//! Helper traits for iterators.

use crate::lib::slice;

#[cfg(feature = "format")]
use super::skip_value::*;

/// An iterator that knows if it has been fully consumed yet.
///
/// A consumed iterator will guarantee to return `None` for the next
/// value. It is effectively a weak variant of `is_empty()` on
/// `ExactSizeIterator`. When the length of an iterator is known,
/// `ConsumedIterator` will be implemented in terms of that length..
pub(crate) trait ConsumedIterator: Iterator {
    /// Return if the iterator has been consumed.
    fn consumed(&self) -> bool;
}

impl<T: ExactSizeIterator> ConsumedIterator for T {
    #[inline]
    fn consumed(&self) -> bool {
        self.len() == 0
    }
}

/// Get access to a raw, const pointer from the underlying data.
///
/// A default implementation is provided for slice iterators.
/// This trait **should never** return null, or be implemented
/// for non-contiguous data.
pub(crate) trait AsPtrIterator<'a, T: 'a>: Iterator<Item=&'a T> {
    /// Get raw pointer from iterator state.
    fn as_ptr(&self) -> *const T;
}

impl<'a, T> AsPtrIterator<'a, T> for slice::Iter<'a, T> {
    #[inline]
    fn as_ptr(&self) -> *const T {
        self.as_slice().as_ptr()
    }
}

// Type for iteration without any digit separators.
pub(crate) type IteratorNoSeparator<'a> = slice::Iter<'a, u8>;

// Iterate without any skipping any digit separators.
#[inline(always)]
pub(crate) fn iterate_digits_no_separator<'a>(bytes: &'a [u8], _: u8)
    -> IteratorNoSeparator<'a>
{
    bytes.iter()
}

// Type for iteration with a digit separator.
#[cfg(feature = "format")]
pub(crate) type IteratorSeparator<'a> = SkipValueIterator<'a, u8>;

// Iterate while skipping digit separators.
#[cfg(feature = "format")]
#[inline(always)]
pub(crate) fn iterate_digits_ignore_separator<'a>(bytes: &'a [u8], digit_separator: u8)
    -> IteratorSeparator<'a>
{
    IteratorSeparator::new(bytes, digit_separator)
}

// TESTS
// -----

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn consumer_iterator_test() {
        let mut iter = b"12345".iter();
        assert_eq!(iter.consumed(), false);
        assert_eq!(iter.nth(4).unwrap(), &b'5');
        assert_eq!(iter.consumed(), true);
    }

    #[test]
    fn as_ptr_iterator_test() {
        let digits = b"12345";
        let mut iter = digits.iter();
        assert_eq!(iter.as_ptr(), digits.as_ptr());
        assert_eq!(iter.nth(4).unwrap(), &b'5');
        assert_eq!(iter.as_ptr(), digits[digits.len()..].as_ptr());
    }

    #[test]
    fn iterate_digits_no_separator_test() {
        assert!(iterate_digits_no_separator(b"01", b'\x00').eq(b"01".iter()));
        assert!(iterate_digits_no_separator(b"01_01", b'_').eq(b"01_01".iter()));
    }

    #[test]
    #[cfg(feature = "format")]
        fn iterate_digits_ignore_separator_test() {
        assert!(iterate_digits_ignore_separator(b"01", b'_').eq(b"01".iter()));
        assert!(iterate_digits_ignore_separator(b"01_01", b'_').eq(b"0101".iter()));
    }
}