package ui

import (
	"fmt"
	"image"
	"image/color"
	"strings"

	"gioui.org/font"
	"gioui.org/layout"
	"gioui.org/op"
	"gioui.org/op/clip"
	"gioui.org/op/paint"
	"gioui.org/unit"
	"gioui.org/widget"
)

// Region defines a screen area in device-independent pixels (Dp).
// All element positions and sizes use Dp for device independence.
type Region struct {
	X, Y Dp
	W, H Dp
}

// String returns a string representation of the Region.
func (r Region) String() string {
	return fmt.Sprintf("Region{x=%g y=%g w=%g h=%g}", r.X, r.Y, r.W, r.H)
}

// Element is the base interface for all UI elements.
// Elements know how to draw themselves when given a Renderer.
type Element interface {
	Region() Region
	Visible() bool
	Draw(gtx layout.Context, r *Renderer)
	String() string
}

// Container holds child elements and draws them within its bounds.
// Children's regions are screen-space; clipping handles containment.
type Container struct {
	id         string
	region     Region
	visible    bool
	background Color
	children   []Element
}

func (c Container) Region() Region     { return c.region }
func (c Container) Visible() bool      { return c.visible }
func (c Container) Draw(gtx layout.Context, r *Renderer) {
	// Draw background — children are drawn by drawElement, not here
	if c.background != (Color{}) {
		r.drawBg(gtx, c.region, c.background)
	}
}

// String returns a string representation of the Container and all children.
func (c Container) String() string {
	var sb strings.Builder
	sb.WriteString(fmt.Sprintf("Container[%s] region=%+v bg=%#v children=%d", c.id, c.region, c.background, len(c.children)))
	for i, child := range c.children {
		if str, ok := any(child).(fmt.Stringer); ok {
			sb.WriteString(fmt.Sprintf("\n  [%d] %s", i, str.String()))
		} else {
			sb.WriteString(fmt.Sprintf("\n  [%d] %T region=%+v", i, child, child.Region()))
		}
	}
	return sb.String()
}

// NewContainer creates a Container with the given region, background, and children.
func NewContainer(region Region, bg Color, children []Element) Container {
	return Container{
		region:     region,
		visible:    true,
		background: bg,
		children:   children,
	}
}

// --- Leaf element types (each implements Element and knows how to Draw itself) ---

// Label displays static text.
type Label struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Text         string
	Align        TextAlign
	FontSize     unit.Sp // 0 = theme default
	Color        Color   // 0 = theme default
	Bold         bool
}

func (l Label) Region() Region          { return l.region }
func (l Label) Visible() bool           { return l.visible }
func (l Label) Interactions() []Interaction { return l.interactions }
func (l Label) Draw(gtx layout.Context, r *Renderer) {
	col := l.Color
	if col == (Color{}) {
		col = Color{R: 0, G: 0, B: 0, A: 255}
	}
	// Click registration is handled by registerInteraction within drawElement,
	// which correctly applies the container offset. No separate RegisterClick needed.
	r.drawText(gtx, l.Text, l.FontSize, l.region, l.Align, col, l.id)
}
func (l Label) ID() string          { return l.id }

// String returns a string representation of the Label.
func (l Label) String() string {
	return fmt.Sprintf("Label[%s] text=%q region=%+v align=%d fontSize=%g", l.id, l.Text, l.region, l.Align, l.FontSize)
}

// NewLabel creates a visible Label element.
func NewLabel(text string, fontSize unit.Sp, region Region, align TextAlign, id string, interactions []Interaction) Label {
	return Label{
		id:           id,
		region:       region,
		visible:      true,
		interactions: interactions,
		Text:         text,
		FontSize:     fontSize,
		Align:        align,
	}
}

// Icon displays a named icon image.
type Icon struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Name         string // icon name, e.g. "cut"
	Size         Dp     // 0 = default icon size
}

func (i Icon) Region() Region          { return i.region }
func (i Icon) Visible() bool           { return i.visible }
func (i Icon) Interactions() []Interaction { return i.interactions }
func (i Icon) Draw(gtx layout.Context, r *Renderer) {
	img := r.icon(i.Name)
	if img == nil {
		return
	}
	// Click registration is handled by registerInteraction within drawElement,
	// which correctly applies the container offset. No separate RegisterClick needed.
	// Auto-scale: if Size is 0, use region dimensions so the icon fills its region
	w, h := Dp(0), Dp(0)
	if i.Size == 0 {
		w, h = i.region.W, i.region.H
	}
	r.drawPng(gtx, img, i.region, w, h)
}
func (i Icon) ID() string          { return i.id }

