grindlemire/go-tui code browser

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package tui

import "strings"

// Buffer is a double-buffered 2D grid of cells.
// Writes go to the back buffer; Flush() computes the diff and swaps buffers.
type Buffer struct {
	front  []Cell // Currently displayed state
	back   []Cell // State being built
	width  int
	height int
}

// CellChange represents a single cell that differs between front and back buffers.
type CellChange struct {
	X, Y int
	Cell Cell
	// EraseToEOL, when true, means "clear from (X, Y) to the end of the row"
	// instead of writing Cell. The diff emits this when a row's trailing cells
	// became empty, so terminals leave them blank (and trim them on copy)
	// rather than recording written spaces.
	EraseToEOL bool
}

// NewBuffer creates a new double-buffered grid of the specified dimensions.
// Both buffers are initialized with spaces and default styling.
func NewBuffer(width, height int) *Buffer {
	if width < 0 {
		width = 0
	}
	if height < 0 {
		height = 0
	}

	size := width * height
	front := make([]Cell, size)
	back := make([]Cell, size)

	// Initialize with spaces (default style is zero value)
	defaultCell := NewCell(' ', NewStyle())
	for i := range front {
		front[i] = defaultCell
		back[i] = defaultCell
	}

	return &Buffer{
		front:  front,
		back:   back,
		width:  width,
		height: height,
	}
}

// Width returns the buffer width in columns.
func (b *Buffer) Width() int {
	return b.width
}

// Height returns the buffer height in rows.
func (b *Buffer) Height() int {
	return b.height
}

// Size returns the buffer dimensions (width, height).
func (b *Buffer) Size() (width, height int) {
	return b.width, b.height
}

// Rect returns the buffer bounds as a Rect starting at (0, 0).
func (b *Buffer) Rect() Rect {
	return NewRect(0, 0, b.width, b.height)
}

// idx converts (x, y) coordinates to a flat index.
// Returns -1 if out of bounds.
func (b *Buffer) idx(x, y int) int {
	if x < 0 || x >= b.width || y < 0 || y >= b.height {
		return -1
	}
	return y*b.width + x
}

// Cell returns the cell at position (x, y) from the back buffer.
// Returns an empty Cell if the position is out of bounds.
func (b *Buffer) Cell(x, y int) Cell {
	idx := b.idx(x, y)
	if idx < 0 {
		return Cell{}
	}
	return b.back[idx]
}

// SetCell sets the cell at position (x, y) in the back buffer.
// Does nothing if the position is out of bounds.
func (b *Buffer) SetCell(x, y int, c Cell) {
	idx := b.idx(x, y)
	if idx < 0 {
		return
	}
	b.back[idx] = c
}

// SetRune sets a rune at position (x, y) with the given style.
// Handles wide characters by setting continuation cells.
// Properly clears overlapped wide characters.
func (b *Buffer) SetRune(x, y int, r rune, style Style) {
	b.setCluster(x, y, string(r), RuneWidth(r), style, "")
}

// setCluster writes a grapheme cluster (text with display width 1 or 2) at
// position (x, y) with the given style and optional hyperlink. It applies the
// same overlap/continuation clearing as a single rune and clones text that is a
// slice of a larger source so the cell owns its bytes.
func (b *Buffer) setCluster(x, y int, text string, width int, style Style, link string) {
	if x < 0 || x >= b.width || y < 0 || y >= b.height {
		return
	}

	currentCell := b.Cell(x, y)

	// If target position is a continuation cell, clear the originating wide char
	if currentCell.IsContinuation() {
		b.clearWideCharAt(x, y)
	}

	// If target position is the START of a wide character, clear its continuation
	if currentCell.Width == 2 && x+1 < b.width {
		b.SetCell(x+1, y, NewCell(' ', NewStyle()))
	}

	// If placing a wide char would overlap an existing wide char at x+1, clear it
	if width == 2 && x+1 < b.width {
		next := b.Cell(x+1, y)
		// If next cell is the start of a wide char (width 2), clear it and its continuation
		if next.Width == 2 {
			b.clearWideCharAt(x+1, y)
		}
		// If next cell is a continuation, clear its originating wide char
		if next.IsContinuation() {
			b.clearWideCharAt(x+1, y)
		}
	}

	// Handle edge case: wide char at last column - can't fit, skip it
	if width == 2 && x+1 >= b.width {
		// Place a space instead since the wide char can't fit
		b.SetCell(x, y, NewCell(' ', style))
		return
	}

	// Set the primary cell (cloning multi-rune text it owns).
	b.SetCell(x, y, newClusterCell(text, uint8(width), style, link))

