// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;
using Microsoft.AspNetCore.Routing;

namespace Microsoft.AspNetCore.Mvc.TagHelpers
{
    /// <summary>
    /// <see cref="ITagHelper"/> implementation targeting &lt;form&gt; elements.
    /// </summary>
    [HtmlTargetElement("form")]
    public class FormTagHelper : TagHelper
    {
        private const string ActionAttributeName = "asp-action";
        private const string AntiforgeryAttributeName = "asp-antiforgery";
        private const string AreaAttributeName = "asp-area";
        private const string PageAttributeName = "asp-page";
        private const string PageHandlerAttributeName = "asp-page-handler";
        private const string FragmentAttributeName = "asp-fragment";
        private const string ControllerAttributeName = "asp-controller";
        private const string RouteAttributeName = "asp-route";
        private const string RouteValuesDictionaryName = "asp-all-route-data";
        private const string RouteValuesPrefix = "asp-route-";
        private const string HtmlActionAttributeName = "action";
        private IDictionary<string, string> _routeValues;

        /// <summary>
        /// Creates a new <see cref="FormTagHelper"/>.
        /// </summary>
        /// <param name="generator">The <see cref="IHtmlGenerator"/>.</param>
        public FormTagHelper(IHtmlGenerator generator)
        {
            Generator = generator;
        }

        // This TagHelper's order must be lower than the RenderAtEndOfFormTagHelper. I.e it must be executed before
        // RenderAtEndOfFormTagHelper does.
        /// <inheritdoc />
        public override int Order => -1000;

        /// <summary>
        /// Gets the <see cref="Rendering.ViewContext"/> of the executing view.
        /// </summary>
        [HtmlAttributeNotBound]
        [ViewContext]
        public ViewContext ViewContext { get; set; }

        /// <summary>
        /// Gets the <see cref="IHtmlGenerator"/> used to generate the <see cref="FormTagHelper"/>'s output.
        /// </summary>
        protected IHtmlGenerator Generator { get; }

        /// <summary>
        /// The name of the action method.
        /// </summary>
        [HtmlAttributeName(ActionAttributeName)]
        public string Action { get; set; }

        /// <summary>
        /// The name of the controller.
        /// </summary>
        [HtmlAttributeName(ControllerAttributeName)]
        public string Controller { get; set; }

        /// <summary>
        /// The name of the area.
        /// </summary>
        [HtmlAttributeName(AreaAttributeName)]
        public string Area { get; set; }

        /// <summary>
        /// The name of the page.
        /// </summary>
        [HtmlAttributeName(PageAttributeName)]
        public string Page { get; set; }

        /// <summary>
        /// The name of the page handler.
        /// </summary>
        [HtmlAttributeName(PageHandlerAttributeName)]
        public string PageHandler { get; set; }

        /// <summary>
        /// Whether the antiforgery token should be generated.
        /// </summary>
        /// <value>Defaults to <c>false</c> if user provides an <c>action</c> attribute
        /// or if the <c>method</c> is <see cref="FormMethod.Get"/>; <c>true</c> otherwise.</value>
        [HtmlAttributeName(AntiforgeryAttributeName)]
        public bool? Antiforgery { get; set; }

        /// <summary>
        /// Gets or sets the URL fragment.
        /// </summary>
        [HtmlAttributeName(FragmentAttributeName)]
        public string Fragment { get; set; }

        /// <summary>
        /// Name of the route.
        /// </summary>
        /// <remarks>
        /// Must be <c>null</c> if <see cref="Action"/> or <see cref="Controller"/> is non-<c>null</c>.
        /// </remarks>
        [HtmlAttributeName(RouteAttributeName)]
        public string Route { get; set; }

        /// <summary>
        /// The HTTP method to use.
        /// </summary>
        /// <remarks>Passed through to the generated HTML in all cases.</remarks>
        [EditorBrowsable(EditorBrowsableState.Never)]
        public string Method { get; set; }

        /// <summary>
        /// Additional parameters for the route.
        /// </summary>
        [HtmlAttributeName(RouteValuesDictionaryName, DictionaryAttributePrefix = RouteValuesPrefix)]
        public IDictionary<string, string> RouteValues
        {
            get
            {
                if (_routeValues == null)
                {
                    _routeValues = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
                }

                return _routeValues;
            }
            set
            {
                _routeValues = value;
            }
        }

        /// <inheritdoc />
        /// <remarks>
        /// Does nothing if user provides an <c>action</c> attribute and <see cref="Antiforgery"/> is <c>null</c> or
        /// <c>false</c>.
        /// </remarks>
        /// <exception cref="InvalidOperationException">
        /// Thrown if <c>action</c> attribute is provided and <see cref="Action"/>, <see cref="Controller"/> or <see cref="Fragment"/> are
        /// non-<c>null</c> or if the user provided <c>asp-route-*</c> attributes.
        /// </exception>
        public override void Process(TagHelperContext context, TagHelperOutput output)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            if (output == null)
            {
                throw new ArgumentNullException(nameof(output));
            }

            if (Method != null)
            {
                output.CopyHtmlAttribute(nameof(Method), context);
            }

            var antiforgeryDefault = true;
            var routeableParametersProvided = Action != null ||
                Controller != null ||
                Area != null ||
                Page != null ||
                PageHandler != null ||
                Fragment != null ||
                Route != null ||
                (_routeValues != null && _routeValues.Count > 0);

