#region CPL License
/*
Nuclex Framework
Copyright (C) 2002-2017 Nuclex Development Labs

This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.

You should have received a copy of the IBM Common Public
License along with this library
*/
#endregion

using System;
using System.IO;
using System.Xml;
#if !USE_XMLDOCUMENT
using System.Xml.Linq;
#endif
using System.Xml.Schema;

namespace Nuclex.Support {

  /// <summary>Helper routines for handling XML code</summary>
  public static class XmlHelper {

#if !NO_XMLSCHEMA

    #region class ValidationEventProcessor

    /// <summary>Handles any events occurring when an XML schema is loaded</summary>
    private class ValidationEventProcessor {

      /// <summary>
      ///   Callback for notifications being sent by the XmlSchema.Read() method
      /// </summary>
      /// <param name="sender">Not used</param>
      /// <param name="arguments">Contains the notification being sent</param>
      public void OnValidationEvent(object sender, ValidationEventArgs arguments) {
        // We're only interested in the first error, so if we already got
        // an exception on record, skip it!
        if(this.OccurredException != null) {
          return;
        }

        // Only errors count as reasons to assume loading has failed
        if(arguments.Severity == XmlSeverityType.Error) {

          // This code uses the ternary operator because I don't know how to
          // stimlate a validation error that has no exception and couldn't achieve
          // 100% test coverage otherwise. MSDN does not tell whether a validation
          // error without an exception can even occur.
          this.OccurredException = (arguments.Exception != null) ?
            arguments.Exception :
            new XmlSchemaValidationException("Unspecified schema validation error");

        }
      }

      /// <summary>Exception that has occurred during schema loading</summary>
      public Exception OccurredException;

    }

    #endregion // class ValidationEventProcessor

    /// <summary>Loads a schema from a file</summary>
    /// <param name="schemaPath">Path to the file containing the schema</param>
    /// <returns>The loaded schema</returns>
    public static XmlSchema LoadSchema(string schemaPath) {
      using(FileStream schemaStream = openFileForSharedReading(schemaPath)) {
        return LoadSchema(schemaStream);
      }
    }

    /// <summary>Loads a schema from the provided stream</summary>
    /// <param name="schemaStream">Stream containing the schema that will be loaded</param>
    /// <returns>The loaded schema</returns>
    public static XmlSchema LoadSchema(Stream schemaStream) {
      return LoadSchema(new StreamReader(schemaStream));
    }

    /// <summary>Loads a schema from a text reader</summary>
    /// <param name="schemaReader">Text reader through which the schema can be read</param>
    /// <returns>The loaded schema</returns>
    public static XmlSchema LoadSchema(TextReader schemaReader) {
      ValidationEventProcessor eventProcessor = new ValidationEventProcessor();
      XmlSchema schema = XmlSchema.Read(schemaReader, eventProcessor.OnValidationEvent);
      if(eventProcessor.OccurredException != null) {
        throw eventProcessor.OccurredException;
      }
      return schema;
    }

    /// <summary>Attempts to load a schema from a file</summary>
    /// <param name="schemaPath">Path to the file containing the schema</param>
    /// <param name="schema">Output parameter that will receive the loaded schema</param>
    /// <returns>True if the schema was loaded successfully, otherwise false</returns>
    public static bool TryLoadSchema(string schemaPath, out XmlSchema schema) {
      FileStream schemaStream;
      if(!tryOpenFileForSharedReading(schemaPath, out schemaStream)) {
        schema = null;
        return false;
      }

      using(schemaStream) {
        return TryLoadSchema(schemaStream, out schema);
      }
    }

    /// <summary>Attempts to load a schema from the provided stream</summary>
    /// <param name="schemaStream">Stream containing the schema that will be loaded</param>
    /// <param name="schema">Output parameter that will receive the loaded schema</param>
    /// <returns>True if the schema was loaded successfully, otherwise false</returns>
    public static bool TryLoadSchema(Stream schemaStream, out XmlSchema schema) {
      return TryLoadSchema(new StreamReader(schemaStream), out schema);
    }

    /// <summary>Attempts to load a schema from the provided text reader</summary>
    /// <param name="schemaReader">Reader from which the schema can be read</param>
    /// <param name="schema">Output parameter that will receive the loaded schema</param>
    /// <returns>True if the schema was loaded successfully, otherwise false</returns>
    public static bool TryLoadSchema(TextReader schemaReader, out XmlSchema schema) {
      try {
        ValidationEventProcessor eventProcessor = new ValidationEventProcessor();
        schema = XmlSchema.Read(schemaReader, eventProcessor.OnValidationEvent);
        if(eventProcessor.OccurredException == null) {
          return true;
        }
      }
      catch(Exception) {
        // Munch!
      }

      schema = null;
      return false;
    }

    /// <summary>Loads an XML document from a file</summary>
    /// <param name="schema">Schema to use for validating the XML document</param>
    /// <param name="documentPath">
    ///   Path to the file containing the XML document that will be loaded
    /// </param>
    /// <returns>The loaded XML document</returns>
    public static XDocument LoadDocument(XmlSchema schema, string documentPath) {
      using(FileStream documentStream = openFileForSharedReading(documentPath)) {
        return LoadDocument(schema, documentStream);
      }
    }

    /// <summary>Loads an XML document from a stream</summary>
    /// <param name="schema">Schema to use for validating the XML document</param>
    /// <param name="documentStream">
    ///   Stream from which the XML document will be read
    /// </param>
    /// <returns>The loaded XML document</returns>
    public static XDocument LoadDocument(XmlSchema schema, Stream documentStream) {
      XmlReaderSettings settings = new XmlReaderSettings();
      settings.Schemas.Add(schema);

      using(XmlReader reader = XmlReader.Create(documentStream, settings)) {
        var document = XDocument.Load(reader, LoadOptions.None);

        // Create a schema set because the Validate() method only accepts
        // schemas in a schemaset
        var schemas = new XmlSchemaSet();
        schemas.Add(schema);

        // Perform the validation and report the first validation error
        // encountered to the caller
        var validationEventProcessor = new ValidationEventProcessor();
        document.Validate(schemas, validationEventProcessor.OnValidationEvent);
        if (validationEventProcessor.OccurredException != null) {
          throw validationEventProcessor.OccurredException;
        }

        return document;
      }
    }

    /// <summary>Opens a file for shared reading</summary>
    /// <param name="path">Path to the file that will be opened</param>
    /// <returns>The opened file's stream</returns>
    private static FileStream openFileForSharedReading(string path) {
      return new FileStream(
        path, FileMode.Open, FileAccess.Read, FileShare.Read
      );
    }

    /// <summary>Opens a file for shared reading</summary>
    /// <param name="path">Path to the file that will be opened</param>
    /// <param name="fileStream">
    ///   Output parameter that receives the opened file's stream
    /// </param>
    /// <returns>True if the file was opened successfully</returns>
    private static bool tryOpenFileForSharedReading(string path, out FileStream fileStream) {
      try {
        fileStream = new FileStream(
          path, FileMode.Open, FileAccess.Read, FileShare.Read
        );
        return true;
      }
      catch(Exception) {
        // Munch!
      }

      fileStream = null;
      return false;
    }

#endif // !NO_XMLSCHEMA

  }

} // namespace Nuclex.Support