Umbraco-CMS/src/Umbraco.Core/Xml/DynamicContext.cs

using System.Xml;
using System.Xml.XPath;
using System.Xml.Xsl;

// source: mvpxml.codeplex.com

namespace Umbraco.Cms.Core.Xml
{
    /// <summary>
    /// Provides the evaluation context for fast execution and custom
    /// variables resolution.
    /// </summary>
    /// <remarks>
    /// This class is responsible for resolving variables during dynamic expression execution.
    /// <para>Discussed in http://weblogs.asp.net/cazzu/archive/2003/10/07/30888.aspx</para>
    /// <para>Author: Daniel Cazzulino, <a href="http://clariusconsulting.net/kzu">blog</a></para>
    /// </remarks>
    public class DynamicContext : XsltContext
    {
        #region Private vars

        readonly IDictionary<string, IXsltContextVariable> _variables =
            new Dictionary<string, IXsltContextVariable>();

        #endregion Private

        #region Constructors & Initialization

        /// <summary>
        /// Initializes a new instance of the <see cref="DynamicContext"/> class.
        /// </summary>
        public DynamicContext()
            : base(new NameTable())
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="DynamicContext"/>
        /// class with the specified <see cref="NameTable"/>.
        /// </summary>
        /// <param name="table">The NameTable to use.</param>
        public DynamicContext(NameTable table)
            : base(table)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="DynamicContext"/> class.
        /// </summary>
        /// <param name="context">A previously filled context with the namespaces to use.</param>
        public DynamicContext(XmlNamespaceManager context)
            : this(context, new NameTable())
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="DynamicContext"/> class.
        /// </summary>
        /// <param name="context">A previously filled context with the namespaces to use.</param>
        /// <param name="table">The NameTable to use.</param>
        public DynamicContext(XmlNamespaceManager context, NameTable table)
            : base(table)
        {
            object xml = table.Add(XmlNamespaces.Xml);
            object xmlns = table.Add(XmlNamespaces.XmlNs);

            if (context == null)
            {
                return;
            }

            foreach (string prefix in context)
            {
                var uri = context.LookupNamespace(prefix);
                // Use fast object reference comparison to omit forbidden namespace declarations.
                if (Equals(uri, xml) || Equals(uri, xmlns))
                {
                    continue;
                }

                if (uri == null)
                {
                    continue;
                }

                base.AddNamespace(prefix, uri);
            }
        }

        #endregion Constructors & Initialization

        #region Common Overrides

        /// <summary>
        /// Implementation equal to <see cref="XsltContext"/>.
        /// </summary>
        public override int CompareDocument(string baseUri, string nextbaseUri) =>
            String.Compare(baseUri, nextbaseUri, false, System.Globalization.CultureInfo.InvariantCulture);

        /// <summary>
        /// Same as <see cref="XmlNamespaceManager"/>.
        /// </summary>
        public override string? LookupNamespace(string prefix)
        {
            var key = NameTable?.Get(prefix);
            return key == null ? null : base.LookupNamespace(key);
        }

        /// <summary>
        /// Same as <see cref="XmlNamespaceManager"/>.
        /// </summary>
        public override string? LookupPrefix(string uri)
        {
            var key = NameTable?.Get(uri);
            return key == null ? null : base.LookupPrefix(key);
        }

        /// <summary>
        /// Same as <see cref="XsltContext"/>.
        /// </summary>
        public override bool PreserveWhitespace(XPathNavigator node)
        {
            return true;
        }

        /// <summary>
        /// Same as <see cref="XsltContext"/>.
        /// </summary>
        public override bool Whitespace
        {
            get { return true; }
        }

        #endregion Common Overrides

        #region Public Members

        /// <summary>
        /// Shortcut method that compiles an expression using an empty navigator.
        /// </summary>
        /// <param name="xpath">The expression to compile</param>
        /// <returns>A compiled <see cref="XPathExpression"/>.</returns>
        public static XPathExpression? Compile(string xpath)
        {
            return new XmlDocument().CreateNavigator()?.Compile(xpath);
        }

