// Copyright 2021 Shin Yoshida
//
// "LGPL-3.0-or-later OR Apache-2.0 OR BSD-2-Clause"
//
// This is part of bsn1
//
//  bsn1 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.
//
//  bsn1 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 bsn1.  If not, see <http://www.gnu.org/licenses/>.
//
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//
// Redistribution and use in source and binary forms, with or without modification, are permitted
// provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
//    conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright notice, this
//    list of conditions and the following disclaimer in the documentation and/or other
//    materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
// IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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// NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
// WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.

//! Provides functions to serialize/deserialize contents octets.

use crate::{Error, StackBuffer};
use core::mem::{size_of, size_of_val};

/// Serializes integer as contents octets.
///
/// This function is common for BER, DER, and CER.
///
/// # Wargnings
///
/// This function assumes that the CPU adopts 2's complement to represent negative value.
pub fn from_integer(val: i128) -> impl AsRef<[u8]> {
    if val < 0 {
        from_integer_negative(val)
    } else {
        from_integer_positive(val)
    }
}

fn from_integer_positive(val: i128) -> StackBuffer {
    debug_assert!(0 <= val);

    let len = (8 * size_of_val(&val) - val.leading_zeros() as usize) / 8 + 1;
    let mut buffer = StackBuffer::new();
    unsafe { buffer.set_len(len) };

    let mut val = val;
    for i in (0..len).rev() {
        buffer[i] = val as u8;
        val >>= 8;
    }

    buffer
}

/// # Wargnings
///
/// This function assumes that the CPU adopt 2's complement to represent negative value.
fn from_integer_negative(val: i128) -> StackBuffer {
    debug_assert!(val < 0);

    // I don't think the behavior is not defined to shift negative value, however, 'ISO/IEC
    // 1539:1991 (C99)' defines the spec of the division and reminder.
    //
    // In short, if the numerator is nagative and the divisor is positive,
    //
    // - The reminder equals to 0 or less than 0.
    // - The result of division is truncated towards 0.
    let shift = |v: i128| -> (i128, u8) { ((v + 1) / 256 - 1, (v % 256 + 256) as u8) };

    let len = (8 * size_of_val(&val) - val.leading_ones() as usize) / 8 + 1;
    let mut buffer = StackBuffer::new();
    unsafe { buffer.set_len(len) };

    let mut val = val;
    for i in (0..len).rev() {
        buffer[i] = shift(val).1;
        val = shift(val).0;
    }

    buffer
}

/// Parses `bytes` as a contents of Integer.
///
/// This function is common for BER, DER, and CER.
///
/// # Wargnings
///
/// This function assumes that the CPU adopts 2's complement to represent negative value.
#[inline]
pub fn to_integer(bytes: &[u8]) -> Result<i128, Error> {
    if size_of::<i128>() < bytes.len() {
        Err(Error::OverFlow)
    } else if bytes.is_empty() {
        Err(Error::UnTerminatedBytes)
    } else {
        if 1 < bytes.len() {
            if (bytes[0] == 0) && (bytes[1] & 0x80 == 0x00) {
                return Err(Error::RedundantBytes);
            }
            if (bytes[0] == 0xff) && (bytes[1] & 0x80 == 0x80) {
                return Err(Error::RedundantBytes);
            }
        }

        let init: i128 = if bytes[0] & 0x80 == 0x80 { -1 } else { 0 };
        let ret = bytes.iter().fold(init, |acc, &o| (acc * 256) + (o as i128));
        Ok(ret)
    }
}

/// Serializes boolean as contents octets.
///
/// This function is common for BER, DER, and CER.
#[inline]
pub fn from_bool(val: bool) -> impl AsRef<[u8]> {
    if val {
        [0xff] as [u8; 1]
    } else {
        [0x00] as [u8; 1]
    }
}

/// Parses `bytes` as a BER contents of Bool.
///
/// This function is valid only for the contents of BER, and not applied to the contents of
/// DER nor CER.
#[inline]
pub fn to_bool_ber(bytes: &[u8]) -> Result<bool, Error> {
    if bytes.is_empty() {
        Err(Error::UnTerminatedBytes)
    } else if 1 < bytes.len() {
        Err(Error::InvalidContents)
    } else if bytes[0] == 0x00 {
        Ok(false)
    } else {
        Ok(true)
    }
}

