sl_liner/
grapheme_iter.rs

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#[derive(Debug)]
pub struct GraphemeIter<'a> {
    data: &'a str,
    offsets: &'a [usize],
    curr_grapheme: usize,
    curr_grapheme_back: isize,
    min_grapheme: usize,
    max_grapheme: usize,
}

impl<'a> Default for GraphemeIter<'a> {
    fn default() -> Self {
        GraphemeIter {
            data: "",
            offsets: &[],
            curr_grapheme: 0,
            curr_grapheme_back: -1,
            min_grapheme: 0,
            max_grapheme: 0,
        }
    }
}

impl<'a> GraphemeIter<'a> {
    pub fn new(
        data: &'a str,
        offsets: &'a [usize],
        curr_grapheme: usize,
        max_grapheme: usize,
    ) -> Self {
        GraphemeIter {
            data,
            offsets,
            curr_grapheme,
            curr_grapheme_back: max_grapheme as isize - 1,
            min_grapheme: curr_grapheme,
            max_grapheme,
        }
    }

    pub fn slice(&self) -> &'a str {
        let min = if self.min_grapheme == 0 {
            None
        } else {
            Some(self.offsets[self.min_grapheme])
        };
        let max = if self.max_grapheme == self.offsets.len() {
            None
        } else {
            Some(self.offsets[self.max_grapheme])
        };
        match (min, max) {
            (None, None) => self.data,
            (Some(start), None) => &self.data[start..],
            (None, Some(end)) => &self.data[..end],
            (Some(start), Some(end)) => &self.data[start..end],
        }
    }

    pub fn get(&self, idx: usize) -> Option<&'a str> {
        if idx < self.max_grapheme {
            let start = self.offsets[idx];
            if idx + 1 == self.max_grapheme {
                Some(&self.data[start..])
            } else {
                let end = self.offsets[idx + 1];
                Some(&self.data[start..end])
            }
        } else {
            None
        }
    }
}

impl<'a> From<GraphemeIter<'a>> for String {
    fn from(g_iter: GraphemeIter) -> Self {
        let mut str = String::new();
        for g in g_iter {
            str.push_str(g);
        }
        str
    }
}

impl<'a> Iterator for GraphemeIter<'a> {
    type Item = &'a str;

    fn next(&mut self) -> Option<Self::Item> {
        if self.offsets.is_empty() || self.curr_grapheme > self.curr_grapheme_back as usize {
            //base case we've iterated over the edge or the buffer is empty.
            None
        } else {
            let start = self.offsets[self.curr_grapheme];
            self.curr_grapheme += 1;

            if self.curr_grapheme as isize == self.curr_grapheme_back + 1 {
                // if cursor is at end of iter
                if self.curr_grapheme == self.offsets.len() {
                    // take care to slice properly if at proper end of self.data
                    Some(&self.data[start..])
                } else {
                    let end = self.offsets[self.curr_grapheme_back as usize + 1];
                    Some(&self.data[start..end])
                }
            } else {
                // somewhere in the middle
                let end = self.offsets[self.curr_grapheme];
                Some(&self.data[start..end])
            }
        }
    }
}

impl<'a> DoubleEndedIterator for GraphemeIter<'a> {
    fn next_back(&mut self) -> Option<Self::Item> {
        if self.offsets.is_empty() || self.curr_grapheme_back < self.curr_grapheme as isize {
            // base case we've run past the min or the buffer is empty.
            None
        } else {
            let start = self.offsets[self.curr_grapheme_back as usize];
            if self.curr_grapheme_back as usize == self.max_grapheme - 1 {
                // first iteration
                if self.max_grapheme == self.offsets.len() {
                    // take care to slice properly if at proper end of self.data
                    self.curr_grapheme_back -= 1;
                    Some(&self.data[start..])
                } else {
                    let max_char = self.offsets[self.curr_grapheme_back as usize + 1];
                    self.curr_grapheme_back -= 1;
                    Some(&self.data[start..max_char])
                }
            } else if self.curr_grapheme_back == self.curr_grapheme as isize {
                // last iteration
                let end = self.offsets[self.curr_grapheme_back as usize + 1];
                self.curr_grapheme_back -= 1;
                if self.curr_grapheme == 0 {
                    // take care to slice properly if at proper end of self.data
                    Some(&self.data[..end])
                } else {
                    Some(&self.data[start..end])
                }
            } else {
                // somewhere in the middle
                let end = self.offsets[self.curr_grapheme_back as usize + 1];
                self.curr_grapheme_back -= 1;
                Some(&self.data[start..end])
            }
        }
    }
}

