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use core::fmt::*;


/// A formatting aid for pretty-printing a byte buffer,
/// not unlike the `hexdump` utility.
///
/// # Examples
/// ```
/// use extfmt::*;
///
/// let dump = Hexdump::new(&[1,2,3,4,5,6,255]);
/// assert_eq!(format!("{}", dump), "00000000\t01 02 03 04 05 06 ff");
/// ```
pub struct Hexdump<'a> {
	data: &'a [u8],
	show_index: bool,
	items_per_row: usize, 
}

impl<'a> Hexdump<'a> {
	/// Creates a new Hexdump instance from a byte slice.
	pub fn new(data: &'a [u8]) -> Self {
		Hexdump {
			data,
			show_index: true,
			items_per_row: 16
		}
	}

	/// Controls whether or not to show the current index at the beginning of each row.
	///
	/// Default: true
	pub fn show_index(&mut self, value: bool) -> &mut Self {
		self.show_index = value;
		self
	}

	/// Controls the amount of bytes to print in each row.
	///
	/// Default: 16
	pub fn items_per_row(&mut self, value: usize) -> &mut Self {
		self.items_per_row = value;
		self
	}
}

impl<'a> Display for Hexdump<'a> {
	fn fmt(&self, f: &mut Formatter) -> Result {
		for i in 0..self.data.len() {
			if self.show_index && i % self.items_per_row == 0 {
				write!(f, "{:08x}\t", i)?;
			}

			write!(f, "{:02x}", self.data[i])?;

			// Items separator
			if i != self.data.len() - 1 {
				// Start a new row when appropriate
				if i % self.items_per_row == self.items_per_row - 1 {
					f.write_char('\n')?;
				}
				else {
					f.write_char(' ')?;
				}
			}
		}

		Ok(())
	}
}

/// A utility trait used to create Hexdump objects.
pub trait AsHexdump {
	fn as_hexdump(&self) -> Hexdump;
}

impl<T: Sized> AsHexdump for T {
	fn as_hexdump(&self) -> Hexdump {
		let slice = unsafe { ::core::slice::from_raw_parts(
    			self as *const _ as *const u8,
    			::core::mem::size_of_val(self)
		)};
		
    	Hexdump::new(slice)
	}
}

impl AsHexdump for [u8] {
	fn as_hexdump(&self) -> Hexdump {
    	Hexdump::new(self)
	}
}

/// Create a hexdump of the given value using the AsHexdump trait.
/// It is implemented by default for Sized types and for [u8].
///
/// `key: value` can be added to control formatting options, where `key` is a method of the `Hexdump` struct.
///
/// # Examples
/// ```
/// use extfmt::*;
/// let data = &[1u8,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16];
/// let expected = "00000000\t01 02 03 04 05 06 07 08 09 0a 0b 0c\n0000000c\t0d 0e 0f 10";
/// assert_eq!(format!("{}", hexdump!(data, items_per_row: 12)), expected);
/// ```
#[macro_export]
macro_rules! hexdump {
    ($value:expr) => (
    	$value.as_hexdump()
    );
    ($value:expr, $($setting:ident: $setting_value: expr)*) => (
    	$value.as_hexdump() $(
    		.$setting($setting_value)
    		)*
    )
}

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

    #[test]
    fn readme() {
    	assert_eq!(format!("{}", hexdump!(&[1u8, 2, 255, 64])), "00000000	01 02 ff 40");
    	assert_eq!(format!("{}", hexdump!(64)), "00000000	40 00 00 00");
		assert_eq!(format!("{}", hexdump!(64, show_index: false)), "40 00 00 00");
    }
}