1 files changed, 144 insertions, 0 deletions
diff --git a/src/ui.rs b/src/ui.rs
new file mode 100644
index 0000000..f855625
--- /dev/null
+++ b/src/ui.rs
@@ -0,0 +1,144 @@
+use crate::utils;
+
+fn compute_reverse(frames: u64, tick: u64, start: u64) -> u64 {
+    let leftover = frames - (tick - start)
+        .clamp(0, frames);
+    tick - leftover
+}
+
+pub enum ModeToggle {
+    Inactive { start: u64 },
+    Active { start: u64 },
+}
+
+pub struct Mode {
+    frames: u64,
+    toggle: ModeToggle,
+    locked: bool,
+}
+
+impl Mode {
+    pub fn new(frames: u64) -> Self {
+        Self {
+            frames,
+            toggle: ModeToggle::Inactive { start: 0 },
+            locked: false,
+        }
+    }
+
+    /// Is the current state active?
+    pub fn is_active(&self) -> bool {
+        match self.toggle {
+            ModeToggle::Inactive {..} => false,
+            ModeToggle::Active {..} => true,
+        }
+    }
+
+    /// Has the current transition finished?
+    pub fn is_ready(&self, tick: u64) -> bool {
+        let started = match self.toggle {
+            ModeToggle::Inactive { start } => start,
+            ModeToggle::Active { start } => start,
+        };
+        tick - started > self.frames
+    }
+
+    pub fn progress(&self, tick: u64) -> f32 {
+        match self.toggle {
+            ModeToggle::Inactive { start } => {
+                1.0 - (((tick - start) as f32) / self.frames as f32)
+                    .clamp(0.0, 1.0)
+            },
+            ModeToggle::Active { start } => {
+                (((tick - start) as f32) / self.frames as f32)
+                    .clamp(0.0, 1.0)
+            }
+        }
+    }
+
+    pub fn reverse(&mut self, tick: u64) -> bool {
+        if !self.locked {
+            self.locked = true;
+            match self.toggle {
+                ModeToggle::Inactive { start } => {
+                    self.toggle = ModeToggle::Active {
+                        start: compute_reverse(self.frames, tick, start)
+                    };
+                },
+                ModeToggle::Active { start } => {
+                    self.toggle = ModeToggle::Inactive {
+                        start: compute_reverse(self.frames, tick, start)
+                    };
+                },
+            }
+            true
+        } else { false }
+    }
+
+    pub fn lock(&mut self) {
+        self.locked = true;
+    }
+
+    pub fn unlock(&mut self) {
+        self.locked = false;
+    }
+}
+
+pub struct Cursor {
+    pub index: i32,
+    pub prev_index: i32,
+    pub change_started: u64,
+    pub bound: i32,
+    pub frames: u64,
+    pub locked: bool,
+}
+
+impl Cursor {
+    pub fn new(bound: i32, frames: u64) -> Self {
+        Self {
+            index: 0,
+            prev_index: 0,
+            change_started: 0,
+            bound,
+            frames,
+            locked: false,
+        }
+    }
+
+    pub fn animation_index(&self, tick: u64) -> f32 {
+        let progress = ((tick - self.change_started) as f32)
+            / (self.frames as f32 / 2.0);
+        utils::lerp(
+            self.prev_index as f32,
+            self.index as f32,
+            progress
+        )
+    }
+
+    pub fn is_ready(&self, tick: u64) -> bool {
+        tick - self.change_started > self.frames
+    }
+
+    pub fn set(&mut self, val: i32, tick: u64) -> bool {
+        if self.is_ready(tick) || !self.locked {
+            self.change_started = tick;
+            self.prev_index = self.index;
+            self.index = val;
+            self.index %= self.bound;
+            self.locked = true;
+            true
+        } else { false }
+    }
+
+    pub fn increment(&mut self, tick: u64) -> bool {
+        self.set(self.index + 1, tick)
+    }
+
+    pub fn decrement(&mut self, tick: u64) -> bool {
+        self.set(self.index + self.bound - 1, tick)
+    }
+
+    pub fn unlock(&mut self) {
+        self.locked = false;
+    }
+}