// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package vm

import (
	"math/big"

	"github.com/dexon-foundation/dexon/common"
	"github.com/dexon-foundation/dexon/crypto"
)

// ContractRef is a reference to the contract's backing object
type ContractRef interface {
	Address() common.Address
}

// AccountRef implements ContractRef.
//
// Account references are used during EVM initialisation and
// it's primary use is to fetch addresses. Removing this object
// proves difficult because of the cached jump destinations which
// are fetched from the parent contract (i.e. the caller), which
// is a ContractRef.
type (
	AccountRef common.Address
	Bitvec     []byte
)

func (bits *Bitvec) Set(pos uint64) {
	(*bits)[pos/8] |= 0x80 >> (pos % 8)
}
func (bits *Bitvec) Set8(pos uint64) {
	(*bits)[pos/8] |= 0xFF >> (pos % 8)
	(*bits)[pos/8+1] |= ^(0xFF >> (pos % 8))
}

// codeSegment checks if the position is in a code segment.
func (bits *Bitvec) CodeSegment(pos uint64) bool {
	return ((*bits)[pos/8] & (0x80 >> (pos % 8))) == 0
}

// Address casts AccountRef to a Address
func (ar AccountRef) Address() common.Address { return (common.Address)(ar) }

// Contract represents an ethereum contract in the state database. It contains
// the contract code, calling arguments. Contract implements ContractRef
type Contract struct {
	// CallerAddress is the result of the caller which initialised this
	// contract. However when the "call method" is delegated this value
	// needs to be initialised to that of the caller's caller.
	CallerAddress common.Address
	caller        ContractRef
	self          ContractRef

	Jumpdests map[common.Hash]Bitvec // Aggregated result of JUMPDEST analysis.
	Analysis  Bitvec                 // Locally cached result of JUMPDEST analysis

	Code     []byte
	CodeHash common.Hash
	CodeAddr *common.Address
	Input    []byte

	Gas   uint64
	Value *big.Int
}

// NewContract returns a new contract environment for the execution of EVM.
func NewContract(caller ContractRef, object ContractRef, value *big.Int, gas uint64) *Contract {
	c := &Contract{CallerAddress: caller.Address(), caller: caller, self: object}

	if parent, ok := caller.(*Contract); ok {
		// Reuse JUMPDEST analysis from parent context if available.
		c.Jumpdests = parent.Jumpdests
	} else {
		c.Jumpdests = make(map[common.Hash]Bitvec)
	}

	// Gas should be a pointer so it can safely be reduced through the run
	// This pointer will be off the state transition
	c.Gas = gas
	// ensures a value is set
	c.Value = value

	return c
}

// AsDelegate sets the contract to be a delegate call and returns the current
// contract (for chaining calls)
func (c *Contract) AsDelegate() *Contract {
	// NOTE: caller must, at all times be a contract. It should never happen
	// that caller is something other than a Contract.
	parent := c.caller.(*Contract)
	c.CallerAddress = parent.CallerAddress
	c.Value = parent.Value

	return c
}

// GetByte returns the n'th byte in the contract's byte array
func (c *Contract) GetByte(n uint64) byte {
	if n < uint64(len(c.Code)) {
		return c.Code[n]
	}

	return 0
}

// Caller returns the caller of the contract.
//
// Caller will recursively call caller when the contract is a delegate
// call, including that of caller's caller.
func (c *Contract) Caller() common.Address {
	return c.CallerAddress
}

// UseGas attempts the use gas and subtracts it and returns true on success
func (c *Contract) UseGas(gas uint64) (ok bool) {
	if c.Gas < gas {
		return false
	}
	c.Gas -= gas
	return true
}

// Address returns the contracts address
func (c *Contract) Address() common.Address {
	return c.self.Address()
}

// SetCallCode sets the code of the contract and address of the backing data
// object
func (c *Contract) SetCallCode(addr *common.Address, hash common.Hash, code []byte) {
	c.Code = code
	c.CodeHash = hash
	c.CodeAddr = addr
}

// SetCodeOptionalHash can be used to provide code, but it's optional to provide hash.
// In case hash is not provided, the jumpdest analysis will not be saved to the parent context
func (c *Contract) SetCodeOptionalHash(addr *common.Address, CodeAndHash *CodeAndHash) {
	c.Code = CodeAndHash.Code
	c.CodeHash = CodeAndHash.Hash()
	c.CodeAddr = addr
}

type CodeAndHash struct {
	Code []byte
	hash common.Hash
}

func (c *CodeAndHash) Hash() common.Hash {
	if c.hash == (common.Hash{}) {
		c.hash = crypto.Keccak256Hash(c.Code)
	}
	return c.hash
}