package main

import (
	"archive/tar"
	"compress/gzip"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"math"
	"net/http"
	"net/netip"
	"net/url"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"time"
)

// Prefs are the dashboard's own settings. They live beside the UI's state,
// not in settings.json: changing them needs no rebuild.
type Prefs struct {
	PingTargets []string `json:"pingTargets"`
}

var defaultPrefs = Prefs{PingTargets: []string{"gateway", "1.1.1.1", "9.9.9.9"}}

func (s System) prefsPath() string { return filepath.Join(s.StateDir, "webui", "dashboard.json") }

func (s System) loadPrefs() Prefs {
	data, err := os.ReadFile(s.prefsPath())
	if err != nil {
		return defaultPrefs
	}
	var p Prefs
	if json.Unmarshal(data, &p) != nil || p.PingTargets == nil {
		return defaultPrefs
	}
	return p
}

func (s System) savePrefs(p Prefs) error {
	data, err := json.MarshalIndent(p, "", "  ")
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(s.prefsPath()), 0o700); err != nil {
		return err
	}
	return writeFileAtomic(s.prefsPath(), append(data, '\n'), 0o600)
}

const maxPingTargets = 5

// parsePingTargets takes targets separated by commas, spaces or lines:
// "gateway" or IP addresses.
func parsePingTargets(text string) ([]string, error) {
	targets := []string{}
	for _, t := range strings.FieldsFunc(text, func(r rune) bool { return r == ',' || r == ' ' || r == '\n' || r == '\r' || r == '\t' }) {
		if t != "gateway" {
			a, err := netip.ParseAddr(t)
			if err != nil {
				return nil, fmt.Errorf("%q is neither \"gateway\" nor an IP address", t)
			}
			t = a.String()
		}
		if !slices.Contains(targets, t) {
			targets = append(targets, t)
		}
	}
	if len(targets) > maxPingTargets {
		return nil, fmt.Errorf("at most %d targets", maxPingTargets)
	}
	return targets, nil
}

// Chart is an SVG line chart, laid out here so the template only draws it.
type Chart struct {
	Title  string
	Unit   string // "bit/s", "ms", "%", "°C"
	Lines  []ChartLine
	YTicks []ChartTick
	XTicks []ChartTick
	Cols   []ChartCol // hover areas with a tooltip each
	Empty  bool
}

type ChartLine struct {
	Label string
	Class string // colour, see style.css
	Path  string // SVG path data; gaps start a new subpath
	Now   string // the latest value, formatted
}

type ChartTick struct {
	Pos   float64
	Label string
}

type ChartCol struct {
	X, W float64
	Tip  string
}

// The chart's drawing area in SVG units (the template adds the margins).
const (
	chartW    = 600.0
	chartH    = 120.0
	chartCols = 200
)

type seriesSpec struct {
	Name  string // in the Store
	Label string
	Scale float64 // e.g. 8 for bytes/s -> bit/s
}

func (a *app) chart(title, unit string, tier int, now time.Time, specs []seriesSpec) Chart {
	c := Chart{Title: title, Unit: unit}
	var start time.Time
	var step time.Duration
	cols := make([][]float64, len(specs))
	ymax := 0.0
	for i, sp := range specs {
		st, stp, vals := a.metrics.store.Read(sp.Name, tier, now)
		start, step = st, stp
		cols[i] = downsample(vals, chartCols, sp.Scale)
		for _, v := range cols[i] {
			if !math.IsNaN(v) {
				ymax = math.Max(ymax, v)
			}
		}
	}
	n := chartCols
	span := step * time.Duration(tiers[tier].Slots)
	colDur := span / time.Duration(n)
	if unit == "%" {
		ymax = math.Max(ymax, 1)
		if ymax > 50 {
			ymax = 100
		}
	}
	ymax = niceCeil(ymax)
	c.Empty = true
	for i, sp := range specs {
		line := ChartLine{Label: sp.Label, Class: fmt.Sprintf("s%d", i), Now: "–"}
		var path strings.Builder
		pen := false
		for j, v := range cols[i] {
			if math.IsNaN(v) {
				pen = false
				continue
			}
			c.Empty = false
			x := (float64(j) + 0.5) * chartW / float64(n)
			y := chartH - v/ymax*chartH
			if pen {
				fmt.Fprintf(&path, "L%.1f %.1f", x, y)
			} else {
				fmt.Fprintf(&path, "M%.1f %.1f", x, y)
				// A lone point still shows up as a short dash.
				if j+1 >= len(cols[i]) || math.IsNaN(cols[i][j+1]) {
					fmt.Fprintf(&path, "h1")
				}
			}
			pen = true
			line.Now = formatValue(v, unit)
		}
		line.Path = path.String()
		c.Lines = append(c.Lines, line)
	}
	for k := 0; k <= 2; k++ {
		v := ymax * float64(k) / 2
		c.YTicks = append(c.YTicks, ChartTick{Pos: chartH - v/ymax*chartH, Label: formatValue(v, unit)})
	}
	layout := "15:04"
	if span > 48*time.Hour {
		layout = "Jan 2"
	}
	for k := 0; k <= 4; k++ {
		t := start.Add(span * time.Duration(k) / 4)
		c.XTicks = append(c.XTicks, ChartTick{Pos: chartW * float64(k) / 4, Label: t.Local().Format(layout)})
	}
	for j := range n {
		t := start.Add(colDur * time.Duration(j))
		var tip strings.Builder
		tip.WriteString(t.Local().Format("Jan 2 15:04:05"))
		for i, sp := range specs {
			fmt.Fprintf(&tip, "\n%s: %s", sp.Label, formatValue(cols[i][j], unit))
		}
		c.Cols = append(c.Cols, ChartCol{X: chartW * float64(j) / float64(n), W: chartW / float64(n), Tip: tip.String()})
	}
	return c
}

