package stackview

import (
	"fmt"
	"strings"

	"github.com/charmbracelet/bubbles/help"
	"github.com/charmbracelet/bubbles/key"
	tea "github.com/charmbracelet/bubbletea"
	"github.com/github/gh-stack/internal/stack"
	"github.com/github/gh-stack/internal/tui/shared"
)

// keyMap defines the key bindings for the stack view.
type keyMap struct {
	Up            key.Binding
	Down          key.Binding
	ToggleCommits key.Binding
	ToggleFiles   key.Binding
	OpenPR        key.Binding
	Checkout      key.Binding
	Quit          key.Binding
}

func (k keyMap) ShortHelp() []key.Binding {
	return []key.Binding{k.Down, k.Up, k.ToggleCommits, k.ToggleFiles, k.OpenPR, k.Checkout, k.Quit}
}

func (k keyMap) FullHelp() [][]key.Binding {
	return [][]key.Binding{k.ShortHelp()}
}

var keys = keyMap{
	Up: key.NewBinding(
		key.WithKeys("up", "k"),
		key.WithHelp("↑/k", "up"),
	),
	Down: key.NewBinding(
		key.WithKeys("down", "j"),
		key.WithHelp("↓/j", "down"),
	),
	ToggleCommits: key.NewBinding(
		key.WithKeys("c"),
		key.WithHelp("c", "commits"),
	),
	ToggleFiles: key.NewBinding(
		key.WithKeys("f"),
		key.WithHelp("f", "files"),
	),
	OpenPR: key.NewBinding(
		key.WithKeys("o"),
		key.WithHelp("o", "open PR"),
	),
	Checkout: key.NewBinding(
		key.WithKeys("enter"),
		key.WithHelp("enter", "checkout"),
	),
	Quit: key.NewBinding(
		key.WithKeys("q", "esc", "ctrl+c"),
		key.WithHelp("q", "quit"),
	),
}

// Model is the Bubbletea model for the interactive stack view.
type Model struct {
	nodes       []BranchNode
	trunk       stack.BranchRef
	version     string
	stackNumber int
	cursor      int // index into nodes (displayed top-down, so 0 = top of stack)
	help        help.Model
	width       int
	height      int

	// scrollOffset tracks vertical scroll position for tall stacks.
	scrollOffset int

	// checkoutBranch is set when the user wants to checkout a branch after quitting.
	checkoutBranch string
}

// New creates a new stack view model. stackNumber is the human-facing stack
// number shown in the header; pass 0 when it is not known.
func New(nodes []BranchNode, trunk stack.BranchRef, version string, stackNumber int) Model {
	h := help.New()
	h.ShowAll = true

	// Cursor starts at the current branch, or the first non-merged branch.
	// When every branch is merged there is nothing selectable, so the cursor
	// is hidden (-1) and the cursor-dependent shortcuts are disabled.
	cursor := -1
	for i, n := range nodes {
		if n.IsCurrent && !n.Ref.IsMerged() {
			cursor = i
			break
		}
	}
	if cursor < 0 {
		for i, n := range nodes {
			if !n.Ref.IsMerged() {
				cursor = i
				break
			}
		}
	}

	return Model{
		nodes:       nodes,
		trunk:       trunk,
		version:     version,
		stackNumber: stackNumber,
		cursor:      cursor,
		help:        h,
	}
}

// CheckoutBranch returns the branch to checkout after the TUI exits, if any.
func (m Model) CheckoutBranch() string {
	return m.checkoutBranch
}

func (m Model) Init() tea.Cmd {
	return nil
}

func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	switch msg := msg.(type) {
	case tea.WindowSizeMsg:
		m.width = msg.Width
		m.height = msg.Height
		m.help.Width = msg.Width
		return m, nil

	case tea.KeyMsg:
		switch {
		case key.Matches(msg, keys.Quit):
			return m, tea.Quit

