// MIT License
//
// Copyright (c) 2024 Robin Doer
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.

#[cfg(test)]
mod tests;

use std::convert::TryInto;
use std::{cmp, mem};
use thiserror::Error;

/// Errors while (de-) serializing binary data.
#[derive(Debug, Error)]
pub enum BufferError {
    #[error("unexpected eof")]
    UnexpectedEof,

    #[error("write zero")]
    WriteZero,

    #[error("vector too large")]
    VecTooLarge,

    #[error("no {0} at {1}")]
    InvalidIndex(String, u32),
}

macro_rules! get_func {
    ($name:ident, $ty:ty) => {
        fn $name(&mut self) -> Result<$ty, BufferError> {
            self.get_array().map(|bytes| <$ty>::from_be_bytes(bytes))
        }
    };
}

fn safe_shl(n: usize, nshift: u8) -> Option<usize> {
    const NBITS: u8 = mem::size_of::<usize>() as u8 * 8;

    if n >> (NBITS - nshift) == 0 {
        Some(n << nshift)
    } else {
        None // would lose some data
    }
}

pub trait Buffer: Sized {
    fn get_chunk(&mut self, len: usize) -> Result<&[u8], BufferError>;

    fn get_array<const N: usize>(&mut self) -> Result<[u8; N], BufferError> {
        let buf = self.get_chunk(N)?;

        buf.try_into().map_err(|_| {
            // `buf` has not the requested/expected size
            BufferError::UnexpectedEof
        })
    }

    get_func!(get_u8, u8);
    get_func!(get_u16, u16);
    get_func!(get_u32, u32);
    get_func!(get_u64, u64);

    fn get_vec<const L: usize>(&mut self) -> Result<Vec<u8>, BufferError> {
        let mut len = 0usize;

        for n in self.get_array::<L>()? {
            // perform: len << 8 | n
            match safe_shl(len, 8) {
                Some(result) => len = result | n as usize,
                None => return Err(BufferError::VecTooLarge),
            }
        }

        self.get_chunk(len).map(|buf| buf.to_vec())
    }
}

pub trait BufferMut: Sized {
    fn put_chunk(&mut self, buf: &[u8]) -> Result<(), BufferError>;

    fn put_u8(&mut self, value: u8) -> Result<(), BufferError> {
        self.put_chunk(&value.to_be_bytes())
    }

    fn put_u16(&mut self, value: u16) -> Result<(), BufferError> {
        self.put_chunk(&value.to_be_bytes())
    }

    fn put_u32(&mut self, value: u32) -> Result<(), BufferError> {
        self.put_chunk(&value.to_be_bytes())
    }

    fn put_u64(&mut self, value: u64) -> Result<(), BufferError> {
        self.put_chunk(&value.to_be_bytes())
    }

    fn put_vec<const L: usize>(&mut self, buf: &[u8]) -> Result<(), BufferError> {
        const U64_LEN: usize = mem::size_of::<u64>();

        let mut len_bytes = [0; L];
        let buf_len_bytes = (buf.len() as u64).to_be_bytes();

        let n = cmp::min(L, U64_LEN);
        let (unwritten, source) = buf_len_bytes.split_at(U64_LEN - n);
        let target = &mut len_bytes[L - n..];

        if unwritten.iter().any(|n| *n > 0) {
            return Err(BufferError::VecTooLarge);
        }

        target.copy_from_slice(source);

        self.put_chunk(&len_bytes)
            .and_then(|()| self.put_chunk(buf))
    }
}

impl Buffer for &[u8] {
    fn get_chunk(&mut self, len: usize) -> Result<&[u8], BufferError> {
        if self.len() >= len {
            let buf = &self[..len];

            *self = &self[len..];

            Ok(buf)
        } else {
            Err(BufferError::UnexpectedEof)
        }
    }
}

impl BufferMut for Vec<u8> {
    fn put_chunk(&mut self, buf: &[u8]) -> Result<(), BufferError> {
        self.extend_from_slice(buf);
        Ok(())
    }
}

impl BufferMut for &mut [u8] {
    fn put_chunk(&mut self, buf: &[u8]) -> Result<(), BufferError> {
        if self.len() >= buf.len() {
            let target = &mut self[..buf.len()];

            target.copy_from_slice(buf);

            // Lifetime dance taken from `impl Write for &mut [u8]`.
            let (_, b) = mem::take(self).split_at_mut(buf.len());

            *self = b;

            Ok(())
        } else {
            Err(BufferError::WriteZero)
        }
    }
}

pub trait FromBuffer: Sized {
    type Error: From<BufferError>;

    fn from_buffer<T: Buffer>(buf: &mut T) -> Result<Self, Self::Error>;
}

pub trait ToBuffer {
    fn to_buffer<T: BufferMut>(&self, buf: &mut T) -> Result<(), BufferError>;
}