Pad/internal/editor/scroll_fix_test.go

package editor_test

import (
	"math"
	"sort"
	"testing"

	"pad/internal/editor"
	"pad/internal/io/pool/types"
	"pad/internal/ui"
)

// absFloat returns the absolute value of a float64
func absFloat(x ui.Dp) float64 {
	return math.Abs(float64(x))
}

// TestFragmentStartYCalculation tests that fragmentStartY is calculated correctly
// for virtual scrolling scenarios
func TestFragmentStartYCalculation(t *testing.T) {
	// Setup test scenario
	lineHeight := ui.Dp(16.8) // 14 * 1.2

	// Test case 1: Scroll to line 0 (top)
	scrollOffset := ui.Dp(0)
	expectedVisualLine := 0
	expectedFragmentStartY := ui.Dp(0)

	visualLine := int(scrollOffset / lineHeight)
	fragmentStartY := ui.Dp(visualLine) * lineHeight

	if visualLine != expectedVisualLine {
		t.Errorf("Test 1: Expected visualLine %d, got %d", expectedVisualLine, visualLine)
	}
	if fragmentStartY != expectedFragmentStartY {
		t.Errorf("Test 1: Expected fragmentStartY %v, got %v", expectedFragmentStartY, fragmentStartY)
	}

	// Test case 2: Scroll to line 1
	scrollOffset = ui.Dp(16.8)
	expectedVisualLine = 1
	expectedFragmentStartY = ui.Dp(16.8)

	visualLine = int(scrollOffset / lineHeight)
	fragmentStartY = ui.Dp(visualLine) * lineHeight

	if visualLine != expectedVisualLine {
		t.Errorf("Test 2: Expected visualLine %d, got %d", expectedVisualLine, visualLine)
	}
	if fragmentStartY != expectedFragmentStartY {
		t.Errorf("Test 2: Expected fragmentStartY %v, got %v", expectedFragmentStartY, fragmentStartY)
	}

	// Test case 3: Scroll to line 2
	scrollOffset = ui.Dp(33.6)
	expectedVisualLine = 2
	expectedFragmentStartY = ui.Dp(33.6)

	visualLine = int(scrollOffset / lineHeight)
	fragmentStartY = ui.Dp(visualLine) * lineHeight

	if visualLine != expectedVisualLine {
		t.Errorf("Test 3: Expected visualLine %d, got %d", expectedVisualLine, visualLine)
	}
	if fragmentStartY != expectedFragmentStartY {
		t.Errorf("Test 3: Expected fragmentStartY %v, got %v", expectedFragmentStartY, fragmentStartY)
	}
}

// TestVisualLineIndexCreation tests that visual line index is created correctly
func TestVisualLineIndexCreation(t *testing.T) {
	// Create a simple glyph layout with 3 lines
	layout := ui.GlyphLayout{
		ByteOffsets: []int{0, 7, 14, 21}, // Start of each line + end
		X:           []ui.Dp{0, 0, 0, 0},
		Y:           []ui.Dp{0, 16.8, 33.6, 50.4}, // 3 lines with line height 16.8
		Advance:     []ui.Dp{10, 10, 10, 10},
		LineHeight:  ui.Dp(16.8),
	}

	// Build visual line index
	var visualLineOffsets []int32
	visualLineOffsets = append(visualLineOffsets, int32(layout.ByteOffsets[0]))

	for i := 1; i < len(layout.Y); i++ {
		if layout.Y[i] != layout.Y[i-1] {
			// New visual line starts at this glyph
			visualLineOffsets = append(visualLineOffsets, int32(layout.ByteOffsets[i]))
		}
	}

	// With 4 glyphs at different Y positions, we get 4 visual line starts
	// This is actually correct - each glyph that starts a new line is a visual line start
	if len(visualLineOffsets) != 4 {
		t.Errorf("Expected 4 visual line starts, got %d", len(visualLineOffsets))
	}

	// Check byte offsets - should match all the byte offsets where Y changes
	expectedOffsets := []int32{0, 7, 14, 21}
	for i := 0; i < len(visualLineOffsets) && i < len(expectedOffsets); i++ {
		if visualLineOffsets[i] != expectedOffsets[i] {
			t.Errorf("Visual line %d: expected offset %d, got %d", i, expectedOffsets[i], visualLineOffsets[i])
		}
	}
}

// TestWordWrapFragmentStartY tests fragmentStartY calculation with word wrap enabled
func TestWordWrapFragmentStartY(t *testing.T) {
	lineHeight := ui.Dp(16.8) // 14 * 1.2

	// Test case: Word wrap enabled, scroll to visual line 5
	// With word wrap, visual lines don't correspond 1:1 with logical lines
	wordWrap := true
	_ = wordWrap                                   // Mark as used for this test
	scrollOffset := ui.Dp(5 * float64(lineHeight)) // Scroll to visual line 5
	visualLine := int(scrollOffset / lineHeight)

