using Microsoft.AspNetCore.Components;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace cwebplusApp.Shared.Services {
    public class PageHistoryManager {

        public EventCallback OnBeforeNavigateBack;

        private readonly List<string> previousPages;

        private NavigationManager NavigationManager;

        public PageHistoryManager(NavigationManager NavigationManager) {
            previousPages = new List<string>();
            this.NavigationManager = NavigationManager;
        }

        public void Reset() {
            previousPages.Clear();
        }

        public void AddPageToHistory(string pageName) {
            previousPages.Add(pageName);
        }

        public string GetPreviousPage() {
            if (CanGoBack()) {
                // You add a page on initialization, so you need to return the 2nd from the last
                string previousPage = previousPages.ElementAt(previousPages.Count - 2);
                previousPages.RemoveAt(previousPages.Count - 1);
                previousPages.RemoveAt(previousPages.Count - 1);
                return previousPage;
            }

            // Can't go back because you didn't navigate enough
            return previousPages.FirstOrDefault();
        }

        public bool CanGoBack() {
            return previousPages.Count > 1;
        }

        public async void NavigateBack() {
            await FireOnBeforeNavigateBackEvent();
            NavigationManager.NavigateTo(GetPreviousPage());
        }

        protected async Task FireOnBeforeNavigateBackEvent() {
            await OnBeforeNavigateBack.InvokeAsync();
        }
    }
}