// downsample averages vals into n columns, ignoring gaps.
func downsample(vals []float64, n int, scale float64) []float64 {
	if scale == 0 {
		scale = 1
	}
	out := make([]float64, n)
	for j := range out {
		lo, hi := j*len(vals)/n, (j+1)*len(vals)/n
		sum, cnt := 0.0, 0
		for _, v := range vals[lo:max(hi, lo+1)] {
			if !math.IsNaN(v) {
				sum += v
				cnt++
			}
		}
		out[j] = math.NaN()
		if cnt > 0 {
			out[j] = sum / float64(cnt) * scale
		}
	}
	return out
}

// niceCeil rounds up to 1, 2 or 5 times a power of ten.
func niceCeil(v float64) float64 {
	if v <= 0 || math.IsNaN(v) {
		return 1
	}
	p := math.Pow(10, math.Floor(math.Log10(v)))
	for _, m := range []float64{1, 2, 5, 10} {
		if v <= m*p {
			return m * p
		}
	}
	return 10 * p
}

func formatValue(v float64, unit string) string {
	if math.IsNaN(v) {
		return "–"
	}
	switch unit {
	case "bit/s":
		return formatSI(v, "bit/s")
	case "ms":
		if v < 10 {
			return fmt.Sprintf("%.1f ms", v)
		}
		return fmt.Sprintf("%.0f ms", v)
	case "%":
		if v > 0 && v < 10 {
			return fmt.Sprintf("%.1f %%", v)
		}
		return fmt.Sprintf("%.0f %%", v)
	case "°C":
		return fmt.Sprintf("%.0f °C", v)
	}
	return fmt.Sprintf("%g %s", v, unit)
}

func formatSI(v float64, unit string) string {
	for _, p := range []struct {
		f float64
		s string
	}{{1e9, "G"}, {1e6, "M"}, {1e3, "k"}} {
		if v >= p.f {
			x := v / p.f
			if x < 10 {
				return fmt.Sprintf("%.1f %s%s", x, p.s, unit)
			}
			return fmt.Sprintf("%.0f %s%s", x, p.s, unit)
		}
	}
	return fmt.Sprintf("%.0f %s", v, unit)
}

func formatBytes(v uint64) string {
	f := float64(v)
	for _, p := range []struct {
		f float64
		s string
	}{{1 << 40, "TiB"}, {1 << 30, "GiB"}, {1 << 20, "MiB"}, {1 << 10, "KiB"}} {
		if f >= p.f {
			return fmt.Sprintf("%.1f %s", f/p.f, p.s)
		}
	}
	return fmt.Sprintf("%d B", v)
}

// formatAge is a rough "3d 4h", "2h 5m", "4m".
func formatAge(d time.Duration) string {
	if d < time.Minute {
		return "<1m"
	}
	d = d.Round(time.Minute)
	days, hours, mins := int(d.Hours())/24, int(d.Hours())%24, int(d.Minutes())%60
	switch {
	case days > 0:
		return fmt.Sprintf("%dd %dh", days, hours)
	case hours > 0:
		return fmt.Sprintf("%dh %dm", hours, mins)
	default:
		return fmt.Sprintf("%dm", mins)
	}
}

type dashboard struct {
	Range    string
	Ranges   []string
	Interval int // seconds between live updates
	Snap     Snapshot
	Leases   []Lease
	Events   []Event
	Charts   []Chart
	Prefs    Prefs
}

func (a *app) dashboardData(rangeName string) dashboard {
	tier, rangeName := rangeTier(rangeName)
	now := time.Now()
	s, _ := loadSettings(a.sys.settingsPath())
	f := s.form()
	d := dashboard{Range: rangeName, Interval: 5, Snap: a.metrics.Snapshot(), Prefs: a.sys.loadPrefs()}
	// Newest first, the last few.
	ev := d.Snap.Uplink.Events
	d.Events = make([]Event, 0, 10)
	for i := len(ev) - 1; i >= 0 && len(d.Events) < 10; i-- {
		d.Events = append(d.Events, ev[i])
	}
	if tier > 0 {
		d.Interval = 60
	}
	for _, r := range ranges {
		d.Ranges = append(d.Ranges, r.Name)
	}
	d.Leases = readLeases(a.metrics.leasesPath, f.LANs, now)

