core: lattice sync (#257)

2 files changed, 41 insertions, 0 deletions

diff --git a/core/types/position.go b/core/types/position.go
index f41be32..d821d16 100644
--- a/core/types/position.go
+++ b/core/types/position.go
@@ -57,6 +57,16 @@ func (pos *Position) Newer(other *Position) bool {
 		(pos.Round == other.Round && pos.Height > other.Height)
 }
 
+// Older checks if one block is older than another one on the same chain.
+// If two blocks on different chain compared by this function, it would panic.
+func (pos *Position) Older(other *Position) bool {
+	if pos.ChainID != other.ChainID {
+		panic(ErrComparePositionOnDifferentChains)
+	}
+	return pos.Round < other.Round ||
+		(pos.Round == other.Round && pos.Height < other.Height)
+}
+
 // Clone a position instance.
 func (pos *Position) Clone() *Position {
 	return &Position{
diff --git a/core/types/position_test.go b/core/types/position_test.go
index 48f8dbd..1ef1813 100644
--- a/core/types/position_test.go
+++ b/core/types/position_test.go
@@ -59,6 +59,37 @@ func (s *PositionTestSuite) TestNewer() {
 	}))
 }
 
+func (s *PositionTestSuite) TestOlder() {
+	pos := Position{
+		Round:   1,
+		ChainID: 1,
+		Height:  1,
+	}
+	s.Panics(func() {
+		pos.Older(&Position{ChainID: 2})
+	})
+	s.False(pos.Older(&Position{
+		Round:   0,
+		ChainID: 1,
+		Height:  0,
+	}))
+	s.False(pos.Older(&Position{
+		Round:   1,
+		ChainID: 1,
+		Height:  0,
+	}))
+	s.True(pos.Older(&Position{
+		Round:   2,
+		ChainID: 1,
+		Height:  0,
+	}))
+	s.True(pos.Older(&Position{
+		Round:   1,
+		ChainID: 1,
+		Height:  100,
+	}))
+}
+
 func (s *PositionTestSuite) TestSearchInAsendingOrder() {
 	positions := []*Position{
 		&Position{Round: 0, Height: 1},