// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
namespace Microsoft.ML.Data;
 
/// <summary>
/// Delegate type to map/convert a value.
/// </summary>
[BestFriend]
internal delegate void ValueMapper<TSrc, TDst>(in TSrc src, ref TDst dst);
 
/// <summary>
/// Delegate type to map/convert among three values, for example, one input with two
/// outputs, or two inputs with one output.
/// </summary>
[BestFriend]
internal delegate void ValueMapper<TVal1, TVal2, TVal3>(in TVal1 val1, ref TVal2 val2, ref TVal3 val3);
 
/// <summary>
/// Interface for mapping a single input value (of an indicated ColumnType) to
/// an output value (of an indicated ColumnType). This interface is commonly implemented
/// by predictors. Note that the input and output ColumnTypes determine the proper
/// type arguments for GetMapper, but typically contain additional information like
/// vector lengths.
/// </summary>
[BestFriend]
internal interface IValueMapper
{
    DataViewType InputType { get; }
    DataViewType OutputType { get; }
 
    /// <summary>
    /// Get a delegate used for mapping from input to output values. Note that the delegate
    /// should only be used on a single thread - it should NOT be assumed to be safe for concurrency.
    /// </summary>
    ValueMapper<TSrc, TDst> GetMapper<TSrc, TDst>();
}
 
/// <summary>
/// Interface for mapping a single input value (of an indicated ColumnType) to an output value
/// plus distribution value (of indicated ColumnTypes). This interface is commonly implemented
/// by predictors. Note that the input, output, and distribution ColumnTypes determine the proper
/// type arguments for GetMapper, but typically contain additional information like
/// vector lengths.
/// </summary>
[BestFriend]
internal interface IValueMapperDist : IValueMapper
{
    DataViewType DistType { get; }
 
    /// <summary>
    /// Get a delegate used for mapping from input to output values. Note that the delegate
    /// should only be used on a single thread - it should NOT be assumed to be safe for concurrency.
    /// </summary>
    ValueMapper<TSrc, TDst, TDist> GetMapper<TSrc, TDst, TDist>();
}