Add field_predicate filter

libimagentryfilter/src/builtin/header/field_predicate.rs

@@ -0,0 +1,45 @@
+use libimagstore::store::Entry;
+
+use builtin::header::field_path::FieldPath;
+use filter::Filter;
+
+use toml::Value;
+
+pub trait Predicate {
+    fn evaluate(&self, Value) -> bool;
+}
+
+/// Check whether certain header field in a entry is equal to a value
+pub struct FieldPredicate<P: Predicate> {
+    header_field_path: FieldPath,
+    predicate: Box<P>,
+}
+
+impl<P: Predicate> FieldPredicate<P> {
+
+    pub fn new(path: FieldPath, predicate: Box<P>) -> FieldPredicate<P> {
+        FieldPredicate {
+            header_field_path: path,
+            predicate: predicate,
+        }
+    }
+
+}
+
+impl<P: Predicate> Filter for FieldPredicate<P> {
+
+    fn filter(&self, e: &Entry) -> bool {
+        e.get_header()
+            .read(&self.header_field_path[..])
+            .map(|val| {
+                match val {
+                    None => false,
+                    Some(v) => (*self.predicate).evaluate(v),
+                }
+            })
+            .unwrap_or(false)
+    }
+
+}
+
+

libimagentryfilter/src/builtin/header/mod.rs

@@ -4,3 +4,4 @@ pub mod field_grep;
 pub mod field_isempty;
 pub mod field_istype;
 pub mod field_path;
+pub mod field_predicate;