1 files changed, 213 insertions, 0 deletions
diff --git a/src/filters/mod.rs b/src/filters/mod.rs
new file mode 100644
index 0000000..62dc04b
--- /dev/null
+++ b/src/filters/mod.rs
@@ -0,0 +1,213 @@
+#![allow(clippy::new_ret_no_self)]
+use std::ops;
+
+use num_derive::FromPrimitive;
+use num_traits::FromPrimitive as _;
+
+pub mod log;
+pub mod player;
+
+/// Early filtering result.
+///
+/// This implements a [three-valued logic](https://en.wikipedia.org/wiki/Three-valued_logic),
+/// similar to SQL's `NULL`.
+#[derive(Debug, Copy, Clone, PartialEq, Eq, FromPrimitive)]
+#[repr(i8)]
+pub enum Inclusion {
+    /// The log should be included.
+    Include = 1,
+    /// The state is yet unknown.
+    Unknown = 0,
+    /// The log should be excluded.
+    Exclude = -1,
+}
+
+impl ops::Not for Inclusion {
+    type Output = Self;
+
+    fn not(self) -> Self::Output {
+        Inclusion::from_i8(-(self as i8)).unwrap()
+    }
+}
+
+impl ops::BitAnd<Inclusion> for Inclusion {
+    type Output = Self;
+
+    fn bitand(self, rhs: Inclusion) -> Self::Output {
+        Inclusion::from_i8((self as i8).min(rhs as i8)).unwrap()
+    }
+}
+
+impl ops::BitOr<Inclusion> for Inclusion {
+    type Output = Self;
+
+    fn bitor(self, rhs: Inclusion) -> Self::Output {
+        Inclusion::from_i8((self as i8).max(rhs as i8)).unwrap()
+    }
+}
+
+impl From<bool> for Inclusion {
+    fn from(data: bool) -> Self {
+        if data {
+            Inclusion::Include
+        } else {
+            Inclusion::Exclude
+        }
+    }
+}
+
+/// The main filter trait.
+///
+/// Filters are usually handled as a `Box<dyn Filter>`.
+pub trait Filter<Early, Late>: Send + Sync {
+    /// Determine early (before processing all events) whether the log stands a chance to be
+    /// included.
+    ///
+    /// Note that you can return [Inclusion::Unkown] if this filter cannot determine yet a definite
+    /// answer.
+    fn filter_early(&self, _: &Early) -> Inclusion {
+        Inclusion::Unknown
+    }
+
+    /// Return whether the log should be included, according to this filter.
+    fn filter(&self, _: &Late) -> bool;
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Const(pub bool);
+
+impl Const {
+    pub fn new<E, L>(output: bool) -> Box<dyn Filter<E, L>> {
+        Box::new(Const(output))
+    }
+}
+
+impl<E, L> Filter<E, L> for Const {
+    fn filter_early(&self, _: &E) -> Inclusion {
+        self.0.into()
+    }
+
+    fn filter(&self, _: &L) -> bool {
+        self.0
+    }
+}
+
+struct AndFilter<E, L>(Box<dyn Filter<E, L>>, Box<dyn Filter<E, L>>);
+
+impl<E, L> Filter<E, L> for AndFilter<E, L> {
+    fn filter_early(&self, partial_evtc: &E) -> Inclusion {
+        let lhs = self.0.filter_early(partial_evtc);
+        // Short circuit behaviour
+        if lhs == Inclusion::Exclude {
+            Inclusion::Exclude
+        } else {
+            lhs & self.1.filter_early(partial_evtc)
+        }
+    }
+
+    fn filter(&self, log: &L) -> bool {
+        self.0.filter(log) && self.1.filter(log)
+    }
+}
+
+impl<E: 'static, L: 'static> ops::BitAnd<Box<dyn Filter<E, L>>> for Box<dyn Filter<E, L>> {
+    type Output = Box<dyn Filter<E, L>>;
+
+    fn bitand(self, rhs: Box<dyn Filter<E, L>>) -> Self::Output {
+        Box::new(AndFilter(self, rhs))
+    }
+}
+
+struct OrFilter<E, L>(Box<dyn Filter<E, L>>, Box<dyn Filter<E, L>>);
+
+impl<E, L> Filter<E, L> for OrFilter<E, L> {
+    fn filter_early(&self, partial_evtc: &E) -> Inclusion {
+        let lhs = self.0.filter_early(partial_evtc);
+        // Short circuit behaviour
+        if lhs == Inclusion::Include {
+            Inclusion::Include
+        } else {
+            lhs | self.1.filter_early(partial_evtc)
+        }
+    }
+
+    fn filter(&self, log: &L) -> bool {
+        self.0.filter(log) || self.1.filter(log)
+    }
+}
+
+impl<E: 'static, L: 'static> ops::BitOr<Box<dyn Filter<E, L>>> for Box<dyn Filter<E, L>> {
+    type Output = Box<dyn Filter<E, L>>;
+
+    fn bitor(self, rhs: Box<dyn Filter<E, L>>) -> Self::Output {
+        Box::new(OrFilter(self, rhs))
+    }
+}
+
+struct NotFilter<E, L>(Box<dyn Filter<E, L>>);
+
+impl<E, L> Filter<E, L> for NotFilter<E, L> {
+    fn filter_early(&self, partial_evtc: &E) -> Inclusion {
+        !self.0.filter_early(partial_evtc)
+    }
+
+    fn filter(&self, log: &L) -> bool {
+        !self.0.filter(log)
+    }
+}
+
+impl<E: 'static, L: 'static> ops::Not for Box<dyn Filter<E, L>> {
+    type Output = Box<dyn Filter<E, L>>;
+
+    fn not(self) -> Self::Output {
+        Box::new(NotFilter(self))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_inclusion_not() {
+        use Inclusion::*;
+
+        assert_eq!(!Exclude, Include);
+        assert_eq!(!Include, Exclude);
+        assert_eq!(!Unknown, Unknown);
+    }
+
+    #[test]
+    fn test_inclusion_and() {
+        use Inclusion::*;
+
+        assert_eq!(Exclude & Exclude, Exclude);
+        assert_eq!(Exclude & Unknown, Exclude);
+        assert_eq!(Exclude & Include, Exclude);
+
+        assert_eq!(Unknown & Exclude, Exclude);
+        assert_eq!(Unknown & Unknown, Unknown);
+        assert_eq!(Unknown & Include, Unknown);
+
+        assert_eq!(Include & Exclude, Exclude);
+        assert_eq!(Include & Unknown, Unknown);
+        assert_eq!(Include & Include, Include);
+    }
+
+    #[test]
+    fn test_inclusion_or() {
+        use Inclusion::*;
+
+        assert_eq!(Exclude | Exclude, Exclude);
+        assert_eq!(Exclude | Unknown, Unknown);
+        assert_eq!(Exclude | Include, Include);
+
+        assert_eq!(Unknown | Exclude, Unknown);
+        assert_eq!(Unknown | Unknown, Unknown);
+        assert_eq!(Unknown | Include, Include);
+
+        assert_eq!(Include | Exclude, Include);
+        assert_eq!(Include | Unknown, Include);
+        assert_eq!(Include | Include, Include);
+    }
+}