replace yank with better insert

Previous prototype of yank was O(n*m). The new code is more effective
O(n+m), and also removes the need for yank function, by extending the
insert function to accept more than 1 rune at once.

2 files changed, 90 insertions, 13 deletions

diff --git a/up.go b/up.go
index cc06d1a..0e815f3 100644
--- a/up.go
+++ b/up.go
@@ -350,7 +350,7 @@ func (e *Editor) HandleKey(ev *tcell.EventKey) bool {
 		e.kill()
 	case key(tcell.KeyCtrlY),
 		ctrlKey(tcell.KeyCtrlY):
-		e.yank()
+		e.insert(e.killspace...)
 	default:
 		// Unknown key/combination, not handled
 		return false
@@ -358,12 +358,12 @@ func (e *Editor) HandleKey(ev *tcell.EventKey) bool {
 	return true
 }
 
-func (e *Editor) insert(ch rune) {
-	// Insert character into value (https://github.com/golang/go/wiki/SliceTricks#insert)
-	e.value = append(e.value, 0)
-	copy(e.value[e.cursor+1:], e.value[e.cursor:])
-	e.value[e.cursor] = ch
-	e.cursor++
+func (e *Editor) insert(ch ...rune) {
+	// Based on https://github.com/golang/go/wiki/SliceTricks#insert
+	e.value = append(e.value, ch...)                     // = PREFIX + SUFFIX + (filler)
+	copy(e.value[e.cursor+len(ch):], e.value[e.cursor:]) // = PREFIX + (filler) + SUFFIX
+	copy(e.value[e.cursor:], ch)                         // = PREFIX + ch + SUFFIX
+	e.cursor += len(ch)
 }
 
 func (e *Editor) delete(dx int) {
@@ -382,12 +382,6 @@ func (e *Editor) kill() {
 	e.value = e.value[:e.cursor]
 }
 
-func (e *Editor) yank() {
-	for _, r := range e.killspace {
-		e.insert(r)
-	}
-}
-
 type BufView struct {
 	// TODO: Wrap bool
 	Y   int // Y of the view in the Buf, for down/up scrolling
diff --git a/up_test.go b/up_test.go
new file mode 100644
index 0000000..de31c59
--- /dev/null
+++ b/up_test.go
@@ -0,0 +1,83 @@
+package main
+
+import "testing"
+
+func Test_Editor_insert(test *testing.T) {
+	cases := []struct {
+		comment   string
+		e         Editor
+		insert    []rune
+		wantValue []rune
+	}{
+		{
+			comment: "prepend ASCII char",
+			e: Editor{
+				value:  []rune(`abc`),
+				cursor: 0,
+			},
+			insert:    []rune{'X'},
+			wantValue: []rune(`Xabc`),
+		},
+		{
+			comment: "prepend UTF char",
+			e: Editor{
+				value:  []rune(`abc`),
+				cursor: 0,
+			},
+			insert:    []rune{'☃'},
+			wantValue: []rune(`☃abc`),
+		},
+		{
+			comment: "insert ASCII char",
+			e: Editor{
+				value:  []rune(`abc`),
+				cursor: 1,
+			},
+			insert:    []rune{'X'},
+			wantValue: []rune(`aXbc`),
+		},
+		{
+			comment: "insert UTF char",
+			e: Editor{
+				value:  []rune(`abc`),
+				cursor: 1,
+			},
+			insert:    []rune{'☃'},
+			wantValue: []rune(`a☃bc`),
+		},
+		{
+			comment: "append ASCII char",
+			e: Editor{
+				value:  []rune(`abc`),
+				cursor: 3,
+			},
+			insert:    []rune{'X'},
+			wantValue: []rune(`abcX`),
+		},
+		{
+			comment: "append UTF char",
+			e: Editor{
+				value:  []rune(`abc`),
+				cursor: 3,
+			},
+			insert:    []rune{'☃'},
+			wantValue: []rune(`abc☃`),
+		},
+		{
+			comment: "insert 2 ASCII chars",
+			e: Editor{
+				value:  []rune(`abc`),
+				cursor: 1,
+			},
+			insert:    []rune{'X', 'Y'},
+			wantValue: []rune(`aXYbc`),
+		},
+	}
+
+	for _, c := range cases {
+		c.e.insert(c.insert...)
+		if string(c.e.value) != string(c.wantValue) {
+			test.Errorf("%q: bad value\nwant: %q\nhave: %q", c.comment, c.wantValue, c.e.value)
+		}
+	}
+}