use std::borrow::Cow;
use std::collections::HashMap;
use crate::compare::RopeScanner;
use crate::delta::{Delta, DeltaElement};
use crate::interval::Interval;
use crate::rope::{LinesMetric, Rope, RopeDelta, RopeInfo};
use crate::tree::{Node, NodeInfo};
pub trait Diff<N: NodeInfo> {
fn compute_delta(base: &Node<N>, target: &Node<N>) -> Delta<N>;
}
const MIN_SIZE: usize = 32;
pub struct LineHashDiff;
impl Diff<RopeInfo> for LineHashDiff {
fn compute_delta(base: &Rope, target: &Rope) -> RopeDelta {
let mut builder = DiffBuilder::default();
let mut scanner = RopeScanner::new(base, target);
let (start_offset, diff_end) = scanner.find_min_diff_range();
let target_end = target.len() - diff_end;
if start_offset > 0 {
builder.copy(0, 0, start_offset);
}
if start_offset == base.len() && target.len() == base.len() {
return builder.to_delta(base, target);
}
if target.len() < base.len() && start_offset + diff_end == target.len() {
builder.copy(base.len() - diff_end, target_end, diff_end);
return builder.to_delta(base, target);
}
if target.len() > base.len() && start_offset + diff_end == base.len() {
builder.copy(base.len() - diff_end, target_end, diff_end);
return builder.to_delta(base, target);
}
let line_hashes = make_line_hashes(&base, MIN_SIZE);
let line_count = target.measure::<LinesMetric>() + 1;
let mut matches = Vec::with_capacity(line_count);
let mut targ_line_offset = 0;
let mut prev_base = 0;
let mut needs_subseq = false;
for line in target.lines_raw(start_offset..target_end) {
let non_ws = non_ws_offset(&line);
if line.len() - non_ws >= MIN_SIZE {
if let Some(base_off) = line_hashes.get(&line[non_ws..]) {
let targ_off = targ_line_offset + non_ws;
matches.push((start_offset + targ_off, *base_off));
if *base_off < prev_base {
needs_subseq = true;
}
prev_base = *base_off;
}
}
targ_line_offset += line.len();
}
let longest_subseq =
if needs_subseq { longest_increasing_region_set(&matches) } else { matches };
let mut prev_end = start_offset;
let mut prev_start = start_offset;
for (targ_off, base_off) in longest_subseq {
if targ_off <= prev_end {
continue;
}
if base_off <= prev_start {
continue;
}
let (mut left_dist, mut right_dist) =
expand_match(base, target, base_off, targ_off, prev_end);
right_dist = right_dist.min(target_end - targ_off);
left_dist = left_dist.min(base_off - prev_start);
let targ_start = targ_off - left_dist;
let base_start = base_off - left_dist;
let len = left_dist + right_dist;
prev_end = targ_start + len;
prev_start = base_start + len;
builder.copy(base_start, targ_start, len);
}
if diff_end > 0 {
builder.copy(base.len() - diff_end, target.len() - diff_end, diff_end);
}
builder.to_delta(base, target)
}
}
fn expand_match(
base: &Rope,
target: &Rope,
base_off: usize,
targ_off: usize,
prev_match_targ_end: usize,
) -> (usize, usize) {
let mut scanner = RopeScanner::new(base, target);
let max_left = targ_off - prev_match_targ_end;
let start = scanner.find_ne_char_back(base_off, targ_off, max_left);
debug_assert!(start <= max_left, "{} <= {}", start, max_left);
let end = scanner.find_ne_char(base_off, targ_off, None);
(start.min(max_left), end)
}
fn longest_increasing_region_set(items: &[(usize, usize)]) -> Vec<(usize, usize)> {
let mut result = vec![0];
let mut prev_chain = vec![0; items.len()];
for i in 1..items.len() {
let last_idx = *result.last().unwrap();
if items[last_idx].1 < items[i].1 {
prev_chain[i] = last_idx;
result.push(i);
continue;
}
let next_idx = match result.binary_search_by(|&j| items[j].1.cmp(&items[i].1)) {
Ok(_) => continue, Err(idx) => idx,
};
if items[i].1 < items[result[next_idx]].1 {
if next_idx > 0 {
prev_chain[i] = result[next_idx - 1];
}
result[next_idx] = i;
}
}
let mut u = result.len();
let mut v = *result.last().unwrap();
while u != 0 {
u -= 1;
result[u] = v;
v = prev_chain[v];
