grindlemire/go-tui code browser

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package tui

import (
	"strings"

	"github.com/grindlemire/go-tui/internal/debug"
)

// inheritedStyle carries cascading visual properties down the element tree.
// Text style (Fg, Attrs) and background color cascade from parent to child.
// Each field is only used when the child does not explicitly set its own value.
type inheritedStyle struct {
	textStyle Style
	bg        *Style // nil = no inherited background
}

// effectiveStyles returns the resolved text style and background for an element,
// taking inheritance into account. If the element explicitly set its textStyle,
// that is used; otherwise the inherited textStyle is used. Similarly for background.
//
// Automatic contrast: If the background is light and no explicit foreground color
// is set, the foreground is automatically set to black for readability.
func effectiveStyles(e *Element, inherited inheritedStyle) (textStyle Style, bg *Style) {
	if e.textStyleSet {
		textStyle = e.textStyle
	} else {
		textStyle = inherited.textStyle
	}

	if e.background != nil {
		bg = e.background
	} else {
		bg = inherited.bg
	}

	// Auto-contrast: if background is light and foreground is default, use black text
	if bg != nil && !bg.Bg.IsDefault() && textStyle.Fg.IsDefault() && bg.Bg.IsLight() {
		textStyle.Fg = Black
	}

	return textStyle, bg
}

// renderContext holds resolved state for rendering an element.
type renderContext struct {
	textStyle      Style
	bg             *Style
	childInherited inheritedStyle
}

// resolveRenderContext resolves effective styles and builds child inherited style.
// Handles style inheritance and <th> bold default.
func resolveRenderContext(e *Element, inherited inheritedStyle) renderContext {
	textStyle, bg := effectiveStyles(e, inherited)
	if e.tag == "th" && !e.textStyleSet {
		textStyle = textStyle.Bold()
	}
	return renderContext{
		textStyle: textStyle,
		bg:        bg,
		childInherited: inheritedStyle{
			textStyle: textStyle,
			bg:        bg,
		},
	}
}

// RenderTree traverses the Element tree and renders to the buffer.
// This renders the element and all its descendants.
func RenderTree(buf *Buffer, root *Element) {
	renderElement(buf, root, inheritedStyle{})
}

// renderElement renders a single element and recurses to its children.
func renderElement(buf *Buffer, e *Element, inherited inheritedStyle) {
	if e.hidden {
		return
	}

	// Call pre-render hook for custom update logic (polling, animations, etc.)
	if e.onUpdate != nil {
		e.onUpdate()
	}

	rect := e.Rect()

	// Skip if outside buffer bounds
	bufRect := buf.Rect()
	if !rect.Intersects(bufRect) {
		return
	}

	// Use custom render hook if set (used by wrappers)
	if e.onRender != nil {
		e.onRender(e, buf)
		return
	}

	// Resolve effective styles (inheritance + <th> bold)
	rc := resolveRenderContext(e, inherited)

	// Handle HR specially - draws a horizontal line and returns (no children)
	if e.hr {
		renderHR(buf, e, rc.textStyle)
		return
	}

	// 1. Fill background
	if e.bgGradient != nil {
		bgStyle := NewStyle()
		if rc.bg != nil {
			bgStyle = *rc.bg
		}
		buf.FillGradient(rect, ' ', *e.bgGradient, bgStyle)
	} else if rc.bg != nil {
		buf.Fill(rect, ' ', *rc.bg)
	}

	// Debug: highlight containers whose children overflow
	if debug.OverflowHighlight() && !e.IsScrollable() && len(e.children) > 0 {
		contentRect := e.ContentRect()
		for _, child := range e.children {
			if !contentRect.ContainsRect(child.Rect()) {
				debugBg := NewStyle().Background(BrightRed)
				buf.Fill(rect, ' ', debugBg)
				break
			}
		}
	}

	if e.border != BorderNone {
		if e.borderGradient != nil {
			DrawBoxGradient(buf, rect, e.border, *e.borderGradient, e.activeBorderStyle())
		} else {
			DrawBox(buf, rect, e.border, e.activeBorderStyle())
		}
		if e.borderTitle != "" {
			drawBoxTitle(buf, rect, e.borderTitle, e.titleStyle(), e.borderTitleAlign)
		}
	}

