Add field_grep filter

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

libimagentryfilter/src/builtin/header/field_grep.rs

@@ -4,20 +4,35 @@ use toml::Value;
 use libimagstore::store::Entry;
 
 use builtin::header::field_path::FieldPath;
+use builtin::header::field_predicate::FieldPredicate;
+use builtin::header::field_predicate::Predicate;
 use filter::Filter;
 
+struct EqGrep{
+    regex: Regex
+}
+
+impl Predicate for EqGrep {
+
+    fn evaluate(&self, v: Value) -> bool {
+        match v {
+            Value::String(s) => self.regex.captures(&s[..]).is_some(),
+            _                 => false,
+        }
+    }
+
+}
+
 /// Check whether certain header field in a entry is equal to a value
 pub struct FieldGrep {
-    header_field_path: FieldPath,
-    grep: Regex,
+    filter: FieldPredicate<EqGrep>,
 }
 
 impl FieldGrep {
 
     pub fn new(path: FieldPath, grep: Regex) -> FieldGrep {
         FieldGrep {
-            header_field_path: path,
-            grep: grep,
+            filter: FieldPredicate::new(path, Box::new(EqGrep { regex: grep})),
         }
     }
 
@@ -26,15 +41,7 @@ impl FieldGrep {
 impl Filter for FieldGrep {
 
     fn filter(&self, e: &Entry) -> bool {
-        e.get_header()
-            .read(&self.header_field_path[..])
-            .map(|v| {
-                match v {
-                    Some(Value::String(s)) => self.grep.captures(&s[..]).is_some(),
-                    _                      => false,
-                }
-            })
-            .unwrap_or(false)
+        self.filter.filter(e)
     }
 
 }