//! Bit level parsers

//!

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

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

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

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

/// Generates a parser taking `count` bits

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::Incomplete(Needed::new(count as usize)))

      } 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)))

      }

    })

  }

}

/// Parses one specific bit as a bool.

///

/// # Example

/// ```rust

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

/// # use nom::IResult;

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

///

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

///     bool(input)

/// }

///

/// assert_eq!(parse(([0b10000000].as_ref(), 0)), Ok((([0b10000000].as_ref(), 1), true)));

/// assert_eq!(parse(([0b10000000].as_ref(), 1)), Ok((([0b10000000].as_ref(), 2), false)));

/// ```

pub fn bool<I, E: ParseError<(I, usize)>>(input: (I, usize)) -> IResult<(I, usize), bool, E>

where

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

{

  let (res, bit): (_, u32) = take(1usize)(input)?;

  Ok((res, bit != 0))

}

#[cfg(test)]

mod test {

  use super::*;

  #[test]

  fn test_take_0() {

    let input = [].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_tag_ok() {

    let input = [0b00011111].as_ref();

    let offset = 0usize;

    let bits_to_take = 4usize;

    let value_to_tag = 0b0001;

    let result: crate::IResult<(&[u8], usize), usize> =

      tag(value_to_tag, bits_to_take)((input, offset));

    assert_eq!(result, Ok(((input, bits_to_take), value_to_tag)));

  }

  #[test]

  fn test_tag_err() {

    let input = [0b00011111].as_ref();

    let offset = 0usize;

    let bits_to_take = 4usize;

    let value_to_tag = 0b1111;

    let result: crate::IResult<(&[u8], usize), usize> =

      tag(value_to_tag, bits_to_take)((input, offset));

    assert_eq!(

      result,

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

        input: (input, offset),

        code: ErrorKind::TagBits

      }))

    );

  }

  #[test]

  fn test_bool_0() {

    let input = [0b10000000].as_ref();

    let result: crate::IResult<(&[u8], usize), bool> = bool((input, 0));

    assert_eq!(result, Ok(((input, 1), true)));

  }

  #[test]

  fn test_bool_eof() {

    let input = [0b10000000].as_ref();

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

    assert_eq!(result, Err(crate::Err::Incomplete(Needed::new(1))));

  }

}