use crate::ascii;
use crate::num::NonZero;
use crate::ops::Range;
const HEX_DIGITS: [ascii::Char; 16] = *b"0123456789abcdef".as_ascii().unwrap();
#[inline]
const fn backslash<const N: usize>(a: ascii::Char) -> ([ascii::Char; N], Range<u8>) {
    const { assert!(N >= 2) };
    let mut output = [ascii::Char::Null; N];
    output[0] = ascii::Char::ReverseSolidus;
    output[1] = a;
    (output, 0..2)
}
#[inline]
const fn hex_escape<const N: usize>(byte: u8) -> ([ascii::Char; N], Range<u8>) {
    const { assert!(N >= 4) };
    let mut output = [ascii::Char::Null; N];
    let hi = HEX_DIGITS[(byte >> 4) as usize];
    let lo = HEX_DIGITS[(byte & 0xf) as usize];
    output[0] = ascii::Char::ReverseSolidus;
    output[1] = ascii::Char::SmallX;
    output[2] = hi;
    output[3] = lo;
    (output, 0..4)
}
#[inline]
const fn verbatim<const N: usize>(a: ascii::Char) -> ([ascii::Char; N], Range<u8>) {
    const { assert!(N >= 1) };
    let mut output = [ascii::Char::Null; N];
    output[0] = a;
    (output, 0..1)
}
const fn escape_ascii<const N: usize>(byte: u8) -> ([ascii::Char; N], Range<u8>) {
    const { assert!(N >= 4) };
    #[cfg(feature = "optimize_for_size")]
    {
        match byte {
            b'\t' => backslash(ascii::Char::SmallT),
            b'\r' => backslash(ascii::Char::SmallR),
            b'\n' => backslash(ascii::Char::SmallN),
            b'\\' => backslash(ascii::Char::ReverseSolidus),
            b'\'' => backslash(ascii::Char::Apostrophe),
            b'"' => backslash(ascii::Char::QuotationMark),
            0x00..=0x1F | 0x7F => hex_escape(byte),
            _ => match ascii::Char::from_u8(byte) {
                Some(a) => verbatim(a),
                None => hex_escape(byte),
            },
        }
    }
    #[cfg(not(feature = "optimize_for_size"))]
    {
        const LOOKUP: [u8; 256] = {
            let mut arr = [0; 256];
            let mut idx = 0;
            while idx <= 255 {
                arr[idx] = match idx as u8 {
                    b'\t' => 0x80 | b't',
                    b'\r' => 0x80 | b'r',
                    b'\n' => 0x80 | b'n',
                    b'\\' => 0x80 | b'\\',
                    b'\'' => 0x80 | b'\'',
                    b'"' => 0x80 | b'"',
                    0x00..=0x1F | 0x7F..=0xFF => 0x80 | b'\0',
                    idx => idx,
                };
                idx += 1;
            }
            arr
        };
        let lookup = LOOKUP[byte as usize];
        let lookup_escaped = lookup & 0x80 != 0;
        let lookup_ascii = unsafe { ascii::Char::from_u8_unchecked(lookup & 0x7F) };
        if lookup_escaped {
            if matches!(lookup_ascii, ascii::Char::Null) {
                hex_escape(byte)
            } else {
                backslash(lookup_ascii)
            }
        } else {
            verbatim(lookup_ascii)
        }
    }
}
const fn escape_unicode<const N: usize>(c: char) -> ([ascii::Char; N], Range<u8>) {
    const { assert!(N >= 10 && N < u8::MAX as usize) };
    let c = c as u32;
    let start = (c | 1).leading_zeros() as usize / 4 - 2;
    let mut output = [ascii::Char::Null; N];
    output[3] = HEX_DIGITS[((c >> 20) & 15) as usize];
    output[4] = HEX_DIGITS[((c >> 16) & 15) as usize];
    output[5] = HEX_DIGITS[((c >> 12) & 15) as usize];
    output[6] = HEX_DIGITS[((c >> 8) & 15) as usize];
    output[7] = HEX_DIGITS[((c >> 4) & 15) as usize];
    output[8] = HEX_DIGITS[((c >> 0) & 15) as usize];
    output[9] = ascii::Char::RightCurlyBracket;
    output[start + 0] = ascii::Char::ReverseSolidus;
    output[start + 1] = ascii::Char::SmallU;
    output[start + 2] = ascii::Char::LeftCurlyBracket;
    (output, (start as u8)..(N as u8))
}
#[derive(Clone, Debug)]
pub(crate) struct EscapeIterInner<const N: usize> {
    data: [ascii::Char; N],
    alive: Range<u8>,
}
impl<const N: usize> EscapeIterInner<N> {
    pub const fn backslash(c: ascii::Char) -> Self {
        let (data, range) = backslash(c);
        Self { data, alive: range }
    }
    pub const fn ascii(c: u8) -> Self {
        let (data, range) = escape_ascii(c);
        Self { data, alive: range }
    }
    pub const fn unicode(c: char) -> Self {
        let (data, range) = escape_unicode(c);
        Self { data, alive: range }
    }
    #[inline]
    pub const fn empty() -> Self {
        Self { data: [ascii::Char::Null; N], alive: 0..0 }
    }
    #[inline]
    pub fn as_ascii(&self) -> &[ascii::Char] {
        unsafe {
            self.data.get_unchecked(usize::from(self.alive.start)..usize::from(self.alive.end))
        }
    }
    #[inline]
    pub fn as_str(&self) -> &str {
        self.as_ascii().as_str()
    }
    #[inline]
    pub fn len(&self) -> usize {
        usize::from(self.alive.end - self.alive.start)
    }
    pub fn next(&mut self) -> Option<u8> {
        let i = self.alive.next()?;
        unsafe { Some(self.data.get_unchecked(usize::from(i)).to_u8()) }
    }
    pub fn next_back(&mut self) -> Option<u8> {
        let i = self.alive.next_back()?;
        unsafe { Some(self.data.get_unchecked(usize::from(i)).to_u8()) }
    }
    pub fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
        self.alive.advance_by(n)
    }
    pub fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
        self.alive.advance_back_by(n)
    }
}