impl<'a> ExactSizeIterator for GraphemeIter<'a> {
    fn len(&self) -> usize {
        if self.curr_grapheme as isize > self.curr_grapheme_back {
            0
        } else {
            (self.curr_grapheme_back - self.curr_grapheme as isize + 1) as usize
        }
    }
}

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

    #[test]
    fn test_get() {
        let base: String = String::from("012\u{924}\u{947}345");
        let offsets: Vec<usize> = vec![0, 1, 2, 3, 9, 10, 11];
        let gs = GraphemeIter::new(&base, &offsets, 0, 7);
        assert_eq!("5", gs.get(6).unwrap());
        assert_eq!("\u{924}\u{947}", gs.get(3).unwrap());
    }

    #[test]
    fn test_slices() {
        let base: String = String::from("012\u{924}\u{947}345");
        let offsets: Vec<usize> = vec![0, 1, 2, 3, 9, 10, 11];
        let true_min_artificial_max = GraphemeIter::new(&base, &offsets, 0, 6);
        assert_eq!("012\u{924}\u{947}34", true_min_artificial_max.slice());

        let true_min_and_max = GraphemeIter::new(&base, &offsets, 0, 7);
        assert_eq!("012\u{924}\u{947}345", true_min_and_max.slice());

        let artificial_min_and_true_max = GraphemeIter::new(&base, &offsets, 2, 7);
        assert_eq!("2\u{924}\u{947}345", artificial_min_and_true_max.slice());

        let artificial_min_and_max = GraphemeIter::new(&base, &offsets, 2, 4);
        assert_eq!("2\u{924}\u{947}", artificial_min_and_max.slice());

        let one_grapheme = GraphemeIter::new(&base, &offsets, 3, 4);
        assert_eq!("\u{924}\u{947}", one_grapheme.slice());

        let no_graphemes = GraphemeIter::new(&base, &offsets, 3, 3);
        assert_eq!("", no_graphemes.slice());
    }

    #[test]
    fn test_iterate() {
        let expected_str: String = String::from("012\u{924}\u{947}345");
        let offsets: Vec<usize> = vec![0, 1, 2, 3, 9, 10, 11];
        let gs = GraphemeIter::new(&expected_str, &offsets, 0, 7);
        let gs2 = GraphemeIter::new(&expected_str, &offsets, 0, 7);
        let mut actual_str = String::with_capacity(12);
        for f in gs {
            actual_str.push_str(f);
        }
        assert_eq!(expected_str, actual_str);
        assert_eq!(expected_str, gs2.slice());
    }

    #[test]
    fn test_iterate_forward_slice() {
        let base: String = String::from("012\u{924}\u{947}345");
        let expected_str = String::from("\u{924}\u{947}34");
        let offsets: Vec<usize> = vec![0, 1, 2, 3, 9, 10, 11];
        let gs = GraphemeIter::new(&base, &offsets, 3, 6);
        let gs2 = GraphemeIter::new(&base, &offsets, 3, 6);
        let mut actual_str = String::with_capacity(8);
        for f in gs {
            actual_str.push_str(f);
        }
        assert_eq!(expected_str, actual_str);
        assert_eq!(expected_str, gs2.slice());
    }

    #[test]
    fn test_iterate_back() {
        let expected_str: String = String::from("012\u{924}\u{947}345");
        let expected_rev_str = String::from("543\u{924}\u{947}210");
        let offsets: Vec<usize> = vec![0, 1, 2, 3, 9, 10, 11];
        let gs = GraphemeIter::new(&expected_str, &offsets, 0, 7);
        let gs2 = GraphemeIter::new(&expected_str, &offsets, 0, 7);
        let mut actual_rev_str = String::with_capacity(12);
        for x in gs.rev() {
            actual_rev_str.push_str(x);
        }
        assert_eq!(expected_rev_str, actual_rev_str);
        assert_eq!(expected_str, gs2.slice());
    }

