ccss 0.1.0

Const CSS parser
Documentation 
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use super::{array_vec::ArrayVec, HasConstDummyValue};

#[derive(Debug, Clone, Copy)]
pub struct LeadVec<T, const CAP: usize> {
    lead: ArrayVec<T, CAP>,
    tail_len: usize,
}

impl<T, const CAP: usize> LeadVec<T, CAP> {
    pub const fn as_slice(&self) -> Option<&[T]> {
        if self.tail_len == 0 {
            Some(self.lead_as_slice())
        } else {
            None
        }
    }

    pub const fn lead_as_slice(&self) -> &[T] {
        self.lead.as_slice()
    }

    pub const fn lead(&self) -> &ArrayVec<T, CAP>
    where
        T: Copy,
    {
        &self.lead
    }

    pub const fn len(&self) -> usize {
        self.lead.len() + self.tail_len
    }

    pub const fn is_empty(&self) -> bool {
        self.len() == 0 // self.lead.len() is insufficient if CAP is 0
    }

    pub(crate) const fn with_push(self, value: T) -> Self
    where
        T: Copy,
    {
        self.with_push_maybe_fake(value).0
    }

    /// `(_, Some(value))` indicates this is a fake push, and the input value is returned as is.
    pub(crate) const fn with_push_maybe_fake(mut self, value: T) -> (Self, Option<T>)
    where
        T: Copy,
    {
        if self.tail_len > 0 {
            self.tail_len += 1;
            return (self, Some(value));
        }

        match self.lead.with_try_push(value) {
            Ok(lead) => {
                self.lead = lead;
                (self, None)
            }
            Err((lead, value)) => {
                self.lead = ArrayVec::new_filled(lead);
                self.tail_len += 1;
                (self, Some(value))
            }
        }
    }
}

impl<T: HasConstDummyValue, const CAP: usize> LeadVec<T, CAP> {
    pub const EMPTY: Self = Self {
        lead: ArrayVec::EMPTY,
        tail_len: 0,
    };
}