/// Parses `bytes` as a DER contents of Bool.
///
/// This function is valid only for the contents of DER, and not applied to the contents of
/// 'CER' nor 'BER.'
#[inline]
pub fn to_bool_der(bytes: &[u8]) -> Result<bool, Error> {
    if bytes.is_empty() {
        Err(Error::UnTerminatedBytes)
    } else if 1 < bytes.len() {
        Err(Error::InvalidContents)
    } else if bytes[0] == 0x00 {
        Ok(false)
    } else if bytes[0] == 0xff {
        Ok(true)
    } else {
        Err(Error::InvalidContents)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_from_integer() {
        // Negative
        {
            // -1
            assert_eq!(&[0xff], from_integer(-1).as_ref());
            // -0x80
            assert_eq!(&[0x80], from_integer(-0x80).as_ref());
            // -0x81
            assert_eq!(&[0xff, 0x7f], from_integer(-0x81).as_ref());
            // -0x0100
            assert_eq!(&[0xff, 0x00], from_integer(-0x0100).as_ref());
            // -0x0101
            assert_eq!(&[0xfe, 0xff], from_integer(-0x0101).as_ref());
            // -0x8000
            assert_eq!(&[0x80, 0x00], from_integer(-0x8000).as_ref());
            // -0x8001
            assert_eq!(&[0xff, 0x7f, 0xff], from_integer(-0x8001).as_ref());
            // i128::MIN
            {
                let bytes: &mut [u8] = &mut [0x00; size_of::<i128>()];
                bytes[0] = 0x80;
                assert_eq!(bytes, from_integer(std::i128::MIN).as_ref());
            }
        }
        // 0
        assert_eq!(&[0x00], from_integer(0).as_ref());
        // Positive
        {
            // 1
            assert_eq!(&[0x01], from_integer(1).as_ref());
            // 0x7f
            assert_eq!(&[0x7f], from_integer(0x7f).as_ref());
            // 0x80
            assert_eq!(&[0x00, 0x80], from_integer(0x80).as_ref());
            // 0xff
            assert_eq!(&[0x00, 0xff], from_integer(0xff).as_ref());
            // 0x0100
            assert_eq!(&[0x01, 0x00], from_integer(0x0100).as_ref());
            // 0x7fff
            assert_eq!(&[0x7f, 0xff], from_integer(0x7fff).as_ref());
            // 0x8000
            assert_eq!(&[0x00, 0x80, 0x00], from_integer(0x8000).as_ref());
            // i128::MAX
            {
                let bytes: &mut [u8] = &mut [0xff; size_of::<i128>()];
                bytes[0] = 0x7f;
                assert_eq!(bytes, from_integer(std::i128::MAX).as_ref());
            }
        }
    }

    #[test]
    fn test_to_integer() {
        // Negative
        {
            // -1
            assert_eq!(-1, to_integer(&[0xff]).unwrap());
            // -0x80
            assert_eq!(-0x80, to_integer(&[0x80]).unwrap());
            // -0x81
            assert_eq!(-0x81, to_integer(&[0xff, 0x7f]).unwrap());
            // -0x0100
            assert_eq!(-0x0100, to_integer(&[0xff, 0x00]).unwrap());
            // -0x0101
            assert_eq!(-0x0101, to_integer(&[0xfe, 0xff]).unwrap());
            // -0x8000
            assert_eq!(-0x8000, to_integer(&[0x80, 0x00]).unwrap());
            // -0x8001
            assert_eq!(-0x8001, to_integer(&[0xff, 0x7f, 0xff]).unwrap());
            // i128::MIN
            {
                let bytes: &mut [u8] = &mut [0x00; size_of::<i128>()];
                bytes[0] = 0x80;
                assert_eq!(std::i128::MIN, to_integer(bytes).unwrap());
            }
        }
        // 0
        assert_eq!(0x00, to_integer(&[0x00]).unwrap());
        // Positive
        {
            // 1
            assert_eq!(1, to_integer(&[0x01]).unwrap());
            // 0x7f
            assert_eq!(0x7f, to_integer(&[0x7f]).unwrap());
            // 0x80
            assert_eq!(0x80, to_integer(&[0x00, 0x80]).unwrap());
            // 0xff
            assert_eq!(0xff, to_integer(&[0x00, 0xff]).unwrap());
            // 0x0100
            assert_eq!(0x0100, to_integer(&[0x01, 0x00]).unwrap());
            // 0x7fff
            assert_eq!(0x7fff, to_integer(&[0x7f, 0xff]).unwrap());
            // 0x8000
            assert_eq!(0x8000, to_integer(&[0x00, 0x80, 0x00]).unwrap());
            // i128::MAX
            {
                let bytes: &mut [u8] = &mut [0xff; size_of::<i128>()];
                bytes[0] = 0x7f;
                assert_eq!(std::i128::MAX, to_integer(bytes).unwrap());
            }
        }
    }
}