// String returns a string representation of the Icon.
func (i Icon) String() string {
	return fmt.Sprintf("Icon[%s] name=%q region=%+v size=%g", i.id, i.Name, i.region, i.Size)
}

// NewIcon creates a visible Icon element.
func NewIcon(name string, region Region, size Dp, interactions []Interaction) Icon {
	return Icon{
		id:           name,
		region:       region,
		visible:      true,
		interactions: interactions,
		Name:         name,
		Size:         size,
	}
}

// TextField accepts text input or displays multiline text.
type TextField struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Value        string
	Placeholder  string
	Focused      bool
	Multiline    bool
	ScrollOffset Dp
	VisibleLines []Line
	WordWrap     bool
	WrapWidth    Dp
}

func (tf TextField) Region() Region          { return tf.region }
func (tf TextField) Visible() bool           { return tf.visible }
func (tf TextField) ID() string              { return tf.id }
func (tf TextField) Interactions() []Interaction { return tf.interactions }

// String returns a string representation of the TextField.
func (tf TextField) String() string {
	return fmt.Sprintf("TextField[%s] region=%+v len=%d multiline=%v", tf.id, tf.region, len(tf.Value), tf.Multiline)
}

// Draw renders the TextField. For multiline text, it shapes with word wrap
// and draws display lines inline — one LayoutString call, no double-shaping.
func (tf TextField) Draw(gtx layout.Context, r *Renderer) {
	r.drawWrappedText(gtx, tf.Value, tf.region, tf.WrapWidth, tf.ScrollOffset)
}

// NewTextField creates a visible multiline TextField.
func NewTextField(id string, value string, region Region, wrapWidth Dp, scrollOffset Dp, interactions []Interaction) TextField {
	return TextField{
		id:           id,
		region:       region,
		visible:      true,
		interactions: interactions,
		Value:        value,
		Multiline:    true,
		WordWrap:     true,
		WrapWidth:    wrapWidth,
		ScrollOffset: scrollOffset,
	}
}

// Line represents a single line of text in a multiline TextField.
type Line struct {
	Text       string
	LineNumber int // 1-indexed, for display
}

// ListView displays a scrollable list of items.
type ListView struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Items        []ListItem
	ScrollOffset Dp // pixel-level scroll offset
	Selected     int
	RowTapHandler func(any) // handler for row taps, receives index as any
}

func (lv ListView) Region() Region          { return lv.region }
func (lv ListView) Visible() bool           { return lv.visible }
func (lv ListView) ID() string              { return lv.id }
func (lv ListView) NeedsClip() bool         { return true }
func (lv ListView) Interactions() []Interaction {
	// ListView registers its scroll in Draw, not via registerInteraction.
	// Filter out Scroll so registerInteraction only handles Tap.
	var filtered []Interaction
	for _, interaction := range lv.interactions {
		if interaction.Gesture != Scroll {
			filtered = append(filtered, interaction)
		}
	}
	return filtered
}

// String returns a string representation of the ListView.
func (lv ListView) String() string {
	var sb strings.Builder
	sb.WriteString(fmt.Sprintf("ListView[%s] region=%+v items=%d selected=%d", lv.id, lv.region, len(lv.Items), lv.Selected))
	for i, item := range lv.Items {
		sb.WriteString(fmt.Sprintf("\n  [%d] %s", i, item.String()))
	}
	return sb.String()
}

