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    // Copyright 2015-2017 Parity Technologies (UK) Ltd.
    // This file is part of Parity.

    // Parity is free software: you can redistribute it and/or modify
    // it under the terms of the GNU General Public License as published by
    // the Free Software Foundation, either version 3 of the License, or
    // (at your option) any later version.

    // Parity 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 General Public License for more details.

    // You should have received a copy of the GNU General Public License
    // along with Parity.  If not, see <http://www.gnu.org/licenses/>.

    use util::*;
    use super::u256_to_address;
    use evm::{self, CostType};
    use evm::instructions::{self, Instruction, InstructionInfo};
    use evm::interpreter::stack::Stack;
    use evm::schedule::Schedule;

    macro_rules! overflowing {
    	($x: expr) => {{
    		let (v, overflow) = $x;
    		if overflow { return Err(evm::Error::OutOfGas); }
    		v
    	}}
    }

    #[cfg_attr(feature="dev", allow(enum_variant_names))]
    enum Request<Cost: CostType> {
    	Gas(Cost),
    	GasMem(Cost, Cost),
    	GasMemProvide(Cost, Cost, Option<U256>),
    	GasMemCopy(Cost, Cost, Cost)
    }

    pub struct InstructionRequirements<Cost: CostType> {
    	pub gas_cost: Cost,
    	pub provide_gas: Option<Cost>,
    	pub memory_total_gas: Cost,
    	pub memory_required_size: usize,
    }

    pub struct Gasometer<Gas: CostType> {
    	pub current_gas: Gas,
    	pub current_mem_gas: Gas,
    }

    impl<Gas: CostType> Gasometer<Gas> {

    	pub fn new(current_gas: Gas) -> Self {
    		Gasometer {
    			current_gas: current_gas,
    			current_mem_gas: Gas::from(0),
    		}
    	}

    	pub fn verify_gas(&self, gas_cost: &Gas) -> evm::Result<()> {
    		match &self.current_gas < gas_cost {
    			true => Err(evm::Error::OutOfGas),
    			false => Ok(())
    		}
    	}

    	/// How much gas is provided to a CALL/CREATE, given that we need to deduct `needed` for this operation
    	/// and that we `requested` some.
    	pub fn gas_provided(&self, schedule: &Schedule, needed: Gas, requested: Option<U256>) -> evm::Result<Gas> {
    		// Try converting requested gas to `Gas` (`U256/u64`)
    		// but in EIP150 even if we request more we should never fail from OOG
    		let requested = requested.map(Gas::from_u256);

    		match schedule.sub_gas_cap_divisor {
    			Some(cap_divisor) if self.current_gas >= needed => {
    				let gas_remaining = self.current_gas - needed;
    				let max_gas_provided = match cap_divisor {
    					64 => gas_remaining - (gas_remaining >> 6),
    					cap_divisor => gas_remaining - gas_remaining / Gas::from(cap_divisor),
    				};

    				if let Some(Ok(r)) = requested {
    					Ok(min(r, max_gas_provided))
    				} else {
    					Ok(max_gas_provided)
    				}
    			},
    			_ => {
    				if let Some(r) = requested {
    					r
    				} else if self.current_gas >= needed {
    					Ok(self.current_gas - needed)
    				} else {
    					Ok(0.into())
    				}
    			},
    		}
    	}

    	#[cfg_attr(feature="dev", allow(cyclomatic_complexity))]
    	/// Determine how much gas is used by the given instruction, given the machine's state.
    	///
    	/// We guarantee that the final element of the returned tuple (`provided`) will be `Some`
    	/// iff the `instruction` is one of `CREATE`, or any of the `CALL` variants. In this case,
    	/// it will be the amount of gas that the current context provides to the child context.
    	pub fn requirements(
    		&mut self,
    		ext: &evm::Ext,
    		instruction: Instruction,
    		info: &InstructionInfo,
    		stack: &Stack<U256>,
    		current_mem_size: usize,
    	) -> evm::Result<InstructionRequirements<Gas>> {
    		let schedule = ext.schedule();
    		let tier = instructions::get_tier_idx(info.tier);
    		let default_gas = Gas::from(schedule.tier_step_gas[tier]);

    		let cost = match instruction {
    			instructions::JUMPDEST => {
    				Request::Gas(Gas::from(1))
    			},
    			instructions::SSTORE => {
    				let address = H256::from(stack.peek(0));
    				let newval = stack.peek(1);
    				let val = U256::from(&*ext.storage_at(&address));

    				let gas = if val.is_zero() && !newval.is_zero() {
    					schedule.sstore_set_gas
    				} else {
    					// Refund for below case is added when actually executing sstore
    					// !is_zero(&val) && is_zero(newval)
    					schedule.sstore_reset_gas
    				};
    				Request::Gas(Gas::from(gas))
    			},
    			instructions::SLOAD => {
    				Request::Gas(Gas::from(schedule.sload_gas))
    			},
    			instructions::BALANCE => {
    				Request::Gas(Gas::from(schedule.balance_gas))
    			},
    			instructions::EXTCODESIZE => {
    				Request::Gas(Gas::from(schedule.extcodesize_gas))
    			},
    			instructions::SUICIDE => {
    				let mut gas = Gas::from(schedule.suicide_gas);

