import { createStack } from 'svelte-undo';

let value = { answer: 42 };

const stack = createStack(value);

// undo/redo have no effect if we're at the
// beginning/end of the stack
console.log((value = stack.undo())); // { answer: 42 }
console.log((value = stack.redo())); // { answer: 42 }

// stack.push returns the new value
value = stack.push({ answer: 43 });
value = stack.push({ answer: 44 });
value = stack.push({ answer: 45 });

console.log(value); // { answer: 45 }

console.log((value = stack.undo())); // { answer: 44 }
console.log((value = stack.undo())); // { answer: 43 }
console.log((value = stack.undo())); // { answer: 42 }
console.log((value = stack.undo())); // { answer: 42 }

console.log((value = stack.redo())); // { answer: 43 }

// pushing clears anything 'forward' in the stack
value = stack.push({ answer: 99 });

// you can also pass a function to `push`
value = stack.push((value) => ({ answer: value.answer + 1 }));

console.log((value = stack.undo())); // { answer: 99 }
console.log((value = stack.undo())); // { answer: 43 }
console.log((value = stack.redo())); // { answer: 99 }
console.log((value = stack.redo())); // { answer: 100 }
console.log((value = stack.redo())); // { answer: 100 }

// you can subscribe to the state of the undo stack
const unsubscribe = stack.subscribe(($stack) => {
	console.log($stack.first); // false
	console.log($stack.last); // true — we're currently at the end of the stack
	console.log($stack.current); // { answer: 99 }
});

unsubscribe();