// Draw renders each list item as a row of text.
// The scroll gesture is registered via the normal interaction path so it
// is clipped to the list region by the element's clip context.
func (lv ListView) Draw(gtx layout.Context, r *Renderer) {
	// Register scroll gesture - clip is already active from drawElement
	if len(lv.interactions) > 0 {
		var scrollHandler func(any)
		for _, interaction := range lv.interactions {
			if interaction.Gesture == Scroll {
				scrollHandler = interaction.Handler
				break
			}
		}
		if scrollHandler != nil {
			r.RegisterScroll(gtx, lv.id, lv.region, scrollHandler)
		}
	}
	rowHeight := Dp(48)
	firstVisibleRow := int(lv.ScrollOffset / rowHeight)
	for i, item := range lv.Items {
		// Account for scroll offset: row Y is shifted up by scroll amount
		rowGlobalIndex := firstVisibleRow + i
		y := lv.region.Y + Dp(rowGlobalIndex)*rowHeight - lv.ScrollOffset
		// Only draw visible rows (virtualized)
		if y+rowHeight < lv.region.Y || y > lv.region.Y+lv.region.H {
			continue
		}
		// Draw background for selected item
		if item.Selected || (lv.Selected == i) {
			r.drawBg(gtx, Region{
				X: lv.region.X, Y: y,
				W: lv.region.W, H: rowHeight,
			}, Color{R: 200, G: 220, B: 255, A: 255})
		}
		// Register click area for this row
		rowID := fmt.Sprintf("list_row_%d", rowGlobalIndex)
		r.RegisterClick(gtx, rowID, Region{
			X: lv.region.X, Y: y,
			W: lv.region.W, H: rowHeight,
		}, func(data any) {
			if lv.RowTapHandler != nil {
				lv.RowTapHandler(rowGlobalIndex)
			} else {
				OpenFile(item.Text)
			}
		})
		// Draw main text
		textRegion := Region{
			X: lv.region.X + Dp(8),
			Y: y + Dp(4),
			W: lv.region.W - Dp(32),
			H: rowHeight - Dp(8),
		}
		r.drawText(gtx, item.Text, 14, textRegion, AlignStart, Color{R: 0, G: 0, B: 0, A: 255}, "")
		// Draw subtext
		if item.Subtext != "" {
			subRegion := Region{
				X: lv.region.X + Dp(8),
				Y: y + rowHeight - Dp(22),
				W: lv.region.W - Dp(32),
				H: Dp(16),
			}
			r.drawText(gtx, item.Subtext, 12, subRegion, AlignStart, Color{R: 128, G: 128, B: 128, A: 255}, "")
		}
	}
}

// NewListView creates a visible ListView element.
func NewListView(id string, items []ListItem, region Region, scrollOffset Dp, selected int, interactions []Interaction, rowTapHandler func(any)) ListView {
	return ListView{
		id:            id,
		region:        region,
		visible:       true,
		interactions:  interactions,
		Items:         items,
		ScrollOffset:  scrollOffset,
		Selected:      selected,
		RowTapHandler: rowTapHandler,
	}
}

// ListItem is a single entry in a ListView.
type ListItem struct {
	Text     string
	Subtext  string
	Selected bool
}

// String returns a string representation of the ListItem.
func (li ListItem) String() string {
	selected := ""
	if li.Selected {
		selected = " *"
	}
	return fmt.Sprintf("ListItem text=%q subtext=%q%s", li.Text, li.Subtext, selected)
}

// AlphaIndex displays an alphabetical index for quick navigation.
type AlphaIndex struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Letters      []string
	ActiveLetter string
}

func (ai AlphaIndex) Region() Region          { return ai.region }
func (ai AlphaIndex) Visible() bool           { return ai.visible }
func (ai AlphaIndex) ID() string              { return ai.id }
func (ai AlphaIndex) Interactions() []Interaction { return ai.interactions }

// String returns a string representation of the AlphaIndex.
func (ai AlphaIndex) String() string {
	return fmt.Sprintf("AlphaIndex[%s] region=%+v letters=%v active=%q", ai.id, ai.region, ai.Letters, ai.ActiveLetter)
}

// Draw renders letters vertically along the right edge.
func (ai AlphaIndex) Draw(gtx layout.Context, r *Renderer) {
	letterHeight := ai.region.H / Dp(len(ai.Letters))
	for i, letter := range ai.Letters {
		region := Region{
			X: ai.region.X,
			Y: ai.region.Y + Dp(i)*letterHeight,
			W: ai.region.W,
			H: letterHeight,
		}
		col := Color{R: 100, G: 100, B: 100, A: 255}
		if letter == ai.ActiveLetter {
			col = Color{R: 0, G: 100, B: 200, A: 255}
		}
		r.drawText(gtx, letter, 10, region, AlignCenter, col, "")
	}
}

// NewAlphaIndex creates a visible AlphaIndex element.
func NewAlphaIndex(region Region, letters []string) AlphaIndex {
	return AlphaIndex{
		region:  region,
		visible: true,
		Letters: letters,
	}
}

