From 9f0dc65dabff2a1e443199ed68292398dcb390b1 Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Fri, 12 Mar 2021 20:24:55 +0530
Subject: init

---
 src/undo.rs | 133 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 133 insertions(+)
 create mode 100644 src/undo.rs

(limited to 'src/undo.rs')

diff --git a/src/undo.rs b/src/undo.rs
new file mode 100644
index 0000000..2249fe7
--- /dev/null
+++ b/src/undo.rs
@@ -0,0 +1,133 @@
+#[derive(Copy, Clone, Debug)]
+pub struct ModifyRecord {
+    pub point: (i32, i32),
+    pub old_val: bool,
+    pub val: bool,
+}
+
+impl ModifyRecord {
+    pub fn new(point: (i32, i32), old_val: bool, val: bool) -> Self {
+        ModifyRecord {
+            point,
+            old_val,
+            val,
+        }
+    }
+}
+
+pub enum OpKind {
+    Undo,
+    Redo,
+}
+
+pub type Operation = Vec<ModifyRecord>;
+
+#[derive(Debug)]
+pub struct UndoStack<T> {
+    operations: Vec<T>,
+    position: Option<u32>,
+}
+
+impl<T> UndoStack<T>
+where
+    T: Clone,
+{
+    pub fn new() -> Self {
+        Self {
+            operations: Vec::with_capacity(64),
+            position: None,
+        }
+    }
+
+    pub fn push(&mut self, op: T) {
+        if let Some(p) = self.position {
+            // remove all operations past the newly pushed operation
+            for _ in 1 + (p as usize)..self.operations.len() {
+                self.operations.pop();
+            }
+            // advance position
+            self.position = Some(p + 1);
+            // add new operation
+            self.operations.push(op);
+        } else {
+            // empty ops list or undone till start of stack
+            // remove all operations past the newly pushed operation
+            self.operations.clear();
+            // advance position
+            self.position = Some(0);
+            // add new operation
+            self.operations.push(op);
+        }
+    }
+
+    pub fn undo(&mut self) -> Option<T> {
+        if let Some(p) = self.position {
+            self.position = p.checked_sub(1);
+            // we want to return a clone and not a reference because push deletes the item
+            return Some(self.operations[p as usize].clone());
+        }
+        return None;
+    }
+
+    pub fn redo(&mut self) -> Option<T> {
+        if let Some(p) = self.position {
+            if p < self.operations.len() as u32 - 1 {
+                self.position = Some(p + 1);
+                return Some(self.operations[1 + p as usize].clone());
+            }
+        } else if !self.operations.is_empty() {
+            self.position = Some(0);
+            return Some(self.operations[0].clone());
+        }
+        return None;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn setup() -> UndoStack<u32> {
+        let mut stack = UndoStack::new();
+        stack.push(10);
+        stack.push(5);
+        stack.push(2);
+        stack
+    }
+
+    #[test]
+    fn undo_works() {
+        let mut stack = setup();
+        assert_eq!(stack.undo(), Some(2));
+        assert_eq!(stack.undo(), Some(5));
+        assert_eq!(stack.undo(), Some(10));
+    }
+    #[test]
+    fn redo_works() {
+        let mut stack = setup();
+        stack.undo();
+        stack.undo();
+        stack.undo();
+        assert_eq!(stack.redo(), Some(10));
+        assert_eq!(stack.redo(), Some(5));
+        assert_eq!(stack.redo(), Some(2));
+    }
+
+    #[test]
+    fn undo_push_redo() {
+        let mut stack = setup();
+        stack.undo();
+        stack.push(16);
+        assert_eq!(stack.redo(), None);
+        assert_eq!(stack.undo(), Some(16));
+    }
+
+    #[test]
+    fn stack_identity() {
+        let mut stack = setup();
+        stack.undo();
+        stack.redo();
+        stack.undo();
+        assert_eq!(stack.operations, setup().operations);
+    }
+}
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