Improvement: move MoveLinesUp and MoveLinesDown to Buffer

enables Undo/Redo with EventHandler, #407

cmd/micro/buffer.go

@@ -363,3 +363,41 @@ func (b *Buffer) Lines(start, end int) []string {
 func (b *Buffer) Len() int {
 	return Count(b.String())
 }
+
+func (b *Buffer) MoveLinesUp(start int, end int) {
+    // 0 < start < end <= len(b.lines)
+    if start < 1 || start >= end || end > len(b.lines) {
+        return // what to do? FIXME
+    }
+    b.Insert(
+        Loc{0, end},
+        b.Line(start - 1) + "\n",
+    )
+    b.Remove(
+        Loc{0, start - 1},
+        Loc{0, start},
+    )
+}
+
+func (b *Buffer) MoveLinesDown(start int, end int) {
+    // 0 <= start < end < len(b.lines)
+    if start < 0 || start >= end || end >= len(b.lines) {
+        return // what to do? FIXME
+    }
+    b.Insert(
+        Loc{0, start},
+        b.Line(end) + "\n",
+    )
+    end += 1
+    rmEndLoc := Loc{0, end + 1}
+    if end >= len(b.lines)-1 {
+        rmEndLoc = Loc{
+            utf8.RuneCount(b.lines[end]) - 1,
+            end,
+        }
+    }
+    b.Remove(
+        Loc{0, end},
+        rmEndLoc,
+    )
+}

cmd/micro/lineArray.go

@@ -132,31 +132,6 @@ func (la *LineArray) DeleteByte(pos Loc) {
 	la.lines[pos.Y] = la.lines[pos.Y][:pos.X+copy(la.lines[pos.Y][pos.X:], la.lines[pos.Y][pos.X+1:])]
 }
 
-func (la *LineArray) MoveLinesUp(y0 int, y1 int) {
-    // 0 < y0 < y1 <= len(la.lines)
-    if y0 < 1 || y0 >= y1 || y1 > len(la.lines) {
-        return // what to do? FIXME
-    }
-    before := la.lines[y0-1]
-    for y := y0 ; y < y1 ; y ++ {
-        la.lines[y-1] = la.lines[y]
-    }
-    la.lines[y1-1] = before
-}
-
-func (la *LineArray) MoveLinesDown(y0 int, y1 int) {
-    // 0 <= y0 < y1 < len(la.lines)
-    if y0 < 0 || y0 >= y1 || y1 >= len(la.lines) {
-        return // what to do? FIXME
-    }
-    after := la.lines[y1]
-    for y := y1-1 ; y >= y0 ; y -- {
-        la.lines[y+1] = la.lines[y]
-    }
-    la.lines[y0] = after
-}
-
-
 // Substr returns the string representation between two locations
 func (la *LineArray) Substr(start, end Loc) string {
 	startX := runeToByteIndex(start.X, la.lines[start.Y])