Scroll by lines that respects ring buf+iterator prevN/nextN+it.Len

main.go

@@ -284,11 +284,9 @@ func (p *program) MainUpdate() {
 		var newPosNewLines int64
 		w, _ := p.GridSize()
 		if mouseWheelYNorm < 0 {
-			// @TODO This is wrong because it deals with data as a normal array while its a ring buffer
-
-			newPosNewLines, _ = find_n_lines_index(p.textBuf.Data, p.scrollPos, p.scrollSpd*mouseWheelYNorm-1, int64(w))
+			newPosNewLines, _ = find_n_lines_index_iterator(p.textBuf.Iterator(), p.scrollPos, p.scrollSpd*mouseWheelYNorm-1, int64(w))
 		} else {
-			newPosNewLines, _ = find_n_lines_index(p.textBuf.Data, p.scrollPos, p.scrollSpd*mouseWheelYNorm, int64(w))
+			newPosNewLines, _ = find_n_lines_index_iterator(p.textBuf.Iterator(), p.scrollPos, p.scrollSpd*mouseWheelYNorm, int64(w))
 		}
 
 		p.scrollPos = clamp(newPosNewLines, 0, p.textBuf.Len)
@@ -831,22 +829,36 @@ func FindNthOrLastIndex[T comparable](arr []T, x T, startIndex, n int64) (lastIn
 //
 // Note: When moving backwards from the start of the line, the first char will be a new line (e.g. \n), so the first counted line is not a full line
 // but only a single rune. So in most cases to get '-n' lines backwards you should request '-n-1' lines.
-func find_n_lines_index(arr []byte, startIndex, n, charsPerLine int64) (lastIndex, lastSize int64) {
+func find_n_lines_index_iterator(it ring.Iterator[byte], startIndex, n, charsPerLine int64) (newIndex, newSize int64) {
+
+	// If nothing changes (e.g. already at end of iterator) then we will stay at the same place
+
+	done := false
+	read := 0
+	bytesToKeep := 0
+	buf := make([]byte, 4)
+	it.GotoIndex(startIndex)
 
-	lastIndex = -1
-	lastSize = 0
-	if n >= 0 {
 	// @Note we should ignore zero width glyphs
 	// @Note is this better in glyphs package?
 	bytesSeen := int64(0)
-		arrSize := int64(len(arr))
 	charsSeenThisLine := int64(0)
-		for startIndex+bytesSeen < arrSize {
 
-			r, size := utf8.DecodeRune(arr[startIndex+bytesSeen:])
+	if n >= 0 {
+
+		// If nothing changes (e.g. already at end of iterator) then we will stay at the same place
+		newIndex = startIndex
+
+		for !done || bytesToKeep > 0 {
+
+			read, done = it.NextN(buf[bytesToKeep:], 4)
+
+			r, size := utf8.DecodeRune(buf[:bytesToKeep+read])
 			if r == utf8.RuneError {
 				break
 			}
+			bytesToKeep += read - size
+			copy(buf, buf[size:size+bytesToKeep])
 
 			charsSeenThisLine++
 			bytesSeen += int64(size)
@@ -855,8 +867,8 @@ func find_n_lines_index(arr []byte, startIndex, n, charsPerLine int64) (lastInde
 			if charsSeenThisLine == charsPerLine || r == '\n' {
 
 				charsSeenThisLine = 0
-				lastSize = int64(size)
-				lastIndex = startIndex + bytesSeen
+				newSize = int64(size)
+				newIndex = startIndex + bytesSeen
 
 				n--
 				if n <= 0 {
@@ -867,14 +879,16 @@ func find_n_lines_index(arr []byte, startIndex, n, charsPerLine int64) (lastInde
 
 	} else {
 
-		bytesSeen := int64(0)
-		charsSeenThisLine := int64(0)
-		for startIndex-bytesSeen > 0 {
+		for !done || bytesToKeep > 0 {
 