	// 3. Draw text content if present
	if e.text != "" || len(e.richText) > 0 {
		renderTextContent(buf, e, rc.textStyle, rc.bg)
	}

	// 4. Render children (with scroll handling if scrollable, or clipping if overflow-hidden)
	if e.IsScrollable() {
		renderScrollableChildren(buf, e, rc.childInherited)
	} else if e.overflow == OverflowHidden {
		clipRect := e.ContentRect()
		for _, child := range e.children {
			if child.overlay {
				continue
			}
			renderClippedElement(buf, child, clipRect, 0, 0, clipRect.X, clipRect.Y, rc.childInherited)
		}
	} else {
		for _, child := range e.children {
			if child.overlay {
				continue
			}
			renderElement(buf, child, rc.childInherited)
		}
	}

	// Capture the cursor at its draw site (after children, so a scrollable's
	// scrollbar state is settled). The content origin is absolute here; a
	// scrollable also clips its own cursor to its viewport (gutter-aware).
	if e.cursorSource != nil {
		cr := e.ContentRect()
		clip := buf.Rect()
		if e.IsScrollable() {
			viewport := cr
			if e.needsVerticalScrollbar() {
				viewport.Width = max(0, viewport.Width-1)
			}
			clip = clip.Intersect(viewport)
		}
		e.captureCursor(cr.X, cr.Y, clip)
	}
}

// renderScrollableChildren renders children with scroll offset and clipping.
func renderScrollableChildren(buf *Buffer, e *Element, childInherited inheritedStyle) {
	// First, do scroll-aware layout
	e.layoutScrollContent()

	// Get viewport (clip region)
	clipRect := e.ContentRect()

	// Reserve space for vertical scrollbar if needed
	if e.needsVerticalScrollbar() {
		clipRect.Width = max(0, clipRect.Width-1)
	}

	// Render each child with scroll offset and clipping
	for _, child := range e.children {
		renderClippedElement(buf, child, clipRect, e.scrollX, e.scrollY, clipRect.X, clipRect.Y, childInherited)
	}

	// Draw scrollbar (scrollbar styles are independent, not inherited)
	if e.needsVerticalScrollbar() {
		renderVerticalScrollbar(buf, e)
	}
}

// renderClippedElement renders an element with scroll offset and clipping.
func renderClippedElement(buf *Buffer, e *Element, clipRect Rect, scrollX, scrollY, viewportX, viewportY int, inherited inheritedStyle) {
	if e.hidden {
		return
	}

	childRect := e.Rect()

	// Translate from content space to screen space
	// Children are laid out starting from (0,0) in content space
	// We add viewport origin and subtract scroll offset
	screenX := viewportX + childRect.X - scrollX
	screenY := viewportY + childRect.Y - scrollY

	screenRect := Rect{
		X:      screenX,
		Y:      screenY,
		Width:  childRect.Width,
		Height: childRect.Height,
	}

	// Check if visible within clip region
	visibleRect := screenRect.Intersect(clipRect)
	if visibleRect.IsEmpty() {
		return
	}

	// Capture the cursor at its draw site, using the same content origin and the
	// active clip (already gutter-shrunk by the enclosing scrollable) the renderer
	// uses for this element's text.
	if e.cursorSource != nil {
		ox := screenX + e.style.Padding.Left
		oy := screenY + e.style.Padding.Top
		if e.border != BorderNone {
			ox++
			oy++
		}
		e.captureCursor(ox, oy, clipRect)
	}

	// Resolve effective styles (inheritance + <th> bold)
	rc := resolveRenderContext(e, inherited)