// Button is an interactive button element.
type Button struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Text         string
	Enabled      bool
	Primary      bool
}

func (b Button) Region() Region          { return b.region }
func (b Button) Visible() bool           { return b.visible }
func (b Button) Interactions() []Interaction { return b.interactions }
func (b Button) Draw(gtx layout.Context, r *Renderer) {
	col := Color{R: 0, G: 0, B: 0, A: 255}
	r.drawText(gtx, b.Text, r.theme.FontSize, b.region, AlignStart, col, b.id)
}
func (b Button) ID() string          { return b.id }

// String returns a string representation of the Button.
func (b Button) String() string {
	return fmt.Sprintf("Button[%s] text=%q region=%+v enabled=%v", b.id, b.Text, b.region, b.Enabled)
}

// NewButton creates a visible Button element.
func NewButton(text string, enabled bool, primary bool, region Region) Button {
	return Button{
		region:  region,
		visible: true,
		Text:    text,
		Enabled: enabled,
		Primary: primary,
	}
}

// SearchBar displays an in-editor search interface.
type SearchBar struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Query        string
	Match        int
	Total        int
	Forward      bool
}

func (sb SearchBar) Region() Region          { return sb.region }
func (sb SearchBar) Visible() bool           { return sb.visible }
func (sb SearchBar) ID() string              { return sb.id }
func (sb SearchBar) Interactions() []Interaction { return sb.interactions }

// String returns a string representation of the SearchBar.
func (sb SearchBar) String() string {
	return fmt.Sprintf("SearchBar[%s] region=%+v query=%q match=%d/%d", sb.id, sb.region, sb.Query, sb.Match, sb.Total)
}

// NewSearchBar creates a visible SearchBar element.
func NewSearchBar(region Region, query string, match, total int, forward bool) SearchBar {
	return SearchBar{
		region:  region,
		visible: true,
		Query:   query,
		Match:   match,
		Total:   total,
		Forward: forward,
	}
}

// Cursor displays the text cursor and optional selection highlight.
type Cursor struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Line         int
	Column       int
	Blinking     bool
	Selection    *Selection
}

func (c Cursor) Region() Region          { return c.region }
func (c Cursor) Visible() bool           { return c.visible }
func (c Cursor) ID() string              { return c.id }
func (c Cursor) Interactions() []Interaction { return c.interactions }

// String returns a string representation of the Cursor.
func (c Cursor) String() string {
	return fmt.Sprintf("Cursor[%s] region=%+v line=%d col=%d", c.id, c.region, c.Line, c.Column)
}

// Selection represents a text selection range.
type Selection struct {
	StartLine, StartCol int
	EndLine, EndCol     int
}

// MergeHunk displays a conflict resolution hunk.
type MergeHunk struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	HunkNumber   int
	TotalHunks   int
	LineRange    string
	ContextLines []string
	OurLines     []string
	TheirLines   []string
	Resolution   HunkResolution
}

func (mh MergeHunk) Region() Region          { return mh.region }
func (mh MergeHunk) Visible() bool           { return mh.visible }
func (mh MergeHunk) ID() string              { return mh.id }
func (mh MergeHunk) Interactions() []Interaction { return mh.interactions }

// String returns a string representation of the MergeHunk.
func (mh MergeHunk) String() string {
	return fmt.Sprintf("MergeHunk[%s] region=%+v hunk=%d/%d lineRange=%s resolution=%d", mh.id, mh.region, mh.HunkNumber, mh.TotalHunks, mh.LineRange, mh.Resolution)
}

// HunkResolution represents the resolution state of a merge hunk.
type HunkResolution int

const (
	Unresolved HunkResolution = iota
	KeepOurs
	KeepTheirs
	MergeBoth
)

// Toast displays a temporary notification.
type Toast struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Text         string
	Timeout      int // milliseconds
}

func (t Toast) Region() Region          { return t.region }
func (t Toast) Visible() bool           { return t.visible }
func (t Toast) ID() string              { return t.id }
func (t Toast) Interactions() []Interaction { return t.interactions }

// String returns a string representation of the Toast.
func (t Toast) String() string {
	return fmt.Sprintf("Toast[%s] text=%q region=%+v timeout=%d", t.id, t.Text, t.region, t.Timeout)
}

// NewToast creates a visible Toast element.
func NewToast(region Region, text string, timeout int) Toast {
	return Toast{
		region:  region,
		visible: true,
		Text:    text,
		Timeout: timeout,
	}
}

// Spacer adds vertical or horizontal space.
type Spacer struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
}

func (s Spacer) Region() Region          { return s.region }
func (s Spacer) Visible() bool           { return s.visible }
func (s Spacer) ID() string              { return s.id }
func (s Spacer) Interactions() []Interaction { return s.interactions }

