From c97b4e89fe6e5c5f1b75535771f0bc649d9bbdef Mon Sep 17 00:00:00 2001
From: Jeffrey Wilcke <geffobscura@gmail.com>
Date: Fri, 30 Oct 2015 09:59:21 +0100
Subject: [PATCH] accounts/contract: implemented callable contracts

---
 accounts/contract/contract.go | 87 +++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 accounts/contract/contract.go

diff --git a/accounts/contract/contract.go b/accounts/contract/contract.go
new file mode 100644
index 0000000000..d339a9b15f
--- /dev/null
+++ b/accounts/contract/contract.go
@@ -0,0 +1,87 @@
+package contract
+
+import (
+	"math/big"
+	"strings"
+
+	"github.com/ethereum/go-ethereum/accounts/abi"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/core/state"
+)
+
+type Contract struct {
+	backend core.Backend
+	abi.ABI
+	Address common.Address
+}
+
+func getAccount(backend core.Backend) *state.StateObject {
+	statedb, _ := state.New(backend.BlockChain().CurrentHeader().Root, backend.ChainDb())
+	accounts, err := backend.AccountManager().Accounts()
+	if err != nil || len(accounts) == 0 {
+		return statedb.GetOrNewStateObject(common.Address{})
+	} else {
+		return statedb.GetOrNewStateObject(accounts[0].Address)
+	}
+}
+
+func New(definition string, addr common.Address, backend core.Backend) (*Contract, error) {
+	abi, err := abi.JSON(strings.NewReader(definition))
+	if err != nil {
+		return nil, err
+	}
+
+	return &Contract{
+		backend: backend,
+		ABI:     abi,
+		Address: addr,
+	}, nil
+}
+
+func (c *Contract) Call(method string, args ...interface{}) ([]byte, *big.Int, error) {
+	msg := CallMessage{
+		gas:      new(big.Int).Set(common.MaxBig),
+		gasPrice: new(big.Int),
+		value:    new(big.Int),
+		from:     getAccount(c.backend),
+	}
+	return c.CallWithMessage(msg, method, args...)
+}
+
+func (c *Contract) CallWithMessage(msg CallMessage, method string, args ...interface{}) ([]byte, *big.Int, error) {
+	input, err := c.ABI.Pack(method, args...)
+	if err != nil {
+		return nil, nil, err
+	}
+	msg.data = input
+	msg.to = &c.Address
+
+	header := c.backend.BlockChain().CurrentHeader()
+	statedb, err := state.New(header.Root, c.backend.ChainDb())
+	if err != nil {
+		return nil, nil, err
+	}
+	vmenv := core.NewEnv(statedb, c.backend.BlockChain(), msg, header)
+	gp := new(core.GasPool).AddGas(common.MaxBig)
+
+	return core.ApplyMessage(vmenv, msg, gp)
+}
+
+// CallMessage is the message type used for call transations.
+type CallMessage struct {
+	from          *state.StateObject
+	to            *common.Address
+	gas, gasPrice *big.Int
+	value         *big.Int
+	data          []byte
+}
+
+// accessor boilerplate to implement core.Message
+func (m CallMessage) From() (common.Address, error) { return m.from.Address(), nil }
+func (m CallMessage) Nonce() uint64                 { return m.from.Nonce() }
+func (m CallMessage) To() *common.Address           { return m.to }
+func (m CallMessage) GasPrice() *big.Int            { return m.gasPrice }
+func (m CallMessage) Gas() *big.Int                 { return m.gas }
+func (m CallMessage) Value() *big.Int               { return m.value }
+func (m CallMessage) Data() []byte                  { return m.data }