	// Handle HR specially - draws a horizontal line and returns (no children)
	if e.hr {
		char := hrCharacter(e.border)
		for x := visibleRect.X; x < visibleRect.Right(); x++ {
			buf.SetRune(x, screenY, char, rc.textStyle)
		}
		return
	}

	// Render background (only visible portion)
	if e.bgGradient != nil {
		bgStyle := NewStyle()
		if rc.bg != nil {
			bgStyle = *rc.bg
		}
		buf.FillGradient(visibleRect, ' ', *e.bgGradient, bgStyle)
	} else if rc.bg != nil {
		buf.Fill(visibleRect, ' ', *rc.bg)
	}

	// Render border clipped to viewport (border style does NOT inherit)
	if e.border != BorderNone {
		if e.borderGradient != nil {
			DrawBoxGradientClipped(buf, screenRect, e.border, *e.borderGradient, e.activeBorderStyle(), clipRect)
		} else {
			DrawBoxClipped(buf, screenRect, e.border, e.activeBorderStyle(), clipRect)
		}
		if e.borderTitle != "" {
			drawBoxTitleClipped(buf, screenRect, e.borderTitle, e.titleStyle(), clipRect, e.borderTitleAlign)
		}
	}

	// Render rich text with clipping (parallel to the plain-text block below).
	// An element has either plain text or rich text, never both.
	if len(e.richText) > 0 {
		textBaseX := screenX + e.style.Padding.Left
		textBaseY := screenY + e.style.Padding.Top
		if e.border != BorderNone {
			textBaseX += 1
			textBaseY += 1
		}
		availTextWidth := childRect.Width - e.style.Padding.Horizontal()
		if e.border != BorderNone {
			availTextWidth -= 2
		}

		ts := rc.textStyle
		if rc.bg != nil && !rc.bg.Bg.IsDefault() {
			ts.Bg = rc.bg.Bg
		}

		var spanLines [][]TextSpan
		if !e.noWrap && availTextWidth > 0 {
			spanLines = wrapSpans(e.richText, availTextWidth)
		} else {
			spanLines = [][]TextSpan{e.richText}
		}
		drawSpanLines(buf, spanLines, textBaseX, textBaseY, availTextWidth, e.textAlign, ts, clipRect)
	}

	// Render text with clipping
	if e.text != "" {
		textBaseX := screenX + e.style.Padding.Left
		textBaseY := screenY + e.style.Padding.Top
		if e.border != BorderNone {
			textBaseX += 1
			textBaseY += 1
		}

		availTextWidth := childRect.Width - e.style.Padding.Horizontal()
		if e.border != BorderNone {
			availTextWidth -= 2
		}

		var lines []string
		if !e.noWrap && availTextWidth > 0 {
			lines = wrapText(e.text, availTextWidth)
		} else {
			lines = []string{e.text}
		}

		if e.truncate {
			if e.noWrap {
				lines[0] = truncateText(lines[0], availTextWidth)
			} else {
				availTextHeight := childRect.Height - e.style.Padding.Vertical()
				if e.border != BorderNone {
					availTextHeight -= 2
				}
				if len(lines) > availTextHeight && availTextHeight > 0 {
					lines = lines[:availTextHeight]
					lines[availTextHeight-1] = truncateText(lines[availTextHeight-1], availTextWidth)
				}
			}
		}

		ts := rc.textStyle
		if rc.bg != nil && !rc.bg.Bg.IsDefault() {
			ts.Bg = rc.bg.Bg
		}
		needPerCell := e.textGradient != nil || ts.Bg.IsDefault()

		for lineIdx, line := range lines {
			textY := textBaseY + lineIdx
			if textY < clipRect.Y || textY >= clipRect.Bottom() {
				continue
			}