-			r, size := utf8.DecodeLastRune(arr[:startIndex-bytesSeen+1])
+			read, done = it.PrevN(buf[bytesToKeep:], 4)
+
+			r, size := utf8.DecodeRune(buf[:bytesToKeep+read])
 			if r == utf8.RuneError {
 				break
 			}
+			bytesToKeep += read - size
+			copy(buf, buf[size:size+bytesToKeep])
 
 			charsSeenThisLine++
 			bytesSeen += int64(size)
@@ -883,8 +897,8 @@ func find_n_lines_index(arr []byte, startIndex, n, charsPerLine int64) (lastInde
 			if charsSeenThisLine == charsPerLine || r == '\n' {
 
 				charsSeenThisLine = 0
-				lastSize = int64(size)
-				lastIndex = startIndex - bytesSeen + 1 + lastSize
+				newSize = int64(size)
+				newIndex = startIndex - bytesSeen + newSize
 
 				n++
 				if n >= 0 {
@@ -893,11 +907,12 @@ func find_n_lines_index(arr []byte, startIndex, n, charsPerLine int64) (lastInde
 			}
 		}
 
-		// Handle reaching beginning before finding nth line
+		// If we reached beginning of buffer before finding a new line then newIndex is zero
 		if startIndex-bytesSeen == 0 {
-			return 0, 0
+			newIndex = 0
+			newSize = 0
 		}
 	}
 
-	return lastIndex, lastSize
+	return newIndex, newSize
 }

ring/ring.go

@@ -143,6 +143,10 @@ type Iterator[T any] struct {
 	InV1 bool
 }
 
+func (it *Iterator[T]) Len() int64 {
+	return int64(len(it.V1) + len(it.V2))
+}
+
 // Next returns the value at Iterator.Curr and done=false
 //
 // If there are no more values to return the default value is returned for v and done=true
@@ -198,6 +202,63 @@ func (it *Iterator[T]) Prev() (v T, done bool) {
 	return v, false
 }
 
+// NextN calls Next() up to n times and places the result in the passed buffer.
+// 'read' is the actual number of elements put in the buffer.
+// We might not be able to put 'n' elements because the buffer is too small or because there aren't enough remaining elements
+func (it *Iterator[T]) NextN(buf []T, n int) (read int, done bool) {
+
+	if n > len(buf) {
+		n = len(buf)
+	}
+
+	var v T
+	for v, done = it.Next(); !done; v, done = it.Next() {
+
+		buf[read] = v
+		read++
+
+		// We must break inside the loop not in the 'for' check because
+		// if we check part of the loop and break before done=true we will waste the last
+		// value
+		n--
+		if n == 0 {
+			break
+		}
+	}
+
+	return read, done
+}
+
+// PrevN calls Prev() up to n times and places the result in the passed buffer in the order they are read from Prev().
+// That is, the first Prev() call is put into index 0, second Prev() call is in index 1, and so on,
+// similar to if you were doing a reverse loop on an array.
+//
+// 'read' is the actual number of elements put in the buffer.
+// We might not be able to put 'n' elements because the buffer is too small or because there aren't enough remaining elements
+func (it *Iterator[T]) PrevN(buf []T, n int) (read int, done bool) {
+
+	if n > len(buf) {
+		n = len(buf)
+	}
+
+	var v T
+	for v, done = it.Prev(); !done; v, done = it.Prev() {
+
+		buf[read] = v
+		read++
+
+		// We must break inside the loop not in the 'for' check because
+		// if we check part of the loop and break before done=true we will waste the last
+		// value
+		n--
+		if n == 0 {
+			break
+		}
+	}
+
+	return read, done
+}
+
 // GotoStart adjusts the iterator such that the following Next() call returns the value at index=0
 // and the next Prev() call returns done=true
 func (it *Iterator[T]) GotoStart() {

ring/ring_test.go

@@ -176,6 +176,28 @@ func TestIterator(t *testing.T) {
 		got = append(got, v)
 	}
 	CheckArr(t, ans, got)
+
+	// NextN
+	got = make([]int, 2)
+	ans = []int{3, 4}
+	it.GotoStart()
+	it.NextN(got, 2)
+	CheckArr(t, ans, got)
+
+	ans = []int{5, 6}
+	it.NextN(got, 2)
+	CheckArr(t, ans, got)
+
+	// PrevN
+	got = make([]int, 2)
+	ans = []int{6, 5}
+	it.GotoEnd()
+	it.PrevN(got, 2)
+	CheckArr(t, ans, got)
+
+	ans = []int{4, 3}
+	it.PrevN(got, 2)
+	CheckArr(t, ans, got)
 }
 
 func Check[T comparable](t *testing.T, expected, got T) {