package monitor

import (
	"context"
	"fmt"
	"sort"
	"strings"
	"time"

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

// Fixed rows at the top of the display.
const (
	rowTopRule    = 0
	rowClock      = 1
	rowBottomRule = 2
	rowRuntime    = 3
	rowFirstIface = 5
)

// Column offsets and spacing within the drawn output.
const (
	colLeft       = 0
	colSpinner    = 3 // after the "== " prefix
	colMeter      = 5 // after the spinner
	colGap        = 1 // single-space gap between fields
	clockGap      = 5 // space between the two clocks
	lineStep      = 1
	blockGap      = 2 // blank line plus the following line
	headerAdvance = 4 // rule + content + rule + blank line
)

// ICMP summary table geometry.
const (
	icmpLabelWidth = 8
	icmpValWidth   = 9
	icmpColGap     = 4
)

// Put writes text to the screen at the specified position with style.
func Put(scr tcell.Screen, x, y int, txt string, st tcell.Style) {
	for i, r := range txt {
		scr.SetContent(x+i, y, r, nil, st)
	}
}

// HLine returns a horizontal line of the specified width.
func HLine(w int) string { return strings.Repeat("=", w) }

// DrawRainbowText draws text cycling through the given color styles.
func DrawRainbowText(scr tcell.Screen, x, y int, text string, colors []tcell.Style) {
	for i, char := range text {
		style := colors[i%len(colors)]
		scr.SetContent(x+i, y, char, nil, style)
	}
}

// msStr formats a millisecond value as a compact "%.0fms" string.
func msStr(v float64) string {
	return fmt.Sprintf("%.0fms", v)
}

// CreateMeter creates a visual meter using ASCII characters.
func (m *Monitor) CreateMeter(value int) (string, tcell.Style) {
	value = max(min(value, m.MaxMeterValue), 0)

	fillCount := min(value*m.MeterFillWidth/m.MaxMeterValue, m.MeterFillWidth)

	var b strings.Builder

	b.WriteRune(MeterStart)

	for range fillCount {
		b.WriteRune(MeterFill)
	}

	for range m.MeterFillWidth - fillCount {
		b.WriteRune(MeterEmpty)
	}

	b.WriteRune(MeterEnd)

	// reverse=true: for packet loss, low values are good.
	style := MeterColorForValue(value, m.MaxMeterValue, true)

	return b.String(), style
}

// DrawInterface draws the interface status on the screen, returning the next
// free row.
func (m *Monitor) DrawInterface(scr tcell.Screen, y, w int, st *InterfaceStatus) int {
	Put(scr, colLeft, y, HLine(w), tcell.StyleDefault)

	healthy := st.IsHealthy(m.TCPTimeout)
	y = m.drawHeader(scr, y, w, st, healthy)

	m.mu.RLock()
	tcpHosts := append([]string{}, m.tcpHosts...)
	m.mu.RUnlock()

	st.mu.RLock()
	defer st.mu.RUnlock()

	y = drawReachability(scr, y, st)
	y = drawPacketLoss(scr, y, st)
	y = m.drawTCPTable(scr, y, st, tcpHosts)
	y = drawICMPStats(scr, y, st)

	// The Starlink lines belong to the physical (non-VPN gateway) pane only.
	if st == m.slPane {
		y = m.drawStarlink(scr, y)
	}

	return y
}

// drawHeader renders the interface title, spinner and meter line.
func (m *Monitor) drawHeader(
	scr tcell.Screen, y, w int, st *InterfaceStatus, healthy bool,
) int {
	style := styleBrightGreen()
	if !healthy {
		style = styleBrightRed()
	}

	st.mu.RLock()
	header := fmt.Sprintf("%s: %s —   %s", st.Name, st.Label, st.IPInfo)
	spinChar := spins()[st.SpinFrame]
	spinnerFrame := st.SpinFrame
	meterValue := st.MeterValue
	st.mu.RUnlock()

	meter, meterStyle := m.CreateMeter(meterValue)
	colors := rainbow()
	spinnerStyle := colors[spinnerFrame%len(colors)]

	Put(scr, colLeft, y+lineStep, "== ", tcell.StyleDefault)
	Put(scr, colSpinner, y+lineStep, string(spinChar)+" ", spinnerStyle)
	Put(scr, colMeter, y+lineStep, meter+" ", meterStyle)
	Put(scr, colMeter+m.MeterWidth+colGap, y+lineStep, header, style)
	Put(scr, colLeft, y+blockGap, HLine(w), tcell.StyleDefault)

	return y + headerAdvance
}

// drawReachability renders the reachability summary. The caller holds
// st.mu.RLock.
func drawReachability(scr tcell.Screen, y int, st *InterfaceStatus) int {
	total := len(st.Reachable)
	good := 0

	for _, ok := range st.Reachable {
		if ok {
			good++
		}
	}

	age := time.Since(st.LastPing).Round(time.Second)

	reachStyle := styleBrightGreen()
	if good != total {
		reachStyle = styleBrightRed()
	}

	dropTimeStr := "never"
	dropAgeStr := "N/A"

	if !st.LastDrop.IsZero() {
		dropTimeStr = st.LastDrop.Format("15:04:05")
		dropAgeStr = time.Since(st.LastDrop).Round(time.Second).String()
	}

