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use crate::{Bytes, Cursor, BytesRead, BytesWrite, BytesSeek};

/// A mutable slice wrapper that implements BytesWrite
#[derive(Debug, PartialEq, Eq, Hash)]
pub struct BytesMut<'a> {
	inner: Cursor<&'a mut [u8]>
}

impl<'a> BytesMut<'a> {

	/// You should probably use:
	///
	/// ```
	/// # use simple_bytes::BytesMut;
	/// # let slice = &mut [1u8, 2u8][..];
	/// let bytes: BytesMut = slice.into();
	/// // or
	/// let bytes = BytesMut::from(slice);
	/// ```
	///
	pub fn new(position: usize, inner: &'a mut [u8]) -> Self {
		let mut cursor = Cursor::new(inner);
		cursor.seek(position);
		Self { inner: cursor }
	}

}

impl BytesRead for BytesMut<'_> {

	#[inline]
	fn as_slice(&self) -> &[u8] {
		self.inner.as_slice()
	}

	fn remaining(&self) -> &[u8] {
		self.inner.remaining()
	}

	fn read(&mut self, len: usize) -> &[u8] {
		self.inner.read(len)
	}

	fn peek(&self, len: usize) -> Option<&[u8]> {
		self.inner.peek(len)
	}

}

impl BytesWrite for BytesMut<'_> {

	#[inline]
	fn as_mut(&mut self) -> &mut [u8] {
		self.inner.as_mut()
	}

	#[inline]
	fn as_bytes(&self) -> Bytes<'_> {
		self.inner.as_bytes()
	}

	#[inline]
	fn remaining_mut(&mut self) -> &mut [u8] {
		self.inner.remaining_mut()
	}

	#[inline]
	fn write(&mut self, slice: &[u8]) {
		self.inner.write(slice)
	}

}

impl BytesSeek for BytesMut<'_> {
	/// Returns the internal position.
	fn position(&self) -> usize {
		self.inner.position()
	}

	/// Sets the internal position.
	/// 
	/// ## Panics
	/// If the position exceeds the slice.
	fn seek(&mut self, pos: usize) {
		self.inner.seek(pos)
	}
}

impl<'a> From<&'a mut [u8]> for BytesMut<'a> {
	fn from(s: &'a mut [u8]) -> Self {
		Self::new(0, s)
	}
}


#[cfg(test)]
mod tests {

	use super::*;
	use crate::BytesRead;

	#[test]
	fn write() {

		let mut bytes = [0u8; 100];
		let mut bytes = BytesMut::from(&mut bytes[..]);
		assert_eq!(bytes.len(), 100);

		let to_write: Vec<u8> = (0..10).collect();
		bytes.write(&to_write);
		bytes.write(&to_write);

		assert_eq!(bytes.remaining().len(), 100 - 20);
		assert_eq!(bytes.remaining().len(), bytes.remaining_mut().len());

		assert_eq!(&bytes.as_mut()[..10], to_write.as_slice());
		assert_eq!(&bytes.as_bytes().peek(20).unwrap()[10..], to_write.as_slice());

		bytes.write_u8(5u8);
		bytes.write_u16(20u16);

		assert_eq!(bytes.remaining_mut().len(), 100 - 23);

		// seek
		bytes.seek(99);
		// should now write to the 99 byte // this is the last byte
		bytes.write_u8(5u8);
		assert_eq!(bytes.remaining_mut().len(), 0);
		assert_eq!(bytes.as_mut()[99], 5u8);

	}

	#[test]
	#[should_panic]
	fn write_overflow() {

		let mut bytes = [0u8; 100];
		let mut bytes = BytesMut::from(&mut bytes[..]);

		// seek
		bytes.seek(100);

		bytes.write_u8(5u8);
	}

}