			lineWidth := stringWidth(line)
			textX := textBaseX

			if availTextWidth > lineWidth {
				switch e.textAlign {
				case TextAlignCenter:
					textX += (availTextWidth - lineWidth) / 2
				case TextAlignRight:
					textX += availTextWidth - lineWidth
				}
			}

			if needPerCell {
				totalClusters := clusterCount(line)
				if totalClusters > 0 {
					curX := textX
					rest := line
					clusterIdx := 0
					for len(rest) > 0 {
						cluster, width, size := nextCluster(rest)
						if size == 0 {
							break
						}
						rest = rest[size:]
						idx := clusterIdx
						clusterIdx++
						if curX >= clipRect.Right() {
							break
						}
						if curX < clipRect.X {
							curX += width
							continue
						}
						if width == 2 && curX+1 >= clipRect.Right() {
							break
						}
						if curX >= clipRect.X && curX < clipRect.Right() {
							style := ts
							if ts.Bg.IsDefault() {
								cellBg := buf.Cell(curX, textY).Style.Bg
								if !cellBg.IsDefault() {
									style.Bg = cellBg
								}
							}
							if e.textGradient != nil {
								t := float64(idx) / float64(totalClusters-1)
								if totalClusters == 1 {
									t = 0
								}
								style.Fg = e.textGradient.At(t)
							}
							buf.setCluster(curX, textY, cluster, width, style, "")
						}
						curX += width
					}
				}
			} else {
				buf.SetStringClipped(textX, textY, line, ts, clipRect)
			}
		}
	}

	// Recurse to children
	// Propagate the original viewport and scroll offsets rather than re-basing
	// to the parent's screen position. Child Rect() values are absolute in the
	// temp container's coordinate space (from layoutScrollContent), so the same
	// viewport+scroll translation applies at every depth.
	for _, child := range e.children {
		renderClippedElement(buf, child, clipRect, scrollX, scrollY, viewportX, viewportY, rc.childInherited)
	}
}

// renderVerticalScrollbar draws the vertical scrollbar for a scrollable element.
func renderVerticalScrollbar(buf *Buffer, e *Element) {
	viewportRect := e.ContentRect()

	// Scrollbar position: right edge of content area
	trackX := viewportRect.Right() - 1
	trackTop := viewportRect.Y
	trackHeight := viewportRect.Height

	if trackHeight <= 0 {
		return
	}

	viewportHeight := viewportRect.Height
	contentHeight := e.contentHeight

	if contentHeight <= viewportHeight {
		return
	}

	// Thumb size proportional to viewport/content ratio
	thumbHeight := max(1, trackHeight*viewportHeight/contentHeight)

	// Thumb position based on scroll offset
	maxScroll := contentHeight - viewportHeight
	if maxScroll <= 0 {
		return
	}
	thumbTop := e.scrollY * (trackHeight - thumbHeight) / maxScroll

	// Draw track and thumb
	for y := range trackHeight {
		screenY := trackTop + y
		if y >= thumbTop && y < thumbTop+thumbHeight {
			buf.SetRune(trackX, screenY, '█', e.scrollbarThumbStyle)
		} else {
			buf.SetRune(trackX, screenY, '│', e.scrollbarStyle)
		}
	}
}

// truncateText truncates a string to fit within maxWidth terminal cells,
// replacing the overflow with an ellipsis character (…).
func truncateText(text string, maxWidth int) string {
	if maxWidth <= 0 {
		return ""
	}
	textWidth := stringWidth(text)
	if textWidth <= maxWidth {
		return text
	}
	// Need to truncate: fit as many clusters as possible + ellipsis (1 cell wide)
	curWidth := 0
	var truncated strings.Builder
	truncated.Grow(len(text))
	rest := text
	for len(rest) > 0 {
		cluster, w, size := nextCluster(rest)
		if size == 0 {
			break
		}
		if curWidth+w+1 > maxWidth { // +1 for ellipsis
			return truncated.String() + "…"
		}
		truncated.WriteString(cluster)
		curWidth += w
		rest = rest[size:]
	}
	return text
}

