JavaScriptServices/src/Microsoft.AspNetCore.SpaServices/Routing/SpaRouteExtensions.cs

using System;
using System.Collections.Generic;
using Microsoft.AspNetCore.Routing;
using Microsoft.AspNetCore.SpaServices;

// Putting in this namespace so it's always available whenever MapRoute is

namespace Microsoft.AspNetCore.Builder
{
    public static class SpaRouteExtensions
    {
        private const string ClientRouteTokenName = "clientRoute";

        public static void MapSpaFallbackRoute(
            this IRouteBuilder routeBuilder,
            string name,
            object defaults,
            object constraints = null,
            object dataTokens = null)
        {
            MapSpaFallbackRoute(
                routeBuilder,
                name,
                /* templatePrefix */ null,
                defaults,
                constraints,
                dataTokens);
        }

        public static void MapSpaFallbackRoute(
            this IRouteBuilder routeBuilder,
            string name,
            string templatePrefix,
            object defaults,
            object constraints = null,
            object dataTokens = null)
        {
            var template = CreateRouteTemplate(templatePrefix);
            var constraintsDict = ObjectToDictionary(constraints);
            constraintsDict.Add(ClientRouteTokenName, new SpaRouteConstraint(ClientRouteTokenName));

            routeBuilder.MapRoute(name, template, defaults, constraintsDict, dataTokens);
        }

        private static string CreateRouteTemplate(string templatePrefix)
        {
            templatePrefix = templatePrefix ?? string.Empty;

            if (templatePrefix.Contains("?"))
            {
                // TODO: Consider supporting this. The {*clientRoute} part should be added immediately before the '?'
                throw new ArgumentException("SPA fallback route templates don't support querystrings");
            }

            if (templatePrefix.Contains("#"))
            {
                throw new ArgumentException(
                    "SPA fallback route templates should not include # characters. The hash part of a URI does not get sent to the server.");
            }

            if (templatePrefix != string.Empty && !templatePrefix.EndsWith("/"))
            {
                templatePrefix += "/";
            }

            return templatePrefix + $"{{*{ClientRouteTokenName}}}";
        }

        private static IDictionary<string, object> ObjectToDictionary(object value)
            => value as IDictionary<string, object> ?? new RouteValueDictionary(value);
    }
}