// Copyright 2015-2019 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.

// Parity Ethereum 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 Ethereum 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 Ethereum.  If not, see <http://www.gnu.org/licenses/>.

//! Evm interface.

use ethereum_types::{U128, U256, U512};
use std::{cmp, fmt, ops};
use vm::{Error, Ext, GasLeft, Result, ReturnData};

/// Finalization result. Gas Left: either it is a known value, or it needs to be computed by processing
/// a return instruction.
#[derive(Debug)]
pub struct FinalizationResult {
    /// Final amount of gas left.
    pub gas_left: U256,
    /// Apply execution state changes or revert them.
    pub apply_state: bool,
    /// Return data buffer.
    pub return_data: ReturnData,
}

/// Types that can be "finalized" using an EVM.
///
/// In practice, this is just used to define an inherent impl on
/// `Reult<GasLeft<'a>>`.
pub trait Finalize {
    /// Consume the externalities, call return if necessary, and produce call result.
    fn finalize<E: Ext>(self, ext: E) -> Result<FinalizationResult>;
}

impl Finalize for Result<GasLeft> {
    fn finalize<E: Ext>(self, ext: E) -> Result<FinalizationResult> {
        match self {
            Ok(GasLeft::Known(gas_left)) => Ok(FinalizationResult {
                gas_left,
                apply_state: true,
                return_data: ReturnData::empty(),
            }),
            Ok(GasLeft::NeedsReturn {
                gas_left,
                data,
                apply_state,
            }) => ext
                .ret(&gas_left, &data, apply_state)
                .map(|gas_left| FinalizationResult {
                    gas_left,
                    apply_state,
                    return_data: data,
                }),
            Err(err) => Err(err),
        }
    }
}

impl Finalize for Error {
    fn finalize<E: Ext>(self, _ext: E) -> Result<FinalizationResult> {
        Err(self)
    }
}

/// Cost calculation type. For low-gas usage we calculate costs using usize instead of U256
pub trait CostType:
    Sized
    + From<usize>
    + Copy
    + Send
    + ops::Mul<Output = Self>
    + ops::Div<Output = Self>
    + ops::Add<Output = Self>
    + ops::Sub<Output = Self>
    + ops::Shr<usize, Output = Self>
    + ops::Shl<usize, Output = Self>
    + cmp::Ord
    + fmt::Debug
{
    /// Converts this cost into `U256`
    fn as_u256(&self) -> U256;
    /// Tries to fit `U256` into this `Cost` type
    fn from_u256(val: U256) -> Result<Self>;
    /// Convert to usize (may panic)
    fn as_usize(&self) -> usize;
    /// Add with overflow
    fn overflow_add(self, other: Self) -> (Self, bool);
    /// Multiple with overflow
    fn overflow_mul(self, other: Self) -> (Self, bool);
    /// Single-step full multiplication and shift: `(self*other) >> shr`
    /// Should not overflow on intermediate steps
    fn overflow_mul_shr(self, other: Self, shr: usize) -> (Self, bool);
}

impl CostType for U256 {
    fn as_u256(&self) -> U256 {
        *self
    }

    fn from_u256(val: U256) -> Result<Self> {
        Ok(val)
    }

    fn as_usize(&self) -> usize {
        self.as_u64() as usize
    }

    fn overflow_add(self, other: Self) -> (Self, bool) {
        self.overflowing_add(other)
    }

    fn overflow_mul(self, other: Self) -> (Self, bool) {
        self.overflowing_mul(other)
    }

    fn overflow_mul_shr(self, other: Self, shr: usize) -> (Self, bool) {
        let x = self.full_mul(other);
        let U512(parts) = x;
        let overflow = (parts[4] | parts[5] | parts[6] | parts[7]) > 0;
        let U512(parts) = x >> shr;
        (U256([parts[0], parts[1], parts[2], parts[3]]), overflow)
    }
}

impl CostType for usize {
    fn as_u256(&self) -> U256 {
        U256::from(*self)
    }

    fn from_u256(val: U256) -> Result<Self> {
        let res = val.low_u64() as usize;

        // validate if value fits into usize
        if U256::from(res) != val {
            return Err(Error::OutOfGas);
        }

        Ok(res)
    }

    fn as_usize(&self) -> usize {
        *self
    }

    fn overflow_add(self, other: Self) -> (Self, bool) {
        self.overflowing_add(other)
    }

    fn overflow_mul(self, other: Self) -> (Self, bool) {
        self.overflowing_mul(other)
    }

    fn overflow_mul_shr(self, other: Self, shr: usize) -> (Self, bool) {
        let (c, o) = U128::from(self).overflowing_mul(U128::from(other));
        let U128(parts) = c;
        let overflow = o | (parts[1] > 0);
        let U128(parts) = c >> shr;
        let result = parts[0] as usize;
        let overflow = overflow | (parts[0] > result as u64);
        (result, overflow)
    }
}

#[cfg(test)]
mod tests {
    use super::CostType;
    use ethereum_types::U256;

    #[test]
    fn should_calculate_overflow_mul_shr_without_overflow() {
        // given
        let num = 1048576;

        // when
        let (res1, o1) = U256::from(num).overflow_mul_shr(U256::from(num), 20);
        let (res2, o2) = num.overflow_mul_shr(num, 20);

        // then
        assert_eq!(res1, U256::from(num));
        assert!(!o1);
        assert_eq!(res2, num);
        assert!(!o2);
    }

    #[test]
    fn should_calculate_overflow_mul_shr_with_overflow() {
        // given
        let max = u64::max_value();
        let num1 = U256([max, max, max, max]);
        let num2 = usize::max_value();

        // when
        let (res1, o1) = num1.overflow_mul_shr(num1, 256);
        let (res2, o2) = num2.overflow_mul_shr(num2, 64);

        // then
        assert_eq!(res2, num2 - 1);
        assert!(o2);

        assert_eq!(res1, !U256::zero() - U256::one());
        assert!(o1);
    }

    #[test]
    fn should_validate_u256_to_usize_conversion() {
        // given
        let v = U256::from(usize::max_value()) + U256::from(1);

        // when
        let res = usize::from_u256(v);

        // then
        assert!(res.is_err());
    }
}