    #[test]
    fn test_iterate_backwards_slice() {
        let expected_str: String = String::from("012\u{924}\u{947}345");
        let expected_rev_str = String::from("43\u{924}\u{947}");
        let expected_slice_str = String::from("\u{924}\u{947}34");
        let offsets: Vec<usize> = vec![0, 1, 2, 3, 9, 10, 11];
        let gs = GraphemeIter::new(&expected_str, &offsets, 3, 6);
        let gs2 = GraphemeIter::new(&expected_str, &offsets, 3, 6);
        let mut actual_rev_str = String::with_capacity(8);
        for x in gs.rev() {
            actual_rev_str.push_str(x);
        }
        assert_eq!(expected_rev_str, actual_rev_str);
        assert_eq!(expected_slice_str, gs2.slice());
    }

    #[test]
    fn test_special_case_back_iter() {
        let expected_str: String = String::from("012\u{924}\u{947}345");
        let offsets: Vec<usize> = vec![0, 1, 2, 3, 9, 10, 11];

        let gs_end = GraphemeIter::new(&expected_str, &offsets, 6, 7);
        let mut iter = gs_end.into_iter();
        let init_len = iter.len();
        assert_eq!(1, init_len);

        let str = iter.next_back();
        assert_eq!("5", str.unwrap());
        let len = iter.len();
        assert_eq!(0, len);

        let gs_beg = GraphemeIter::new(&expected_str, &offsets, 0, 1);
        let mut iter = gs_beg.into_iter();
        let init_len = iter.len();
        assert_eq!(1, init_len);

        let str = iter.next_back();
        assert_eq!("0", str.unwrap());
        let len = iter.len();
        assert_eq!(0, len);
    }

    #[test]
    fn test_special_case_forward_iter() {
        let expected_str: String = String::from("012\u{924}\u{947}345");
        let offsets: Vec<usize> = vec![0, 1, 2, 3, 9, 10, 11];

        let gs_end = GraphemeIter::new(&expected_str, &offsets, 6, 7);
        let mut iter = gs_end.into_iter();
        let init_len = iter.len();
        assert_eq!(1, init_len);

        let str = iter.next();
        assert_eq!("5", str.unwrap());
        let len = iter.len();
        assert_eq!(0, len);

        let gs_beg = GraphemeIter::new(&expected_str, &offsets, 0, 1);
        let mut iter = gs_beg.into_iter();
        let init_len = iter.len();
        assert_eq!(1, init_len);

        let str = iter.next();
        assert_eq!("0", str.unwrap());
        let len = iter.len();
        assert_eq!(0, len);
    }

    #[test]
    fn test_exact_size_iter() {
        let expected_str: String = String::from("012\u{924}\u{947}345");
        let offsets: Vec<usize> = vec![0, 1, 2, 3, 9, 10, 11];
        let gs = GraphemeIter::new(&expected_str, &offsets, 3, 6);
        let mut iter = gs.into_iter();
        let init_len = iter.len();
        assert_eq!(3, init_len);

        let str = iter.next_back();
        assert_eq!("4", str.unwrap());
        let len = iter.len();
        assert_eq!(2, len);

        let str = iter.next();
        assert_eq!("\u{924}\u{947}", str.unwrap());
        let len = iter.len();
        assert_eq!(1, len);

        let str = iter.next_back();
        assert_eq!("3", str.unwrap());
        let len = iter.len();
        assert_eq!(0, len);
    }

    #[test]
    fn test_empty_grapheme_iter() {
        let gs = GraphemeIter::default();
        assert_eq!(None, gs.get(8));
        assert_eq!("", gs.slice());
        assert_eq!(0, gs.len());
        let g: String = gs.into();
        assert_eq!("", g);

        let mut gs = GraphemeIter::default();
        assert_eq!(None, gs.next());
        let mut gs = GraphemeIter::default();
        assert_eq!(None, gs.next_back());
    }
}