SparqlResultSetXmlCodec.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;
using System.Xml;
using Waher.Content.Semantic.Model;
using Waher.Content.Semantic.Model.Literals;
using Waher.Runtime.Inventory;
using Waher.Script.Objects.Matrices;
 
namespace Waher.Content.Semantic
{
    public class SparqlResultSetXmlCodec : IContentDecoder, IContentEncoder
    {
        public SparqlResultSetXmlCodec()
        {
        }
 
        public string[] ContentTypes => SparqlResultSetContentTypes;
 
        private static readonly string[] SparqlResultSetContentTypes = new string[]
        {
            "application/sparql-results+xml"
        };
 
        public string[] FileExtensions => SparqlResultSetFileExtensions;
 
        private static readonly string[] SparqlResultSetFileExtensions = new string[]
        {
            "srx"
        };
 
        public bool Decodes(string ContentType, out Grade Grade)
        {
            if (Array.IndexOf(SparqlResultSetContentTypes, ContentType) >= 0)
            {
                Grade = Grade.Excellent;
                return true;
            }
            else
            {
                Grade = Grade.NotAtAll;
                return false;
            }
        }
 
        public Task<object> DecodeAsync(string ContentType, byte[] Data, Encoding Encoding, KeyValuePair<string, string>[] Fields, Uri BaseUri)
        {
            string s = CommonTypes.GetString(Data, Encoding ?? Encoding.UTF8);
            SparqlResultSet Parsed = new SparqlResultSet(s, BaseUri);
            return Task.FromResult<object>(Parsed);
        }
 
        public bool Encodes(object Object, out Grade Grade, params string[] AcceptedContentTypes)
        {
            if (Object is SparqlResultSet &&
                InternetContent.IsAccepted(SparqlResultSetContentTypes, AcceptedContentTypes))
            {
                Grade = Grade.Excellent;
                return true;
            }
            else if (Object is ObjectMatrix M && M.HasColumnNames &&
                InternetContent.IsAccepted(SparqlResultSetContentTypes, AcceptedContentTypes))
            {
                Grade = Grade.Ok;
                return true;
            }
            else if (Object is bool &&
                InternetContent.IsAccepted(SparqlResultSetContentTypes, AcceptedContentTypes))
            {
                Grade = Grade.Barely;
                return true;
            }
            else
            {
                Grade = Grade.NotAtAll;
                return false;
            }
        }
 
        public Task<KeyValuePair<byte[], string>> EncodeAsync(object Object, Encoding Encoding, params string[] AcceptedContentTypes)
        {
            if (Encoding is null)
                Encoding = Encoding.UTF8;
 
            StringBuilder sb = new StringBuilder();
            sb.Append("<?xml version=\"1.0\" encoding=\"");
            sb.Append(Encoding.WebName);
            sb.AppendLine("\"?>");
 
            XmlWriterSettings Settings = new XmlWriterSettings()
            {
                ConformanceLevel = ConformanceLevel.Document,
                Encoding = Encoding,
                Indent = false,
                NamespaceHandling = NamespaceHandling.OmitDuplicates,
                NewLineHandling = NewLineHandling.None,
                NewLineOnAttributes = false,
                OmitXmlDeclaration = true,
                WriteEndDocumentOnClose = true
            };
 
            if (Object is SparqlResultSet Result && Result.Pretty)
            {
                Settings.Indent = true;
                Settings.IndentChars = "\t";
            }
 
            using (XmlWriter w = XmlWriter.Create(sb, Settings))
            {
                if (Object is SparqlResultSet Result2)
                    this.EncodeAsync(Result2, w);
                else if (Object is ObjectMatrix M)
                    this.EncodeAsync(M, w);
                else if (Object is bool b)
                    this.EncodeAsync(b, w);
                else
                    throw new ArgumentException("Unable to encode object.", nameof(Object));
 
                w.Flush();
 
                string Text = sb.ToString();
 
                byte[] Bin = Encoding.GetBytes(Text);
                string ContentType = SparqlResultSetContentTypes[0] + "; charset=" + Encoding.WebName;
 
                return Task.FromResult(new KeyValuePair<byte[], string>(Bin, ContentType));
            }
        }
 
        private void EncodeAsync(SparqlResultSet Result, XmlWriter w)
        {
            w.WriteStartElement(SparqlResultSet.LocalName, SparqlResultSet.Namespace);
 
            w.WriteStartElement("head");
 
            if (!(Result.Variables is null))
            {
                foreach (string Name in Result.Variables)
                {
                    w.WriteStartElement("variable");
                    w.WriteAttributeString("name", Name);
                    w.WriteEndElement();
                }
            }
 
            if (!(Result.Links is null))
            {
                foreach (Uri Link in Result.Links)
                {
                    w.WriteStartElement("link");
                    w.WriteAttributeString("href", Link.ToString());
                    w.WriteEndElement();
                }
            }
 
            w.WriteEndElement();
 
            if (Result.BooleanResult.HasValue)
                w.WriteElementString("boolean", CommonTypes.Encode(Result.BooleanResult.Value));
            else
            {
                w.WriteStartElement("results");
 
                if (!(Result.Records is null))
                {
                    foreach (ISparqlResultRecord Record in Result.Records)
                    {
                        w.WriteStartElement("result");
 
