add half-life to history weighting

4 files changed, 17 insertions, 9 deletions

diff --git a/Cargo.lock b/Cargo.lock
index f5b2350..91b1eb3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -314,7 +314,7 @@ checksum = "cf8baf1c55e62ffcace7a9f06f4bd9cd3f0c4beb022d3b367256b91b87513d98"
 
 [[package]]
 name = "mood"
-version = "0.4.0"
+version = "0.5.0"
 dependencies = [
  "chrono",
  "directories",
diff --git a/Cargo.toml b/Cargo.toml
index 2996395..762f2d5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "mood"
-version = "0.4.0"
+version = "0.5.0"
 description = "A music player governed by your moods."
 edition = "2024"
 license = "GPL-3.0-or-later"
diff --git a/src/config.rs b/src/config.rs
index 67721b4..5fdcfe8 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -14,6 +14,7 @@ pub struct Config {
     pub mid_weight: f32,
     pub high_weight: f32,
     pub max_weight: f32,
+    pub lookback_window_halflife_in_entries: u16,
 }
 
 fn default_config_path() -> String {
@@ -65,6 +66,7 @@ impl Default for Config {
             mid_weight: 0.5,
             high_weight: 0.75,
             max_weight: 1.0,
+            lookback_window_halflife_in_entries: 128,
         }
     }
 }
diff --git a/src/intuition.rs b/src/intuition.rs
index f994029..46eb92a 100644
--- a/src/intuition.rs
+++ b/src/intuition.rs
@@ -91,6 +91,11 @@ impl Intuition {
         candidates: &HashSet<String>,
         config: &Config,
     ) -> Option<(String, f32)> {
+        let decay = f32::powf(
+            0.5,
+            1.0 / (config.lookback_window_halflife_in_entries as f32),
+        );
+
         let trajectory: HashSet<_> = trajectory.iter().collect();
 
         let candidates: Vec<_> = candidates
@@ -105,16 +110,17 @@ impl Intuition {
         let mut items: HashMap<String, f32> =
             candidates.into_iter().map(|c| (c.clone(), 0.0)).collect();
 
-        for episode in &self.history {
+        for (dist, episode) in self.history.iter().rev().enumerate() {
+            let kernel = decay.powf(dist as f32);
             match (episode, action) {
                 (Episode::Escape { from, to, .. }, Action::Skip) => {
                     let w = compute_weight(from, &trajectory);
                     if let Some(to_w) = items.get_mut(to) {
-                        *to_w += config.max_weight * w;
+                        *to_w += config.max_weight * w * kernel;
                     }
                     for f in from {
                         if let Some(from_weight) = items.get_mut(f) {
-                            *from_weight -= config.mid_weight * w;
+                            *from_weight -= config.mid_weight * w * kernel;
                         }
                     }
                 }
@@ -123,7 +129,7 @@ impl Intuition {
                     if trajectory.contains(to) {
                         for f in from {
                             if let Some(f_w) = items.get_mut(f) {
-                                *f_w -= config.low_weight * w;
+                                *f_w -= config.low_weight * w * kernel;
                             }
                         }
                     }
@@ -132,18 +138,18 @@ impl Intuition {
                     let w = compute_weight(group, &trajectory);
                     for g in group {
                         if let Some(g_w) = items.get_mut(g) {
-                            *g_w += config.max_weight * w;
+                            *g_w += config.max_weight * w * kernel;
                         }
                     }
                     if let Some(a_w) = items.get_mut(avoid) {
-                        *a_w -= config.low_weight * w;
+                        *a_w -= config.low_weight * w * kernel;
                     }
                 }
                 (Episode::Continue { group, .. }, Action::Skip) => {
                     let w = compute_weight(group, &trajectory);
                     for g in group {
                         if let Some(v) = items.get_mut(g) {
-                            *v -= config.high_weight * w;
+                            *v -= config.high_weight * w * kernel;
                         }
                     }
                 }