnce(st.Name, host)
					mu.Lock()
					results[host] = ok
					mu.Unlock()
				}(h)
			}
			wg.Wait()

			st.mu.Lock()
			st.Reachable = results
			st.LastPing = time.Now()
			st.mu.Unlock()
		}
	}
}

func lossLoop(ctx context.Context, st *InterfaceStatus, hosts []string) {
	tick := time.NewTicker(packetLossPeriod)
	defer tick.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-tick.C:
			var wg sync.WaitGroup
			results := make(map[string]float64, len(hosts))
			mu := sync.Mutex{}

			for _, h := range hosts {
				wg.Add(1)
				go func(host string) {
					defer wg.Done()
					lp := lossPercent(st.Name, host)
					mu.Lock()
					results[host] = lp
					mu.Unlock()
				}(h)
			}
			wg.Wait()

			st.mu.Lock()
			for k, v := range results {
				st.Loss[k] = v
			}
			st.mu.Unlock()
		}
	}
}

func tcpLoop(ctx context.Context, st *InterfaceStatus, hosts []string) {
	tick := time.NewTicker(time.Second)
	defer tick.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-tick.C:
			for _, hp := range hosts {
				ms := float64(tcpDuration(st.Name, hp).Milliseconds())

				st.mu.Lock()
				hist := st.TCP[hp]
				if len(hist) >= statsHistory {
					hist = hist[1:] // drop oldest
				}
				st.TCP[hp] = append(hist, ms)
				st.mu.Unlock()
			}
		}
	}
}

//-----------------------------------------------------------------------------
// UI
//-----------------------------------------------------------------------------

var spin = []rune{'|', '/', '-', '\\'}

func writeLine(s tcell.Screen, x, y int, str string) {
	for i, r := range str {
		s.SetContent(x+i, y, r, nil, tcell.StyleDefault)
	}
}

func drawSection(s tcell.Screen, x, y, w int, st *InterfaceStatus) {
	st.mu.RLock()
	defer st.mu.RUnlock()

	// header
	writeLine(s, x, y, fmt.Sprintf("%s — %s", st.Label, st.IPInfo))

	// reachability
	total := len(st.Reachable)
	rc := 0
	var down []string
	for h, ok := range st.Reachable {
		if ok {
			rc++
		} else {
			down = append(down, h)
		}
	}
	age := time.Since(st.LastPing).Round(time.Second)
	writeLine(s, x, y+1,
		fmt.Sprintf("Reachable: %d/%d (at %s, age %s)",
			rc, total, st.LastPing.Format("15:04:05"), age))
	if len(down) > 0 {
		writeLine(s, x, y+2, "Unreachable: "+strings.Join(down, ", "))
	} else {
		writeLine(s, x, y+2, "Unreachable: none")
	}

	// packet loss
	row := y + 4
	writeLine(s, x, row, "Packet Loss:")
	row++
	for _, h := range packetLossHosts {
		lp := st.Loss[h] * 100
		writeLine(s, x, row, fmt.Sprintf("%-16s %.0f%%", h+":", lp))
		row++
	}

	// TCP stats
	writeLine(s, x, row, "TCP Connect Stats:")
	row++
	for _, hp := range tcpTestHosts {
		samples := st.TCP[hp]
		if len(samples) == 0 {
			continue
		}
		mi, ma, av, sd := minMaxAvgStd(samples)
		writeLine(s, x, row,
			fmt.Sprintf("%-16s %.0f/%.0f/%.0f/%.0fms",
				hp, mi, av, ma, sd))
		row++
	}
}

func uiLoop(ctx context.Context, scr tcell.Screen, a, b *InterfaceStatus) {
	defer scr.Fini()
	tick := time.NewTicker(screenRefresh)
	defer tick.Stop()
	frame := 0

	for {
		select {
		case <-ctx.Done():
			return
		case <-tick.C:
			scr.Clear()
			w, h := scr.Size()
			mid := h / 2

			ts := time.Now().Format(time.RFC1123Z)
			writeLine(scr, 0, 0, fmt.Sprintf("%c %s", spin[frame%len(spin)], ts))
			frame++

			drawSection(scr, 0, 1, w, a)
			drawSection(scr, 0, mid, w, b)

			scr.Show()
		}
	}
}

//-----------------------------------------------------------------------------
// Entry
//-----------------------------------------------------------------------------

var (
	reachabilityHosts []string
	packetLossHosts   = []string{"datavi.be", "google.com", "fast.com", "cloudflare.com", "github.com"}
	tcpTestHosts      = []string{"google.com:443", "github.com:443", "1.1.1.1:443", "8.8.8.8:53"}
)

func main() {
	flag.Parse()
	reachabilityHosts = strings.Split(*hostCSV, ",")

	// prepare interface status objects
	stA := &InterfaceStatus{
		Name:      *ifaceA,
		Label:     *labelA,
		Reachable: make(map[string]bool),
		Loss:      make(map[string]float64),
		TCP:       make(map[string][]float64),
		IPInfo:    fetchIPInfo(*ifaceA),
	}
	stB := &InterfaceStatus{
		Name:      *ifaceB,
		Label:     *labelB,
		Reachable: make(map[string]bool),
		Loss:      make(map[string]float64),
		TCP:       make(map[string][]float64),
		IPInfo:    fetchIPInfo(*ifaceB),
	}

	screen, err := tcell.NewScreen()
	if err != nil {
		panic(err)
	}
	if err := screen.Init(); err != nil {
		panic(err)
	}

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	// background jobs
	go reachabilityLoop(ctx, stA, reachabilityHosts)
	go reachabilityLoop(ctx, stB, reachabilityHosts)

	go lossLoop(ctx, stA, packetLossHosts)
	go lossLoop(ctx, stB, packetLossHosts)

	go tcpLoop(ctx, stA, tcpTestHosts)
	go tcpLoop(ctx, stB, tcpTestHosts)

	// UI (blocks)
	uiLoop(ctx, screen, stA, stB)
}