use crate::{decode_inner, encoded_len, Error};

#[cfg(feature = "alloc")]

use crate::{decoded_len, String, Vec};

/// Decode a lower Base16 (hex) string into the provided destination buffer.

pub fn decode(src: impl AsRef<[u8]>, dst: &mut [u8]) -> Result<&[u8], Error> {

    decode_inner(src.as_ref(), dst, decode_nibble)

}

/// Decode a lower Base16 (hex) string into a byte vector.

#[cfg(feature = "alloc")]

pub fn decode_vec(input: impl AsRef<[u8]>) -> Result<Vec<u8>, Error> {

    let mut output = vec![0u8; decoded_len(input.as_ref())?];

    decode(input, &mut output)?;

    Ok(output)

}

/// Encode the input byte slice as lower Base16.

///

/// Writes the result into the provided destination slice, returning an

/// ASCII-encoded lower Base16 (hex) string value.

pub fn encode<'a>(src: &[u8], dst: &'a mut [u8]) -> Result<&'a [u8], Error> {

    let dst = dst

        .get_mut(..encoded_len(src))

        .ok_or(Error::InvalidLength)?;

    for (src, dst) in src.iter().zip(dst.chunks_exact_mut(2)) {

        dst[0] = encode_nibble(src >> 4);

        dst[1] = encode_nibble(src & 0x0f);

    }

    Ok(dst)

}

/// Encode input byte slice into a [`&str`] containing lower Base16 (hex).

pub fn encode_str<'a>(src: &[u8], dst: &'a mut [u8]) -> Result<&'a str, Error> {

    encode(src, dst).map(|r| unsafe { core::str::from_utf8_unchecked(r) })

}

/// Encode input byte slice into a [`String`] containing lower Base16 (hex).

///

/// # Panics

/// If `input` length is greater than `usize::MAX/2`.

#[cfg(feature = "alloc")]

pub fn encode_string(input: &[u8]) -> String {

    let elen = encoded_len(input);

    let mut dst = vec![0u8; elen];

    let res = encode(input, &mut dst).expect("dst length is correct");

    debug_assert_eq!(elen, res.len());

    unsafe { String::from_utf8_unchecked(dst) }

}

/// Decode a single nibble of lower hex

#[inline(always)]

fn decode_nibble(src: u8) -> u16 {

    // 0-9  0x30-0x39

    // A-F  0x41-0x46 or a-f  0x61-0x66

    let byte = src as i16;

    let mut ret: i16 = -1;

    // 0-9  0x30-0x39

    // if (byte > 0x2f && byte < 0x3a) ret += byte - 0x30 + 1; // -47

    ret += (((0x2fi16 - byte) & (byte - 0x3a)) >> 8) & (byte - 47);

    // a-f  0x61-0x66

    // if (byte > 0x60 && byte < 0x67) ret += byte - 0x61 + 10 + 1; // -86

    ret += (((0x60i16 - byte) & (byte - 0x67)) >> 8) & (byte - 86);

    ret as u16

}

/// Encode a single nibble of hex

#[inline(always)]

fn encode_nibble(src: u8) -> u8 {

    let mut ret = src as i16 + 0x30;

    // 0-9  0x30-0x39

    // a-f  0x61-0x66

    ret += ((0x39i16 - ret) >> 8) & (0x61i16 - 0x3a);

    ret as u8

}