	// Set continuation cell for wide characters
	if width == 2 {
		b.SetCell(x+1, y, NewCellWithWidth(0, style, 0))
	}
}

// SetRuneLink sets a rune like SetRune and, when link is non-empty, attaches it
// as the cell's OSC 8 hyperlink target. Wide-character handling matches SetRune.
func (b *Buffer) SetRuneLink(x, y int, r rune, style Style, link string) {
	b.setCluster(x, y, string(r), RuneWidth(r), style, link)
}

// clearWideCharAt clears a wide character that includes position (x, y).
// If (x, y) is a continuation cell, finds and clears the originating cell.
// If (x, y) is a wide char start, clears it and its continuation.
func (b *Buffer) clearWideCharAt(x, y int) {
	cell := b.Cell(x, y)
	defaultCell := NewCell(' ', NewStyle())

	if cell.IsContinuation() {
		// This is a continuation - the wide char starts at x-1
		if x > 0 {
			b.SetCell(x-1, y, defaultCell)
		}
		b.SetCell(x, y, defaultCell)
	} else if cell.Width == 2 {
		// This is the start of a wide char
		b.SetCell(x, y, defaultCell)
		if x+1 < b.width {
			b.SetCell(x+1, y, defaultCell)
		}
	}
}

// SetString writes a string starting at position (x, y) with the given style.
// Returns the total display width consumed (handles wide characters).
// Stops at buffer edge without wrapping.
func (b *Buffer) SetString(x, y int, s string, style Style) int {
	if y < 0 || y >= b.height {
		return 0
	}

	totalWidth := 0
	curX := x

	for len(s) > 0 {
		cluster, width, size := nextCluster(s)
		if size == 0 {
			break
		}
		s = s[size:]

		if curX >= b.width {
			break
		}
		if curX < 0 {
			// Skip clusters before the visible area
			curX += width
			continue
		}

		// Check if wide cluster fits
		if width == 2 && curX+1 >= b.width {
			// Wide cluster doesn't fit, stop here
			break
		}

		b.setCluster(curX, y, cluster, width, style, "")
		curX += width
		totalWidth += width
	}

	return totalWidth
}

// SetStringClipped writes a string clipped to a rectangle.
// Characters outside clipRect are not rendered.
// Returns the total display width of rendered characters.
func (b *Buffer) SetStringClipped(x, y int, s string, style Style, clipRect Rect) int {
	if y < clipRect.Y || y >= clipRect.Bottom() {
		return 0
	}

	totalWidth := 0
	curX := x

	for len(s) > 0 {
		cluster, width, size := nextCluster(s)
		if size == 0 {
			break
		}
		s = s[size:]

		// Skip if entirely before clip region
		if curX+width <= clipRect.X {
			curX += width
			continue
		}

		// Stop if past clip region
		if curX >= clipRect.Right() {
			break
		}

		// Render if within clip (also check buffer bounds)
		if curX >= clipRect.X && curX < clipRect.Right() {
			// For wide clusters, ensure both cells fit in clip region
			if width == 2 && curX+1 >= clipRect.Right() {
				// Wide cluster doesn't fit, skip it
				curX += width
				continue
			}
			b.setCluster(curX, y, cluster, width, style, "")
			totalWidth += width
		}

		curX += width
	}

	return totalWidth
}

// Fill a rectangle with the given rune and style.
// Handles wide characters appropriately.
func (b *Buffer) Fill(rect Rect, r rune, style Style) {
	// Intersect with buffer bounds
	rect = rect.Intersect(b.Rect())
	if rect.IsEmpty() {
		return
	}

	width := RuneWidth(r)

	for y := rect.Y; y < rect.Bottom(); y++ {
		for x := rect.X; x < rect.Right(); {
			if width == 2 && x+1 >= rect.Right() {
				// Wide char doesn't fit in remaining space, fill with space
				b.SetRune(x, y, ' ', style)
				x++
			} else {
				b.SetRune(x, y, r, style)
				x += width
			}
		}
	}
}

// SetStringGradient writes a string with a gradient applied per grapheme cluster.
// The gradient is applied horizontally along the string; each cluster (CJK, emoji,
// flag, ZWJ family) gets a single color and occupies its full display width.
// Returns the total display width consumed (handles wide characters).
func (b *Buffer) SetStringGradient(x, y int, s string, g Gradient, baseStyle Style) int {
	if y < 0 || y >= b.height || s == "" {
		return 0
	}

	total := clusterCount(s)
	totalWidth := 0
	curX := x
	idx := 0

	for len(s) > 0 {
		cluster, width, size := nextCluster(s)
		if size == 0 {
			break
		}
		s = s[size:]

		if curX >= b.width {
			break
		}
		if curX < 0 {
			// Skip clusters before the visible area.
			curX += width
			idx++
			continue
		}
		// Wide cluster that does not fit at the right edge: stop.
		if width == 2 && curX+1 >= b.width {
			break
		}

