// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Diagnostics.CodeAnalysis;
 
namespace System.ComponentModel.Composition
{
    /// <summary>
    ///     Specifies that a type, property, field, or method provides a particular export.
    /// </summary>
    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Field | AttributeTargets.Property | AttributeTargets.Method,
                    AllowMultiple = true, Inherited = false)]
    public class ExportAttribute : Attribute
    {
        /// <summary>
        ///     Initializes a new instance of the <see cref="ExportAttribute"/> class, exporting the
        ///     type or member marked with this attribute under the default contract name.
        /// </summary>
        /// <remarks>
        ///     <para>
        ///         The default contract name is the result of calling
        ///         <see cref="AttributedModelServices.GetContractName(Type)"/> on the type of the
        ///         property or field, or the type itself, that is marked with this attribute.
        ///     </para>
        ///     <para>
        ///         The contract name is compared using a case-sensitive, non-linguistic comparison
        ///         using <see cref="StringComparer.Ordinal"/>.
        ///     </para>
        /// </remarks>
        public ExportAttribute()
            : this((string?)null, (Type?)null)
        {
        }
 
        /// <summary>
        ///     Initializes a new instance of the <see cref="ExportAttribute"/> class, exporting the
        ///     type or member marked with this attribute under a contract name derived from the
        ///     specified type.
        /// </summary>
        /// <param name="contractType">
        ///     A <see cref="Type"/> of which to derive the contract name to export the type or
        ///     member marked with this attribute, under; or <see langword="null"/> to use the
        ///     default contract name.
        /// </param>
        /// <remarks>
        ///     <para>
        ///         The contract name is the result of calling
        ///         <see cref="AttributedModelServices.GetContractName(Type)"/> on
        ///         <paramref name="contractType"/>.
        ///     </para>
        ///     <para>
        ///         The default contract name is the result of calling
        ///         <see cref="AttributedModelServices.GetContractName(Type)"/> on the type of the
        ///         property or field, or the type itself, that is marked with this attribute.
        ///     </para>
        ///     <para>
        ///         The contract name is compared using a case-sensitive, non-linguistic comparison
        ///         using <see cref="StringComparer.Ordinal"/>.
        ///     </para>
        /// </remarks>
        public ExportAttribute(Type? contractType)
            : this((string?)null, contractType)
        {
        }
 
        /// <summary>
        ///     Initializes a new instance of the <see cref="ExportAttribute"/> class, exporting the
        ///     type or member marked with this attribute under the specified contract name.
        /// </summary>
        /// <param name="contractName">
        ///      A <see cref="string"/> containing the contract name to export the type or member
        ///      marked with this attribute, under; or <see langword="null"/> or an empty string
        ///      ("") to use the default contract name.
        /// </param>
        /// <remarks>
        ///     <para>
        ///         The default contract name is the result of calling
        ///         <see cref="AttributedModelServices.GetContractName(Type)"/> on the property or field
        ///         type, or the type itself that this is marked with this attribute.
        ///     </para>
        ///     <para>
        ///         The contract name is compared using a case-sensitive, non-linguistic comparison
        ///         using <see cref="StringComparer.Ordinal"/>.
        ///     </para>
        /// </remarks>
        public ExportAttribute(string? contractName)
            : this(contractName, (Type?)null)
        {
        }
 
        /// <summary>
        ///     Initializes a new instance of the <see cref="ExportAttribute"/> class, exporting the
        ///     type or member marked with this attribute under the specified contract name.
        /// </summary>
        /// <param name="contractName">
        ///      A <see cref="string"/> containing the contract name to export the type or member
        ///      marked with this attribute, under; or <see langword="null"/> or an empty string
        ///      ("") to use the default contract name.
        /// </param>
        /// <param name="contractType">
        ///     A <see cref="Type"/> of which to derive the contract name to export the type or
        ///     member marked with this attribute, under; or <see langword="null"/> to use the
        ///     default contract name.
        /// </param>
        /// <remarks>
        ///     <para>
        ///         The default contract name is the result of calling
        ///         <see cref="AttributedModelServices.GetContractName(Type)"/> on the property or field
        ///         type, or the type itself that this is marked with this attribute.
        ///     </para>
        ///     <para>
        ///         The contract name is compared using a case-sensitive, non-linguistic comparison
        ///         using <see cref="StringComparer.Ordinal"/>.
        ///     </para>
        /// </remarks>
        public ExportAttribute(string? contractName, Type? contractType)
        {
            ContractName = contractName;
            ContractType = contractType;
        }
 
        /// <summary>
        ///     Gets the contract name to export the type or member under.
        /// </summary>
        /// <value>
        ///      A <see cref="string"/> containing the contract name to export the type or member
        ///      marked with this attribute, under. The default value is an empty string ("").
        /// </value>
        public string? ContractName { get; }
 
        /// <summary>
        ///     Get the contract type that is exported by the member that this attribute is attached to.
        /// </summary>
        /// <value>
        ///     A <see cref="Type"/> of the export that is be provided. The default value is
        ///     <see langword="null"/> which means that the type will be obtained by looking at the type on
        ///     the member that this export is attached to.
        /// </value>
        public Type? ContractType { get; }
    }
}