use core::fmt;

/// Alternative implementation of `fmt::Debug` for byte slice.

///

/// Standard `Debug` implementation for `[u8]` is comma separated

/// list of numbers. Since large amount of byte strings are in fact

/// ASCII strings or contain a lot of ASCII strings (e. g. HTTP),

/// it is convenient to print strings as ASCII when possible.

///

/// This struct wraps `&[u8]` just to override `fmt::Debug`.

///

/// `BsDebug` is not a part of public API of bytes crate.

pub(crate) struct BsDebug<'a>(pub(crate) &'a [u8]);

impl fmt::Debug for BsDebug<'_> {

    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {

        write!(fmt, "b\"")?;

        for &c in self.0 {

            // https://doc.rust-lang.org/reference.html#byte-escapes

            if c == b'\n' {

                write!(fmt, "\\n")?;

            } else if c == b'\r' {

                write!(fmt, "\\r")?;

            } else if c == b'\t' {

                write!(fmt, "\\t")?;

            } else if c == b'\\' || c == b'"' {

                write!(fmt, "\\{}", c as char)?;

            } else if c == b'\0' {

                write!(fmt, "\\0")?;

                // ASCII printable

            } else if (0x20..0x7f).contains(&c) {

                write!(fmt, "{}", c as char)?;

            } else {

                write!(fmt, "\\x{c:02x}")?;

            }

        }

        write!(fmt, "\"")?;

        Ok(())

    }

}

#[cfg(test)]

mod tests {

    use std::format;

    use std::prelude::v1::*;

    use super::BsDebug;

    #[test]

    fn debug() {

        let vec: Vec<_> = (0..0x100).map(|b| b as u8).collect();

        let expected = "b\"\

            \\0\\x01\\x02\\x03\\x04\\x05\\x06\\x07\

            \\x08\\t\\n\\x0b\\x0c\\r\\x0e\\x0f\

            \\x10\\x11\\x12\\x13\\x14\\x15\\x16\\x17\

            \\x18\\x19\\x1a\\x1b\\x1c\\x1d\\x1e\\x1f\

            \x20!\\\"#$%&'()*+,-./0123456789:;<=>?\

            @ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\\\]^_\

            `abcdefghijklmnopqrstuvwxyz{|}~\\x7f\

            \\x80\\x81\\x82\\x83\\x84\\x85\\x86\\x87\

            \\x88\\x89\\x8a\\x8b\\x8c\\x8d\\x8e\\x8f\

            \\x90\\x91\\x92\\x93\\x94\\x95\\x96\\x97\

            \\x98\\x99\\x9a\\x9b\\x9c\\x9d\\x9e\\x9f\

            \\xa0\\xa1\\xa2\\xa3\\xa4\\xa5\\xa6\\xa7\

            \\xa8\\xa9\\xaa\\xab\\xac\\xad\\xae\\xaf\

            \\xb0\\xb1\\xb2\\xb3\\xb4\\xb5\\xb6\\xb7\

            \\xb8\\xb9\\xba\\xbb\\xbc\\xbd\\xbe\\xbf\

            \\xc0\\xc1\\xc2\\xc3\\xc4\\xc5\\xc6\\xc7\

            \\xc8\\xc9\\xca\\xcb\\xcc\\xcd\\xce\\xcf\

            \\xd0\\xd1\\xd2\\xd3\\xd4\\xd5\\xd6\\xd7\

            \\xd8\\xd9\\xda\\xdb\\xdc\\xdd\\xde\\xdf\

            \\xe0\\xe1\\xe2\\xe3\\xe4\\xe5\\xe6\\xe7\

            \\xe8\\xe9\\xea\\xeb\\xec\\xed\\xee\\xef\

            \\xf0\\xf1\\xf2\\xf3\\xf4\\xf5\\xf6\\xf7\

            \\xf8\\xf9\\xfa\\xfb\\xfc\\xfd\\xfe\\xff\"";

        assert_eq!(expected, format!("{:?}", BsDebug(&vec)));

    }

}