Implementing EIP-1559

- Add required constants to Web3
- Add public Web3 extension with `verifyEip1559Block` and `calcBaseFee` methods
- Add draft ChainVersion enum to differ Blockchain versions

Sources/web3swift/Web3/Web3+Constants.swift

@@ -7,9 +7,16 @@
 //
 
 import Foundation
+import BigInt
 
 struct Constants {
     static let infuraHttpScheme = ".infura.io/v3/"
     static let infuraWsScheme = ".infura.io/ws/v3/"
     static let infuraToken = "4406c3acf862426c83991f1752c46dd8"
 }
+
+extension Web3 {
+    static let BaseFeeChangeDenominator: BigUInt = 8           // Bounds the amount the base fee can change between blocks.
+    static let ElasticityMultiplier: BigUInt     = 2           // Bounds the maximum gas limit an EIP-1559 block may have.
+    static let InitialBaseFee: BigUInt           = 1000000000  // Initial base fee for EIP-1559 blocks.
+}

Sources/web3swift/Web3/Web3+EIP1559.swift

@@ -0,0 +1,69 @@
+//
+//  File.swift
+//  
+//
+//  Created by Yaroslav on 14.03.2022.
+//
+
+import Foundation
+import BigInt
+
+/// EIP-1559 Base fee extension
+public extension Web3 {
+    func verifyEip1559Block(chain version: ChainVersion, parent: Block, current: Block) -> Bool {
+        return true
+    }
+
+    func calcBaseFee(chain version: ChainVersion, parent: Block) -> BigUInt {
+        // If the current block is the first EIP-1559 block, return the InitialBaseFee.
+        guard .London == version else { return Web3.InitialBaseFee }
+
+        let parentGasTarget = parent.gasLimit / Web3.ElasticityMultiplier
+
+        // If the parent gasUsed is the same as the target, the baseFee remains unchanged.
+        if parent.gasUsed == parentGasTarget {
+            return parent.baseFeePerGas
+
+        } else if parent.gasUsed > parentGasTarget {
+            // If the parent block used more gas than its target, the baseFee should increase.
+            let gasUsedDelta = parent.gasUsed - parentGasTarget
+            let baseFeePerGasDelta = max(parent.baseFeePerGas * gasUsedDelta / parentGasTarget / Web3.BaseFeeChangeDenominator, 1)
+            let expectedBaseFeePerGas = parent.baseFeePerGas + baseFeePerGasDelta
+
+            return expectedBaseFeePerGas
+        } else {
+            // Otherwise if the parent block used less gas than its target, the baseFee should decrease.
+            let gasUsedDelta = parentGasTarget - parent.gasUsed
+            let baseFeePerGasDelta = parent.baseFeePerGas * gasUsedDelta / parentGasTarget / Web3.BaseFeeChangeDenominator
+            let expectedBaseFeePerGas = parent.baseFeePerGas - baseFeePerGasDelta
+
+            return expectedBaseFeePerGas
+        }
+    }
+}
+
+
+public extension Web3 {
+    enum ChainVersion {
+        case Byzantium
+        case Petersburg
+        case Istanbul
+        case MuirGlacier
+        case Berlin
+        case London
+        case ArrowGlacier
+        case MergeFork
+        /* 
+            ByzantiumBlock          // Byzantium switch block
+            ConstantinopleBlock     // Constantinople switch block
+            PetersburgBlock         // Petersburg switch block
+            IstanbulBlock           // Istanbul switch block
+            MuirGlacierBlock        // Eip-2384 (bomb delay) switch block
+            BerlinBlock             // Berlin switch block
+            LondonBlock             // London switch block
+            ArrowGlacierBlock       // Eip-4345 (bomb delay) switch block
+            MergeForkBlock
+        */
+    }
+}
+