                        foreach (ISparqlResultItem Item in Record)
                        {
                            w.WriteStartElement("binding");
                            w.WriteAttributeString("name", Item.Name);
 
                            OutputValue(w, Item.Value);
 
                            w.WriteEndElement();
                        }
 
                        w.WriteEndElement();
                    }
                }
 
                w.WriteEndElement();
            }
 
            w.WriteEndElement();
        }
 
        private void EncodeAsync(ObjectMatrix Result, XmlWriter w)
        {
            w.WriteStartElement(SparqlResultSet.LocalName, SparqlResultSet.Namespace);
 
            w.WriteStartElement("head");
 
            if (!(Result.ColumnNames is null))
            {
                foreach (string Name in Result.ColumnNames)
                {
                    w.WriteStartElement("variable");
                    w.WriteAttributeString("name", Name);
                    w.WriteEndAttribute();
                }
            }
 
            w.WriteEndElement();
            w.WriteStartElement("results");
 
            int x, y;
            int NrRows = Result.Rows;
            int NrColumns = Result.Columns;
 
            for (y = 0; y < NrRows; y++)
            {
                w.WriteStartElement("result");
 
                for (x = 0; x < NrColumns; x++)
                {
                    w.WriteStartElement("binding");
                    w.WriteAttributeString("name", Result.ColumnNames[x]);
 
                    OutputValue(w, Result.GetElement(x, y)?.AssociatedObjectValue);
 
                    w.WriteEndElement();
                }
 
                w.WriteEndElement();
            }
 
            w.WriteEndElement();
            w.WriteEndElement();
        }
 
        private void EncodeAsync(bool Result, XmlWriter w)
        {
            w.WriteStartElement(SparqlResultSet.LocalName, SparqlResultSet.Namespace);
            w.WriteElementString("head", string.Empty);
            w.WriteElementString("boolean", CommonTypes.Encode(Result));
            w.WriteEndElement();
        }
 
        private static void OutputValue(XmlWriter w, object Value)
        {
            if (Value is ISemanticElement E)
            {
                if (E is ISemanticLiteral Literal)
                {
                    w.WriteStartElement("literal");
 
                    if (!string.IsNullOrEmpty(Literal.StringType))
                        w.WriteAttributeString("datatype", Literal.StringType);
 
                    if (Literal is StringLiteral StringLiteral &&
                        !string.IsNullOrEmpty(StringLiteral.Language))
                    {
                        w.WriteAttributeString("xml:lang", StringLiteral.Language);
                    }
                    else if (Literal is CustomLiteral CustomLiteral &&
                        !string.IsNullOrEmpty(CustomLiteral.Language))
                    {
                        w.WriteAttributeString("xml:lang", CustomLiteral.Language);
                    }
 
                    w.WriteValue(Literal.Value);
                    w.WriteEndElement();
                }
                else if (E is UriNode N)
                    w.WriteElementString("uri", N.Uri.ToString());
                else if (E is BlankNode N2)
                    w.WriteElementString("bnode", N2.NodeId);
                else if (E is ISemanticTriple T)
                {
                    w.WriteStartElement("triple");
 
                    w.WriteStartElement("subject");
                    OutputValue(w, T.Subject);
                    w.WriteEndElement();
 
                    w.WriteStartElement("predicate");
                    OutputValue(w, T.Predicate);
                    w.WriteEndElement();
 
                    w.WriteStartElement("object");
                    OutputValue(w, T.Object);
                    w.WriteEndElement();
 
                    w.WriteEndElement();
                }
                else
                    w.WriteElementString("literal", Value?.ToString() ?? string.Empty);
            }
            else
                w.WriteElementString("literal", Value?.ToString() ?? string.Empty);
        }
 
        public bool TryGetContentType(string FileExtension, out string ContentType)
        {
            if (string.Compare(FileExtension, SparqlResultSetFileExtensions[0], true) == 0)
            {
                ContentType = SparqlResultSetContentTypes[0];
                return true;
            }
            else
            {
                ContentType = null;
                return false;
            }
        }
 
        public bool TryGetFileExtension(string ContentType, out string FileExtension)
        {
            if (Array.IndexOf(SparqlResultSetContentTypes, ContentType) >= 0)
            {
                FileExtension = SparqlResultSetFileExtensions[0];
                return true;
            }
            else
            {
                FileExtension = null;
                return false;
            }
        }
    }
}