Calculate Event topic

contractabi/selector.nim

@@ -8,12 +8,16 @@ export address
 export stint
 
 type FunctionSelector* = distinct array[4, byte]
+type EventTopic* = distinct array[32, byte]
 
 proc toArray*(selector: FunctionSelector): array[4, byte] =
   array[4, byte](selector)
 
-proc `$`*(selector: FunctionSelector): string =
+proc toArray*(topic: EventTopic): array[32, byte] =
-  "0x" & selector.toArray.toHex
+  array[32, byte](topic)
+
+proc `$`*(value: FunctionSelector | EventTopic): string =
+  "0x" & value.toArray.toHex
 
 template solidityType(T: type, s: string) =
   func solidityType*(_: type T): string = s
@@ -64,3 +68,6 @@ func selector*(function: string, parameters: type tuple): FunctionSelector =
   var selector: array[4, byte]
   selector[0..<4] = hash[0..<4]
   FunctionSelector(selector)
+
+func topic*(event: string, parameters: type tuple): EventTopic =
+  EventTopic(hash(signature(event, parameters)))

tests/contractabi/testSelector.nim

@@ -1,5 +1,6 @@
 import std/unittest
-import pkg/contractabi/selector
+import pkg/stew/byteutils
+import pkg/contractabi
 
 suite "function selector":
 
@@ -29,3 +30,8 @@ suite "function selector":
   test "calculates solidity function selector":
     check $selector("transfer", (Address, UInt256)) == "0xa9059cbb"
     check $selector("transferFrom", (Address, Address, UInt256)) == "0x23b872dd"
+
+  test "calculates solidity event topic":
+    let expected = "0xddf252ad1be2c89b69c2b068fc378daa" &
+                     "952ba7f163c4a11628f55a4df523b3ef"
+    check $topic("Transfer", (Address, Address, UInt256)) == expected