		// Gradient position t in [0, 1], one step per cluster.
		t := 0.0
		if total > 1 {
			t = float64(idx) / float64(total-1)
		}
		style := baseStyle
		style.Fg = g.At(t)

		b.setCluster(curX, y, cluster, width, style, "")
		curX += width
		totalWidth += width
		idx++
	}

	return totalWidth
}

// FillGradient fills a rectangle with a gradient background.
// The gradient direction determines how it's applied:
// - Horizontal: left to right
// - Vertical: top to bottom
// - DiagonalDown: top-left to bottom-right
// - DiagonalUp: bottom-left to top-right
func (b *Buffer) FillGradient(rect Rect, r rune, g Gradient, baseStyle Style) {
	// Intersect with buffer bounds
	rect = rect.Intersect(b.Rect())
	if rect.IsEmpty() {
		return
	}

	width := RuneWidth(r)
	rectWidth := float64(rect.Width)
	rectHeight := float64(rect.Height)

	// Avoid division by zero
	if rectWidth <= 0 {
		rectWidth = 1
	}
	if rectHeight <= 0 {
		rectHeight = 1
	}

	for y := rect.Y; y < rect.Bottom(); y++ {
		for x := rect.X; x < rect.Right(); {
			if width == 2 && x+1 >= rect.Right() {
				// Wide char doesn't fit in remaining space, fill with space
				style := baseStyle
				var t float64
				switch g.Direction {
				case GradientHorizontal:
					t = float64(x-rect.X) / rectWidth
				case GradientVertical:
					t = float64(y-rect.Y) / rectHeight
				case GradientDiagonalDown:
					tx := float64(x-rect.X) / rectWidth
					ty := float64(y-rect.Y) / rectHeight
					t = (tx + ty) / 2
				case GradientDiagonalUp:
					tx := float64(x-rect.X) / rectWidth
					ty := float64(rect.Bottom()-1-y-rect.Y) / rectHeight
					t = (tx + ty) / 2
				default:
					t = float64(x-rect.X) / rectWidth
				}
				style.Bg = g.At(t)
				b.SetRune(x, y, ' ', style)
				x++
			} else {
				// Calculate gradient position based on direction
				var t float64
				switch g.Direction {
				case GradientHorizontal:
					t = float64(x-rect.X) / rectWidth
				case GradientVertical:
					t = float64(y-rect.Y) / rectHeight
				case GradientDiagonalDown:
					tx := float64(x-rect.X) / rectWidth
					ty := float64(y-rect.Y) / rectHeight
					t = (tx + ty) / 2
				case GradientDiagonalUp:
					tx := float64(x-rect.X) / rectWidth
					ty := float64(rect.Bottom()-1-y-rect.Y) / rectHeight
					t = (tx + ty) / 2
				default:
					t = float64(x-rect.X) / rectWidth
				}

				// Get gradient color and apply to style
				gradColor := g.At(t)
				style := baseStyle
				style.Bg = gradColor

				b.SetRune(x, y, r, style)
				x += width
			}
		}
	}
}

// ApplyDim applies the dim attribute to every cell in the back buffer.
// Used by modal backdrop to visually fade background content.
func (b *Buffer) ApplyDim() {
	for i := range b.back {
		b.back[i].Style.Attrs |= AttrDim
	}
}

// FillBlank fills the entire back buffer with default-styled spaces.
// Used by modal backdrop="blank" to hide background content entirely.
func (b *Buffer) FillBlank() {
	defaultCell := NewCell(' ', NewStyle())
	for i := range b.back {
		b.back[i] = defaultCell
	}
}

// Clear clears the entire back buffer to spaces with default style.
func (b *Buffer) Clear() {
	b.ClearRect(b.Rect())
}

// ClearRect clears a rectangular region to spaces with default style.
func (b *Buffer) ClearRect(rect Rect) {
	// Intersect with buffer bounds
	rect = rect.Intersect(b.Rect())
	if rect.IsEmpty() {
		return
	}

	defaultCell := NewCell(' ', NewStyle())

	for y := rect.Y; y < rect.Bottom(); y++ {
		for x := rect.X; x < rect.Right(); x++ {
			// First, handle any wide character cleanup at the edges
			cell := b.Cell(x, y)
			if cell.IsContinuation() && x == rect.X {
				// Clearing starts at a continuation - clear the originating char too
				if x > 0 {
					b.SetCell(x-1, y, defaultCell)
				}
			}
			if cell.Width == 2 && x+1 == rect.Right() {
				// Clearing ends at a wide char - also clear the continuation
				if x+1 < b.width {
					b.SetCell(x+1, y, defaultCell)
				}
			}
			b.SetCell(x, y, defaultCell)
		}
	}
}

