// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum 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.

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

use std::time::{Duration, SystemTime, UNIX_EPOCH};

/// Temporary trait for `checked operations` on SystemTime until these are available in the standard library
pub trait CheckedSystemTime {
    /// Returns `Some<SystemTime>` when the result less or equal to `i32::max_value` to prevent `SystemTime` to panic because
    /// it is platform specific, possible representations are i32, i64, u64 or Duration. `None` otherwise
    fn checked_add(self, _d: Duration) -> Option<SystemTime>;
    /// Returns `Some<SystemTime>` when the result is successful and `None` when it is not
    fn checked_sub(self, _d: Duration) -> Option<SystemTime>;
}

impl CheckedSystemTime for SystemTime {
    fn checked_add(self, dur: Duration) -> Option<SystemTime> {
        let this_dur = self.duration_since(UNIX_EPOCH).ok()?;
        let total_time = this_dur.checked_add(dur)?;

        if total_time.as_secs() <= i32::max_value() as u64 {
            Some(self + dur)
        } else {
            None
        }
    }

    fn checked_sub(self, dur: Duration) -> Option<SystemTime> {
        let this_dur = self.duration_since(UNIX_EPOCH).ok()?;
        let total_time = this_dur.checked_sub(dur)?;

        if total_time.as_secs() <= i32::max_value() as u64 {
            Some(self - dur)
        } else {
            None
        }
    }
}

#[cfg(test)]
mod tests {
    #[test]
    fn it_works() {
        use super::CheckedSystemTime;
        use std::time::{Duration, SystemTime, UNIX_EPOCH};

        assert!(CheckedSystemTime::checked_add(
            UNIX_EPOCH,
            Duration::new(i32::max_value() as u64 + 1, 0)
        )
        .is_none());
        assert!(CheckedSystemTime::checked_add(
            UNIX_EPOCH,
            Duration::new(i32::max_value() as u64, 0)
        )
        .is_some());
        assert!(CheckedSystemTime::checked_add(
            UNIX_EPOCH,
            Duration::new(i32::max_value() as u64 - 1, 1_000_000_000)
        )
        .is_some());

        assert!(CheckedSystemTime::checked_sub(UNIX_EPOCH, Duration::from_secs(120)).is_none());
        assert!(
            CheckedSystemTime::checked_sub(SystemTime::now(), Duration::from_secs(1000)).is_some()
        );
    }
}
