package app

import (
	"fmt"
	"os"
	"strings"

	"github.com/charmbracelet/lipgloss"
	"github.com/charmbracelet/x/ansi"
)

const (
	statusH = 1
	footerH = 1
	inputH  = 4 // rounded box: 2 borders + 2 content lines
)

// View renders the whole frame purely from the model (immediate-mode).
func (m Model) View() string {
	if m.quitting {
		return ""
	}
	if m.width < 20 || m.height < 8 {
		return m.theme.Screen.Render("correx — terminal too small")
	}

	bottom := m.renderInput()
	bottomH := inputH
	if m.displayState() == StateApproval {
		bottomH = m.approvalBandHeight()
		bottom = m.renderApprovalBand(bottomH)
	}

	mainH := m.height - statusH - footerH - bottomH
	if mainH < 3 {
		mainH = 3
	}

	base := lipgloss.JoinVertical(lipgloss.Left,
		m.renderStatus(),
		m.renderMain(mainH),
		bottom,
		m.renderFooter(),
	)

	if m.overlay != OverlayNone {
		return m.renderOverlay(base)
	}
	return base
}

// --- top status bar ---

func (m Model) renderStatus() string {
	t := m.theme
	bg := t.P.BgPanel
	span := func(s string, fg lipgloss.Color) string {
		return lipgloss.NewStyle().Foreground(fg).Background(bg).Render(s)
	}
	sep := span("  ·  ", t.P.Faint)

	parts := []string{span("correx", t.P.Dim)}
	if m.connected {
		parts = append(parts, span("●", t.P.OK)+span(" connected", t.P.Dim))
	} else if m.reconnecting {
		parts = append(parts, span("◌", t.P.Warn)+span(" reconnecting", t.P.Warn))
	} else {
		parts = append(parts, span("○", t.P.Bad)+span(" disconnected", t.P.Bad))
	}

	if s := m.session(m.selectedID); s != nil && m.displayState() != StateIdle {
		parts = append(parts, span(s.Name, t.P.FgStrong))
		if s.CurrentStage != "" {
			parts = append(parts, span("⟐ "+s.CurrentStage, t.P.Accent2))
		}
		if s.Status != "" {
			parts = append(parts, lipgloss.NewStyle().Foreground(statusColor(t, s.Status)).Background(bg).Render(statusLabel(s.Status)))
		}
		if s.WorkspaceRoot != "" {
			parts = append(parts, span("⌂ "+shortPath(s.WorkspaceRoot), t.P.Faint))
		}
	}

	model := m.currentModel
	if model == "" {
		model = "no model"
	}
	loc := "local"
	if m.providerType == "REMOTE" {
		loc = "remote"
	}
	parts = append(parts, span(model, t.P.Fg)+span(" ("+loc+")", t.P.Faint))
	left := strings.Join(parts, sep)

	var right []string
	if g := m.gaugeText(); g != "" {
		right = append(right, span(g, t.P.Faint))
	}
	if s := m.session(m.selectedID); s != nil && s.Active {
		right = append(right, lipgloss.NewStyle().Foreground(t.P.Accent).Background(bg).Render(m.spinner())+span(" active", t.P.Accent2))
	}
	if m.bgUpdates > 0 {
		right = append(right, span(itoa(m.bgUpdates)+" elsewhere", t.P.Warn))
	}
	if len(right) == 0 {
		return m.fill(left, m.width, bg)
	}
	return m.justify(left, strings.Join(right, span("  ·  ", t.P.Faint)), m.width, bg)
}

// gaugeText renders the live VRAM/GPU/RAM gauge, omitting any unavailable field.
func (m Model) gaugeText() string {
	var parts []string
	if m.gpuUsedMB != nil && m.gpuTotalMB != nil {
		parts = append(parts, "VRAM "+itoa(int(*m.gpuUsedMB))+"/"+itoa(int(*m.gpuTotalMB))+"M")
	}
	if m.gpuUtil != nil {
		parts = append(parts, "GPU "+itoa(*m.gpuUtil)+"%")
	}
	if m.sysRamUsedMB != nil && m.sysRamTotalMB != nil {
		parts = append(parts, "RAM "+itoa(int(*m.sysRamUsedMB))+"/"+itoa(int(*m.sysRamTotalMB))+"M")
	}
	if m.ramMB != nil {
		parts = append(parts, "proc "+itoa(int(*m.ramMB))+"M")
	}
	return strings.Join(parts, " ")
}

var spinnerFrames = []string{"⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"}

func (m Model) spinner() string { return spinnerFrames[m.frame%len(spinnerFrames)] }

