fix: utf8-indexed previews (#34)

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "zeditor"
-version = "0.1.1-a"
+version = "0.1.1-b"
 edition = "2021"
 
 [dependencies]

src/search.rs

@@ -104,21 +104,12 @@ fn search_text(
                     let start = hit.start() + substart;
                     let end = start + subend;
 
-                    // be careful not to slice in the middle of  utf8 chars
-                    let text_utf8 = text.chars().collect::<Vec<_>>();
                     hits.push(Hit {
                         path: path.clone(),
                         search: term.to_string(),
                         start,
                         end,
-                        preview: text_utf8[start.checked_sub(peek_size).unwrap_or_default()
-                            ..std::cmp::min(
-                                end.checked_add(peek_size).unwrap_or(text_utf8.len()),
-                                text_utf8.len(),
-                            )]
-                            .iter()
-                            .cloned()
-                            .collect::<String>(),
+                        preview: make_preview(text, start, end, peek_size),
                     })
                 }
             }
@@ -128,6 +119,33 @@ fn search_text(
     Ok(hits)
 }
 
+/// generate a preview of the area around our search target,
+/// looking forward _and_ behind by `peek_size` chars
+///
+/// will not to slice in the middle of UTF8 chars
+fn make_preview(text: &str, start: usize, end: usize, peek_size: usize) -> String {
+    let chars_before = &text[0..start].chars().collect::<Vec<_>>();
+
+    let chars_after = &text[end..text.len()].chars().collect::<Vec<_>>();
+
+    let search_target = &text[start..end];
+
+    let peek_before = chars_before
+        .iter()
+        .rev()
+        .take(peek_size)
+        .rev()
+        .cloned()
+        .collect::<String>();
+
+    let peek_after = chars_after
+        .iter()
+        .take(peek_size)
+        .cloned()
+        .collect::<String>();
+    format!("{}{}{}", peek_before, search_target, peek_after)
+}
+
 fn make_regex_vec(terms: &[&str]) -> Vec<(String, regex::Regex)> {
     terms
         .iter()