// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.
// http://code.google.com/p/protobuf/
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
using System.Collections.Generic;
using Google.ProtocolBuffers.DescriptorProtos;

namespace Google.ProtocolBuffers.Descriptors {

  /// <summary>
  /// Describes a message type.
  /// </summary>
  public sealed class MessageDescriptor : IndexedDescriptorBase<DescriptorProto, MessageOptions> {

    private readonly MessageDescriptor containingType;
    private readonly IList<MessageDescriptor> nestedTypes;
    private readonly IList<EnumDescriptor> enumTypes;
    private readonly IList<FieldDescriptor> fields;
    private readonly IList<FieldDescriptor> extensions;
    private bool hasRequiredFields;

    internal MessageDescriptor(DescriptorProto proto, FileDescriptor file, MessageDescriptor parent, int typeIndex)
        : base(proto, file, ComputeFullName(file, parent, proto.Name), typeIndex) {
      containingType = parent;

      nestedTypes = DescriptorUtil.ConvertAndMakeReadOnly(proto.NestedTypeList,
          (type, index) => new MessageDescriptor(type, file, this, index));

      enumTypes = DescriptorUtil.ConvertAndMakeReadOnly(proto.EnumTypeList,
          (type, index) => new EnumDescriptor(type, file, this, index));

      fields = DescriptorUtil.ConvertAndMakeReadOnly(proto.FieldList,
          (field, index) => new FieldDescriptor(field, file, this, index, false));

      extensions = DescriptorUtil.ConvertAndMakeReadOnly(proto.ExtensionList,
          (field, index) => new FieldDescriptor(field, file, this, index, true));

      file.DescriptorPool.AddSymbol(this);
    }

    /// <value>
    /// If this is a nested type, get the outer descriptor, otherwise null.
    /// </value>
    public MessageDescriptor ContainingType {
      get { return containingType; }
    }

    /// <value>
    /// An unmodifiable list of this message type's fields.
    /// </value>
    public IList<FieldDescriptor> Fields {
      get { return fields; }
    }

    /// <value>
    /// An unmodifiable list of this message type's extensions.
    /// </value>
    public IList<FieldDescriptor> Extensions {
      get { return extensions; }
    }

    /// <value>
    /// An unmodifiable list of this message type's nested types.
    /// </value>
    public IList<MessageDescriptor> NestedTypes {
      get { return nestedTypes; }
    }

    /// <value>
    /// An unmodifiable list of this message type's enum types.
    /// </value>
    public IList<EnumDescriptor> EnumTypes {
      get { return enumTypes; }
    }

    /// <summary>
    /// Returns a pre-computed result as to whether this message
    /// has required fields. This includes optional fields which are
    /// message types which in turn have required fields, and any 
    /// extension fields.
    /// </summary>
    internal bool HasRequiredFields {
      get { return hasRequiredFields; }
    }

    /// <summary>
    /// Determines if the given field number is an extension.
    /// </summary>
    public bool IsExtensionNumber(int number) {
      foreach (DescriptorProto.Types.ExtensionRange range in Proto.ExtensionRangeList) {
        if (range.Start <= number && number < range.End) {
          return true;
        }
      }
      return false;
    }

    /// <summary>
    /// Finds a field by field number.
    /// </summary>
    /// <param name="number">The field number within this message type.</param>
    /// <returns>The field's descriptor, or null if not found.</returns>
    public FieldDescriptor FindFieldByNumber(int number) {
      return File.DescriptorPool.FindFieldByNumber(this, number);
    }

    /// <summary>
    /// Finds a nested descriptor by name. The is valid for fields, nested
    /// message types and enums.
    /// </summary>
    /// <param name="name">The unqualified name of the descriptor, e.g. "Foo"</param>
    /// <returns>The descriptor, or null if not found.</returns>
    public T FindDescriptor<T>(string name) 
        where T : class, IDescriptor {
      return File.DescriptorPool.FindSymbol<T>(FullName + "." + name);
    }

    /// <summary>
    /// Looks up and cross-links all fields, nested types, and extensions.
    /// </summary>
    internal void CrossLink() {
      foreach (MessageDescriptor message in nestedTypes) {
        message.CrossLink();
      }

      foreach (FieldDescriptor field in fields) {
        field.CrossLink();
      }

      foreach (FieldDescriptor extension in extensions) {
        extension.CrossLink();
      }
    }

    internal void CheckRequiredFields() {
      IDictionary<MessageDescriptor, byte> alreadySeen = new Dictionary<MessageDescriptor, byte>();
      hasRequiredFields = CheckRequiredFields(alreadySeen);
    }

    private bool CheckRequiredFields(IDictionary<MessageDescriptor,byte> alreadySeen) {

      if (alreadySeen.ContainsKey(this)) {
        // The type is already in the cache. This means that either:
        // a. The type has no required fields.
        // b. We are in the midst of checking if the type has required fields,
        //    somewhere up the stack.  In this case, we know that if the type
        //    has any required fields, they'll be found when we return to it,
        //    and the whole call to HasRequiredFields() will return true.
        //    Therefore, we don't have to check if this type has required fields
        //    here.
        return false;
      }
      alreadySeen[this] = 0; // Value is irrelevant; we want set semantics

      // If the type allows extensions, an extension with message type could contain
      // required fields, so we have to be conservative and assume such an
      // extension exists.
      if (Proto.ExtensionRangeCount != 0) {
        return true;
      }

      foreach (FieldDescriptor field in Fields) {
        if (field.IsRequired) {
          return true;
        }
        if (field.MappedType == MappedType.Message) {
          if (field.MessageType.CheckRequiredFields(alreadySeen)) {
            return true;
          }
        }
      }
      return false;
    }
  }
}