// caretVisible blinks the insert caret roughly twice a second.
func (m Model) caretVisible() bool { return (m.frame/4)%2 == 0 }

// --- bottom footer hints ---

func (m Model) renderFooter() string {
	t := m.theme
	bg := t.P.BgDeep
	hint := func(key, label string) string {
		k := lipgloss.NewStyle().Foreground(t.P.Accent).Background(bg).Bold(true).Render(key)
		l := lipgloss.NewStyle().Foreground(t.P.Faint).Background(bg).Render(" " + label)
		return k + l
	}
	gap := lipgloss.NewStyle().Background(bg).Render("   ")

	var hints []string
	switch {
	case m.editMode == ModeInsert:
		hints = []string{hint("enter", "send"), hint("esc", "normal"), hint("↑↓", "history")}
	case m.displayState() == StateApproval:
		// Approval actions live in the band itself; the footer offers navigation only.
		hints = []string{hint("l", "back"), hint("e", "events"), hint("q", "quit")}
	case m.displayState() == StateIdle:
		hints = []string{hint("i", "name"), hint("/", "filter"), hint("enter", "open"), hint("jk", "move"), hint("w", "workflows"), hint("p", "cmds"), hint("q", "quit")}
	default: // StateInSession
		hints = []string{hint("i", "message"), hint("e", "events"), hint("t", "tools"), hint("m", "model"), hint("s", "mode"), hint("l", "back"), hint("p", "cmds"), hint("q", "quit")}
		if s := m.session(m.selectedID); s != nil && s.Pending != nil {
			hints = append(hints, hint("a", "approval (pending)"))
		}
	}
	left := strings.Join(hints, gap)

	right := lipgloss.NewStyle().Foreground(t.P.Dim).Background(bg).Render("Soft") +
		lipgloss.NewStyle().Foreground(t.P.Faint).Background(bg).Render(" · ") +
		lipgloss.NewStyle().Foreground(t.P.Accent).Background(bg).Render("blue")

	return m.justify(left, right, m.width, bg)
}

// --- main split ---

func (m Model) renderMain(h int) string {
	leftW := m.width * 63 / 100
	rightW := m.width - leftW

	var leftTitle, rightTitle string
	var leftBody, rightBody []string
	leftActive, rightActive := false, false

	switch m.displayState() {
	case StateIdle:
		leftTitle = "sessions"
		if m.wfVisible {
			leftTitle = "workflows"
			leftBody = m.workflowRows(leftW - 4)
		} else {
			leftBody = m.sessionRows(leftW - 4)
		}
		leftActive = true
		rightTitle = "welcome"
		rightBody = m.welcomeRows(rightW - 4)
	case StateInSession, StateApproval:
		leftTitle = "output"
		leftBody = m.routerRows(leftW-4, h-2)
		leftActive = true
		rightTitle = "events"
		rightBody = m.eventRows(rightW-4, h)
	}

	left := m.theme.box(leftTitle, leftBody, leftW, h, leftActive)
	right := m.theme.box(rightTitle, rightBody, rightW, h, rightActive)
	return lipgloss.JoinHorizontal(lipgloss.Top, left, right)
}

// --- input bar ---

// flattenForDisplay collapses control characters (newlines from a multi-line paste, tabs)
// to a single visible line so the fixed-height input box can't overflow and smear stale cells
// (F-006). The underlying inputBuffer keeps its real characters for submission.
func flattenForDisplay(s string) string {
	repl := strings.NewReplacer("\r\n", "↵ ", "\r", "↵ ", "\n", "↵ ", "\t", " ")
	return repl.Replace(s)
}

func (m Model) renderInput() string {
	t := m.theme

	placeholder := "Ask anything…"
	switch {
	case m.inputMode == ModeIntent:
		placeholder = "Describe the task for " + m.wfPendingName + " (Enter to start, empty = none)…"
	case m.inputMode == ModeFilter:
		placeholder = "Filter sessions…"
	case m.displayState() == StateIdle:
		placeholder = "Session name…"
	}

	insert := m.editMode == ModeInsert
	caret := t.span(" ", t.P.Bg)
	if insert && m.caretVisible() {
		caret = lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Render("▏")
	}
	var line string
	switch {
	case m.inputBuffer == "" && !insert:
		line = t.span(placeholder, t.P.Faint)
	case m.inputBuffer == "":
		line = caret + t.span(placeholder, t.P.Faint)
	default:
		line = t.span(flattenForDisplay(m.inputBuffer), t.P.FgStrong) + caret
	}

