db: Addressed comments.

Signed-off-by: Bartek Plotka <bwplotka@gmail.com>

db.go

@@ -569,22 +569,41 @@ func validateBlockSequence(bs []*Block) error {
 
 	overlaps := OverlappingBlocks(metas)
 	if len(overlaps) > 0 {
-		return errors.Errorf("block time ranges overlap: %s", SprintOverlappedBlocks(overlaps))
+		return errors.Errorf("block time ranges overlap: %s", overlaps)
 	}
 
 	return nil
 }
 
+// TimeRange specifies minTime and maxTime range.
 type TimeRange struct {
 	Min, Max int64
 }
 
-// OverlappingBlocks returns all overlapping blocks from given meta files aggregated by overlaping range.
-// We sort blocks by minTime. Then we iterate over each block minTime and treat it as our "current" timestamp.
-// We check all the pending blocks (blocks that we have seen their minTimes, but their maxTime was still ahead current
-// timestamp) if they finish. If not, it means they overlap with our current b. In the same time b is assumed as
-// pending.
-func OverlappingBlocks(bm []BlockMeta) map[TimeRange][]BlockMeta {
+// Overlaps contains overlapping blocks aggregated by overlapping range.
+type Overlaps map[TimeRange][]BlockMeta
+
+// String returns human readable string form of overlapped blocks.
+func (o Overlaps) String() string {
+	var res []string
+	for r, overlaps := range o {
+		var groups []string
+		for _, m := range overlaps {
+			groups = append(groups, fmt.Sprintf(
+				"[id: %s mint: %d maxt: %d range: %s]",
+				m.ULID.String(),
+				m.MinTime,
+				m.MaxTime,
+				(time.Duration((m.MaxTime-m.MinTime)/1000)*time.Second).String(),
+			))
+		}
+		res = append(res, fmt.Sprintf("[%d %d]: <%s> ", r.Min, r.Max, strings.Join(groups, "")))
+	}
+	return strings.Join(res, "")
+}
+
+// OverlappingBlocks returns all overlapping blocks from given meta files.
+func OverlappingBlocks(bm []BlockMeta) Overlaps {
 	if len(bm) <= 1 {
 		return nil
 	}
@@ -600,6 +619,10 @@ func OverlappingBlocks(bm []BlockMeta) map[TimeRange][]BlockMeta {
 		// continuousPending helps to aggregate same overlaps to single group.
 		continuousPending = true
 	)
+
+	// We have here blocks sorted by minTime. We iterate over each block and treat its minTime as our "current" timestamp.
+	// We check if any of the pending block finished (blocks that we have seen before, but their maxTime was still ahead current
+	// timestamp). If not, it means they overlap with our current block. In the same time current block is assumed pending.
 	for _, b := range bm[1:] {
 		var newPending []BlockMeta
 
@@ -631,7 +654,7 @@ func OverlappingBlocks(bm []BlockMeta) map[TimeRange][]BlockMeta {
 	}
 
 	// Fetch the critical overlapped time range foreach overlap groups.
-	overlapGroups := map[TimeRange][]BlockMeta{}
+	overlapGroups := Overlaps{}
 	for _, overlap := range overlaps {
 
 		minRange := TimeRange{Min: 0, Max: math.MaxInt64}
@@ -650,25 +673,6 @@ func OverlappingBlocks(bm []BlockMeta) map[TimeRange][]BlockMeta {
 	return overlapGroups
 }
 
-// SprintOverlappedBlocks returns human readable string form of overlapped blocks.
-func SprintOverlappedBlocks(overlaps map[TimeRange][]BlockMeta) string {
-	var res []string
-	for r, o := range overlaps {
-		var groups []string
-		for _, m := range o {
-			groups = append(groups, fmt.Sprintf(
-				"[id: %s mint: %d maxt: %d range: %s]",
-				m.ULID.String(),
-				m.MinTime,
-				m.MaxTime,
-				(time.Duration((m.MaxTime-m.MinTime)/1000)*time.Second).String(),
-			))
-		}
-		res = append(res, fmt.Sprintf("[%d %d]: <%s> ", r.Min, r.Max, strings.Join(groups, "")))
-	}
-	return strings.Join(res, "")
-}
-
 func (db *DB) String() string {
 	return "HEAD"
 }

db_test.go

@@ -907,13 +907,13 @@ func TestOverlappingBlocksDetectsAllOverlaps(t *testing.T) {
 
