// CommandHistory — undo/redo stack for timeline block mutations
// Supports min 50 steps. execute() clears redo stack to prevent branching corruption.

export class CommandHistory {
    constructor(maxSteps = 50) {
        this.undoStack = [];
        this.redoStack = [];
        this.maxSteps = maxSteps;
    }

    execute(cmd) {
        cmd.execute();
        this.undoStack.push(cmd);
        if (this.undoStack.length > this.maxSteps) this.undoStack.shift();
        this.redoStack = [];  // clear redo on new action (prevents branching corruption)
    }

    undo() {
        const cmd = this.undoStack.pop();
        if (!cmd) return false;
        cmd.undo();
        this.redoStack.push(cmd);
        return true;
    }

    redo() {
        const cmd = this.redoStack.pop();
        if (!cmd) return false;
        cmd.execute();
        this.undoStack.push(cmd);
        return true;
    }

    get canUndo() { return this.undoStack.length > 0; }
    get canRedo() { return this.redoStack.length > 0; }
}