add ReverseSequence projection

src/projection/mod.rs

@@ -22,4 +22,5 @@ pub mod map_index_item;
 pub mod map_index_key;
 pub mod grid_offset;
 pub mod decorate_sequence;
+pub mod reverse_sequence;
 

src/projection/reverse_sequence.rs

@@ -0,0 +1,142 @@
+use {
+    crate::{
+        view::{
+            Observer, ObserverBroadcast, ObserverExt, OuterViewPort, View, ViewPort,
+            sequence::SequenceView,
+        },
+    },
+    std::sync::Arc,
+    std::sync::RwLock,
+};
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+impl<Item: 'static> OuterViewPort<dyn SequenceView<Item = Item>> {
+    pub fn reverse(&self) -> OuterViewPort<dyn SequenceView<Item = Item>> {
+        let port = ViewPort::new();
+        port.add_update_hook(Arc::new(self.0.clone()));
+
+        let map = Arc::new(RwLock::new(ReverseSequence {
+            src_view: None,
+            end: 0,
+            cast: port.inner().get_broadcast(),
+        }));
+
+        self.add_observer(map.clone());
+        port.inner().set_view(Some(map));
+        port.into_outer()
+    }
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+pub struct ReverseSequence<SrcView>
+where SrcView: SequenceView + ?Sized
+{
+    src_view: Option<Arc<SrcView>>,
+    end: usize,
+    cast: Arc<RwLock<ObserverBroadcast<dyn SequenceView<Item = SrcView::Item>>>>
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+impl<SrcView> View for ReverseSequence<SrcView>
+where SrcView: SequenceView + ?Sized
+{
+    type Msg = usize;
+}
+
+impl<SrcView> SequenceView for ReverseSequence<SrcView>
+where SrcView: SequenceView + ?Sized
+{
+    type Item = SrcView::Item;
+
+    fn len(&self) -> Option<usize> {
+        self.src_view.len()
+    }
+
+    fn get(&self, idx: &usize) -> Option<Self::Item> {
+        let len = self.src_view.len().unwrap();
+        if *idx < len {
+            let end = len - 1;
+            self.src_view.get( &(end - idx) )
+        } else {
+            None
+        }
+    }
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+impl<SrcView> Observer<SrcView> for ReverseSequence<SrcView>
+where SrcView: SequenceView + ?Sized
+{
+    fn reset(&mut self, view: Option<Arc<SrcView>>) {
+        let old_len = self.len();
+        self.src_view = view;
+        let new_len = self.len();
+
+        if let Some(len) = old_len {
+            self.cast.notify_each(0..len);
+        }
+        if let Some(len) = new_len {
+            self.cast.notify_each(0..len);
+            self.end = if len > 0 { len - 1 } else { 0 };
+        }
+    }
+
+    fn notify(&mut self, idx: &usize) {
+        /* todo optimize
+         */
+        let len = self.src_view.len().unwrap();
+        let new_end = if len > 0 { len - 1 } else { 0 };
+        if new_end < self.end {
+            self.cast.notify_each( 0 ..= self.end );
+            self.end = new_end;
+        } else {
+            self.cast.notify_each( 0 ..= new_end );
+            self.end = new_end;
+//            self.cast.notify( &(self.end - idx) );
+        }
+    }
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+#[cfg(test)]
+mod tests {
+    use crate::buffer::vec::*;
+    use crate::projection::map_sequence::*;
+
+    use crate::view::{port::UpdateTask, sequence::SequenceView};
+
+    #[test]
+    fn rev_seq1() {
+        let mut buffer = VecBuffer::new();
+
+        let target_port = buffer.get_port().to_sequence().reverse();
+        let target_view = target_port.get_view();
+
+        buffer.push(0);
+        buffer.push(7);
+        buffer.push(9);
+
+        target_port.0.update();
+
+        assert_eq!(target_view.len(), Some(3));
+
+        assert_eq!(target_view.get(&0), Some(9));
+        assert_eq!(target_view.get(&1), Some(7));
+        assert_eq!(target_view.get(&2), Some(0));
+        assert_eq!(target_view.get(&3), None);
+
+        buffer.remove(0);
+
+        target_port.0.update();
+        assert_eq!(target_view.len(), Some(2));
+        assert_eq!(target_view.get(&0), Some(9));
+        assert_eq!(target_view.get(&1), Some(7));
+        assert_eq!(target_view.get(&2), None);
+     }
+}
+