// String returns a string representation of the Spacer.
func (s Spacer) String() string {
	return fmt.Sprintf("Spacer[%s] region=%+v", s.id, s.region)
}

// NewSpacer creates a visible Spacer element.
func NewSpacer(height Dp) Spacer {
	return Spacer{
		region:  Region{H: height},
		visible: true,
	}
}

// GioEditor wraps a Gio widget.Editor for single-line or multiline text input.
type GioEditor struct {
	id           string
	region       Region
	visible      bool
	interactions []Interaction
	Editor       *widget.Editor
}

func (ge GioEditor) Region() Region          { return ge.region }
func (ge GioEditor) Visible() bool           { return ge.visible }
func (ge GioEditor) ID() string              { return ge.id }
func (ge GioEditor) Interactions() []Interaction { return ge.interactions }

// String returns a string representation of the GioEditor.
func (ge GioEditor) String() string {
	return fmt.Sprintf("GioEditor[%s] region=%+v", ge.id, ge.region)
}

// Draw renders the Gio Editor widget.
func (ge GioEditor) Draw(gtx layout.Context, r *Renderer) {
	ge.Editor.SingleLine = true

	// Position and clip to the editor's region
	stack := op.Offset(image.Pt(int(r.toPx(ge.region.X)), int(r.toPx(ge.region.Y)))).Push(gtx.Ops)
	defer stack.Pop()

	// Draw a simple background for the search bar
	rect := image.Rectangle{Max: image.Pt(int(r.toPx(ge.region.W)), int(r.toPx(ge.region.H)))}
	paint.FillShape(gtx.Ops, color.NRGBA{R: 245, G: 245, B: 245, A: 255}, clip.Rect(rect).Op())

	// Create paint color macros for text and selection colors
	textMacro := op.Record(gtx.Ops)
	paint.ColorOp{Color: color.NRGBA{R: 0, G: 0, B: 0, A: 255}}.Add(gtx.Ops)
	textColor := textMacro.Stop()
	selectionMacro := op.Record(gtx.Ops)
	paint.ColorOp{Color: color.NRGBA{R: 200, G: 220, B: 255, A: 255}}.Add(gtx.Ops)
	selectionColor := selectionMacro.Stop()

	// Set constraints so the editor knows its size for hit-testing
	gtx.Constraints = layout.Exact(rect.Size())

	// Use our RegisterClick to ensure the full region is clickable
	r.RegisterClick(gtx, ge.id, ge.region, nil)

	ge.Editor.Layout(gtx, r.shp, font.Font{}, r.theme.FontSize, textColor, selectionColor)
}

// NewGioEditor creates a GioEditor element wrapping a widget.Editor.
func NewGioEditor(id string, region Region, editor *widget.Editor) GioEditor {
	return GioEditor{
		id:      id,
		region:  region,
		visible: true,
		Editor:  editor,
	}
}

// --- Utility types ---

// OpenFile is called by the browser list when a file row is tapped.
// Set by the editor package after initialization.
var OpenFile func(any)

// Color is an RGBA color.
type Color struct {
	R, G, B, A uint8
}

// String returns a string representation of the Color.
func (c Color) String() string {
	return fmt.Sprintf("Color{R:%d G:%d B:%d A:%d}", c.R, c.G, c.B, c.A)
}

// Theme holds styling defaults for the UI.
type Theme struct {
	FontSize unit.Sp // Gio's shaper requires unit.Sp for font sizes
}

// TextAlign specifies horizontal text alignment.
type TextAlign int

const (
	AlignStart TextAlign = iota
	AlignCenter
	AlignEnd
)

// InputType specifies the type of user input event.
type InputType int

const (
	Tap InputType = iota
	DoubleTap
	LongPress
	Scroll
	KeyDown
	KeyUp
)

// Interaction pairs a gesture type with a handler function.
type Interaction struct {
	Gesture InputType
	Handler func(any)
}

// Interactive is implemented by elements that respond to input events.
type Interactive interface {
	ID() string
	Interactions() []Interaction
}

// InputEvent represents a user input event with its handler.
type InputEvent struct {
	Handler func(any)
	Data    any
}

// ConfigEvent represents a window configuration change (resize, orientation).
// Width and Height are in device-independent pixels (Dp).
type ConfigEvent struct {
	Width  Dp
	Height Dp
}