Iterative impl of explode_gap (#31)

* Iterative impl of `explode_gap`

* Fmt

* Fix lint

background_tasks.py

@@ -48,13 +48,17 @@ def run(self):
 def explode_gap(start_slot, end_slot, sprp):
     next_boundary = (start_slot // sprp + 1) * sprp
 
-    if end_slot > next_boundary:
-        return [(start_slot, next_boundary)] + explode_gap(
-            next_boundary + 1, end_slot, sprp
-        )
-    else:
+    if end_slot <= next_boundary:
         return [(start_slot, end_slot)]
 
+    gaps = []
+    while end_slot > next_boundary:
+        gaps.append((start_slot, next_boundary))
+        start_slot = next_boundary + 1
+        next_boundary += sprp
+
+    return gaps
+
 
 def explode_gaps(gaps, sprp=2048):
     "Divide sync gaps into manageable chunks aligned to Lighthouse's restore points"

tests/test_explode_gaps.py

@@ -0,0 +1,35 @@
+from background_tasks import explode_gap
+
+
+def check_gaps(start_slot, end_slot, sprp):
+    result = explode_gap(start_slot, end_slot, sprp=sprp)
+
+    assert len(result) > 0
+
+    prev_end = None
+    for start, end in result:
+        assert start < end
+        assert start == start_slot or (start == prev_end + 1 and start % sprp == 1)
+        assert end == end_slot or (end < end_slot and end % sprp == 0)
+        prev_end = end
+
+
+def test_explode_large_gap():
+    start_slot = 14273
+    end_slot = 7530327
+    sprp = 2048
+    check_gaps(start_slot, end_slot, sprp)
+
+
+def test_explode_small_gap_unaligned():
+    start_slot = 1
+    end_slot = 10
+    sprp = 2048
+    check_gaps(start_slot, end_slot, sprp)
+
+
+def test_explode_small_gap_aligned():
+    start_slot = 1
+    end_slot = 2048
+    sprp = 2048
+    check_gaps(start_slot, end_slot, sprp)