iterator: add functionality to move indices

Extract the index acrobatics from the message store and move it to
iterator package for re-use and to add unit tests.

Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>

1 files changed, 133 insertions, 0 deletions

diff --git a/lib/iterator/index_test.go b/lib/iterator/index_test.go
new file mode 100644
index 00000000..c9b79304
--- /dev/null
+++ b/lib/iterator/index_test.go
@@ -0,0 +1,133 @@
+package iterator_test
+
+import (
+	"testing"
+
+	"git.sr.ht/~rjarry/aerc/lib/iterator"
+)
+
+type indexer struct {
+	start int
+	end   int
+}
+
+func (ip *indexer) StartIndex() int {
+	return ip.start
+}
+
+func (ip *indexer) EndIndex() int {
+	return ip.end
+}
+
+func TestMoveIndex(t *testing.T) {
+	tests := []struct {
+		idx      int
+		delta    int
+		start    int
+		end      int
+		cb       iterator.BoundsCheckFunc
+		expected int
+	}{
+		{
+			idx:      0,
+			delta:    1,
+			start:    0,
+			end:      2,
+			cb:       iterator.FixBounds,
+			expected: 1,
+		},
+		{
+			idx:      0,
+			delta:    5,
+			start:    0,
+			end:      2,
+			cb:       iterator.FixBounds,
+			expected: 2,
+		},
+		{
+			idx:      0,
+			delta:    -1,
+			start:    0,
+			end:      2,
+			cb:       iterator.FixBounds,
+			expected: 0,
+		},
+		{
+			idx:      0,
+			delta:    2,
+			start:    0,
+			end:      2,
+			cb:       iterator.WrapBounds,
+			expected: 2,
+		},
+		{
+			idx:      0,
+			delta:    3,
+			start:    0,
+			end:      2,
+			cb:       iterator.WrapBounds,
+			expected: 0,
+		},
+		{
+			idx:      0,
+			delta:    -1,
+			start:    0,
+			end:      2,
+			cb:       iterator.WrapBounds,
+			expected: 2,
+		},
+		{
+			idx:      2,
+			delta:    2,
+			start:    0,
+			end:      2,
+			cb:       iterator.WrapBounds,
+			expected: 1,
+		},
+		{
+			idx:      0,
+			delta:    -2,
+			start:    0,
+			end:      2,
+			cb:       iterator.WrapBounds,
+			expected: 1,
+		},
+		{
+			idx:      1,
+			delta:    1,
+			start:    2,
+			end:      0,
+			cb:       iterator.FixBounds,
+			expected: 0,
+		},
+		{
+			idx:      0,
+			delta:    1,
+			start:    2,
+			end:      0,
+			cb:       iterator.FixBounds,
+			expected: 0,
+		},
+		{
+			idx:      0,
+			delta:    1,
+			start:    2,
+			end:      0,
+			cb:       iterator.WrapBounds,
+			expected: 2,
+		},
+	}
+
+	for i, test := range tests {
+		idx := iterator.MoveIndex(
+			test.idx,
+			test.delta,
+			&indexer{test.start, test.end},
+			test.cb,
+		)
+		if idx != test.expected {
+			t.Errorf("test %d [%#v] failed: got %d but expected %d",
+				i, test, idx, test.expected)
+		}
+	}
+}