using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace WebSameSite
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }


        #region snippet5
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseCookiePolicy();
            app.UseAuthentication();
            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapRazorPages();
            });
        }
        #endregion

        #region snippet
        public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<CookiePolicyOptions>(options =>
            {
                options.MinimumSameSitePolicy = (SameSiteMode)(-1);
                options.OnAppendCookie = cookieContext =>
                    CheckSameSite(cookieContext.Context, cookieContext.CookieOptions);
                options.OnDeleteCookie = cookieContext =>
                    CheckSameSite(cookieContext.Context, cookieContext.CookieOptions);
            });

            services.AddRazorPages();
        }

        private void CheckSameSite(HttpContext httpContext, CookieOptions options)
        {
            if (options.SameSite == SameSiteMode.None)
            {
                var userAgent = httpContext.Request.Headers["User-Agent"].ToString();
                if (MyUserAgentDetectionLib.DisallowsSameSiteNone(userAgent))
                {
                    options.SameSite = (SameSiteMode)(-1);
                }

            }
        }
        #endregion

        public static class MyUserAgentDetectionLib
        {
            public static bool DisallowsSameSiteNone(string userAgent)
            {
             // Check if a null or empty string has been passed in, since this
             // will cause further interrogation of the useragent to fail.
             if (String.IsNullOrWhiteSpace(userAgent))
                return false;
            
                // Cover all iOS based browsers here. This includes:
                // - Safari on iOS 12 for iPhone, iPod Touch, iPad
                // - WkWebview on iOS 12 for iPhone, iPod Touch, iPad
                // - Chrome on iOS 12 for iPhone, iPod Touch, iPad
                // All of which are broken by SameSite=None, because they use the iOS networking
                // stack.
                if (userAgent.Contains("CPU iPhone OS 12") ||
                    userAgent.Contains("iPad; CPU OS 12"))
                {
                    return true;
                }

                // Cover Mac OS X based browsers that use the Mac OS networking stack. This includes:
                // - Safari on Mac OS X.
                // This does not include:
                // - Chrome on Mac OS X
                // Because they do not use the Mac OS networking stack.
                if (userAgent.Contains("Macintosh; Intel Mac OS X 10_14") &&
                    userAgent.Contains("Version/") && userAgent.Contains("Safari"))
                {
                    return true;
                }

                // Cover Chrome 50-69, because some versions are broken by SameSite=None, 
                // and none in this range require it.
                // Note: this covers some pre-Chromium Edge versions, 
                // but pre-Chromium Edge does not require SameSite=None.
                if (userAgent.Contains("Chrome/5") || userAgent.Contains("Chrome/6"))
                {
                    return true;
                }

                return false;
            }
        }
    }
}