		case key.Matches(msg, keys.Up):
			m.moveCursor(-1)
			return m, nil

		case key.Matches(msg, keys.Down):
			m.moveCursor(1)
			return m, nil

		case key.Matches(msg, keys.ToggleCommits):
			if m.cursor >= 0 && m.cursor < len(m.nodes) {
				m.nodes[m.cursor].CommitsExpanded = !m.nodes[m.cursor].CommitsExpanded
				m.clampScroll()
				m.ensureVisible()
			}
			return m, nil

		case key.Matches(msg, keys.ToggleFiles):
			if m.cursor >= 0 && m.cursor < len(m.nodes) {
				m.nodes[m.cursor].FilesExpanded = !m.nodes[m.cursor].FilesExpanded
				m.clampScroll()
				m.ensureVisible()
			}
			return m, nil

		case key.Matches(msg, keys.OpenPR):
			if m.cursor >= 0 && m.cursor < len(m.nodes) {
				node := m.nodes[m.cursor]
				if node.PR != nil && node.PR.URL != "" {
					shared.OpenBrowserInBackground(node.PR.URL)
				}
			}
			return m, nil

		case key.Matches(msg, keys.Checkout):
			if m.cursor >= 0 && m.cursor < len(m.nodes) {
				node := m.nodes[m.cursor]
				if !node.IsCurrent && !node.Ref.IsMerged() {
					m.checkoutBranch = node.Ref.Branch
					return m, tea.Quit
				}
			}
			return m, nil
		}

	case tea.MouseMsg:
		switch msg.Action {
		case tea.MouseActionPress:
			if msg.Button == tea.MouseButtonLeft {
				return m.handleMouseClick(msg.X, msg.Y)
			}
			if msg.Button == tea.MouseButtonWheelUp {
				if m.scrollOffset > 0 {
					m.scrollOffset--
				}
				return m, nil
			}
			if msg.Button == tea.MouseButtonWheelDown {
				m.scrollOffset++
				m.clampScroll()
				return m, nil
			}
		}
	}

	return m, nil
}

// toBranchNodeData converts a BranchNode to shared.BranchNodeData.
func toBranchNodeData(node BranchNode) shared.BranchNodeData {
	return shared.BranchNodeData{
		Ref:              node.Ref,
		IsCurrent:        node.IsCurrent,
		IsLinear:         node.IsLinear,
		BaseBranch:       node.BaseBranch,
		Commits:          node.Commits,
		FilesChanged:     node.FilesChanged,
		PR:               node.PR,
		Additions:        node.Additions,
		Deletions:        node.Deletions,
		CommitsExpanded:  node.CommitsExpanded,
		FilesExpanded:    node.FilesExpanded,
		ShowCurrentLabel: true,
	}
}

// handleMouseClick processes a mouse click at the given screen position.
func (m Model) handleMouseClick(screenX, screenY int) (tea.Model, tea.Cmd) {
	nodes := make([]shared.BranchNodeData, len(m.nodes))
	for i, n := range m.nodes {
		nodes[i] = toBranchNodeData(n)
	}

	result := shared.HandleClick(screenX, screenY, nodes, m.width, m.height, m.scrollOffset, m.headerHeight(), true)
	if result.NodeIndex < 0 {
		return m, nil
	}

	// Don't allow selecting merged branches.
	if m.nodes[result.NodeIndex].Ref.IsMerged() {
		return m, nil
	}

	m.cursor = result.NodeIndex

	if result.OpenURL != "" {
		shared.OpenBrowserInBackground(result.OpenURL)
	}
	if result.ToggleFiles {
		m.nodes[result.NodeIndex].FilesExpanded = !m.nodes[result.NodeIndex].FilesExpanded
		m.clampScroll()
	}
	if result.ToggleCommits {
		m.nodes[result.NodeIndex].CommitsExpanded = !m.nodes[result.NodeIndex].CommitsExpanded
		m.clampScroll()
	}

	return m, nil
}

// nodeLineCount returns how many rendered lines a node occupies.
func (m Model) nodeLineCount(idx int) int {
	return shared.NodeLineCount(toBranchNodeData(m.nodes[idx]))
}

