Pad/internal/editor/wrap_mapping_test.go

package editor

import (
	"math/rand"
	"testing"

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

// TestScrollVisualDecompose_ViewportIdentity is the regression test for the
// word-wrap scroll jump: when the viewport top crosses the bottom of a
// wrapped logical line, the view jumped past the wrapped remainder instead of
// moving pixel-by-pixel with the finger.
//
// The invariant under test: the document visual offset at the viewport top is
// ALWAYS exactly the scroll offset s. If k is the logical line at the viewport
// top with sub-line shift r, the viewport top sits V(k)*lh + r into the
// document (V(k) = visual lines before line k, each lh tall, plus r into the
// next). Any mapping that does not satisfy V(k)*lh + r == s silently skips or
// re-shows content — the jump.
//
// Before the fix, all mapping sites assumed V(k) == k (1 logical line = 1
// visual line), so for any wrapped file the identity failed by exactly
// (V(k)-k)*lh once the first wrapped line had been scrolled past.
func TestScrollVisualDecompose_ViewportIdentity(t *testing.T) {
	const n = 500 // logical lines
	rng := rand.New(rand.NewSource(11))
	counts := make([]int32, n)
	for i := range counts {
		counts[i] = int32(1 + rng.Intn(4)) // each line wraps into 1..4 visual lines
	}

	cb := newTestBufferForWrap(n, counts)

	lh := float64(EffectiveLineHeight())
	w := cb.WrapIndex
	totalVisuals := float64(w.TotalVisuals())
	maxS := (totalVisuals - 1) * lh // stay inside the last visual line

	check := func(s ui.Dp, label string) {
		TheState.ScrollOffset = s
		k, r := scrollVisualDecompose()

		if k < 0 || k >= n {
			t.Fatalf("%s: k = %d out of range [0,%d)", label, k, n)
		}
		// r = s - V(k)*lh places the viewport top r below the TOP of line k;
		// for a wrapped line the top may be several visual lines above the
		// viewport, so r spans [0, count(k)*lh).
		if r < -1e-9 || r >= float64(w.Get(k))*lh+1e-9 {
			t.Fatalf("%s: r = %f outside [0, count(k)*lh = %f*lh)", label, r, float64(w.Get(k)))
		}
		// The viewport top must lie inside line k's visual span.
		vk := float64(w.VisualsBefore(k))
		if vk*lh > float64(s)+1e-9 {
			t.Fatalf("%s: s = %f is above line k's span start V(k)*lh = %f", label, float64(s), vk*lh)
		}
		if k+1 < n && float64(s) >= float64(w.VisualsBefore(k+1))*lh-1e-9 {
			t.Fatalf("%s: s = %f is at/past line %d's span start (k should be >= %d)", label, float64(s), k+1, k+1)
		}
		// The identity: the viewport top is exactly s into the document's
		// visual space.
		got := vk*lh + r
		if d := got - float64(s); d < -1e-9 || d > 1e-9 {
			t.Fatalf("%s: s = %f: V(k)*lh + r = %f, want s = %f (off by %f — a scroll jump)", label, float64(s), got, float64(s), d)
		}
		// k must be the logical line containing the viewport-top visual line.
		v0 := int32(float64(s) / lh)
		if want := w.LineForVisual(v0); k != want {
			t.Fatalf("%s: s = %f: k = %d, want LineForVisual(%d) = %d", label, float64(s), k, v0, want)
		}
	}

	// Sub-line sweep in fine steps across the whole document.
	steps := 4000
	for i := 0; i <= steps; i++ {
		s := ui.Dp(maxS * float64(i) / float64(steps))
		check(s, "sweep")
	}
	// Random offsets (arbitrary sub-line positions).
	for i := 0; i < 2000; i++ {
		s := ui.Dp(rng.Float64() * maxS)
		check(s, "random")
	}
}

// TestScrollVisualDecompose_LegacyIdentity pins the legacy behavior: with an
// all-ones WrapIndex (no wrap corrections applied, i.e. pre-shaping) or no
// WrapIndex at all, the mapping must be exactly the old 1:1 mapping, so
// non-wrapped files and pre-shaping frames are unchanged.
func TestScrollVisualDecompose_LegacyIdentity(t *testing.T) {
	const n = 100
	cb := newTestBufferForWrap(n, nil) // all ones
	cb.WrapIndex.ResetAll()

	lh := float64(EffectiveLineHeight())
	maxS := float64(n)*lh - lh/2
	rng := rand.New(rand.NewSource(13))
	check := func(s ui.Dp, label string) {
		TheState.ScrollOffset = s
		k, r := scrollVisualDecompose()
		v0, r0 := scrollDecompose(s, ui.Dp(lh))
		if float64(k) != float64(v0) || r != r0 {
			t.Fatalf("%s: s = %f: (k,r) = (%d,%f), want legacy (v0,r0) = (%d,%f)", label, float64(s), k, r, v0, r0)
		}
	}
	steps := 500
	for i := 0; i <= steps; i++ {
		check(ui.Dp(maxS*float64(i)/float64(steps)), "sweep")
	}
	for i := 0; i < 500; i++ {
		check(ui.Dp(rng.Float64()*maxS), "random")
	}

