using System;
using System.Collections.Generic;
using System.Reflection;
using Google.ProtocolBuffers.Collections;

namespace Google.ProtocolBuffers.Descriptors {
  public class FieldDescriptor {

    private FieldDescriptor(DescriptorProtos.FieldDescriptorProto proto,
                            FileDescriptor file,
                            MessageDescriptor parent,
                            int index,
                            bool isExtension) {
      enumType = null;
    }

    private EnumDescriptor enumType;

    public bool IsRequired {
      get;
      set;
    }

    public MappedType MappedType { get; set; }

    public bool IsRepeated { get; set; }

    public FieldType FieldType { get; set; }
    public int FieldNumber { get; set; }

    public bool IsExtension { get; set; }

    public MessageDescriptor ContainingType { get; set; }

    public string FullName { get; set; }

    public bool IsOptional { get; set; }

    public MessageDescriptor MessageType { get; set; }

    public MessageDescriptor ExtensionScope { get; set; }

    /// <summary>
    /// For enum fields, returns the field's type.
    /// </summary>
    public EnumDescriptor EnumType {
      get {
        if (MappedType != MappedType.Enum) {
          throw new InvalidOperationException("EnumType is only valid for enum fields.");
        }
        return enumType;
      }
    }   

    /// <summary>
    /// The default value for this field. For repeated fields
    /// this will always be an empty list. For message fields it will
    /// always be null. For singular values, it will depend on the descriptor.
    /// </summary>
    public object DefaultValue {
      get { throw new NotImplementedException(); }
    }

    public string Name {
      get { throw new NotImplementedException(); }
    }

    /// <summary>
    /// Immutable mapping from field type to mapped type. Built using the attributes on
    /// FieldType values.
    /// </summary>
    public static readonly IDictionary<FieldType, MappedType> FieldTypeToWireFormatMap = MapFieldTypes();

    private static IDictionary<FieldType, MappedType> MapFieldTypes() {
      var map = new Dictionary<FieldType, MappedType>();
      foreach (FieldInfo field in typeof(FieldType).GetFields(BindingFlags.Static | BindingFlags.Public)) {
        FieldType fieldType = (FieldType)field.GetValue(null);
        FieldMappingAttribute mapping = (FieldMappingAttribute)field.GetCustomAttributes(typeof(FieldMappingAttribute), false)[0];
        map[fieldType] = mapping.MappedType;
      }
      return Dictionaries.AsReadOnly(map);
    }
  }
}