// moveCursor moves the cursor by delta, skipping merged branches.
func (m *Model) moveCursor(delta int) {
	next := m.cursor + delta
	for next >= 0 && next < len(m.nodes) {
		if !m.nodes[next].Ref.IsMerged() {
			m.cursor = next
			m.ensureVisible()
			return
		}
		next += delta
	}
}

// ensureVisible adjusts scroll offset so the cursor is visible.
func (m *Model) ensureVisible() {
	if m.height == 0 {
		return
	}

	// Calculate the line range for the cursor node, accounting for separator lines
	startLine := 0
	prevWasMerged := false
	prevWasQueued := false
	for i := 0; i < m.cursor; i++ {
		isMerged := m.nodes[i].Ref.IsMerged()
		isQueued := m.nodes[i].Ref.IsQueued()
		if isMerged && !prevWasMerged && i > 0 {
			startLine++ // separator line
		} else if isQueued && !prevWasQueued && !prevWasMerged && i > 0 {
			startLine++ // separator line
		}
		prevWasMerged = isMerged
		prevWasQueued = isQueued
		startLine += m.nodeLineCount(i)
	}
	// Check if the cursor node itself is preceded by a separator
	if m.cursor < len(m.nodes) {
		isMerged := m.nodes[m.cursor].Ref.IsMerged()
		isQueued := m.nodes[m.cursor].Ref.IsQueued()
		if isMerged && !prevWasMerged && m.cursor > 0 {
			startLine++
		} else if isQueued && !prevWasQueued && !prevWasMerged && m.cursor > 0 {
			startLine++
		}
	}
	endLine := startLine + m.nodeLineCount(m.cursor)

	viewHeight := m.contentViewHeight()
	m.scrollOffset = shared.EnsureVisible(startLine, endLine, m.scrollOffset, viewHeight)
}

// totalContentLines returns the total number of rendered content lines (excluding header).
func (m Model) totalContentLines() int {
	lines := 0
	prevWasMerged := false
	prevWasQueued := false
	for i := 0; i < len(m.nodes); i++ {
		isMerged := m.nodes[i].Ref.IsMerged()
		isQueued := m.nodes[i].Ref.IsQueued()
		if isMerged && !prevWasMerged && i > 0 {
			lines++ // separator line
		} else if isQueued && !prevWasQueued && !prevWasMerged && i > 0 {
			lines++ // separator line
		}
		prevWasMerged = isMerged
		prevWasQueued = isQueued
		lines += m.nodeLineCount(i)
	}
	lines++ // trunk line
	return lines
}

// headerHeight returns the number of rows the header occupies for this model's
// config, or 0 when the header is hidden.
func (m Model) headerHeight() int {
	if shared.ShouldShowHeader(m.width, m.height) {
		return shared.HeaderHeightFor(m.buildHeaderConfig())
	}
	return 0
}

// contentViewHeight returns the number of lines available for stack content.
func (m Model) contentViewHeight() int {
	h := m.height - m.headerHeight()
	if h < 1 {
		h = 1
	}
	return h
}

// clampScroll ensures scrollOffset doesn't exceed content bounds.
func (m *Model) clampScroll() {
	m.scrollOffset = shared.ClampScroll(m.totalContentLines(), m.contentViewHeight(), m.scrollOffset)
}

func (m Model) View() string {
	if m.width == 0 {
		return ""
	}

	var out strings.Builder

	showHeader := shared.ShouldShowHeader(m.width, m.height)
	reservedLines := 0
	if showHeader {
		// Build the header config once and reuse it for both rendering and the
		// height reservation, so View does not rebuild it twice per frame.
		cfg := m.buildHeaderConfig()
		shared.RenderHeader(&out, cfg, m.width, m.height)
		reservedLines = shared.HeaderHeightFor(cfg)
	} else {
		// The header (and its inline-image logo) is hidden; clear any logo that
		// was previously drawn so it does not linger in the graphics layer.
		out.WriteString(shared.ClearLogo())
	}

