//! Bit level parsers

//!

use crate::error::{ErrorKind, ParseError};

use crate::internal::{Err, IResult};

use crate::lib::std::ops::{AddAssign, Div, RangeFrom, Shl, Shr};

use crate::traits::{InputIter, InputLength, Slice, ToUsize};

/// Generates a parser taking `count` bits

///

/// # Example

/// ```rust

/// # use nom::bits::complete::take;

/// # use nom::IResult;

/// # use nom::error::{Error, ErrorKind};

/// // Input is a tuple of (input: I, bit_offset: usize)

/// fn parser(input: (&[u8], usize), count: usize)-> IResult<(&[u8], usize), u8> {

///  take(count)(input)

/// }

///

/// // Consumes 0 bits, returns 0

/// assert_eq!(parser(([0b00010010].as_ref(), 0), 0), Ok((([0b00010010].as_ref(), 0), 0)));

///

/// // Consumes 4 bits, returns their values and increase offset to 4

/// assert_eq!(parser(([0b00010010].as_ref(), 0), 4), Ok((([0b00010010].as_ref(), 4), 0b00000001)));

///

/// // Consumes 4 bits, offset is 4, returns their values and increase offset to 0 of next byte

/// assert_eq!(parser(([0b00010010].as_ref(), 4), 4), Ok((([].as_ref(), 0), 0b00000010)));

///

/// // Tries to consume 12 bits but only 8 are available

/// assert_eq!(parser(([0b00010010].as_ref(), 0), 12), Err(nom::Err::Error(Error{input: ([0b00010010].as_ref(), 0), code: ErrorKind::Eof })));

/// ```

pub fn take<I, O, C, E: ParseError<(I, usize)>>(

  count: C,

) -> impl Fn((I, usize)) -> IResult<(I, usize), O, E>

where

  I: Slice<RangeFrom<usize>> + InputIter<Item = u8> + InputLength,

  C: ToUsize,

  O: From<u8> + AddAssign + Shl<usize, Output = O> + Shr<usize, Output = O>,

{

  let count = count.to_usize();

  move |(input, bit_offset): (I, usize)| {

    if count == 0 {

      Ok(((input, bit_offset), 0u8.into()))

    } else {

      let cnt = (count + bit_offset).div(8);

      if input.input_len() * 8 < count + bit_offset {

        Err(Err::Error(E::from_error_kind(

          (input, bit_offset),

          ErrorKind::Eof,

        )))

      } else {

        let mut acc: O = 0_u8.into();

        let mut offset: usize = bit_offset;

        let mut remaining: usize = count;

        let mut end_offset: usize = 0;

        for byte in input.iter_elements().take(cnt + 1) {

          if remaining == 0 {

            break;

          }

          let val: O = if offset == 0 {

            byte.into()

          } else {

            ((byte << offset) as u8 >> offset).into()

          };

          if remaining < 8 - offset {

            acc += val >> (8 - offset - remaining);

            end_offset = remaining + offset;

            break;

          } else {

            acc += val << (remaining - (8 - offset));

            remaining -= 8 - offset;

            offset = 0;

          }

        }

        Ok(((input.slice(cnt..), end_offset), acc))

      }

    }

  }

}

/// Generates a parser taking `count` bits and comparing them to `pattern`

pub fn tag<I, O, C, E: ParseError<(I, usize)>>(

  pattern: O,

  count: C,

) -> impl Fn((I, usize)) -> IResult<(I, usize), O, E>

where

  I: Slice<RangeFrom<usize>> + InputIter<Item = u8> + InputLength + Clone,

  C: ToUsize,

  O: From<u8> + AddAssign + Shl<usize, Output = O> + Shr<usize, Output = O> + PartialEq,

{

  let count = count.to_usize();

  move |input: (I, usize)| {

    let inp = input.clone();

    take(count)(input).and_then(|(i, o)| {

      if pattern == o {

        Ok((i, o))

      } else {

        Err(Err::Error(error_position!(inp, ErrorKind::TagBits)))

      }

    })

  }

}

#[cfg(test)]

mod test {

  use super::*;

  #[test]

  fn test_take_0() {

    let input = [0b00010010].as_ref();

    let count = 0usize;

    assert_eq!(count, 0usize);

    let offset = 0usize;

    let result: crate::IResult<(&[u8], usize), usize> = take(count)((input, offset));

    assert_eq!(result, Ok(((input, offset), 0)));

  }

  #[test]

  fn test_take_eof() {

    let input = [0b00010010].as_ref();

    let result: crate::IResult<(&[u8], usize), usize> = take(1usize)((input, 8));

    assert_eq!(

      result,

      Err(crate::Err::Error(crate::error::Error {

        input: (input, 8),

        code: ErrorKind::Eof

      }))

    )

  }

  #[test]

  fn test_take_span_over_multiple_bytes() {

    let input = [0b00010010, 0b00110100, 0b11111111, 0b11111111].as_ref();

    let result: crate::IResult<(&[u8], usize), usize> = take(24usize)((input, 4));

    assert_eq!(

      result,

      Ok((([0b11111111].as_ref(), 4), 0b1000110100111111111111))

    );

  }

}