            // If "action" is already set, it means the user is attempting to use a normal <form>.
            if (output.Attributes.TryGetAttribute(HtmlActionAttributeName, out var actionAttribute))
            {
                if (routeableParametersProvided)
                {
                    // User also specified bound attributes we cannot use.
                    throw new InvalidOperationException(
                        Resources.FormatFormTagHelper_CannotOverrideAction(
                            HtmlActionAttributeName,
                            "<form>",
                            RouteValuesPrefix,
                            ActionAttributeName,
                            ControllerAttributeName,
                            FragmentAttributeName,
                            AreaAttributeName,
                            RouteAttributeName,
                            PageAttributeName,
                            PageHandlerAttributeName));
                }

                string attributeValue = null;
                switch (actionAttribute.Value)
                {
                    case HtmlString htmlString:
                        attributeValue = htmlString.ToString();
                        break;
                    case string stringValue:
                        attributeValue = stringValue;
                        break;
                }

                if (string.IsNullOrEmpty(attributeValue))
                {
                    // User is using the FormTagHelper like a normal <form> tag that has an empty or complex IHtmlContent action attribute.
                    // e.g. <form action="" method="..."> or <form action="@CustomUrlIHtmlContent" method="...">

                    if (string.Equals(Method ?? "get", "get", StringComparison.OrdinalIgnoreCase))
                    {
                        antiforgeryDefault = false;
                    }
                    else
                    {
                        // Antiforgery default is already set to true
                    }
                }
                else
                {
                    // User is likely using the <form> element to submit to another site. Do not send an antiforgery token to unknown sites.
                    antiforgeryDefault = false;
                }
            }
            else
            {
                var routeLink = Route != null;
                var actionLink = Controller != null || Action != null;
                var pageLink = Page != null || PageHandler != null;

                if ((routeLink && actionLink) || (routeLink && pageLink) || (actionLink && pageLink))
                {
                    var message = string.Join(
                        Environment.NewLine,
                        Resources.FormatCannotDetermineAttributeFor(HtmlActionAttributeName, "<form>"),
                        RouteAttributeName,
                        ControllerAttributeName + ", " + ActionAttributeName,
                        PageAttributeName);

                    throw new InvalidOperationException(message);
                }

                RouteValueDictionary routeValues = null;
                if (_routeValues != null && _routeValues.Count > 0)
                {
                    routeValues = new RouteValueDictionary(_routeValues);
                }

                if (Area != null)
                {
                    if (routeValues == null)
                    {
                        routeValues = new RouteValueDictionary();
                    }

                    // Unconditionally replace any value from asp-route-area.
                    routeValues["area"] = Area;
                }

                TagBuilder tagBuilder = null;
                if (!routeableParametersProvided &&
                    _routeValues == null &&
                    // Antiforgery will sometime be set globally via TagHelper Initializers, verify it was provided in the cshtml. 
                    !context.AllAttributes.ContainsName(AntiforgeryAttributeName))
                {
                    // A <form> tag that doesn't utilize asp-* attributes. Let it flow to the output.
                    Method = Method ?? "get";
                }
                else if (pageLink)
                {
                    tagBuilder = Generator.GeneratePageForm(
                        ViewContext,
                        Page,
                        PageHandler,
                        routeValues,
                        Fragment,
                        method: null,
                        htmlAttributes: null);
                }
                else if (routeLink)
                {
                    tagBuilder = Generator.GenerateRouteForm(
                        ViewContext,
                        Route,
                        routeValues,
                        Fragment,
                        method: null,
                        htmlAttributes: null);
                }
                else
                {
                    tagBuilder = Generator.GenerateForm(
                        ViewContext,
                        Action,
                        Controller,
                        Fragment,
                        routeValues,
                        method: null,
                        htmlAttributes: null);
                }

                if (tagBuilder != null)
                {
                    output.MergeAttributes(tagBuilder);
                    if (tagBuilder.HasInnerHtml)
                    {
                        output.PostContent.AppendHtml(tagBuilder.InnerHtml);
                    }
                }

                if (string.Equals(Method, "get", StringComparison.OrdinalIgnoreCase))
                {
                    antiforgeryDefault = false;
                }
            }

            if (Antiforgery ?? antiforgeryDefault)
            {
                var antiforgeryTag = Generator.GenerateAntiforgery(ViewContext);
                if (antiforgeryTag != null)
                {
                    output.PostContent.AppendHtml(antiforgeryTag);
                }
            }
        }
    }
}