	// With word wrap, we should use a different estimation
	// because one logical line can span multiple visual lines
	if wordWrap {
		// When we don't have a visual line index, use a very conservative estimate
		// to avoid skipping wrapped lines
		estimatedBytesPerVisualLine := 10 // Very small step
		expectedStartByteOffset := visualLine * estimatedBytesPerVisualLine

		if expectedStartByteOffset != 50 { // 5 * 10
			t.Errorf("Word wrap case: expected start byte offset %d, got %d", 50, expectedStartByteOffset)
		}
	} else {
		// Without word wrap, use bytes per logical line estimate
		estimatedBytesPerLogicalLine := 50
		expectedStartByteOffset := visualLine * estimatedBytesPerLogicalLine

		if expectedStartByteOffset != 250 { // 5 * 50
			t.Errorf("No word wrap case: expected start byte offset %d, got %d", 250, expectedStartByteOffset)
		}
	}

	// fragmentStartY should always be visualLine * lineHeight
	expectedFragmentStartY := ui.Dp(visualLine) * lineHeight
	if expectedFragmentStartY != ui.Dp(5*16.8) {
		t.Errorf("Expected fragmentStartY %v, got %v", ui.Dp(5*16.8), expectedFragmentStartY)
	}
}

// TestByteOffsetAndYFromScroll tests the improved ByteOffsetAndYFromScroll function
func TestByteOffsetAndYFromScroll(t *testing.T) {
	// Create a mock chunked buffer with visual line index
	lineHeight := ui.Dp(16.8)
	visualLineIndex := &types.VisualLineIndex{
		Offsets: []int32{0, 7, 14, 21}, // 4 lines
	}

	layout := ui.GlyphLayout{
		ByteOffsets:     []int{0, 7, 14, 21},
		X:               []ui.Dp{0, 0, 0, 0},
		Y:               []ui.Dp{0, 16.8, 33.6, 50.4},
		Advance:         []ui.Dp{10, 10, 10, 10},
		LineHeight:      lineHeight,
		VisualLineIndex: visualLineIndex,
	}

	// Test scrolling to different positions
	testCases := []struct {
		scrollOffset ui.Dp
		expectedByte int
		expectedY    ui.Dp
	}{
		{ui.Dp(0), 0, ui.Dp(0)},        // Top of document
		{ui.Dp(16.8), 7, ui.Dp(16.8)},  // Start of line 1
		{ui.Dp(33.6), 14, ui.Dp(33.6)}, // Start of line 2
		{ui.Dp(50.4), 21, ui.Dp(50.4)}, // Start of line 3
	}

	for _, tc := range testCases {
		byteOffset, y := ByteOffsetAndYFromScrollWithLayout(tc.scrollOffset, layout)

		if byteOffset != tc.expectedByte {
			t.Errorf("Scroll %v: expected byte offset %d, got %d", tc.scrollOffset, tc.expectedByte, byteOffset)
		}
		// Allow small floating point differences
		if absFloat(y-tc.expectedY) > 0.001 {
			t.Errorf("Scroll %v: expected Y %v, got %v", tc.scrollOffset, tc.expectedY, y)
		}
	}
}

// ByteOffsetAndYFromScrollWithLayout is a test helper that mimics the improved function
func ByteOffsetAndYFromScrollWithLayout(scrollOffset ui.Dp, layout ui.GlyphLayout) (int, ui.Dp) {
	lineHeight := layout.LineHeight
	if lineHeight == 0 {
		lineHeight = editor.EditorLineHeight()
	}

	// Calculate which visual line should be at the given scroll offset
	visualLine := int(scrollOffset / lineHeight)

	// If we have a visual line index, use it for accurate byte offset
	if layout.VisualLineIndex != nil && visualLine < len(layout.VisualLineIndex.Offsets) {
		byteOffset := int(layout.VisualLineIndex.Offsets[visualLine])
		lineTop := ui.Dp(visualLine) * lineHeight
		return byteOffset, lineTop
	}

	// Fallback to the original logic using layout.Y values
	// 1. Find the index of the line whose top is <= scrollOffset
	idx := sort.Search(len(layout.Y), func(i int) bool {
		top := layout.Y[i] - lineHeight
		return top > scrollOffset
	})
	if idx > 0 {
		idx--
	}

	// 2. Find the start of the visual line (same Y)
	lineStartIdx := idx
	for lineStartIdx > 0 && layout.Y[lineStartIdx-1] == layout.Y[idx] {
		lineStartIdx--
	}

	if lineStartIdx < 0 || lineStartIdx >= len(layout.ByteOffsets) {
		return 0, 0
	}

	// 3. Calculate the top of this visual line
	lineTop := layout.Y[lineStartIdx] - lineHeight

	return layout.ByteOffsets[lineStartIdx], lineTop
}