//! Bit level parsers

//!

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

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

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

use crate::traits::{Input, 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: Input<Item = u8>,

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

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

        (input, bit_offset),

        ErrorKind::Eof,

      )))

    } else {

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

      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) >> 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.take_from(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: Input<Item = u8> + 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: Input<Item = u8>,

{

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

  Ok((res, bit != 0))

}

#[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))

    );

  }

  #[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::Error(crate::error::Error {

        input: (input, 8),

        code: ErrorKind::Eof

      }))

    );

  }

}