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use crate::range::{DiffRange, SliceLike};
// Walks through all edits and shifts them up and then down, trying to see if they run into similar
// edits which can be merged
pub fn compact<'a, 'b, T: ?Sized + SliceLike>(diffs: &mut Vec<DiffRange<'a, 'b, T>>) {
// First attempt to compact all Deletions
let mut pointer = 0;
while let Some(&diff) = diffs.get(pointer) {
if let DiffRange::Delete(_) = diff {
pointer = shift_diff_up(diffs, pointer);
pointer = shift_diff_down(diffs, pointer);
}
pointer += 1;
}
// TODO maybe able to merge these and do them in the same pass?
// Then attempt to compact all Insertions
let mut pointer = 0;
while let Some(&diff) = diffs.get(pointer) {
if let DiffRange::Insert(_) = diff {
pointer = shift_diff_up(diffs, pointer);
pointer = shift_diff_down(diffs, pointer);
}
pointer += 1;
}
}
// Attempts to shift the Insertion or Deletion at location `pointer` as far upwards as possible.
fn shift_diff_up<'a, 'b, T: ?Sized + SliceLike>(
diffs: &mut Vec<DiffRange<'a, 'b, T>>,
mut pointer: usize,
) -> usize {
while let Some(&prev_diff) = pointer.checked_sub(1).and_then(|idx| diffs.get(idx)) {
match (diffs[pointer], prev_diff) {
//
// Shift Inserts Upwards
//
(DiffRange::Insert(this_diff), DiffRange::Equal(prev_diff1, _)) => {
// check common suffix for the amount we can shift
let suffix_len = this_diff.common_suffix_len(prev_diff1);
if suffix_len != 0 {
if let Some(DiffRange::Equal(..)) = diffs.get(pointer + 1) {
diffs[pointer + 1].grow_up(suffix_len);
} else {
diffs.insert(
pointer + 1,
DiffRange::Equal(
prev_diff1.slice(prev_diff1.len() - suffix_len..),
this_diff.slice(this_diff.len() - suffix_len..),
),
);
}
diffs[pointer].shift_up(suffix_len);
diffs[pointer - 1].shrink_back(suffix_len);
if diffs[pointer - 1].is_empty() {
diffs.remove(pointer - 1);
pointer -= 1;
}
} else if diffs[pointer - 1].is_empty() {
diffs.remove(pointer - 1);
pointer -= 1;
} else {
// We can't shift upwards anymore
break;
}
}
//
// Shift Deletions Upwards
//
(DiffRange::Delete(this_diff), DiffRange::Equal(_, prev_diff2)) => {
// check common suffix for the amount we can shift
let suffix_len = this_diff.common_suffix_len(prev_diff2);
if suffix_len != 0 {
if let Some(DiffRange::Equal(..)) = diffs.get(pointer + 1) {
diffs[pointer + 1].grow_up(suffix_len);
} else {
diffs.insert(
pointer + 1,
DiffRange::Equal(
this_diff.slice(this_diff.len() - suffix_len..),
prev_diff2.slice(prev_diff2.len() - suffix_len..),
),
);
}
diffs[pointer].shift_up(suffix_len);
diffs[pointer - 1].shrink_back(suffix_len);
if diffs[pointer - 1].is_empty() {
diffs.remove(pointer - 1);
pointer -= 1;
}
} else if diffs[pointer - 1].is_empty() {
diffs.remove(pointer - 1);
pointer -= 1;
} else {
// We can't shift upwards anymore
break;
}
}
//
// Swap the Delete and Insert
//
(DiffRange::Insert(_), DiffRange::Delete(_))
| (DiffRange::Delete(_), DiffRange::Insert(_)) => {
diffs.swap(pointer - 1, pointer);
pointer -= 1;
}
//
// Merge the two ranges
//
(this_diff @ DiffRange::Insert(_), DiffRange::Insert(_))
| (this_diff @ DiffRange::Delete(_), DiffRange::Delete(_)) => {
diffs[pointer - 1].grow_down(this_diff.len());
diffs.remove(pointer);
pointer -= 1;
}
_ => panic!("range to shift must be either Insert or Delete"),
}
}
pointer
}
// Attempts to shift the Insertion or Deletion at location `pointer` as far downwards as possible.
fn shift_diff_down<'a, 'b, T: ?Sized + SliceLike>(
diffs: &mut Vec<DiffRange<'a, 'b, T>>,
mut pointer: usize,
) -> usize {
while let Some(&next_diff) = pointer.checked_add(1).and_then(|idx| diffs.get(idx)) {
match (diffs[pointer], next_diff) {
//
// Shift Insert Downward
//
(DiffRange::Insert(this_diff), DiffRange::Equal(next_diff1, _)) => {
// check common prefix for the amoutn we can shift
let prefix_len = this_diff.common_prefix_len(next_diff1);
if prefix_len != 0 {
if let Some(DiffRange::Equal(..)) =
pointer.checked_sub(1).and_then(|idx| diffs.get(idx))
{
diffs[pointer - 1].grow_down(prefix_len);
} else {
diffs.insert(
pointer,
DiffRange::Equal(
next_diff1.slice(..prefix_len),
this_diff.slice(..prefix_len),
),
);
pointer += 1;
}
diffs[pointer].shift_down(prefix_len);
diffs[pointer + 1].shrink_front(prefix_len);
if diffs[pointer + 1].is_empty() {
diffs.remove(pointer + 1);
}
} else if diffs[pointer + 1].is_empty() {
diffs.remove(pointer + 1);
} else {
// We can't shift downwards anymore
break;
}
}
//
// Shift Deletion Downward
//
(DiffRange::Delete(this_diff), DiffRange::Equal(_, next_diff2)) => {
// check common prefix for the amoutn we can shift
let prefix_len = this_diff.common_prefix_len(next_diff2);
if prefix_len != 0 {
if let Some(DiffRange::Equal(..)) =
pointer.checked_sub(1).and_then(|idx| diffs.get(idx))
{
diffs[pointer - 1].grow_down(prefix_len);
} else {
diffs.insert(
pointer,
DiffRange::Equal(
this_diff.slice(..prefix_len),
next_diff2.slice(..prefix_len),
),
);
pointer += 1;
}
diffs[pointer].shift_down(prefix_len);
diffs[pointer + 1].shrink_front(prefix_len);
if diffs[pointer + 1].is_empty() {
diffs.remove(pointer + 1);
}
} else if diffs[pointer + 1].is_empty() {
diffs.remove(pointer + 1);
} else {
// We can't shift downwards anymore
break;
}
}
//
// Swap the Delete and Insert
//
(DiffRange::Insert(_), DiffRange::Delete(_))
| (DiffRange::Delete(_), DiffRange::Insert(_)) => {
diffs.swap(pointer, pointer + 1);
pointer += 1;
}
//
// Merge the two ranges
//
(DiffRange::Insert(_), next_diff @ DiffRange::Insert(_))
| (DiffRange::Delete(_), next_diff @ DiffRange::Delete(_)) => {
diffs[pointer].grow_down(next_diff.len());
diffs.remove(pointer + 1);
}
_ => panic!("range to shift must be either Insert or Delete"),
}
}
pointer
}