	// status sub-line: <session/none> · <uuid> · <mode>
	name := "(no session)"
	if s := m.session(m.selectedID); s != nil {
		name = s.Name
	}
	mode := "chat"
	if m.chatMode == ChatModeSteering {
		mode = "steering"
	}
	if m.inputMode == ModeFilter {
		mode = "filter"
	}
	if m.inputMode == ModeIntent {
		mode = "task"
	}
	sub := lipgloss.NewStyle().Foreground(t.P.Accent2).Background(t.P.Bg).Render(name)
	if m.selectedID != "" {
		sub += t.span(" · ", t.P.Faint) +
			t.span(m.selectedID, t.P.Faint)
	}
	sub += t.span(" · ", t.P.Faint) +
		t.span(mode, t.P.Dim)

	body := []string{line, sub}
	return t.box("", body, m.width, inputH, insert)
}

// --- body row builders ---

func (m Model) sessionRows(w int) []string {
	t := m.theme
	list := m.filteredSessions()
	if len(list) == 0 {
		return []string{t.span("no sessions yet", t.P.Faint), "", t.span("type a name below to begin", t.P.Faint)}
	}
	rows := make([]string, 0, len(list))
	for _, s := range list {
		sel := s.ID == m.selectedID && !m.wfVisible
		short := s.ID
		if len(short) > 6 {
			short = short[:6]
		}
		nameFg := t.P.Fg
		bar := t.span("  ", t.P.Bg)
		if sel {
			bar = lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Render("▌ ")
			nameFg = t.P.FgStrong
		}
		idCell := t.span("["+short+"] ", t.P.Faint)
		statusCell := lipgloss.NewStyle().Foreground(statusColor(t, s.Status)).Background(t.P.Bg).Bold(true).
			Render(padRaw(statusLabel(s.Status), 9))
		nameCell := lipgloss.NewStyle().Foreground(nameFg).Background(t.P.Bg).Render(" " + s.Name)
		stage := ""
		if s.CurrentStage != "" {
			stage = t.span(" ["+s.CurrentStage+"]", t.P.Dim)
		}
		rows = append(rows, bar+idCell+statusCell+nameCell+stage)
	}
	return rows
}

func (m Model) workflowRows(w int) []string {
	t := m.theme
	if len(m.workflows) == 0 {
		return []string{t.span("no workflows advertised", t.P.Faint)}
	}
	rows := make([]string, 0, len(m.workflows))
	for i, wf := range m.workflows {
		marker := t.span("  ", t.P.Bg)
		fg := t.P.Fg
		if i == m.wfIndex {
			marker = lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Render("▸ ")
			fg = t.P.FgStrong
		}
		rows = append(rows, marker+lipgloss.NewStyle().Foreground(fg).Background(t.P.Bg).Render(wf.ID)+t.span("  "+wf.Description, t.P.Faint))
	}
	return rows
}

func (m Model) welcomeRows(w int) []string {
	t := m.theme
	title := lipgloss.NewStyle().Foreground(t.P.FgStrong).Background(t.P.Bg).Bold(true).Render("Corre") +
		lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Bold(true).Render("x") +
		lipgloss.NewStyle().Foreground(t.P.FgStrong).Background(t.P.Bg).Bold(true).Render(" Agent Harness")

	var status string
	if m.connected {
		status = lipgloss.NewStyle().Foreground(t.P.OK).Background(t.P.Bg).Render("Connected") +
			t.span(" · ", t.P.Faint) + t.span(plural(len(m.sessions), "session"), t.P.Dim)
	} else {
		status = lipgloss.NewStyle().Foreground(t.P.Bad).Background(t.P.Bg).Render("Disconnected")
	}

	rows := []string{title, status, "",
		t.span("Select a session from the left", t.P.Dim),
		t.span("or type a name to start a new one.", t.P.Dim), ""}

	if n := len(m.sessions); n > 0 {
		rows = append(rows, t.span("recent:", t.P.Faint))
		start := 0
		if n > 5 {
			start = n - 5
		}
		for _, s := range m.sessions[start:] {
			mark := statusGlyph(t, s.Status)
			rows = append(rows, t.span("  "+s.Name+"  ", t.P.Fg)+t.span(formatTime(s.LastEventAt), t.P.Faint)+" "+mark)
		}
	}
	return rows
}