	traffic := func(title, dev string) Chart {
		return a.chart(title, "bit/s", tier, now, []seriesSpec{
			{"if:" + dev + ":rx", "down", 8},
			{"if:" + dev + ":tx", "up", 8},
		})
	}
	up := uplinkDevice(f.WAN)
	d.Charts = append(d.Charts, traffic("Internet ("+up+")", up))
	for _, l := range f.LANs {
		dev := l.Interface
		if l.VLAN != "" {
			dev += "." + l.VLAN
		}
		c := traffic("LAN "+l.Name+" ("+dev+")", dev)
		// From the LAN's side: what the router sends is what the LAN downloads.
		c.Lines[0].Label, c.Lines[1].Label = "to router", "from router"
		d.Charts = append(d.Charts, c)
	}
	for _, wg := range wireguardDevices(s) {
		d.Charts = append(d.Charts, traffic("Tunnel "+wg, wg))
	}
	var rtt, loss []seriesSpec
	for _, t := range d.Prefs.PingTargets {
		rtt = append(rtt, seriesSpec{"ping:" + t + ":rtt", t, 1})
		loss = append(loss, seriesSpec{"ping:" + t + ":loss", t, 1})
	}
	if len(rtt) > 0 {
		d.Charts = append(d.Charts, a.chart("Latency", "ms", tier, now, rtt), a.chart("Packet loss", "%", tier, now, loss))
	}
	d.Charts = append(d.Charts,
		a.chart("CPU and memory", "%", tier, now, []seriesSpec{{"sys:cpu", "CPU", 1}, {"sys:mem", "memory", 1}}))
	if temp := a.chart("Temperature", "°C", tier, now, []seriesSpec{{"sys:temp", "hottest sensor", 1}}); !temp.Empty || !math.IsNaN(d.Snap.System.Temperature) {
		d.Charts = append(d.Charts, temp)
	}
	return d
}

func wireguardDevices(s Settings) []string {
	router, _ := s["router"].(map[string]any)
	wgs, _ := router["wireguard"].(map[string]any)
	var devs []string
	for name, v := range wgs {
		dev := "wg-" + name
		if m, ok := v.(map[string]any); ok && str(m, "interface") != "" {
			dev = str(m, "interface")
		}
		devs = append(devs, dev)
	}
	slices.Sort(devs)
	return devs
}

// dashboardFragment is the live part of the overview, fetched by dashboard.js.
func (a *app) dashboardFragment(w http.ResponseWriter, r *http.Request, sess session) {
	p := page{CSRF: sess.csrf, LoggedIn: true, Data: overviewData{Dashboard: a.dashboardData(r.URL.Query().Get("range"))}}
	if err := a.page("overview").ExecuteTemplate(w, "dashboard", p); err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

func (a *app) savePrefs(w http.ResponseWriter, r *http.Request, sess session) {
	targets, err := parsePingTargets(r.PostFormValue("pingTargets"))
	if err == nil {
		err = a.sys.savePrefs(Prefs{PingTargets: targets})
	}
	if err != nil {
		http.Redirect(w, r, "/advanced?msg="+url.QueryEscape("Ping targets not saved: "+err.Error()), http.StatusSeeOther)
		return
	}
	http.Redirect(w, r, "/advanced?msg="+url.QueryEscape("Ping targets saved."), http.StatusSeeOther)
}

// backup streams the state directory (settings, secrets, certificate, metric
// history) as router-backup-<host>-<time>.tar.gz; router-setup can install
// from it.
func (a *app) backup(w http.ResponseWriter, r *http.Request, _ session) {
	a.metrics.Save()
	s, _ := loadSettings(a.sys.settingsPath())
	host := str(s, "system", "hostName")
	if host == "" {
		host = "router"
	}
	name := fmt.Sprintf("router-backup-%s-%s.tar.gz", host, time.Now().Format("20060102-1504"))
	w.Header().Set("Content-Type", "application/gzip")
	w.Header().Set("Content-Disposition", `attachment; filename="`+name+`"`)
	if err := writeBackup(w, a.sys.StateDir); err != nil {
		// Headers are gone; a truncated archive fails to extract.
		panic(http.ErrAbortHandler)
	}
}

func writeBackup(w io.Writer, dir string) error {
	gz := gzip.NewWriter(w)
	tw := tar.NewWriter(gz)
	err := filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if !d.IsDir() && !d.Type().IsRegular() {
			return nil // sockets, symlinks (e.g. a result link)
		}
		info, err := d.Info()
		if err != nil {
			return err
		}
		rel, _ := filepath.Rel(dir, path)
		hdr, err := tar.FileInfoHeader(info, "")
		if err != nil {
			return err
		}
		hdr.Name = filepath.ToSlash(filepath.Join("router", rel))
		if d.IsDir() {
			hdr.Name += "/"
		}
		hdr.Uname, hdr.Gname, hdr.Uid, hdr.Gid = "", "", 0, 0
		if err := tw.WriteHeader(hdr); err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		f, err := os.Open(path)
		if err != nil {
			return err
		}
		defer f.Close()
		_, err = io.CopyN(tw, f, info.Size())
		return err
	})
	return errors.Join(err, tw.Close(), gz.Close())
}