From 89a6f84114da52d4738cc42d4fc1363e96dfcea7 Mon Sep 17 00:00:00 2001
From: Michael Sippel <micha@fragmental.art>
Date: Sat, 15 May 2021 03:33:24 +0200
Subject: [PATCH] sequence filter

---
 nested/src/sequence/filter.rs | 154 ++++++++++++++++++++++++++++++++++
 nested/src/sequence/mod.rs    |   1 +
 2 files changed, 155 insertions(+)
 create mode 100644 nested/src/sequence/filter.rs

diff --git a/nested/src/sequence/filter.rs b/nested/src/sequence/filter.rs
new file mode 100644
index 0000000..0cfba42
--- /dev/null
+++ b/nested/src/sequence/filter.rs
@@ -0,0 +1,154 @@
+use {
+    std::sync::Arc,
+    std::sync::RwLock,
+    crate::{
+        sequence::{SequenceView},
+        core::{
+            Observer, ObserverExt, ObserverBroadcast,
+            View, ViewPort, OuterViewPort
+        }
+    }
+};
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+impl<V: SequenceView + ?Sized + 'static> OuterViewPort<V>
+{
+    pub fn filter<
+        P: Fn(&V::Item) -> bool + Send + Sync + 'static
+    >(&self, pred: P) -> OuterViewPort<dyn SequenceView<Item = V::Item>> {
+        let port = ViewPort::new();
+        let filter = Arc::new(RwLock::new(
+            Filter {
+                src_view: None,
+                pred,
+                old_preds: RwLock::new(Vec::new()),
+                cast: port.inner().get_broadcast()
+            }
+        ));
+
+        self.add_observer(filter.clone());
+        port.inner().set_view(Some(filter));
+        port.into_outer()
+    }
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+struct Filter<SrcView, P>
+where SrcView: SequenceView + ?Sized + 'static,
+      P: Fn(&SrcView::Item) -> bool + Send + Sync + 'static
+{
+    src_view: Option<Arc<SrcView>>,
+    pred: P,
+    old_preds: RwLock<Vec<bool>>,
+    cast: Arc<RwLock<ObserverBroadcast<dyn SequenceView<Item = SrcView::Item>>>>
+}
+
+impl<SrcView, P> Filter<SrcView, P>
+where SrcView: SequenceView + ?Sized + 'static,
+      P: Fn(&SrcView::Item) -> bool + Send + Sync + 'static
+{
+    fn get_offset(&self, idx: usize) -> usize {
+        if let Some(v) = self.src_view.clone() {
+            let mut i = 0;
+            let mut j = 0;
+            let mut offset = 0;
+
+            while let (Some(x), true) = (v.get(&i), j <= idx) {
+                if (self.pred)(&x) {
+                    j += 1;
+                } else {
+                    offset += 1;
+                }
+                i+=1;
+            }
+
+            offset
+        } else {
+           0
+        }
+    }
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+impl<SrcView, P> View for Filter<SrcView, P>
+where SrcView: SequenceView + ?Sized + 'static,
+      P: Fn(&SrcView::Item) -> bool + Send + Sync + 'static
+{
+    type Msg = usize;
+}
+
+impl<SrcView, P> SequenceView for Filter<SrcView, P>
+where SrcView: SequenceView + ?Sized + 'static,
+      P: Fn(&SrcView::Item) -> bool + Send + Sync + 'static
+{
+    type Item = SrcView::Item;
+
+    fn len(&self) -> Option<usize> {
+        if let Some(src_len) = self.src_view.len() {
+            Some(src_len - self.get_offset(src_len) )
+        } else {
+            None
+        }
+    }
+
+    fn get(&self, idx: &usize) -> Option<Self::Item> {
+        self.src_view.get(&( idx + self.get_offset(*idx) ))
+    }
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+impl<SrcView, P> Observer<SrcView> for Filter<SrcView, P>
+where SrcView: SequenceView + ?Sized + 'static,
+      P: Fn(&SrcView::Item) -> bool + Send + Sync + 'static
+{
+    fn reset(&mut self, new_src: Option<Arc<SrcView>>) {
+        let old_len = self.len();
+        self.src_view = new_src;
+        self.old_preds = RwLock::new(Vec::new());
+        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); }
+    }
+
+    fn notify(&self, idx: &usize) {
+        let l = self.len().unwrap_or(0)+1;
+        let np = 
+            if let Some(x) = self.src_view.get(idx) {
+                (self.pred)(&x)
+            } else {
+                false
+            };
+
+        let mut opds = self.old_preds.write().unwrap();
+
+        opds.resize_with(1+*idx, || false);
+        let op = opds.get(*idx).cloned().unwrap_or(false);
+        *opds.get_mut(*idx).unwrap() = np;
+
+        drop(opds);
+
+        let i =
+            (0 .. *idx)
+            .map(
+                |j|
+                if let Some(x) = self.src_view.get(&j) {
+                    if (self.pred)(&x) { 1 } else { 0 }
+                } else {
+                    0
+                }
+            )
+            .sum();
+
+        if np != op {
+            self.cast.notify_each(i .. l);
+        } else {
+            self.cast.notify(&i);
+        }
+    }
+}
+
diff --git a/nested/src/sequence/mod.rs b/nested/src/sequence/mod.rs
index d0f8366..eb1d9a0 100644
--- a/nested/src/sequence/mod.rs
+++ b/nested/src/sequence/mod.rs
@@ -2,6 +2,7 @@
 pub mod seq2idx;
 pub mod vec_buffer;
 pub mod map;
+pub mod filter;
 pub mod flatten;
 
 pub use {