refactor: print errors instead of panicking (#40)

* minor tweaks and error handling

* adding quotes around messages

* restoring test

* Adding a 'sad path' test

* Reverting a change and updating a message.

src/lib.rs

@@ -13,6 +13,7 @@ pub mod utils;
 
 const MAX_LINK_NESTED_DEPTH: usize = 10;
 
+#[derive(Default)]
 pub struct Template;
 
 impl Template {
@@ -38,13 +39,8 @@ impl Preprocessor for Template {
                         .map(|dir| src_dir.join(dir))
                         .expect("All book items have a parent");
 
-                    let content = replace_template(
-                        &chapter.content,
-                        &SystemFileReader::default(),
-                        base,
-                        source,
-                        0,
-                    );
+                    let content =
+                        replace_template(&chapter.content, &SystemFileReader, base, source, 0);
                     chapter.content = content;
                 }
             }
@@ -79,7 +75,7 @@ where
     for link in links::extract_template_links(chapter_content) {
         replaced.push_str(&chapter_content[previous_end_index..link.start_index]);
 
-        match link.replace_args(&path, file_reader) {
+        match link.replace_args(path, file_reader) {
             Ok(new_content) => {
                 if depth < MAX_LINK_NESTED_DEPTH {
                     if let Some(rel_path) = link.link_type.relative_path(path) {
@@ -296,4 +292,24 @@ mod lib_tests {
 
         assert_eq!(actual_chapter_content, start_chapter_content);
     }
+
+    #[test]
+    fn test_sad_path_bad_template() {
+        let start_chapter_content = [
+            "This is {{#template template.md",
+            "text=valid text",
+            "this has no key for the value and is going to break things}}",
+        ]
+        .join("\n");
+        let end_chapter_content = "This is valid text";
+        let file_name: PathBuf = PathBuf::from("template.md");
+        let template_file_contents = "[[#text]]".to_string();
+        let map = HashMap::from([(file_name, template_file_contents)]);
+        let file_reader = &TestFileReader::from(map);
+
+        let actual_chapter_content =
+            replace_template(&start_chapter_content, file_reader, "", "", 0);
+
+        assert_eq!(actual_chapter_content, end_chapter_content);
+    }
 }

src/links.rs

@@ -113,23 +113,39 @@ impl<'a> Link<'a> {
                         .split(LINE_BREAKS)
                         .map(|str| str.trim())
                         .filter(|trimmed| !trimmed.is_empty())
-                        .map(|mat| {
+                        .filter_map(|mat| {
                             let mut split_n = mat.splitn(2, '=');
-                            let key = split_n.next().unwrap().trim();
-                            let value = split_n.next().unwrap();
-                            (key, value)
+                            if let Some(key) = split_n.next() {
+                                let key = key.trim();
+                                if let Some(value) = split_n.next() {
+                                    return Some((key, value));
+                                }
+                            }
+                            eprintln!(
+                                "Couldn't find a key/value pair while parsing the argument '{}'",
+                                mat
+                            );
+                            None
                         })
                         .collect::<Vec<_>>(),
 
                     // This looks like {{#template <file> <args>}}
                     false => TEMPLATE_ARGS
                         .captures_iter(args.as_str())
-                        .into_iter()
-                        .map(|mat| {
-                            let mut split_n = mat.unwrap().get(0).unwrap().as_str().splitn(2, '=');
-                            let key = split_n.next().unwrap().trim();
-                            let value = split_n.next().unwrap();
-                            (key, value)
+                        .filter_map(|mat| {
+                            let captures = mat.ok()?;
+                            let mut split_n = captures.get(0)?.as_str().splitn(2, '=');
+                            if let Some(key) = split_n.next() {
+                                let key = key.trim();
+                                if let Some(value) = split_n.next() {
+                                    return Some((key.trim(), value));
+                                }
+                            }
+                            eprintln!(
+                                "Couldn't parse key or value while parsing '{:?}'",
+                                &args.as_str()
+                            );
+                            None
                         })
                         .collect::<Vec<_>>(),
                 };
@@ -157,7 +173,7 @@ impl<'a> Link<'a> {
         FR: FileReader,
     {
         match self.link_type {
-            LinkType::Escaped => Ok((&self.link_text[1..]).to_owned()),
+            LinkType::Escaped => Ok((self.link_text[1..]).to_owned()),
             LinkType::Template(ref pat) => {
                 let target = base.as_ref().join(pat);
                 let contents = file_reader.read_to_string(&target, self.link_text)?;
@@ -195,7 +211,7 @@ impl<'a> Iterator for LinkIter<'a> {
 
     fn next(&mut self) -> Option<Self::Item> {
         for cap in &mut self.0 {
-            if let Some(inc) = Link::from_capture(cap.unwrap()) {
+            if let Some(inc) = Link::from_capture(cap.ok()?) {
                 return Some(inc);
             }
         }
@@ -499,11 +515,14 @@ year=2022
 
     #[test]
     fn test_extract_template_links_with_newlines_malformed() {
-        let s = "{{#template test.rs 
-        lang=rust
-        year=2022}}";
+        let s = [
+            "{{#template test.rs \n",
+            "        lang=rust\n",
+            "        year=2022}}",
+        ]
+        .concat();
 
-        let res = extract_template_links(s).collect::<Vec<_>>();
+        let res = extract_template_links(&s).collect::<Vec<_>>();
 
         assert_eq!(
             res,