/*!

Provides convenience routines for escaping raw bytes.

This was copied from `regex-automata` with a few light edits.

*/

/// Provides a convenient `Debug` implementation for a `u8`.

///

/// The `Debug` impl treats the byte as an ASCII, and emits a human readable

/// representation of it. If the byte isn't ASCII, then it's emitted as a hex

/// escape sequence.

#[derive(Clone, Copy)]

pub struct Byte(pub u8);

impl core::fmt::Display for Byte {

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

        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())

    }

}

impl core::fmt::Debug for Byte {

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

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

        core::fmt::Display::fmt(self, f)?;

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

        Ok(())

    }

}

/// Provides a convenient `Debug` implementation for `&[u8]`.

///

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

/// but will work for anything. For any bytes that aren't UTF-8, they are

/// emitted as hex escape sequences.

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

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

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

        // 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())?;

                }

            }

        }

        Ok(())

    }

}

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

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

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

        core::fmt::Display::fmt(self, f)?;

        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.

///

/// This never panics.

///

/// *WARNING*: This is not designed for performance. If you're looking for a

/// fast UTF-8 decoder, this is not it. If you feel like you need one in this

/// crate, then please file an issue and discuss your use case.

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

    if bytes.is_empty() {

        return None;

    }

    let len = match utf8_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])),

    }

}

/// Given a UTF-8 leading byte, this returns the total number of code units

/// in the following encoded codepoint.

///

/// If the given byte is not a valid UTF-8 leading byte, then this returns

/// `None`.

fn utf8_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

    }

}