// renderTextContent draws the text content within the element's content rect.
//
// Text is wrapped to fit within the content rect width when wrapping is enabled
// (the default). Each wrapped line is aligned independently according to textAlign.
//
// When the element width equals text width (intrinsic sizing), the text is drawn
// at the content rect origin - the parent's AlignItems handles centering.
//
// When the element width is larger than text width (explicit sizing), text-level
// alignment is applied. This supports use cases like centered text in a fixed-width
// button, while avoiding jitter for intrinsic-width text in a centered layout.
func renderTextContent(buf *Buffer, e *Element, textStyle Style, bg *Style) {
	contentRect := e.ContentRect()

	// Skip if content rect is empty or outside buffer
	if contentRect.IsEmpty() {
		return
	}

	// Rich text takes its own path (parallel to the plain-text logic below).
	// Note: e.truncate and per-element vertical auto-scroll are not yet applied
	// to rich text (unlike the plain-text path); rich text relies on a
	// container's clipping/scrolling instead.
	if len(e.richText) > 0 {
		ts := textStyle
		if bg != nil && !bg.Bg.IsDefault() {
			ts.Bg = bg.Bg
		}
		var spanLines [][]TextSpan
		if !e.noWrap && contentRect.Width > 0 {
			spanLines = wrapSpans(e.richText, contentRect.Width)
		} else {
			spanLines = [][]TextSpan{e.richText}
		}
		drawSpanLines(buf, spanLines, contentRect.X, contentRect.Y, contentRect.Width, e.textAlign, ts, contentRect)
		return
	}

	// Compute wrapped lines
	var lines []string
	if !e.noWrap && contentRect.Width > 0 {
		lines = wrapText(e.text, contentRect.Width)
	} else {
		lines = []string{e.text}
	}

	// Apply truncation
	if e.truncate {
		if e.noWrap {
			// Single-line truncation (existing behavior)
			lines[0] = truncateText(lines[0], contentRect.Width)
		} else if len(lines) > contentRect.Height && contentRect.Height > 0 {
			// Truncate at last visible line
			lines = lines[:contentRect.Height]
			lines[contentRect.Height-1] = truncateText(lines[contentRect.Height-1], contentRect.Width)
		}
	}

	ts := textStyle
	// Merge background color into text style so text preserves the background
	if bg != nil && !bg.Bg.IsDefault() {
		ts.Bg = bg.Bg
	}

	// Determine visible line count
	maxLines := len(lines)
	if contentRect.Height > 0 && maxLines > contentRect.Height {
		maxLines = contentRect.Height
	}

	// Auto-scroll: if wrapped content overflows, use scrollY as line offset
	startLine := 0
	if len(lines) > contentRect.Height && contentRect.Height > 0 {
		e.contentHeight = len(lines) // store for scroll bounds
		startLine = max(min(e.scrollY, len(lines)-contentRect.Height), 0)
		maxLines = contentRect.Height
	}

	// Total cluster count across visible lines (for gradient calculation).
	// One gradient color is applied per cluster.
	totalClusters := 0
	if e.textGradient != nil {
		for i := startLine; i < startLine+maxLines && i < len(lines); i++ {
			totalClusters += clusterCount(lines[i])
		}
	}

	needPerCell := e.textGradient != nil || ts.Bg.IsDefault()
	clusterOffset := 0 // running offset for gradient

	for lineIdx := 0; lineIdx < maxLines; lineIdx++ {
		srcIdx := startLine + lineIdx
		if srcIdx >= len(lines) {
			break
		}
		line := lines[srcIdx]
		lineWidth := stringWidth(line)
		x := contentRect.X
		y := contentRect.Y + lineIdx

