From a812fd3faedc794678009dcf3c14571c1e284a25 Mon Sep 17 00:00:00 2001
From: Jordan Hrycaj <jordan@status.im>
Date: Tue, 2 Aug 2022 09:08:17 +0100
Subject: [PATCH] Retrive envelop interval for point (#136)

---
 stew/interval_set.nim       | 15 +++++++++++++++
 tests/test_interval_set.nim | 28 ++++++++++++++++++++++++----
 2 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/stew/interval_set.nim b/stew/interval_set.nim
index fad7fad..0c83923 100644
--- a/stew/interval_set.nim
+++ b/stew/interval_set.nim
@@ -825,6 +825,21 @@ proc le*[P,S](ds: IntervalSetRef[P,S]): IntervalRc[P,S] =
   ds.le(high(P))
 
 
+proc envelope*[P,S](ds: IntervalSetRef[P,S]; pt: P): IntervalRc[P,S] =
+  ## Find the interval that contains the argument point `pt` (if any)
+  let rc = ds.leftPos.le(pt)
+  if rc.isOk:
+    if ds.lastHigh and high(P) <= rc.value.right:
+      # This interval ranges `[left,high(P)]`, so `pt` is certainly contained
+      return ok(Interval[P,S].new(rc.value.left,high(P)))
+    if pt < rc.value.right:
+      return ok(Interval[P,S].new(rc.value))
+    # Otherwise: interval `[left,right)` ends before `pt`
+  if ds.lastHigh and high(P) <= pt:
+    return ok(Interval[P,S].new(high(P),high(P)))
+  err()
+
+
 proc delete*[P,S](ds: IntervalSetRef[P,S]; minPt: P): IntervalRc[P,S] =
   ## Find the interval `[minPt,maxPt]` for some point `maxPt` in the interval
   ## set `ds` and remove it from `ds`. The function returns the deleted
diff --git a/tests/test_interval_set.nim b/tests/test_interval_set.nim
index 8b50821..7ead9ad 100644
--- a/tests/test_interval_set.nim
+++ b/tests/test_interval_set.nim
@@ -102,6 +102,9 @@ proc le(br: FancyRanges; start: uint64): Result[FancyInterval,void] =
 proc ge(br: FancyRanges; start: uint64): Result[FancyInterval,void] =
   br.ge(start.to(FancyPoint))
 
+proc envelope(br: FancyRanges; start: uint64): Result[FancyInterval,void] =
+  br.envelope(start.to(FancyPoint))
+
 proc iv(left, right: uint64): FancyInterval =
   FancyInterval.new(left.to(FancyPoint), right.to(FancyPoint))
 
@@ -202,16 +205,12 @@ suite "IntervalSet: Intervals of FancyPoint entries over FancyScalar":
 
     br.clear() # from blockchain snap sync odd behaviour
     check br.merge(0,uHigh) == 0
-    check br.chunks == 1
-    check br.total == 0
     check br.ge(1000) == ivError
     check 0 < br.reduce(99999,uHigh-1)
     check br.ge(1000) == iv(uHigh,uHigh)
 
     br.clear()
     check br.merge(0,uHigh) == 0
-    check br.chunks == 1
-    check br.total == 0
     check br.le(uHigh) == iv(0,uHigh)
     check br.le(uHigh-1) == ivError
     check 0 < br.reduce(99999,uHigh-1)
@@ -219,6 +218,27 @@ suite "IntervalSet: Intervals of FancyPoint entries over FancyScalar":
     check br.le(uHigh-1) == iv(0,99998)
     check br.le(uHigh-2) == iv(0,99998)
 
+  test "Interval envelopes":
+    br.clear()
+    check br.merge(0,uHigh) == 0
+    check br.ge(1000) == ivError
+    check br.le(1000) == ivError
+    check br.envelope(1000) == iv(0,uHigh)
+
+    check 0 < br.reduce(1000,1000)
+    check br.envelope(1000) == ivError
+
+    check 0 < br.reduce(uHigh,uHigh)
+    check br.envelope(2000) == iv(1001,uHigh-1)
+    check br.envelope(uHigh-1) == iv(1001,uHigh-1)
+
+    check 0 < br.merge(0,uHigh) # actually == 2
+    check 0 < br.reduce(uHigh-1,uHigh-1)
+    check br.envelope(uHigh-1) == ivError
+    check br.envelope(uHigh-2) == iv(0,uHigh-2)
+    check br.ge(uHigh) == iv(uHigh,uHigh)
+    check br.envelope(uHigh) == iv(uHigh,uHigh)
+
   test "Merge disjunct intervals on 1st set":
     br.clear()
     check br.merge(  0,  99) == 100