	var b strings.Builder

	// Render nodes in order (index 0 = top of stack, displayed first)
	prevWasMerged := false
	prevWasQueued := false
	for i := 0; i < len(m.nodes); i++ {
		isMerged := m.nodes[i].Ref.IsMerged()
		isQueued := m.nodes[i].Ref.IsQueued()
		if isMerged && !prevWasMerged && i > 0 {
			shared.RenderMergedSeparator(&b)
		} else if isQueued && !prevWasQueued && !prevWasMerged && i > 0 {
			shared.RenderQueuedSeparator(&b)
		}
		m.renderNode(&b, i)
		prevWasMerged = isMerged
		prevWasQueued = isQueued
	}

	// Trunk
	shared.RenderTrunk(&b, m.trunk.Branch)

	content := b.String()

	// Apply scrolling
	viewHeight := m.height - reservedLines
	if viewHeight < 1 {
		viewHeight = 1
	}

	out.WriteString(shared.ApplyScrollToContent(content, m.scrollOffset, viewHeight))

	return out.String()
}

// buildHeaderConfig produces the header configuration for the stack view.
func (m Model) buildHeaderConfig() shared.HeaderConfig {
	mergedCount := 0
	queuedCount := 0
	for _, n := range m.nodes {
		if n.Ref.IsMerged() {
			mergedCount++
		}
		if n.Ref.IsQueued() {
			queuedCount++
		}
	}

	branchCount := len(m.nodes)
	branchInfo := fmt.Sprintf("%d branches", branchCount)
	if branchCount == 1 {
		branchInfo = "1 branch"
	}
	if mergedCount > 0 {
		branchInfo += fmt.Sprintf(" (%d merged)", mergedCount)
	}
	if queuedCount > 0 {
		branchInfo += fmt.Sprintf(" (%d queued)", queuedCount)
	}

	branchIcon := "○"
	if mergedCount > 0 && mergedCount < branchCount {
		branchIcon = "◐"
	} else if branchCount > 0 && mergedCount == branchCount {
		branchIcon = "●"
	}

	// When every branch is merged there is no selectable branch, so the cursor
	// is hidden and the actions that depend on it are dimmed; only quit works.
	allMerged := branchCount > 0 && mergedCount == branchCount

	infoLines := make([]shared.HeaderInfoLine, 0, 3)
	if m.stackNumber > 0 {
		infoLines = append(infoLines, shared.HeaderInfoLine{Icon: "◆", Label: fmt.Sprintf("Stack #%d", m.stackNumber)})
	} else {
		infoLines = append(infoLines, shared.HeaderInfoLine{Icon: "✓", Label: "Stack initialized"})
	}
	infoLines = append(infoLines,
		shared.HeaderInfoLine{Icon: "◼", Label: "Base: " + m.trunk.Branch},
		shared.HeaderInfoLine{Icon: branchIcon, Label: branchInfo},
	)

	return shared.HeaderConfig{
		ShowArt:         true,
		Title:           "View Stack",
		Subtitle:        "v" + m.version,
		InfoLines:       infoLines,
		ShortcutColumns: 1,
		Shortcuts: []shared.ShortcutEntry{
			{Key: "↓↑/jk", Desc: "navigate", Disabled: allMerged},
			{Key: "c", Desc: "commits", Disabled: allMerged},
			{Key: "f", Desc: "files", Disabled: allMerged},
			{Key: "o", Desc: "open PR", Disabled: allMerged},
			{Key: "↵", Desc: "checkout", Disabled: allMerged},
			{Key: "q", Desc: "quit"},
		},
	}
}

// renderNode renders a single branch node.
func (m Model) renderNode(b *strings.Builder, idx int) {
	node := m.nodes[idx]
	isFocused := idx == m.cursor
	shared.RenderNode(b, toBranchNodeData(node), isFocused, m.width, nil)
}