    				let is_value_transfer = !ext.origin_balance().is_zero();
    				let address = u256_to_address(stack.peek(0));
    				if (
    					!schedule.no_empty && !ext.exists(&address)
    				) || (
    					schedule.no_empty && is_value_transfer && !ext.exists_and_not_null(&address)
    				) {
    					gas = overflowing!(gas.overflow_add(schedule.suicide_to_new_account_cost.into()));
    				}

    				Request::Gas(gas)
    			},
    			instructions::MSTORE | instructions::MLOAD => {
    				Request::GasMem(default_gas, mem_needed_const(stack.peek(0), 32)?)
    			},
    			instructions::MSTORE8 => {
    				Request::GasMem(default_gas, mem_needed_const(stack.peek(0), 1)?)
    			},
    			instructions::RETURN => {
    				Request::GasMem(default_gas, mem_needed(stack.peek(0), stack.peek(1))?)
    			},
    			instructions::SHA3 => {
    				let w = overflowing!(add_gas_usize(Gas::from_u256(*stack.peek(1))?, 31));
    				let words = w >> 5;
    				let gas = Gas::from(schedule.sha3_gas) + (Gas::from(schedule.sha3_word_gas) * words);
    				Request::GasMem(gas, mem_needed(stack.peek(0), stack.peek(1))?)
    			},
    			instructions::CALLDATACOPY | instructions::CODECOPY => {
    				Request::GasMemCopy(default_gas, mem_needed(stack.peek(0), stack.peek(2))?, Gas::from_u256(*stack.peek(2))?)
    			},
    			instructions::EXTCODECOPY => {
    				Request::GasMemCopy(schedule.extcodecopy_base_gas.into(), mem_needed(stack.peek(1), stack.peek(3))?, Gas::from_u256(*stack.peek(3))?)
    			},
    			instructions::LOG0...instructions::LOG4 => {
    				let no_of_topics = instructions::get_log_topics(instruction);
    				let log_gas = schedule.log_gas + schedule.log_topic_gas * no_of_topics;

    				let data_gas = overflowing!(Gas::from_u256(*stack.peek(1))?.overflow_mul(Gas::from(schedule.log_data_gas)));
    				let gas = overflowing!(data_gas.overflow_add(Gas::from(log_gas)));
    				Request::GasMem(gas, mem_needed(stack.peek(0), stack.peek(1))?)
    			},
    			instructions::CALL | instructions::CALLCODE => {
    				let mut gas = Gas::from(schedule.call_gas);
    				let mem = cmp::max(
    					mem_needed(stack.peek(5), stack.peek(6))?,
    					mem_needed(stack.peek(3), stack.peek(4))?
    				);

    				let address = u256_to_address(stack.peek(1));
    				let is_value_transfer = !stack.peek(2).is_zero();

    				if instruction == instructions::CALL && (
    					(!schedule.no_empty && !ext.exists(&address))
    					||
    					(schedule.no_empty && is_value_transfer && !ext.exists_and_not_null(&address))
    				) {
    					gas = overflowing!(gas.overflow_add(schedule.call_new_account_gas.into()));
    				}

    				if is_value_transfer {
    					gas = overflowing!(gas.overflow_add(schedule.call_value_transfer_gas.into()));
    				}

    				let requested = *stack.peek(0);

    				Request::GasMemProvide(gas, mem, Some(requested))
    			},
    			instructions::DELEGATECALL => {
    				let gas = Gas::from(schedule.call_gas);
    				let mem = cmp::max(
    					mem_needed(stack.peek(4), stack.peek(5))?,
    					mem_needed(stack.peek(2), stack.peek(3))?
    				);
    				let requested = *stack.peek(0);

    				Request::GasMemProvide(gas, mem, Some(requested))
    			},
    			instructions::CREATE => {
    				let gas = Gas::from(schedule.create_gas);
    				let mem = mem_needed(stack.peek(1), stack.peek(2))?;

    				Request::GasMemProvide(gas, mem, None)
    			},
    			instructions::EXP => {
    				let expon = stack.peek(1);
    				let bytes = ((expon.bits() + 7) / 8) as usize;
    				let gas = Gas::from(schedule.exp_gas + schedule.exp_byte_gas * bytes);
    				Request::Gas(gas)
    			},
    			_ => Request::Gas(default_gas),
    		};

