From 64c562ed20840145de3093d7ec44a5e08a8fec3e Mon Sep 17 00:00:00 2001
From: oppiliappan <me@oppi.li>
Date: Sun, 12 Apr 2026 04:45:43 +0100
Subject: [PATCH] feat: implement basic 2-stack undo-redo

this is quite basic, uses a snapshot style history instead of a
command-style storage, where we could store forward/reverse callbacks.

as a result, this can presently only be used for storing and loading
full snapshots. you cannot undo favourites/ratings with this model.

to improve this, i would probably update this down the line to make each
item of the undostack store a:

    {forwardOp, reverseOp}

and the queue snapshotting logic can be augmented to simply be:

    {() => {return newState;}, () => {return oldState;}}

Signed-off-by: oppiliappan <me@oppi.li>
---
 src/js/history.js | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 src/js/history.js

diff --git a/src/js/history.js b/src/js/history.js
new file mode 100644
index 0000000..0251535
--- /dev/null
+++ b/src/js/history.js
@@ -0,0 +1,35 @@
+class History {
+	constructor() {
+		this.undoStack = new BoundedStack(32);
+		this.redoStack = new BoundedStack(32);
+	}
+
+	saveState(snapshot) {
+		this.undoStack.push(snapshot);
+		this.redoStack.clear();
+	}
+
+	undo(currentSnapshot) {
+		if (this.undoStack.isEmpty()) return null;
+
+		// save current state to redo stack before undoing
+		if (currentSnapshot) {
+			this.redoStack.push(currentSnapshot);
+		}
+
+		return this.undoStack.pop();
+	}
+
+	redo(currentSnapshot) {
+		if (this.redoStack.isEmpty()) return null;
+
+		// save current state to undo stack before redoing
+		if (currentSnapshot) {
+			this.undoStack.push(currentSnapshot);
+		}
+
+		return this.redoStack.pop();
+	}
+}
+
+const history = new History();
-- 
2.51.2