	// No WrapIndex at all (the String-Buffer fallback / pre-build state).
	cb.WrapIndex = nil
	for i := 0; i < 100; i++ {
		check(ui.Dp(rng.Float64()*maxS), "no-wi")
	}
}

// TestScrollVisualDecompose_WrappedBoundarySweep walks the scroll offset
// across every wrapped-line boundary and checks that the viewport top moves
// pixel-by-pixel: the logical line at the top advances by exactly the number
// of visual lines the previous line occupies, and the fixed-line position
// identity T(i) = V(i)*lh - s holds across the boundary (no skip, no repeat).
func TestScrollVisualDecompose_WrappedBoundarySweep(t *testing.T) {
	counts := []int32{1, 3, 1, 2, 4, 1}
	cb := newTestBufferForWrap(len(counts), counts)
	lh := float64(EffectiveLineHeight())
	w := cb.WrapIndex

	eps := lh / 8
	var prevK int
	var prevS float64
	for v := int32(0); v < w.TotalVisuals(); v++ {
		for _, s := range []ui.Dp{ui.Dp(float64(v)*lh - eps/2), ui.Dp(float64(v) * lh), ui.Dp(float64(v)*lh + eps/2)} {
			if float64(s) < 0 {
				continue
			}
			TheState.ScrollOffset = s
			k, r := scrollVisualDecompose()
			if k < prevK {
				t.Fatalf("s = %f: k decreased (%d -> %d): content re-shown", float64(s), prevK, k)
			}
			// A fixed line moves exactly finger-speed across the boundary:
			// T(i) = V(i)*lh - s for the line that was at the top before.
			if i, ok := firstVisualToLogical(w, v-1); ok && k > i {
				Tbefore := float64(w.VisualsBefore(i))*lh - prevS
				Tafter := float64(w.VisualsBefore(i))*lh - float64(s)
				if d := (Tbefore - Tafter) - (float64(s) - prevS); d < -1e-9 || d > 1e-9 {
					t.Fatalf("s = %f: fixed line moved by %f for scroll delta %f (jump!)", float64(s), Tbefore-Tafter, float64(s)-prevS)
				}
			}
			if k == prevK && float64(s) > prevS {
				// Same top line: the sub-line shift must advance by the delta.
				if d := (r - (prevS - float64(w.VisualsBefore(k))*lh)) - (float64(s) - prevS); d < -1e-9 || d > 1e-9 {
					t.Fatalf("s = %f: r advanced by %f for delta %f", float64(s), d, float64(s)-prevS)
				}
			}
			_ = r
			prevK, prevS = k, float64(s)
		}
	}
}

// firstVisualToLogical maps visual line v to its logical line (mirrors
// LineForVisual; the test wants a named helper for readability).
func firstVisualToLogical(w *WrapIndex, v int32) (int, bool) {
	if v < 0 {
		return 0, false
	}
	return w.LineForVisual(v), true
}

// newTestBufferForWrap builds a minimal editor State backed by a chunked
// buffer whose WrapIndex is seeded with the given per-line visual counts
// (nil = all ones). It points TheState at it for the scroll mapping under
// test. The buffer content is one short line per logical line; only the
// WrapIndex matters to the mapping.
func newTestBufferForWrap(n int, counts []int32) *ChunkedBuffer {
	var buf []byte
	for i := 0; i < n; i++ {
		buf = append(buf, 'x')
		if i < n-1 {
			buf = append(buf, '\n')
		}
	}
	cb := NewChunkedBuffer("/wrap-map.txt", DefaultChunkSize, nil, "")
	cb.SetContent(buf)
	offsets := []int32{0}
	for i := 0; i < len(buf); i++ {
		if buf[i] == '\n' {
			offsets = append(offsets, int32(i+1))
		}
	}
	cb.LineIndex = types.NewLineIndex(offsets, 0, int64(len(buf)))
	w := NewWrapIndex(len(offsets))
	for i, c := range counts {
		w.Set(i, c)
	}
	cb.WrapIndex = w

	TheState = NewState()
	TheState.Editor.ChunkedBuffer = cb
	TheState.Editor.GlyphLayout = ui.GlyphLayout{} // LineHeight 0 -> EffectiveLineHeight
	TheState.ScrollOffset = 0
	return cb
}