Implement FieldPath::walk()

libimagentryfilter/src/builtin/header/field_path/element.rs

@@ -1,11 +1,40 @@
 use std::fmt::{Display, Formatter};
 use std::fmt::Error as FmtError;
 
-#[derive(Debug)]
+use toml::Value;
+
+#[derive(Clone, Debug)]
 pub struct FieldPathElement {
     name: String
 }
 
+impl FieldPathElement {
+
+    pub fn new(name: String) -> FieldPathElement {
+        FieldPathElement { name: name }
+    }
+
+    pub fn apply(&self, value: Value) -> Option<Value> {
+        use std::str::FromStr;
+        use std::ops::Index;
+
+        match value {
+            Value::Table(t) => {
+                t.get(&self.name).map(|a| a.clone())
+            },
+
+            Value::Array(a) => {
+                usize::from_str(&self.name[..])
+                    .ok()
+                    .and_then(|i| Some(a[i].clone()))
+            },
+
+            _ => None,
+        }
+    }
+
+}
+
 impl Display for FieldPathElement {
 
     fn fmt(&self, fmt: &mut Formatter) -> Result<(), FmtError> {

libimagentryfilter/src/builtin/header/field_path/mod.rs

@@ -20,7 +20,9 @@ pub struct FieldPath {
 impl FieldPath {
 
     pub fn new(elements: Vec<FieldPathElement>) -> FieldPath {
-        unimplemented!()
+        FieldPath {
+            elements: elements,
+        }
     }
 
     pub fn compile(source: String) -> Result<FieldPath, FieldPathParsingError> {
@@ -28,7 +30,14 @@ impl FieldPath {
     }
 
     pub fn walk(&self, e: &EntryHeader) -> Option<Value> {
-        unimplemented!()
+        let init_val : Value = Value::Table(e.toml().clone());
+
+        self.elements
+            .clone()
+            .into_iter()
+            .fold(Some(init_val), |acc: Option<Value>, token: FieldPathElement| {
+                acc.and_then(|element| token.apply(element))
+            })
     }
 
 }