}
result.iter().map(|i| items[*i]).collect()
}
#[inline]
fn non_ws_offset(s: &str) -> usize {
s.as_bytes().iter().take_while(|b| **b == b' ' || **b == b'\t').count()
}
#[derive(Debug, Clone, Copy)]
struct DiffOp {
target_idx: usize,
base_idx: usize,
len: usize,
}
#[derive(Debug, Clone, Default)]
pub struct DiffBuilder {
ops: Vec<DiffOp>,
}
impl DiffBuilder {
fn copy(&mut self, base: usize, target: usize, len: usize) {
if let Some(prev) = self.ops.last_mut() {
let prev_end = prev.target_idx + prev.len;
let base_end = prev.base_idx + prev.len;
assert!(prev_end <= target, "{} <= {} prev {:?}", prev_end, target, prev);
if prev_end == target && base_end == base {
prev.len += len;
return;
}
}
self.ops.push(DiffOp { target_idx: target, base_idx: base, len })
}
fn to_delta(self, base: &Rope, target: &Rope) -> RopeDelta {
let mut els = Vec::with_capacity(self.ops.len() * 2);
let mut targ_pos = 0;
for DiffOp { base_idx, target_idx, len } in self.ops {
if target_idx > targ_pos {
let iv = Interval::new(targ_pos, target_idx);
els.push(DeltaElement::Insert(target.subseq(iv)));
}
els.push(DeltaElement::Copy(base_idx, base_idx + len));
targ_pos = target_idx + len;
}
if targ_pos < target.len() {
let iv = Interval::new(targ_pos, target.len());
els.push(DeltaElement::Insert(target.subseq(iv)));
}
Delta { els, base_len: base.len() }
}
}
fn make_line_hashes<'a>(base: &'a Rope, min_size: usize) -> HashMap<Cow<'a, str>, usize> {
let mut offset = 0;
let mut line_hashes = HashMap::with_capacity(base.len() / 60);
for line in base.lines_raw(..) {
let non_ws = non_ws_offset(&line);
if line.len() - non_ws >= min_size {
let cow = match line {
Cow::Owned(ref s) => Cow::Owned(s[non_ws..].to_string()),
Cow::Borrowed(s) => Cow::Borrowed(&s[non_ws..]),
};
line_hashes.insert(cow, offset + non_ws);
}
offset += line.len();
}
line_hashes
}
#[cfg(test)]
mod tests {
use super::*;
static SMALL_ONE: &str = "This adds FixedSizeAdler32, that has a size set at construction, and keeps bytes in a cyclic buffer of that size to be removed when it fills up.
Current logic (and implementing Write) might be too much, since bytes will probably always be fed one by one anyway. Otherwise a faster way of removing a sequence might be needed (one by one is inefficient).";
static SMALL_TWO: &str = "This adds some function, I guess?, that has a size set at construction, and keeps bytes in a cyclic buffer of that size to be ground up and injested when it fills up.
Currently my sense of smell (and the pain of implementing Write) might be too much, since bytes will probably always be fed one by one anyway. Otherwise crying might be needed (one by one is inefficient).";
static INTERVAL_STR: &str = include_str!("../src/interval.rs");
static BREAKS_STR: &str = include_str!("../src/breaks.rs");
#[test]
fn diff_smoke_test() {
let one = SMALL_ONE.into();
let two = SMALL_TWO.into();
let delta = LineHashDiff::compute_delta(&one, &two);
println!("delta: {:?}", &delta);
let result = delta.apply(&one);
assert_eq!(result, two);
let delta = LineHashDiff::compute_delta(&one, &two);
println!("delta: {:?}", &delta);
let result = delta.apply(&one);
assert_eq!(result, two);
}
#[test]
fn simple_diff() {
let one = "This is a simple string".into();
let two = "This is a string".into();
let delta = LineHashDiff::compute_delta(&one, &two);
println!("delta: {:?}", &delta);
let result = delta.apply(&one);
assert_eq!(result, two);
let delta = LineHashDiff::compute_delta(&two, &one);
println!("delta: {:?}", &delta);
let result = delta.apply(&two);
assert_eq!(result, one);
}
#[test]
fn test_larger_diff() {
let one = INTERVAL_STR.into();
let two = BREAKS_STR.into();
let delta = LineHashDiff::compute_delta(&one, &two);
let result = delta.apply(&one);
assert_eq!(String::from(result), String::from(two));
}
}