nomo/src/input.rs

use std::ops::Deref;
use std::ops::Range;
use std::sync::Arc;

use winnow::stream::Compare;
use winnow::stream::FindSlice;
use winnow::stream::Offset;
use winnow::stream::Stream;
use winnow::stream::StreamIsPartial;

#[derive(Clone, PartialEq, Eq)]
pub struct NomoInput {
    backing: Arc<str>,
    range: Range<usize>,
}

impl NomoInput {
    pub fn from_parts(backing: Arc<str>, range: Range<usize>) -> NomoInput {
        NomoInput { backing, range }
    }

    pub fn into_parts(self) -> (Arc<str>, Range<usize>) {
        (self.backing, self.range)
    }

    pub fn get_range(&self) -> Range<usize> {
        self.range.clone()
    }
}

#[derive(Debug, Clone)]
pub struct NomoInputCheckpoint {
    range: Range<usize>,
}

impl std::fmt::Debug for NomoInput {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{:?} ({:?})", self.as_str(), self.range)
    }
}

impl From<String> for NomoInput {
    fn from(value: String) -> Self {
        let range = 0..value.len();
        let backing = Arc::from(value);

        NomoInput { backing, range }
    }
}

impl From<&str> for NomoInput {
    fn from(value: &str) -> Self {
        let backing = Arc::from(value.to_string());
        let range = 0..value.len();

        NomoInput { backing, range }
    }
}

impl FindSlice<&str> for NomoInput {
    fn find_slice(&self, substr: &str) -> Option<core::ops::Range<usize>> {
        self.as_str().find_slice(substr)
    }
}

impl Compare<&str> for NomoInput {
    fn compare(&self, t: &str) -> winnow::stream::CompareResult {
        self.as_str().compare(t)
    }
}

impl Deref for NomoInput {
    type Target = str;

    fn deref(&self) -> &Self::Target {
        &self.backing[self.range.clone()]
    }
}

impl NomoInput {
    pub fn as_str(&self) -> &str {
        self.deref()
    }
}

impl Offset for NomoInputCheckpoint {
    fn offset_from(&self, start: &Self) -> usize {
        self.range.start - start.range.start
    }
}

impl Offset<NomoInputCheckpoint> for NomoInput {
    fn offset_from(&self, start: &NomoInputCheckpoint) -> usize {
        self.range.start - start.range.start
    }
}

impl Offset for NomoInput {
    fn offset_from(&self, start: &Self) -> usize {
        self.as_str().offset_from(&start.as_str())
    }
}

pub struct NomoInputIter {
    idx: usize,
    input: NomoInput,
}

impl Iterator for NomoInputIter {
    type Item = (usize, char);

    fn next(&mut self) -> Option<Self::Item> {
        let val = self.input.as_str().char_indices().nth(self.idx);
        self.idx += 1;
        val
    }
}

impl StreamIsPartial for NomoInput {
    type PartialState = ();

    fn complete(&mut self) -> Self::PartialState {
        // Always complete
    }

    fn restore_partial(&mut self, _state: Self::PartialState) {}

    fn is_partial_supported() -> bool {
        false
    }
}

impl Stream for NomoInput {
    type Token = char;

    type Slice = NomoInput;

    type IterOffsets = NomoInputIter;

    type Checkpoint = NomoInputCheckpoint;

    fn iter_offsets(&self) -> Self::IterOffsets {
        NomoInputIter {
            idx: 0,
            input: self.clone(),
        }
    }

    fn eof_offset(&self) -> usize {
        self.len()
    }

    fn next_token(&mut self) -> Option<Self::Token> {
        let c = self.chars().next()?;

        self.range.start += c.len_utf8();
        Some(c)
    }

    fn peek_token(&self) -> Option<Self::Token> {
        self.chars().next()
    }

    fn offset_for<P>(&self, predicate: P) -> Option<usize>
    where
        P: Fn(Self::Token) -> bool,
    {
        self.as_str().offset_for(predicate)
    }

    fn offset_at(&self, tokens: usize) -> Result<usize, winnow::error::Needed> {
        self.as_str().offset_at(tokens)
    }

    fn next_slice(&mut self, offset: usize) -> Self::Slice {
        let mut next = self.clone();

        self.range.start += offset;
        next.range.end = self.range.start;

        next
    }

    fn peek_slice(&self, offset: usize) -> Self::Slice {
        let mut next = self.clone();
        next.range.end = self.range.start + offset;
        next
    }

    fn checkpoint(&self) -> Self::Checkpoint {
        NomoInputCheckpoint {
            range: self.get_range(),
        }
    }

    fn reset(&mut self, checkpoint: &Self::Checkpoint) {
        self.range = checkpoint.range.clone();
    }

    fn raw(&self) -> &dyn core::fmt::Debug {
        self
    }

    fn trace(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.write_str(self.as_str())
    }
}

#[cfg(test)]
mod tests {
    use winnow::stream::Stream;

    use crate::input::NomoInput;

    #[test]
    fn check_stream_impl() {
        let mut stream = NomoInput::from("checking");

        let checkpoint = stream.checkpoint();

        assert_eq!(stream.peek_token(), Some('c'));
        assert_eq!(stream.next_token(), Some('c'));
        let next_slice = stream.next_slice(4);
        assert_eq!(next_slice.as_str(), "heck");
        assert_eq!(stream.peek_token(), Some('i'));

        stream.reset(&checkpoint);
        assert_eq!(stream.peek_token(), Some('c'));

        let peek = stream.peek_slice(4);
        assert_eq!(peek.as_str(), "chec");

        let eof_offset = stream.eof_offset();
        assert_eq!(eof_offset, 8);
    }
}