// Diff returns all cells that changed between front and back buffers.
// Cells are returned in row-major order (top-to-bottom, left-to-right)
// which optimizes terminal output by minimizing cursor moves.
func (b *Buffer) Diff() []CellChange {
	changes := make([]CellChange, 0, b.width) // Pre-allocate one row
	for y := 0; y < b.height; y++ {
		// Rightmost non-empty cell in the new (back) row. Everything past it is
		// empty, so a trailing clear can replace per-cell space writes there.
		lastContent := -1
		for x := b.width - 1; x >= 0; x-- {
			c := b.back[y*b.width+x]
			if !c.IsEmpty() && !c.IsContinuation() {
				lastContent = x
				// A wide character also occupies the next column via its
				// continuation cell. Keep that column inside the content region
				// so the trailing erase can never clip the glyph's second half.
				if c.Width == 2 && x+1 < b.width {
					lastContent = x + 1
				}
				break
			}
		}

		// Emit changed cells up to and including the last content cell.
		for x := 0; x <= lastContent; x++ {
			idx := y*b.width + x
			if !b.back[idx].Equal(b.front[idx]) {
				changes = append(changes, CellChange{X: x, Y: y, Cell: b.back[idx]})
			}
		}

		// The trailing region (lastContent+1 .. width-1) is all empty in the new
		// frame. If any of it changed (the row used to have content there), clear
		// it with one erase-to-end-of-line instead of writing spaces.
		tailStart := lastContent + 1
		tailChanged := false
		for x := tailStart; x < b.width; x++ {
			idx := y*b.width + x
			if !b.back[idx].Equal(b.front[idx]) {
				tailChanged = true
				break
			}
		}
		if tailChanged {
			changes = append(changes, CellChange{X: tailStart, Y: y, EraseToEOL: true})
		}
	}
	return changes
}

// Swap copies the back buffer to the front buffer.
// Call this after flushing changes to the terminal.
func (b *Buffer) Swap() {
	copy(b.front, b.back)
}

// String renders the back buffer to a string for debugging.
// Each row is separated by a newline. Continuation cells (from wide characters) are skipped.
func (b *Buffer) String() string {
	var sb strings.Builder
	for y := 0; y < b.height; y++ {
		for x := 0; x < b.width; x++ {
			cell := b.back[y*b.width+x]
			if cell.IsContinuation() {
				continue // Skip continuation cells
			}
			if cell.Text == "" {
				sb.WriteRune(' ')
			} else {
				sb.WriteString(cell.Text)
			}
		}
		if y < b.height-1 {
			sb.WriteRune('\n')
		}
	}
	return sb.String()
}

// StringTrimmed returns the back buffer content with trailing spaces removed from each line.
func (b *Buffer) StringTrimmed() string {
	var sb strings.Builder
	for y := 0; y < b.height; y++ {
		var line strings.Builder
		for x := 0; x < b.width; x++ {
			cell := b.back[y*b.width+x]
			if cell.IsContinuation() {
				continue
			}
			if cell.Text == "" {
				line.WriteRune(' ')
			} else {
				line.WriteString(cell.Text)
			}
		}
		sb.WriteString(strings.TrimRight(line.String(), " "))
		if y < b.height-1 {
			sb.WriteRune('\n')
		}
	}
	return sb.String()
}

// Resize changes the buffer dimensions, preserving content where possible.
// Content in the overlapping region is preserved; new areas are cleared.
func (b *Buffer) Resize(width, height int) {
	if width < 0 {
		width = 0
	}
	if height < 0 {
		height = 0
	}

	if width == b.width && height == b.height {
		return
	}

	newSize := width * height
	newFront := make([]Cell, newSize)
	newBack := make([]Cell, newSize)

	// Initialize with spaces
	defaultCell := NewCell(' ', NewStyle())
	for i := range newFront {
		newFront[i] = defaultCell
		newBack[i] = defaultCell
	}

	// Copy overlapping content
	copyWidth := min(width, b.width)
	copyHeight := min(height, b.height)

	for y := range copyHeight {
		for x := range copyWidth {
			oldIdx := y*b.width + x
			newIdx := y*width + x
			newFront[newIdx] = b.front[oldIdx]
			newBack[newIdx] = b.back[oldIdx]
		}
	}

	b.front = newFront
	b.back = newBack
	b.width = width
	b.height = height
}