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use ropey::Rope;
use crate::{Change, Transaction};
/// Compares `old` and `new` to generate a [`Transaction`] describing
/// the steps required to get from `old` to `new`.
pub fn compare_ropes(old: &Rope, new: &Rope) -> Transaction {
// `similar` only works on contiguous data, so a `Rope` has
// to be temporarily converted into a `String`.
let old_converted = old.to_string();
let new_converted = new.to_string();
// A timeout is set so after 1 seconds, the algorithm will start
// approximating. This is especially important for big `Rope`s or
// `Rope`s that are extremely dissimilar to each other.
//
// Note: Ignore the clippy warning, as the trait bounds of
// `Transaction::change()` require an iterator implementing
// `ExactIterator`.
let mut config = similar::TextDiff::configure();
config.timeout(std::time::Duration::from_secs(1));
let diff = config.diff_chars(&old_converted, &new_converted);
// The current position of the change needs to be tracked to
// construct the `Change`s.
let mut pos = 0;
let changes: Vec<Change> = diff
.ops()
.iter()
.map(|op| op.as_tag_tuple())
.filter_map(|(tag, old_range, new_range)| {
// `old_pos..pos` is equivalent to `start..end` for where
// the change should be applied.
let old_pos = pos;
pos += old_range.end - old_range.start;
match tag {
// Semantically, inserts and replacements are the same thing.
similar::DiffTag::Insert | similar::DiffTag::Replace => {
// This is the text from the `new` rope that should be
// inserted into `old`.
let text: &str = {
let start = new.char_to_byte(new_range.start);
let end = new.char_to_byte(new_range.end);
&new_converted[start..end]
};
Some((old_pos, pos, Some(text.into())))
}
similar::DiffTag::Delete => Some((old_pos, pos, None)),
similar::DiffTag::Equal => None,
}
})
.collect();
Transaction::change(old, changes.into_iter())
}
#[cfg(test)]
mod tests {
use super::*;
quickcheck::quickcheck! {
fn test_compare_ropes(a: String, b: String) -> bool {
let mut old = Rope::from(a);
let new = Rope::from(b);
compare_ropes(&old, &new).apply(&mut old);
old.to_string() == new.to_string()
}
}
}
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