    		Ok(match cost {
    			Request::Gas(gas) => {
    				InstructionRequirements {
    					gas_cost: gas,
    					provide_gas: None,
    					memory_required_size: 0,
    					memory_total_gas: self.current_mem_gas,
    				}
    			},
    			Request::GasMem(gas, mem_size) => {
    				let (mem_gas_cost, new_mem_gas, new_mem_size) = self.mem_gas_cost(schedule, current_mem_size, &mem_size)?;
    				let gas = overflowing!(gas.overflow_add(mem_gas_cost));
    				InstructionRequirements {
    					gas_cost: gas,
    					provide_gas: None,
    					memory_required_size: new_mem_size,
    					memory_total_gas: new_mem_gas,
    				}
    			},
    			Request::GasMemProvide(gas, mem_size, requested) => {
    				let (mem_gas_cost, new_mem_gas, new_mem_size) = self.mem_gas_cost(schedule, current_mem_size, &mem_size)?;
    				let gas = overflowing!(gas.overflow_add(mem_gas_cost));
    				let provided = self.gas_provided(schedule, gas, requested)?;
    				let total_gas = overflowing!(gas.overflow_add(provided));

    				InstructionRequirements {
    					gas_cost: total_gas,
    					provide_gas: Some(provided),
    					memory_required_size: new_mem_size,
    					memory_total_gas: new_mem_gas,
    				}
    			},
    			Request::GasMemCopy(gas, mem_size, copy) => {
    				let (mem_gas_cost, new_mem_gas, new_mem_size) = self.mem_gas_cost(schedule, current_mem_size, &mem_size)?;
    				let copy = overflowing!(add_gas_usize(copy, 31)) >> 5;
    				let copy_gas = Gas::from(schedule.copy_gas) * copy;
    				let gas = overflowing!(gas.overflow_add(copy_gas));
    				let gas = overflowing!(gas.overflow_add(mem_gas_cost));

    				InstructionRequirements {
    					gas_cost: gas,
    					provide_gas: None,
    					memory_required_size: new_mem_size,
    					memory_total_gas: new_mem_gas,
    				}
    			},
    		})
    	}

    	fn mem_gas_cost(&self, schedule: &evm::Schedule, current_mem_size: usize, mem_size: &Gas) -> evm::Result<(Gas, Gas, usize)> {
    		let gas_for_mem = |mem_size: Gas| {
    			let s = mem_size >> 5;
    			// s * memory_gas + s * s / quad_coeff_div
    			let a = overflowing!(s.overflow_mul(Gas::from(schedule.memory_gas)));

    			// Calculate s*s/quad_coeff_div
    			assert_eq!(schedule.quad_coeff_div, 512);
    			let b = overflowing!(s.overflow_mul_shr(s, 9));
    			Ok(overflowing!(a.overflow_add(b)))
    		};

    		let current_mem_size = Gas::from(current_mem_size);
    		let req_mem_size_rounded = (overflowing!(mem_size.overflow_add(Gas::from(31 as usize))) >> 5) << 5;

    		let (mem_gas_cost, new_mem_gas) = if req_mem_size_rounded > current_mem_size {
    			let new_mem_gas = gas_for_mem(req_mem_size_rounded)?;
    			(new_mem_gas - self.current_mem_gas, new_mem_gas)
    		} else {
    			(Gas::from(0), self.current_mem_gas)
    		};

    		Ok((mem_gas_cost, new_mem_gas, req_mem_size_rounded.as_usize()))
    	}
    }

    #[inline]
    fn mem_needed_const<Gas: CostType>(mem: &U256, add: usize) -> evm::Result<Gas> {
    	Gas::from_u256(overflowing!(mem.overflowing_add(U256::from(add))))
    }

    #[inline]
    fn mem_needed<Gas: CostType>(offset: &U256, size: &U256) -> evm::Result<Gas> {
    	if size.is_zero() {
    		return Ok(Gas::from(0));
    	}

    	Gas::from_u256(overflowing!(offset.overflowing_add(*size)))
    }

    #[inline]
    fn add_gas_usize<Gas: CostType>(value: Gas, num: usize) -> (Gas, bool) {
    	value.overflow_add(Gas::from(num))
    }

    #[test]
    fn test_mem_gas_cost() {
    	// given
    	let gasometer = Gasometer::<U256>::new(U256::zero());
    	let schedule = evm::Schedule::default();
    	let current_mem_size = 5;
    	let mem_size = !U256::zero();

    	// when
    	let result = gasometer.mem_gas_cost(&schedule, current_mem_size, &mem_size);

    	// then
    	if result.is_ok() {
    		assert!(false, "Should fail with OutOfGas");
    	}
    }

    #[test]
    fn test_calculate_mem_cost() {
    	// given
    	let gasometer = Gasometer::<usize>::new(0);
    	let schedule = evm::Schedule::default();
    	let current_mem_size = 0;
    	let mem_size = 5;

    	// when
    	let (mem_cost, new_mem_gas, mem_size) = gasometer.mem_gas_cost(&schedule, current_mem_size, &mem_size).unwrap();

    	// then
    	assert_eq!(mem_cost, 3);
    	assert_eq!(new_mem_gas, 3);
    	assert_eq!(mem_size, 32);
    }

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