Move things around and get some tests in place

2 files changed, 161 insertions, 0 deletions

diff --git a/src/path/mod.rs b/src/path/mod.rs
new file mode 100644
index 0000000..f889283
--- /dev/null
+++ b/src/path/mod.rs
@@ -0,0 +1,41 @@
+use std::str::FromStr;
+use nom::ErrorKind;
+use error::*;
+use value::{Value, ValueKind};
+
+mod parser;
+
+#[derive(Debug, Eq, PartialEq, Clone, Hash)]
+pub enum Expression {
+    Identifier(String),
+    Child(Box<Expression>, String),
+    Subscript(Box<Expression>, i32),
+}
+
+impl FromStr for Expression {
+    type Err = ConfigError;
+
+    fn from_str(s: &str) -> Result<Expression> {
+        parser::from_str(s).map_err(|kind| ConfigError::PathParse(kind))
+    }
+}
+
+impl Expression {
+    pub fn get<'a>(self, root: &'a Value) -> Option<&'a Value> {
+        match self {
+            Expression::Identifier(id) => {
+                match root.kind {
+                    // `x` access on a table is equivalent to: map[x]
+                    ValueKind::Table(ref map) => map.get(&id),
+
+                    // all other variants return None
+                    _ => None,
+                }
+            }
+
+            _ => {
+                unimplemented!();
+            }
+        }
+    }
+}
diff --git a/src/path/parser.rs b/src/path/parser.rs
new file mode 100644
index 0000000..eea4343
--- /dev/null
+++ b/src/path/parser.rs
@@ -0,0 +1,120 @@
+use nom::*;
+use std::str::{FromStr, from_utf8};
+use super::Expression;
+
+named!(ident_<String>,
+    map!(
+        map_res!(is_a!(
+            "abcdefghijklmnopqrstuvwxyz \
+             ABCDEFGHIJKLMNOPQRSTUVWXYZ \
+             0123456789 \
+             _-"
+        ), from_utf8),
+        |s: &str| {
+            s.to_string()
+        }
+    )
+);
+
+named!(integer <i32>,
+    map_res!(
+        map_res!(
+            ws!(digit),
+            from_utf8
+        ),
+        FromStr::from_str
+    )
+);
+
+named!(ident<Expression>, map!(ident_, Expression::Identifier));
+
+fn postfix(expr: Expression) -> Box<Fn(&[u8]) -> IResult<&[u8], Expression>> {
+    return Box::new(move |i: &[u8]| {
+        alt!(i,
+            do_parse!(
+                tag!(".") >>
+                id: ident_ >>
+                (Expression::Child(Box::new(expr.clone()), id))
+            ) |
+            delimited!(
+                char!('['),
+                do_parse!(
+                    negative: opt!(tag!("-")) >>
+                    num: integer >>
+                    (Expression::Subscript(
+                        Box::new(expr.clone()),
+                        num * (if negative.is_none() { 1 } else { -1 })
+                    ))
+                ),
+                char!(']')
+            )
+        )
+    });
+}
+
+pub fn from_str(input: &str) -> Result<Expression, ErrorKind> {
+    match ident(input.as_bytes()) {
+        IResult::Done(mut rem, mut expr) => {
+            while rem.len() > 0 {
+                match postfix(expr)(rem) {
+                    IResult::Done(rem_, expr_) => {
+                        rem = rem_;
+                        expr = expr_;
+                    }
+
+                    // Forward Incomplete and Error
+                    result @ _ => {
+                        return result.to_result();
+                    }
+                }
+            }
+
+            Ok(expr)
+        }
+
+        // Forward Incomplete and Error
+        result @ _ => result.to_result(),
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use super::Expression::*;
+
+    #[test]
+    fn test_id() {
+        let parsed: Expression = from_str("abcd").unwrap();
+        assert_eq!(parsed, Identifier("abcd".into()));
+    }
+
+    #[test]
+    fn test_id_dash() {
+        let parsed: Expression = from_str("abcd-efgh").unwrap();
+        assert_eq!(parsed, Identifier("abcd-efgh".into()));
+    }
+
+    #[test]
+    fn test_child() {
+        let parsed: Expression = from_str("abcd.efgh").unwrap();
+        let expected = Child(Box::new(Identifier("abcd".into())), "efgh".into());
+
+        assert_eq!(parsed, expected);
+    }
+
+    #[test]
+    fn test_subscript() {
+        let parsed: Expression = from_str("abcd[12]").unwrap();
+        let expected = Subscript(Box::new(Identifier("abcd".into())), 12);
+
+        assert_eq!(parsed, expected);
+    }
+
+    #[test]
+    fn test_subscript_neg() {
+        let parsed: Expression = from_str("abcd[-1]").unwrap();
+        let expected = Subscript(Box::new(Identifier("abcd".into())), -1);
+
+        assert_eq!(parsed, expected);
+    }
+}