        #endregion Public Members

        #region Variable Handling Code

        /// <summary>
        /// Adds the variable to the dynamic evaluation context.
        /// </summary>
        /// <param name="name">The name of the variable to add to the context.</param>
        /// <param name="value">The value of the variable to add to the context.</param>
        /// <remarks>
        /// Value type conversion for XPath evaluation is as follows:
        /// <list type="table">
        ///        <listheader>
        ///            <term>CLR Type</term>
        ///            <description>XPath type</description>
        ///        </listheader>
        ///        <item>
        ///            <term>System.String</term>
        ///            <description>XPathResultType.String</description>
        ///        </item>
        ///        <item>
        ///            <term>System.Double (or types that can be converted to)</term>
        ///            <description>XPathResultType.Number</description>
        ///        </item>
        ///        <item>
        ///            <term>System.Boolean</term>
        ///            <description>XPathResultType.Boolean</description>
        ///        </item>
        ///        <item>
        ///            <term>System.Xml.XPath.XPathNavigator</term>
        ///            <description>XPathResultType.Navigator</description>
        ///        </item>
        ///        <item>
        ///            <term>System.Xml.XPath.XPathNodeIterator</term>
        ///            <description>XPathResultType.NodeSet</description>
        ///        </item>
        ///        <item>
        ///            <term>Others</term>
        ///            <description>XPathResultType.Any</description>
        ///        </item>
        /// </list>
        /// <note type="note">See the topic "Compile, Select, Evaluate, and Matches with
        /// XPath and XPathExpressions" in MSDN documentation for additional information.</note>
        /// </remarks>
        /// <exception cref="ArgumentNullException">The <paramref name="value"/> is null.</exception>
        public void AddVariable(string name, object value)
        {
            if (value == null)
            {
                throw new ArgumentNullException("value");
            }

            _variables[name] = new DynamicVariable(name, value);
        }

        /// <summary>
        /// See <see cref="XsltContext"/>. Not used in our implementation.
        /// </summary>
        public override IXsltContextFunction ResolveFunction(string prefix, string name, XPathResultType[] argTypes) => throw new NotImplementedException();

        /// <summary>
        /// Resolves the dynamic variables added to the context. See <see cref="XsltContext"/>.
        /// </summary>
        public override IXsltContextVariable ResolveVariable(string prefix, string name)
        {
            IXsltContextVariable var;
            _variables.TryGetValue(name, out var!);
            return var;
        }

        #endregion Variable Handling Code

        #region Internal DynamicVariable class

        /// <summary>
        /// Represents a variable during dynamic expression execution.
        /// </summary>
        internal class DynamicVariable : IXsltContextVariable
        {
            private readonly string _name;
            private readonly object _value;

            #region Public Members

            public string Name { get { return _name; } }

            /// <summary>
            /// Initializes a new instance of the class.
            /// </summary>
            /// <param name="name">The name of the variable.</param>
            /// <param name="value">The value of the variable.</param>
            public DynamicVariable(string name, object value)
            {

                _name = name;
                _value = value;

                if (value is string)
                {
                    _type = XPathResultType.String;
                }
                else if (value is bool)
                {
                    _type = XPathResultType.Boolean;
                }
                else if (value is XPathNavigator)
                {
                    _type = XPathResultType.Navigator;
                }
                else if (value is XPathNodeIterator)
                {
                    _type = XPathResultType.NodeSet;
                }
                else
                {
                    // Try to convert to double (native XPath numeric type)
                    if (value is double)
                    {
                        _type = XPathResultType.Number;
                    }
                    else
                    {
                        if (value is IConvertible)
                        {
                            try
                            {
                                _value = Convert.ToDouble(value);
                                // We succeeded, so it's a number.
                                _type = XPathResultType.Number;
                            }
                            catch (FormatException)
                            {
                                _type = XPathResultType.Any;
                            }
                            catch (OverflowException)
                            {
                                _type = XPathResultType.Any;
                            }
                        }
                        else
                        {
                            _type = XPathResultType.Any;
                        }
                    }
                }
            }

            #endregion Public Members

            #region IXsltContextVariable Implementation

            XPathResultType IXsltContextVariable.VariableType
            {
                get { return _type; }
            }

            private readonly XPathResultType _type;

            object IXsltContextVariable.Evaluate(XsltContext context)
            {
                return _value;
            }

            bool IXsltContextVariable.IsLocal
            {
                get { return false; }
            }

            bool IXsltContextVariable.IsParam
            {
                get { return false; }
            }

            #endregion IXsltContextVariable Implementation
        }

        #endregion Internal DynamicVariable class
    }
}