/// A type that wraps a single byte with a convenient fmt::Debug impl that

/// escapes the byte.

pub(crate) struct Byte(pub(crate) u8);

impl core::fmt::Debug for Byte {

    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {

        // Special case ASCII space. It's too hard to read otherwise, so

        // put quotes around it. I sometimes wonder whether just '\x20' would

        // be better...

        if self.0 == b' ' {

            return write!(f, "' '");

        }

        // 10 bytes is enough to cover any output from ascii::escape_default.

        let mut bytes = [0u8; 10];

        let mut len = 0;

        for (i, mut b) in core::ascii::escape_default(self.0).enumerate() {

            // capitalize \xab to \xAB

            if i >= 2 && b'a' <= b && b <= b'f' {

                b -= 32;

            }

            bytes[len] = b;

            len += 1;

        }

        write!(f, "{}", core::str::from_utf8(&bytes[..len]).unwrap())

    }

}

/// A type that provides a human readable debug impl for arbitrary bytes.

///

/// This generally works best when the bytes are presumed to be mostly UTF-8,

/// but will work for anything.

///

/// N.B. This is copied nearly verbatim from regex-automata. Sigh.

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

impl<'a> core::fmt::Debug for Bytes<'a> {

    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {

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

        // This is a sad re-implementation of a similar impl found in bstr.

        let mut bytes = self.0;

        while let Some(result) = utf8_decode(bytes) {

            let ch = match result {

                Ok(ch) => ch,

                Err(byte) => {

                    write!(f, r"\x{:02x}", byte)?;

                    bytes = &bytes[1..];

                    continue;

                }

            };

            bytes = &bytes[ch.len_utf8()..];

            match ch {

                '\0' => write!(f, "\\0")?,

                // ASCII control characters except \0, \n, \r, \t

                '\x01'..='\x08'

                | '\x0b'

                | '\x0c'

                | '\x0e'..='\x19'

                | '\x7f' => {

                    write!(f, "\\x{:02x}", u32::from(ch))?;

                }

                '\n' | '\r' | '\t' | _ => {

                    write!(f, "{}", ch.escape_debug())?;

                }

            }

        }

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

        Ok(())

    }

}

/// Decodes the next UTF-8 encoded codepoint from the given byte slice.

///

/// If no valid encoding of a codepoint exists at the beginning of the given

/// byte slice, then the first byte is returned instead.

///

/// This returns `None` if and only if `bytes` is empty.

pub(crate) fn utf8_decode(bytes: &[u8]) -> Option<Result<char, u8>> {

    fn len(byte: u8) -> Option<usize> {

        if byte <= 0x7F {

            return Some(1);

        } else if byte & 0b1100_0000 == 0b1000_0000 {

            return None;

        } else if byte <= 0b1101_1111 {

            Some(2)

        } else if byte <= 0b1110_1111 {

            Some(3)

        } else if byte <= 0b1111_0111 {

            Some(4)

        } else {

            None

        }

    }

    if bytes.is_empty() {

        return None;

    }

    let len = match len(bytes[0]) {

        None => return Some(Err(bytes[0])),

        Some(len) if len > bytes.len() => return Some(Err(bytes[0])),

        Some(1) => return Some(Ok(char::from(bytes[0]))),

        Some(len) => len,

    };

    match core::str::from_utf8(&bytes[..len]) {

        Ok(s) => Some(Ok(s.chars().next().unwrap())),

        Err(_) => Some(Err(bytes[0])),

    }

}