	Put(scr, colLeft, y, fmt.Sprintf("Reachable: %d/%d (at %s, age %s)",
		good, total, st.LastPing.Format("15:04:05"), age), reachStyle)
	y += lineStep

	if good == total {
		Put(scr, colLeft, y, "Unreachable: none", tcell.StyleDefault)
	} else {
		down := make([]string, 0, len(st.Reachable))

		for h, ok := range st.Reachable {
			if !ok {
				down = append(down, h)
			}
		}

		sort.Strings(down)
		Put(scr, colLeft, y, fmt.Sprintf("Unreachable: %s (last drop at %s, age %s)",
			strings.Join(down, ", "), dropTimeStr, dropAgeStr), styleBrightRed())
	}

	return y + blockGap
}

// drawPacketLoss renders the per-host packet-loss list. The caller holds
// st.mu.RLock.
func drawPacketLoss(scr tcell.Screen, y int, st *InterfaceStatus) int {
	Put(scr, colLeft, y, "Packet Loss:", tcell.StyleDefault)
	y += lineStep

	lossHosts := make([]string, 0, len(st.Loss))
	for host := range st.Loss {
		lossHosts = append(lossHosts, host)
	}

	sort.Strings(lossHosts)

	maxHostLen := 0
	for _, host := range lossHosts {
		maxHostLen = max(maxHostLen, len(host))
	}

	maxHostLen++ // room for the colon

	for _, host := range lossHosts {
		p := st.Loss[host] * percentFull
		Put(scr, colLeft, y, fmt.Sprintf("%-*s %5.0f%%", maxHostLen, host+":", p),
			StyleLoss(p))
		y += lineStep
	}

	dAge := "N/A"
	if !st.LastDrop.IsZero() {
		dAge = time.Since(st.LastDrop).Round(time.Second).String()
	}

	Put(scr, colLeft, y, fmt.Sprintf("Dropped: %d (last at %s, age %s)",
		st.DroppedCount, st.LastDrop.Format("15:04:05"), dAge), tcell.StyleDefault)

	return y + blockGap
}

// drawTCPTable renders the TCP connect-stats table. The caller holds
// st.mu.RLock.
func (m *Monitor) drawTCPTable(
	scr tcell.Screen, y int, st *InterfaceStatus, tcpHosts []string,
) int {
	Put(scr, colLeft, y, "TCP Connect Stats:", tcell.StyleDefault)
	y += lineStep

	headerRow := fmt.Sprintf("%-*s %*s %*s %*s %*s %*s %*s %*s",
		m.HostWidth, "Host", m.NumWidth, "last", m.NumWidth, "min", m.NumWidth, "avg",
		m.NumWidth, "max", m.StdWidth, "stddev", m.NWidth, "n", m.LostWidth, "lost")
	Put(scr, colLeft, y, headerRow, tcell.StyleDefault)
	y += lineStep

	for _, hp := range tcpHosts {
		hist := st.TCP[hp]
		if len(hist) == 0 {
			continue
		}

		m.drawTCPRow(scr, y, st, hp, hist)
		y += lineStep
	}

	return y + lineStep
}

// drawTCPRow renders one TCP host's statistics row. The caller holds
// st.mu.RLock.
func (m *Monitor) drawTCPRow(
	scr tcell.Screen, y int, st *InterfaceStatus, hp string, hist []float64,
) {
	last := hist[len(hist)-1]
	mi, ma, av, sd := MinMaxAvgStd(hist)

	host := strings.Split(hp, ":")[0]
	lost := st.LostPackets[host]

	row := fmt.Sprintf("%-*s %*s %*s %*s %*s %*s %*d %*d",
		m.HostWidth, hp,
		m.NumWidth, msStr(last),
		m.NumWidth, msStr(mi),
		m.NumWidth, msStr(av),
		m.NumWidth, msStr(ma),
		m.StdWidth, msStr(sd),
		m.NWidth, len(hist),
		m.LostWidth, lost,
	)
	Put(scr, colLeft, y, row, tcell.StyleDefault)

