fix: build regex once instead of once per file

src/parser.rs

@@ -17,11 +17,16 @@ pub fn process_files(
     pattern: &str,
     cli: &Cli,
 ) -> anyhow::Result<Matches, anyhow::Error> {
+    let reg = RegexBuilder::new(pattern)
+        .case_insensitive(cli.ignore_case)
+        .build()
+        .with_context(|| format!("invalid regex: {:?}", pattern))?;
+
     let mut matches = Matches { items: vec![], pattern: String::from(pattern) };
 
     for file_path in file_paths {
         let lines_iter = read_lines(file_path)?;
-        let mut _matches = match_pattern(lines_iter, pattern, file_path, cli)?;
+        let mut _matches = match_pattern(lines_iter, pattern, file_path, &reg, cli)?;
         matches.append(&mut _matches);
     }
 
@@ -60,19 +65,15 @@ pub fn match_pattern(
     iter: impl Iterator<Item = std::io::Result<String>>,
     pattern: &str,
     file_path: &Path,
+    regex: &Regex,
     cli: &Cli,
 ) -> anyhow::Result<Matches, anyhow::Error> {
-    let reg = RegexBuilder::new(pattern)
-        .case_insensitive(cli.ignore_case)
-        .build()
-        .with_context(|| format!("invalid regex: {:?}", pattern))?;
-
     let mut matches = Vec::new();
 
     for (idx, line) in iter.enumerate() {
         let line = line?;
 
-        if reg.is_match(&line) {
+        if regex.is_match(&line) {
             let m = Match {
                 line_number: idx + 1,
                 text: line,