// 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.
 
using System.IO;
using Microsoft.ML.Data;
using Microsoft.ML.Runtime;
 
namespace Microsoft.ML.EntryPoints;
 
/// <summary>
/// Interface for standard transform model port type.
/// </summary>
[BestFriend]
internal abstract class TransformModel
{
    [BestFriend]
    private protected TransformModel()
    {
    }
 
    /// <summary>
    /// The input schema that this transform model was originally instantiated on.
    /// Note that the schema may have columns that aren't needed by this transform model.
    /// If an <see cref="IDataView"/> exists with this schema, then applying this transform model to it
    /// shouldn't fail because of column type issues.
    /// </summary>
    // REVIEW: Would be nice to be able to trim this to the minimum needed somehow. Note
    // however that doing so may cause issues for composing transform models. For example,
    // if transform model A needs column X and model B needs Y, that is NOT produced by A,
    // then trimming A's input schema would cause composition to fail.
    [BestFriend]
    internal abstract DataViewSchema InputSchema { get; }
 
    /// <summary>
    /// The output schema that this transform model was originally instantiated on. The schema resulting
    /// from <see cref="Apply(IHostEnvironment, TransformModel)"/> may differ from this, similarly to how
    /// <see cref="InputSchema"/> may differ from the schema of dataviews we apply this transform model to.
    /// </summary>
    [BestFriend]
    internal abstract DataViewSchema OutputSchema { get; }
 
    /// <summary>
    /// Apply the transform(s) in the model to the given input data.
    /// </summary>
    [BestFriend]
    internal abstract IDataView Apply(IHostEnvironment env, IDataView input);
 
    /// <summary>
    /// Apply the transform(s) in the model to the given transform model.
    /// </summary>
    [BestFriend]
    internal abstract TransformModel Apply(IHostEnvironment env, TransformModel input);
 
    /// <summary>
    /// Save the model to the given stream.
    /// </summary>
    [BestFriend]
    internal abstract void Save(IHostEnvironment env, Stream stream);
 
    /// <summary>
    /// Returns the transform model as an <see cref="IRowToRowMapper"/> that can output a row
    /// given a row with the same schema as <see cref="InputSchema"/>.
    /// </summary>
    /// <returns>The transform model as an <see cref="IRowToRowMapper"/>. If not all transforms
    /// in the pipeline are <see cref="IRowToRowMapper"/> then it returns <see langword="null"/>.</returns>
    [BestFriend]
    internal abstract IRowToRowMapper AsRowToRowMapper(IExceptionContext ectx);
}