	// Overlay the numeric columns colored by value, at the same offsets the
	// base row above laid them out.
	x := m.HostWidth + colGap
	Put(scr, x, y, fmt.Sprintf("%*s", m.NumWidth, msStr(last)), StyleLatency(last))
	x += m.NumWidth + colGap
	Put(scr, x, y, fmt.Sprintf("%*s", m.NumWidth, msStr(mi)), StyleLatency(mi))
	x += m.NumWidth + colGap
	Put(scr, x, y, fmt.Sprintf("%*s", m.NumWidth, msStr(av)), StyleLatency(av))
	x += m.NumWidth + colGap
	Put(scr, x, y, fmt.Sprintf("%*s", m.NumWidth, msStr(ma)), StyleLatency(ma))
	x += m.NumWidth + colGap
	Put(scr, x, y, fmt.Sprintf("%*s", m.StdWidth, msStr(sd)), tcell.StyleDefault)
	x += m.StdWidth + colGap
	x += m.NWidth + colGap // n column already drawn by the base row

	lostStyle := tcell.StyleDefault
	if lost > 0 {
		lostStyle = styleRed()
	}

	Put(scr, x, y, fmt.Sprintf("%*d", m.LostWidth, lost), lostStyle)
}

// drawICMPStats renders the ICMP request/reply/lost summary. The caller
// holds st.mu.RLock.
func drawICMPStats(scr tcell.Screen, y int, st *InterfaceStatus) int {
	lost := max(st.TotalICMPReq-st.TotalICMPRep, 0)

	lostStyle := tcell.StyleDefault
	if lost > 0 {
		lostStyle = styleRed()
	}

	reqCol := icmpLabelWidth
	repCol := reqCol + icmpValWidth + icmpColGap
	lostCol := repCol + icmpValWidth + icmpColGap

	Put(scr, reqCol, y, fmt.Sprintf("%*s", icmpValWidth, "Requests"), tcell.StyleDefault)
	Put(scr, repCol, y, fmt.Sprintf("%*s", icmpValWidth, "Replies"), tcell.StyleDefault)
	Put(scr, lostCol, y, fmt.Sprintf("%*s", icmpValWidth, "Lost"), tcell.StyleDefault)
	y += lineStep

	reqStr := fmt.Sprintf("%*d", icmpValWidth, st.TotalICMPReq)
	repStr := fmt.Sprintf("%*d", icmpValWidth, st.TotalICMPRep)
	lostStr := fmt.Sprintf("%*d", icmpValWidth, lost)

	Put(scr, colLeft, y, "ICMP:   ", tcell.StyleDefault)
	Put(scr, reqCol, y, reqStr, tcell.StyleDefault)
	Put(scr, repCol, y, repStr, tcell.StyleDefault)
	Put(scr, lostCol, y, lostStr, lostStyle)

	return y + blockGap
}

// uiLoop runs the UI event loop.
func (m *Monitor) uiLoop(ctx context.Context) {
	m.logf("UI loop started")

	defer func() {
		m.logf("UI loop cleanup")
		m.screen.Clear()
		m.screen.ShowCursor(0, 0)
		m.screen.Fini()
		m.logf("Screen finalized")
	}()

	pstLoc, err := time.LoadLocation("America/Los_Angeles")
	if err != nil {
		m.logf("Error loading PST location: %v", err)

		pstLoc = time.UTC
	}

	timestampSpinFrame := 0
	lastTimestampSpinUpdate := time.Now()

	drawScreen := func() {
		w, _ := m.screen.Size()
		m.screen.Clear()

		Put(m.screen, colLeft, rowTopRule, HLine(w), tcell.StyleDefault)

		now := time.Now()
		timeStr := now.Format(time.RFC1123Z)
		pstTimeStr := now.In(pstLoc).Format(time.RFC1123Z)

		if time.Since(lastTimestampSpinUpdate) >= time.Second {
			timestampSpinFrame = (timestampSpinFrame + 1) % len(brailleSpins())
			lastTimestampSpinUpdate = now
		}

		brailleChar := brailleSpins()[timestampSpinFrame]
		colors := rainbow()

		Put(m.screen, colLeft, rowClock, "== ", tcell.StyleDefault)
		Put(m.screen, colSpinner, rowClock, string(brailleChar)+" ", tcell.StyleDefault)
		DrawRainbowText(m.screen, colMeter, rowClock, timeStr, colors)
		DrawRainbowText(m.screen, colMeter+len(timeStr)+clockGap, rowClock,
			pstTimeStr, colors)
		Put(m.screen, colLeft, rowBottomRule, HLine(w), tcell.StyleDefault)

		runtime := time.Since(m.startTime).Round(time.Second).String()
		Put(m.screen, colLeft, rowRuntime, "Runtime: "+runtime, tcell.StyleDefault)

		// Draw one pane per interface; a single interface draws one pane.
		y := rowFirstIface
		for _, st := range m.interfaces {
			y = m.DrawInterface(m.screen, y, w, st)
		}

		m.screen.Show()
	}

	drawScreen()

	backupTicker := time.NewTicker(time.Second)
	defer backupTicker.Stop()

	for {
		select {
		case <-ctx.Done():
			m.logf("Context cancelled, exiting UI loop")

			return
		case <-m.uiUpdate:
			drawScreen()
		case <-backupTicker.C:
			drawScreen()
		}
	}
}