Pad/internal/editor/wrap_index_test.go

package editor

import (
	"math/rand"
	"testing"
)

// TestWrapIndex_NaiveModel is a property test: a random sequence of
// Set / InsertLines / DeleteLines operations on a WrapIndex must keep the
// Fenwick structure exactly consistent with a naive []int32 model.
func TestWrapIndex_NaiveModel(t *testing.T) {
	rng := rand.New(rand.NewSource(7))

	w := NewWrapIndex(50)
	model := make([]int32, 50)
	for i := range model {
		model[i] = 1
	}

	naivePrefix := func(m []int32, k int) int32 {
		var s int32
		for i := 0; i < k && i < len(m); i++ {
			s += m[i]
		}
		return s
	}
	naiveLineForVisual := func(m []int32, v int32) int {
		if len(m) == 0 {
			return 0
		}
		if v <= 0 {
			return 0
		}
		var s int32
		for i, c := range m {
			s += c
			if s > v {
				return i
			}
		}
		return len(m) - 1
	}

	ops := 0
	for i := 0; i < 3000; i++ {
		switch rng.Intn(4) {
		case 0: // Set
			if len(model) == 0 {
				continue
			}
			li := rng.Intn(len(model))
			c := int32(1 + rng.Intn(8))
			w.Set(li, c)
			model[li] = c
		case 1: // InsertLines
			pos := rng.Intn(len(model) + 1)
			n := 1 + rng.Intn(5)
			w.InsertLines(pos, n)
			inserted := make([]int32, n)
			for j := range inserted {
				inserted[j] = 1
			}
			model = append(model[:pos], append(inserted, model[pos:]...)...)
		case 2: // DeleteLines
			if len(model) == 0 {
				continue
			}
			pos := rng.Intn(len(model))
			n := 1 + rng.Intn(min(5, len(model)-pos))
			w.DeleteLines(pos, n)
			model = append(model[:pos], model[pos+n:]...)
		case 3: // SetRange (the shaped-window correction shape)
			if len(model) == 0 {
				continue
			}
			pos := rng.Intn(len(model))
			n := 1 + rng.Intn(min(10, len(model)-pos))
			counts := make([]int32, n)
			for j := range counts {
				counts[j] = int32(1 + rng.Intn(6))
				model[pos+j] = counts[j]
			}
			w.SetRange(pos, counts)
		}
		ops++

		// Full consistency check after every op.
		if w.Len() != len(model) {
			t.Fatalf("op %d (%d): Len = %d, model %d", i, ops, w.Len(), len(model))
		}
		for i := 0; i < w.Len(); i++ {
			if w.Get(i) != model[i] {
				t.Fatalf("op %d: Get(%d) = %d, model %d", i, i, w.Get(i), model[i])
			}
		}
		// Prefix sums (V(k)) for a sample of k values plus the ends.
		for _, k := range []int{0, 1, len(model) / 2, len(model) - 1, len(model), len(model) + 5} {
			if got, want := w.VisualsBefore(k), naivePrefix(model, k); got != want {
				t.Fatalf("op %d: VisualsBefore(%d) = %d, want %d", i, k, got, want)
			}
		}
		if got, want := w.TotalVisuals(), naivePrefix(model, len(model)); got != want {
			t.Fatalf("op %d: TotalVisuals = %d, want %d", i, got, want)
		}
		// LineForVisual for every visual line (bounded: total is small here).
		if total := w.TotalVisuals(); total < 5000 {
			for v := int32(0); v < total; v++ {
				if got, want := w.LineForVisual(v), naiveLineForVisual(model, v); got != want {
					t.Fatalf("op %d: LineForVisual(%d) = %d, want %d", i, v, got, want)
				}
			}
		}
	}
}

// TestWrapIndex_AllOnesIsIdentity pins the legacy-mapping property: an
// all-ones index (no wrap corrections applied) must map visual lines to
// logical lines 1:1, so pre-shaping behavior is exactly the old code path.
func TestWrapIndex_AllOnesIsIdentity(t *testing.T) {
	w := NewWrapIndex(1000)
	for v := int32(0); v < 1000; v++ {
		if got := w.LineForVisual(v); got != int(v) {
			t.Fatalf("LineForVisual(%d) = %d, want %d (all-ones must be identity)", v, got, v)
		}
	}
	for k := 0; k <= 1000; k++ {
		if got := w.VisualsBefore(k); got != int32(k) {
			t.Fatalf("VisualsBefore(%d) = %d, want %d", k, got, k)
		}
	}
	if got := w.TotalVisuals(); got != 1000 {
		t.Fatalf("TotalVisuals = %d, want 1000", got)
	}
}

// TestWrapIndex_LineForVisualWrapped checks the mapping against a hand-built
// wrap pattern: lines wrap as W = [1,3,1,2,1,...] so V(0)=0, V(1)=1,
// V(2)=4, V(3)=5, V(4)=7, V(5)=8.
func TestWrapIndex_LineForVisualWrapped(t *testing.T) {
	w := NewWrapIndex(5)
	counts := []int32{1, 3, 1, 2, 1}
	w.SetRange(0, counts)

	// Visual line v belongs to the smallest k with V(k+1) > v.
	want := map[int32]int{
		0: 0, 1: 1, 2: 1, 3: 1, // line 0: v0; line 1: v1..v3
		4: 2,       // line 2: v4
		5: 3, 6: 3, // line 3: v5..v6
		7:  4, // line 4: v7
		8:  4, // clamped: v >= total(8) -> last line
		99: 4,
	}
	for v, k := range want {
		if got := w.LineForVisual(v); got != k {
			t.Errorf("LineForVisual(%d) = %d, want %d", v, got, k)
		}
	}
	if got := w.TotalVisuals(); got != 8 {
		t.Errorf("TotalVisuals = %d, want 8", got)
	}
}