[PSDK-102] Implement wallet hydration

lib/coinbase/address.rb

@@ -39,6 +39,14 @@ def id
       @model.address_id
     end
 
+    # Sets the private key backing the Address. This key is used to sign transactions.
+    # @param key [Eth::Key] The key backing the Address
+    def key=(key)
+      raise 'Private key is already set' unless @key.nil?
+
+      @key = key
+    end
+
     # Returns the balances of the Address.
     # @return [BalanceMap] The balances of the Address, keyed by asset ID. Ether balances are denominated
     #  in ETH.

lib/coinbase/wallet.rb

@@ -76,7 +76,7 @@ def initialize(model, seed: nil, address_models: [])
 
       # TODO: Adjust derivation path prefix based on network protocol.
       @address_path_prefix = "m/44'/60'/0'/0"
-      @address_index = 0
+      @private_key_index = 0
 
       if address_models.any?
         derive_addresses(address_models)
@@ -99,6 +99,24 @@ def network_id
       Coinbase.to_sym(@model.network_id)
     end
 
+    # Sets the seed of the Wallet. This seed is used to derive keys and sign transactions.
+    # @param seed [String] The seed to set. Expects a 32-byte hexadecimal with no 0x prefix.
+    def seed=(seed)
+      raise ArgumentError, 'Seed must be 32 bytes' if seed.length != 64
+      raise 'Seed is already set' unless @master.nil?
+      raise 'Cannot set seed for Wallet with non-zero private key index' if @private_key_index.positive?
+
+      @master = MoneyTree::Master.new(seed_hex: seed)
+
+      @addresses.each do
+        key = derive_key
+        a = address(key.address.to_s)
+        raise "Seed does not match wallet; cannot find address #{key.address}" if a.nil?
+
+        a.key = key
+      end
+    end
+
     # Creates a new Address in the Wallet.
     # @return [Address] The new Address
     def create_address
@@ -122,7 +140,7 @@ def create_address
     # Returns the default address of the Wallet.
     # @return [Address] The default address
     def default_address
-      address(@model.default_address.address_id)
+      address(@model.default_address&.address_id)
     end
 
     # Returns the Address with the given ID.
@@ -275,8 +293,9 @@ def derive_address(address_map, address_model)
     def derive_key
       raise 'Cannot derive key for Wallet without seed loaded' if @master.nil?
 
-      path = "#{@address_path_prefix}/#{@address_index}"
+      path = "#{@address_path_prefix}/#{@private_key_index}"
       private_key = @master.node_for_path(path).private_key.to_hex
+      @private_key_index += 1
       Eth::Key.new(priv: private_key)
     end
 
@@ -287,7 +306,6 @@ def derive_key
     def cache_address(address_model, key)
       address = Address.new(address_model, key)
       @addresses << address
-      @address_index += 1
       address
     end
 

spec/unit/coinbase/address_spec.rb

@@ -104,6 +104,18 @@
     end
   end
 
+  describe '#key=' do
+    let(:unhydrated_address) { described_class.new(model, nil) }
+
+    it 'sets the key' do
+      expect { unhydrated_address.key = key }.not_to raise_error
+    end
+
+    it 'raises an error if the key is already set' do
+      expect { address.key = key }.to raise_error('Private key is already set')
+    end
+  end
+
   describe '#balance' do
     let(:response) do
       Coinbase::Client::Balance.new(

spec/unit/coinbase/wallet_spec.rb

@@ -159,6 +159,36 @@
     end
   end
 
+  describe '#seed=' do
+    let(:seedless_wallet) do
+      described_class.new(model_with_default_address, seed: '', address_models: [address_model1])
+    end
+
+    it 'sets the seed' do
+      seedless_wallet.seed = '86fc9fba421dcc6ad42747f14132c3cd975bd9fb1454df84ce5ea554f2542fbe'
+      expect(seedless_wallet.can_sign?).to be true
+      expect(seedless_wallet.default_address.can_sign?).to be true
+    end
+
+    it 'raises an error for an invalid seed' do
+      expect do
+        seedless_wallet.seed = 'invalid seed'
+      end.to raise_error(ArgumentError, 'Seed must be 32 bytes')
+    end
+
+    it 'raises an error if the wallet is already hydrated' do
+      expect do
+        wallet.seed = '86fc9fba421dcc6ad42747f14132c3cd975bd9fb1454df84ce5ea554f2542fbe'
+      end.to raise_error('Seed is already set')
+    end
+
+    it 'raises an error if it is the wrong seed' do
+      expect do
+        seedless_wallet.seed = '86fc9fba421dcc6ad42747f14132c3cd975bd9fb1454df84ce5ea554f2542fbf'
+      end.to raise_error(/Seed does not match wallet/)
+    end
+  end
+
   describe '#create_address' do
     it 'creates a new address' do
       expect(wallet.addresses.length).to eq(1)