		if y >= contentRect.Bottom() {
			break
		}

		// Per-line text alignment
		if contentRect.Width > lineWidth {
			switch e.textAlign {
			case TextAlignCenter:
				x += (contentRect.Width - lineWidth) / 2
			case TextAlignRight:
				x += contentRect.Width - lineWidth
			}
		}

		if needPerCell {
			curX := x
			rest := line
			for len(rest) > 0 {
				cluster, width, size := nextCluster(rest)
				if size == 0 {
					break
				}
				rest = rest[size:]
				if curX >= contentRect.Right() {
					break
				}
				if width == 2 && curX+1 >= contentRect.Right() {
					break
				}
				style := ts
				if ts.Bg.IsDefault() {
					cellBg := buf.Cell(curX, y).Style.Bg
					if !cellBg.IsDefault() {
						style.Bg = cellBg
					}
				}
				if e.textGradient != nil {
					t := 0.0
					if totalClusters > 1 {
						t = float64(clusterOffset) / float64(totalClusters-1)
					}
					style.Fg = e.textGradient.At(t)
					clusterOffset++
				}
				buf.setCluster(curX, y, cluster, width, style, "")
				curX += width
			}
		} else {
			buf.SetStringClipped(x, y, line, ts, contentRect)
		}
	}
}

// drawSpanLines renders pre-wrapped rich-text lines into the buffer.
// originX/originY is the top-left content cell, contentWidth is the line box used
// for alignment, base is the element's resolved text style (with background
// already merged), and clip bounds the drawable region. Cells outside clip are
// skipped but still advance x (so horizontal scroll offsets line up).
func drawSpanLines(buf *Buffer, lines [][]TextSpan, originX, originY, contentWidth int, align TextAlign, base Style, clip Rect) {
nextLine:
	for li, line := range lines {
		y := originY + li
		if y < clip.Y || y >= clip.Bottom() {
			continue
		}
		x := originX
		if lw := spanLineWidth(line); contentWidth > lw {
			switch align {
			case TextAlignCenter:
				x += (contentWidth - lw) / 2
			case TextAlignRight:
				x += contentWidth - lw
			}
		}
		// Flatten the line's spans into a styled-rune stream, then segment into
		// clusters so a cluster whose base and combining mark fall in adjacent
		// spans stays one cell. Each cluster takes its base rune's style/link.
		clusters := segmentLineClusters(line, base)
		for _, cl := range clusters {
			// Reached the right clip edge: clip this line and move to the next
			// (matching the plain-text paths' per-line break), rather than
			// abandoning all remaining lines.
			if x >= clip.Right() {
				continue nextLine
			}
			if cl.width == 2 && x+1 >= clip.Right() {
				continue nextLine
			}
			if x >= clip.X {
				style := cl.st
				if style.Bg.IsDefault() {
					if cellBg := buf.Cell(x, y).Style.Bg; !cellBg.IsDefault() {
						style.Bg = cellBg
					}
				}
				buf.setCluster(x, y, cl.text, cl.width, style, cl.link)
			}
			x += cl.width
		}
	}
}

// Render calculates layout (if needed) and renders the entire tree to the buffer.
// This is the main entry point for rendering an Element tree.
// Note: onUpdate hooks are called in renderElement for each element in the tree.
func (e *Element) Render(buf *Buffer, width, height int) {
	if e.dirty {
		Calculate(e, width, height)
	}
	RenderTree(buf, e)
}

// hrCharacter returns the horizontal rule character based on border style.
func hrCharacter(border BorderStyle) rune {
	switch border {
	case BorderDouble:
		return '═' // U+2550
	case BorderThick:
		return '━' // U+2501
	default:
		return '─' // U+2500
	}
}

// renderHR draws a horizontal rule across the element's width.
func renderHR(buf *Buffer, e *Element, textStyle Style) {
	rect := e.ContentRect()
	char := hrCharacter(e.border)

	for x := rect.X; x < rect.Right(); x++ {
		buf.SetRune(x, rect.Y, char, textStyle)
	}
}