func (m Model) routerRows(w, h int) []string {
	t := m.theme
	msgs := m.routerMessages[m.selectedID]
	if len(msgs) == 0 {
		return []string{t.span("awaiting router response…", t.P.Faint)}
	}
	var rows []string
	for _, e := range msgs {
		switch e.Role {
		case "user":
			tag := lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Bold(true).Render("›")
			rows = append(rows, tag+" "+t.span(e.Content, t.P.FgStrong))
		case "router":
			for _, ln := range wrap(e.Content, w) {
				rows = append(rows, t.span(ln, t.P.Fg))
			}
			if s := metricsSuffix(e.Metrics); s != "" {
				rows = append(rows, t.span(s, t.P.Faint))
			}
		case "tool":
			rows = append(rows, t.span("· tool output ("+itoaLen(e.Content)+" chars) — ^x to view", t.P.Dim))
		case "narration_llm":
			diamond := lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Bold(true).Render("◆")
			lines := wrap(e.Content, w-2)
			for i, ln := range lines {
				if i == 0 {
					rows = append(rows, diamond+" "+t.span(ln, t.P.FgStrong))
				} else {
					rows = append(rows, "  "+t.span(ln, t.P.FgStrong))
				}
			}
			if s := metricsSuffix(e.Metrics); s != "" {
				rows = append(rows, t.span(s, t.P.Faint))
			}
		case "narration", "stage":
			rows = append(rows, t.span(e.Content, t.P.Dim))
		}
	}
	// keep last h rows
	if len(rows) > h {
		rows = rows[len(rows)-h:]
	}
	return rows
}

func (m Model) eventRows(w, h int) []string {
	t := m.theme
	header := lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Bold(true).Render("event stream") +
		t.span("   ", t.P.Bg)
	if m.connected {
		header += lipgloss.NewStyle().Foreground(t.P.OK).Background(t.P.Bg).Render("● live")
	} else {
		header += t.span("○ idle", t.P.Faint)
	}

	s := m.session(m.selectedID)
	if s == nil || len(s.Events) == 0 {
		return []string{header, "", t.span("no events yet", t.P.Faint)}
	}
	evRows := make([]string, 0, len(s.Events))
	for _, e := range s.Events {
		cat := inferCategory(e.Type)
		catCell := lipgloss.NewStyle().Foreground(t.categoryColor(cat)).Background(t.P.BgPanel).
			Render(" " + padRaw(cat, 9) + " ")
		evRows = append(evRows,
			t.span(e.Time+" ", t.P.Faint)+catCell+" "+
				t.span(padRaw(e.Type, 18), t.P.Fg)+t.span(e.Detail, t.P.Dim))
	}
	// Show the latest events that fit under the 2-line header (box inner = h-2).
	if avail := h - 4; avail >= 1 && len(evRows) > avail {
		evRows = evRows[len(evRows)-avail:]
	}
	return append([]string{header, ""}, evRows...)
}

// --- width helpers ---

// shortPath abbreviates the user's home dir to ~ for a compact cwd in the status bar.
func shortPath(p string) string {
	if home := os.Getenv("HOME"); home != "" && strings.HasPrefix(p, home) {
		return "~" + p[len(home):]
	}
	return p
}

// fill left-justifies a styled line and pads with bg to width w.
func (m Model) fill(s string, w int, bg lipgloss.Color) string {
	return " " + padTo(s, w-1, bg)
}

// justify places left and right segments on a bg-filled line of width w.
func (m Model) justify(left, right string, w int, bg lipgloss.Color) string {
	lw := lipgloss.Width(left)
	rw := lipgloss.Width(right)
	mid := w - lw - rw - 2
	if mid < 1 {
		mid = 1
	}
	pad := lipgloss.NewStyle().Background(bg).Render(strings.Repeat(" ", mid))
	return " " + left + pad + right + lipgloss.NewStyle().Background(bg).Render(" ")
}

// padTo pads (or truncates) a possibly-styled string to visible width w, filling
// with the given background so the panel stays opaque.
func padTo(s string, w int, bg lipgloss.Color) string {
	vw := lipgloss.Width(s)
	if vw == w {
		return s
	}
	if vw > w {
		return ansi.Truncate(s, w, "")
	}
	return s + lipgloss.NewStyle().Background(bg).Render(strings.Repeat(" ", w-vw))
}

