Takes into account that <<earliest>> block available is not necessarily the genesis block

codex/contracts/market.nim

@@ -432,7 +432,7 @@ proc binarySearchFindClosestBlock*(provider: Provider,
     await provider.blockNumberAndTimestamp(BlockTag.init(low))
   let (_, highTimestamp) =
     await provider.blockNumberAndTimestamp(BlockTag.init(high))
-  trace "[binarySearchFindClosestBlock]:", epochTime = epochTime,
+  debug "[binarySearchFindClosestBlock]:", epochTime = epochTime,
     lowTimestamp = lowTimestamp, highTimestamp = highTimestamp, low = low, high = high
   if abs(lowTimestamp.truncate(int) - epochTime) <
       abs(highTimestamp.truncate(int) - epochTime):
@@ -442,9 +442,10 @@ proc binarySearchFindClosestBlock*(provider: Provider,
 
 proc binarySearchBlockNumberForEpoch*(provider: Provider,
                                      epochTime: UInt256,
-                                     latestBlockNumber: UInt256):
+                                     latestBlockNumber: UInt256,
+                                     earliestBlockNumber: UInt256):
                                       Future[UInt256] {.async.} =
-  var low = 0.u256
+  var low = earliestBlockNumber
   var high = latestBlockNumber
 
   debug "[binarySearchBlockNumberForEpoch]:", low = low, high = high
@@ -472,18 +473,22 @@ proc blockNumberForEpoch*(provider: Provider, epochTime: int64): Future[UInt256]
   let epochTimeUInt256 = epochTime.u256
   let (latestBlockNumber, latestBlockTimestamp) = 
     await provider.blockNumberAndTimestamp(BlockTag.latest)
+  let (earliestBlockNumber, earliestBlockTimestamp) = 
+    await provider.blockNumberAndTimestamp(BlockTag.earliest)
   
   debug "[blockNumberForEpoch]:", latestBlockNumber = latestBlockNumber,
     latestBlockTimestamp = latestBlockTimestamp
+  debug "[blockNumberForEpoch]:", earliestBlockNumber = earliestBlockNumber,
+    earliestBlockTimestamp = earliestBlockTimestamp
 
   let timeDiff = latestBlockTimestamp - epochTimeUInt256
   let blockDiff = timeDiff div avgBlockTime
 
-  if blockDiff >= latestBlockNumber:
+  if blockDiff >= latestBlockNumber - earliestBlockNumber:
-    return 0.u256
+    return earliestBlockNumber
 
   return await provider.binarySearchBlockNumberForEpoch(
-    epochTimeUInt256, latestBlockNumber)
+    epochTimeUInt256, latestBlockNumber, earliestBlockNumber)
 
 method queryPastSlotFilledEvents*(
   market: OnChainMarket,

tests/contracts/testMarket.nim

@@ -512,17 +512,25 @@ ethersuite "On-Chain Market":
     check expected == simulatedBlockTime
     check actual == expected
   
-  test "blockNumberForEpoch returns the earliest block when block height " &
+  test "blockNumberForEpoch returns the earliest block when retained history " &
-       "is less than the given epoch time":
+       "is shorter than the given epoch time":
-    let (_, timestampEarliest) =
+    # create predictable conditions for computing average block time
+    let averageBlockTime = 10.u256
+    await ethProvider.mineNBlocks(1)
+    await ethProvider.advanceTime(averageBlockTime)
+    let (earliestBlockNumber, earliestTimestamp) =
       await ethProvider.blockNumberAndTimestamp(BlockTag.earliest)
     
-    let fromTime = timestampEarliest - 1
+    let fromTime = earliestTimestamp - 1
 
-    let expected = await ethProvider.blockNumberForEpoch(
+    let actual = await ethProvider.blockNumberForEpoch(
       fromTime.truncate(int64))
 
-    check expected == 0.u256
+    # Notice this could fail in a network where "earliest" block is
+    # not the genesis block - we run the tests agains local network
+    # so we know the earliest block is the same as genesis block
+    # earliestBlockNumber is 0.u256 in our case.
+    check actual == earliestBlockNumber
   
   test "blockNumberForEpoch finds closest blockNumber for given epoch time":
     proc createBlockHistory(n: int, blockTime: int):