feat: Parse tagline (#5)

Cargo.toml

@@ -6,3 +6,5 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+pest = "2.7.6"
+pest_derive = "2.7.6"

src/lib.rs

@@ -0,0 +1,2 @@
+/// parsers contains the relevant grammar parsers
+pub mod parsers;

src/parsers.rs

@@ -0,0 +1,83 @@
+use pest_derive::Parser;
+
+#[derive(Parser)]
+#[grammar = "tagline.pest"]
+/// TaglineParser is responsible for parsing the taglines at the start of each searched file.
+pub struct TaglineParser;
+
+#[cfg(test)]
+mod tests {
+    use pest::Parser;
+
+    use super::*;
+
+    #[test]
+    fn test_tagline_parser() {
+        struct TestCase<'a> {
+            name: &'a str,
+            input: &'a str,
+            expected_tags: Vec<&'a str>,
+            expected_error: bool,
+        }
+
+        let test_cases = [
+            TestCase {
+                name: "success_with_space",
+                input: "tags: [#1 #2 #3]",
+                expected_tags: vec!["#1", "#2", "#3"],
+                expected_error: false,
+            },
+            TestCase {
+                name: "success_without_space",
+                input: "tags:[#1#asdf#something-idk]",
+                expected_tags: vec!["#1", "#asdf", "#something-idk"],
+                expected_error: false,
+            },
+            TestCase {
+                name: "success_with_newline",
+                input: "tags:\n[\n\t#something_else\n]",
+                expected_tags: vec!["#something_else"],
+                expected_error: false,
+            },
+            TestCase {
+                name: "fail_no_brackets",
+                input: "tags:#1#2#3",
+                expected_tags: vec![],
+                expected_error: true,
+            },
+            TestCase {
+                name: "fail_no_tags",
+                input: "[#1#2#3]",
+                expected_tags: vec![],
+                expected_error: true,
+            },
+            TestCase {
+                name: "fail_wrong_tag",
+                input: "tags:[##]",
+                expected_tags: vec![],
+                expected_error: true,
+            },
+        ];
+
+        test_cases.iter().for_each(|test_case| {
+            println!("Testing {}", test_case.name);
+
+            let res = TaglineParser::parse(Rule::tagline, test_case.input);
+            if res.is_err() {
+                assert!(test_case.expected_error);
+                return;
+            }
+
+            assert!(!test_case.expected_error);
+
+            for (i, tag) in res.unwrap().next().unwrap().into_inner().enumerate() {
+                match tag.as_rule() {
+                    Rule::tag => {
+                        assert!(tag.as_str() == test_case.expected_tags[i])
+                    }
+                    _ => unreachable!(),
+                }
+            }
+        })
+    }
+}

tagline.pest

@@ -0,0 +1,6 @@
+tag = {"#" ~ (LETTER|NUMBER|CONNECTOR_PUNCTUATION|DASH_PUNCTUATION)+}
+taglist = _{"[" ~ tag* ~ "]"}
+tagline = _{"tags:" ~ taglist}
+
+WHITESPACE = _{" " | "\t" | NEWLINE}
+