// padRaw pads a plain (unstyled) string to width w with spaces, truncating with
// an ellipsis only when it genuinely overflows.
func padRaw(s string, w int) string {
	n := len([]rune(s))
	if n == w {
		return s
	}
	if n > w {
		if w <= 1 {
			return string([]rune(s)[:w])
		}
		return string([]rune(s)[:w-1]) + "…"
	}
	return s + strings.Repeat(" ", w-n)
}

func statusColor(t Theme, status string) lipgloss.Color {
	u := strings.ToUpper(status)
	switch {
	case strings.Contains(u, "FAIL"):
		return t.P.Bad
	case strings.Contains(u, "COMPLETE"):
		return t.P.Dim
	case strings.Contains(u, "PAUSE"), strings.Contains(u, "STARTING"):
		return t.P.Warn
	case strings.Contains(u, "CHAT"), strings.Contains(u, "ACTIVE"):
		return t.P.Accent
	default:
		return t.P.Dim
	}
}

func statusLabel(status string) string {
	u := strings.ToUpper(status)
	if i := strings.Index(u, " "); i > 0 {
		return u[:i]
	}
	return u
}

func statusGlyph(t Theme, status string) string {
	u := strings.ToUpper(status)
	switch {
	case strings.Contains(u, "FAIL"):
		return lipgloss.NewStyle().Foreground(t.P.Bad).Background(t.P.Bg).Render("✗")
	case strings.Contains(u, "COMPLETE"):
		return lipgloss.NewStyle().Foreground(t.P.OK).Background(t.P.Bg).Render("✓")
	default:
		return t.span("·", t.P.Faint)
	}
}

// span renders text with foreground fg over the panel background.
func (t Theme) span(s string, fg lipgloss.Color) string {
	return lipgloss.NewStyle().Foreground(fg).Background(t.P.Bg).Render(s)
}

// box draws a rounded, opaque panel with the title embedded in the top border.
func (t Theme) box(title string, body []string, w, h int, active bool) string {
	if w < 4 {
		w = 4
	}
	if h < 2 {
		h = 2
	}
	inner := w - 2
	textW := inner - 2
	bc := t.P.Border
	if active {
		bc = t.P.BorderHi
	}
	bs := lipgloss.NewStyle().Foreground(bc).Background(t.P.Bg)
	cell := lipgloss.NewStyle().Background(t.P.Bg)

	var top string
	if title == "" {
		top = bs.Render("╭" + strings.Repeat("─", inner) + "╮")
	} else {
		ts := t.PanelTitle
		if active {
			ts = t.TitleHi
		}
		label := strings.ToUpper(title)
		fill := inner - (2 + lipgloss.Width(label) + 1)
		if fill < 0 {
			fill = 0
		}
		top = bs.Render("╭─ ") + ts.Render(label) + bs.Render(" "+strings.Repeat("─", fill)) + bs.Render("╮")
	}
	lines := make([]string, 0, h)
	lines = append(lines, top)
	for i := 0; i < h-2; i++ {
		content := ""
		if i < len(body) {
			content = body[i]
		}
		padded := padTo(content, textW, t.P.Bg)
		lines = append(lines, bs.Render("│")+cell.Render(" ")+padded+cell.Render(" ")+bs.Render("│"))
	}
	lines = append(lines, bs.Render("╰"+strings.Repeat("─", inner)+"╯"))
	return strings.Join(lines, "\n")
}

func plural(n int, word string) string {
	s := itoa(n) + " " + word
	if n != 1 {
		s += "s"
	}
	return s
}

func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	neg := n < 0
	if neg {
		n = -n
	}
	var b [20]byte
	i := len(b)
	for n > 0 {
		i--
		b[i] = byte('0' + n%10)
		n /= 10
	}
	if neg {
		i--
		b[i] = '-'
	}
	return string(b[i:])
}

func itoaLen(s string) string { return itoa(len(s)) }

// metricsSuffix formats the faint latency+token annotation for a ROUTER turn.
func metricsSuffix(mtr *TurnMetrics) string {
	if mtr == nil {
		return ""
	}
	return fmt.Sprintf("  %.1fs · %d tokens", float64(mtr.LatencyMs)/1000.0, mtr.TotalTokens)
}

// wrap splits s into lines no wider than w (rune-based, whitespace-greedy).
func wrap(s string, w int) []string {
	if w < 1 {
		w = 1
	}
	words := strings.Fields(s)
	if len(words) == 0 {
		return []string{""}
	}
	var lines []string
	cur := ""
	for _, word := range words {
		if cur == "" {
			cur = word
		} else if len(cur)+1+len(word) <= w {
			cur += " " + word
		} else {
			lines = append(lines, cur)
			cur = word
		}
	}
	if cur != "" {
		lines = append(lines, cur)
	}
	return lines
}