 	// o1 overlaps with 10-20.
 	o1 := BlockMeta{MinTime: 15, MaxTime: 17}
-	testutil.Equals(t, map[TimeRange][]BlockMeta{
+	testutil.Equals(t, Overlaps{
 		{Min: 15, Max: 17}: {metas[1], o1},
 	}, OverlappingBlocks(append(metas, o1)))
 
 	// o2 overlaps with 20-30 and 30-40.
 	o2 := BlockMeta{MinTime: 21, MaxTime: 31}
-	testutil.Equals(t, map[TimeRange][]BlockMeta{
+	testutil.Equals(t, Overlaps{
 		{Min: 21, Max: 30}: {metas[2], o2},
 		{Min: 30, Max: 31}: {o2, metas[3]},
 	}, OverlappingBlocks(append(metas, o2)))
@@ -921,19 +921,19 @@ func TestOverlappingBlocksDetectsAllOverlaps(t *testing.T) {
 	// o3a and o3b overlaps with 30-40 and each other.
 	o3a := BlockMeta{MinTime: 33, MaxTime: 39}
 	o3b := BlockMeta{MinTime: 34, MaxTime: 36}
-	testutil.Equals(t, map[TimeRange][]BlockMeta{
+	testutil.Equals(t, Overlaps{
 		{Min: 34, Max: 36}: {metas[3], o3a, o3b},
 	}, OverlappingBlocks(append(metas, o3a, o3b)))
 
 	// o4 is 1:1 overlap with 50-60.
 	o4 := BlockMeta{MinTime: 50, MaxTime: 60}
-	testutil.Equals(t, map[TimeRange][]BlockMeta{
+	testutil.Equals(t, Overlaps{
 		{Min: 50, Max: 60}: {metas[5], o4},
 	}, OverlappingBlocks(append(metas, o4)))
 
 	// o5 overlaps with 60-70, 70-80 and 80-90.
 	o5 := BlockMeta{MinTime: 61, MaxTime: 85}
-	testutil.Equals(t, map[TimeRange][]BlockMeta{
+	testutil.Equals(t, Overlaps{
 		{Min: 61, Max: 70}: {metas[6], o5},
 		{Min: 70, Max: 80}: {o5, metas[7]},
 		{Min: 80, Max: 85}: {o5, metas[8]},
@@ -942,13 +942,13 @@ func TestOverlappingBlocksDetectsAllOverlaps(t *testing.T) {
 	// o6a overlaps with 90-100, 100-110 and o6b, o6b overlaps with 90-100 and o6a.
 	o6a := BlockMeta{MinTime: 92, MaxTime: 105}
 	o6b := BlockMeta{MinTime: 94, MaxTime: 99}
-	testutil.Equals(t, map[TimeRange][]BlockMeta{
+	testutil.Equals(t, Overlaps{
 		{Min: 94, Max: 99}:   {metas[9], o6a, o6b},
 		{Min: 100, Max: 105}: {o6a, metas[10]},
 	}, OverlappingBlocks(append(metas, o6a, o6b)))
 
 	// All together.
-	testutil.Equals(t, map[TimeRange][]BlockMeta{
+	testutil.Equals(t, Overlaps{
 		{Min: 15, Max: 17}: {metas[1], o1},
 		{Min: 21, Max: 30}: {metas[2], o2}, {Min: 30, Max: 31}: {o2, metas[3]},
 		{Min: 34, Max: 36}: {metas[3], o3a, o3b},
@@ -969,7 +969,7 @@ func TestOverlappingBlocksDetectsAllOverlaps(t *testing.T) {
 	nc1 = append(nc1, BlockMeta{MinTime: 5, MaxTime: 7})
 	nc1 = append(nc1, BlockMeta{MinTime: 7, MaxTime: 10})
 	nc1 = append(nc1, BlockMeta{MinTime: 8, MaxTime: 9})
-	testutil.Equals(t, map[TimeRange][]BlockMeta{
+	testutil.Equals(t, Overlaps{
 		{Min: 2, Max: 3}: {nc1[0], nc1[1], nc1[2], nc1[3], nc1[4], nc1[5]}, // 1-5, 2-3, 2-3, 2-3, 2-3, 2,6
 		{Min: 3, Max: 5}: {nc1[0], nc1[5], nc1[6]},                         // 1-5, 2-6, 3-5
 		{Min: 5, Max: 6}: {nc1[5], nc1[7]},                                 // 2-6, 5-7