feat: diff output for --preview

Cargo.toml

@@ -30,6 +30,7 @@ ignore = "0.4.20"
 ansi_term = "0.12.1"
 is-terminal = "0.4.9"
 clap = { version = "4.4.3", features = ["derive", "deprecated", "wrap_help"] }
+similar = { version = "2.3.0", features = ["inline", "bytes"] }
 
 [dev-dependencies]
 assert_cmd = "2.0.12"

src/replacer.rs

@@ -1,5 +1,6 @@
 use crate::{utils, Error, Result};
 use regex::bytes::Regex;
+use similar::{TextDiff, ChangeTag};
 use std::{fs, fs::File, io::prelude::*, path::Path};
 
 pub(crate) struct Replacer {
@@ -94,28 +95,61 @@ impl Replacer {
         &'a self,
         content: &[u8],
     ) -> std::borrow::Cow<'a, [u8]> {
+        use ansi_term::{Color, Style};
+
+        let replaced = self.replace(content);
+        let diff = TextDiff::from_lines(&*content, &*replaced);
+
         let mut v = Vec::<u8>::new();
-        let mut captures = self.regex.captures_iter(content);
-
-        self.regex.split(content).for_each(|sur_text| {
-            use regex::bytes::Replacer;
-
-            v.extend(sur_text);
-            if let Some(capture) = captures.next() {
-                v.extend_from_slice(
-                    ansi_term::Color::Green.prefix().to_string().as_bytes(),
-                );
-                if self.is_literal {
-                    regex::bytes::NoExpand(&self.replace_with)
-                        .replace_append(&capture, &mut v);
-                } else {
-                    (&*self.replace_with).replace_append(&capture, &mut v);
+
+        for group in diff.grouped_ops(3).iter() {
+            for op in group {
+                for change in diff.iter_inline_changes(op) {
+                    match change.tag() {
+                        ChangeTag::Delete => {
+                            v.extend(Color::Red.prefix().to_string().as_bytes());
+                            let idx = match change.old_index() {
+                                Some(old_idx) => format!("{:>3} ", old_idx).into_bytes(),
+                                None => b"    ".to_vec(),
+                            };
+                            v.extend(idx);
+                            v.push(b'-');
+                        },
+                        ChangeTag::Insert => {
+                            v.extend(Color::Green.prefix().to_string().as_bytes());
+                            let idx = match change.new_index() {
+                                Some(new_idx) => format!("{:>3} ", new_idx).into_bytes(),
+                                None => b"    ".to_vec(),
+                            };
+                            v.extend(idx);
+                            v.push(b'+');
+                        },
+                        ChangeTag::Equal => {
+                            v.extend(b"     ");
+                        },
+                    }
+                    v.push(b' ');
+
+                    for (emphasized, value) in change.iter_strings_lossy() {
+                        if emphasized {
+                            v.extend(Style::new().bold().paint(value).as_bytes());
+                        } else {
+                            v.extend(value.as_bytes());
+                        }
+                    }
+
+                    match change.tag() {
+                        ChangeTag::Delete => v.extend(Color::Red.suffix().to_string().as_bytes()),
+                        ChangeTag::Insert => v.extend(Color::Green.suffix().to_string().as_bytes()),
+                        ChangeTag::Equal => (),
+                    }
+
+                    if change.missing_newline() {
+                        v.push(b'\n');
+                    }
                 }
-                v.extend_from_slice(
-                    ansi_term::Color::Green.suffix().to_string().as_bytes(),
-                );
             }
-        });
+        }
 
         return std::borrow::Cow::Owned(v);
     }