using System.Data;
using JdeScoping.DataSync.Etl.Contracts;

namespace JdeScoping.DataSync.Etl.Transformers;

/// <summary>
/// Base class for data transformers that modify data during the ETL process.
/// Derived classes can override specific methods to customize transformation behavior.
/// </summary>
public abstract class DataTransformerBase : IDataTransformer
{
    /// <inheritdoc />
    public abstract string TransformerName { get; }

    /// <inheritdoc />
    public IDataReader Transform(IDataReader source)
    {
        ArgumentNullException.ThrowIfNull(source);
        OnInitialize(source);
        return new TransformingDataReader(source, this);
    }

    /// <summary>
    /// Called when the transformer is initialized with a source reader.
    /// Override to perform initialization logic.
    /// </summary>
    /// <param name="source">The source data reader.</param>
    protected virtual void OnInitialize(IDataReader source) { }

    /// <summary>
    /// Gets the field count from the source reader.
    /// Override to add or remove fields.
    /// </summary>
    public virtual int GetFieldCount(IDataReader source) => source.FieldCount;

    /// <summary>
    /// Gets the name of a field at the specified ordinal.
    /// Override to rename fields.
    /// </summary>
    public virtual string GetName(int ordinal, IDataReader source) => source.GetName(ordinal);

    /// <summary>
    /// Gets the type of a field at the specified ordinal.
    /// Override to change field types.
    /// </summary>
    public virtual Type GetFieldType(int ordinal, IDataReader source) => source.GetFieldType(ordinal);

    /// <summary>
    /// Gets the value of a field at the specified ordinal.
    /// Override to transform values.
    /// </summary>
    public virtual object GetValue(int ordinal, IDataReader source) => source.GetValue(ordinal);

    /// <summary>
    /// Gets the ordinal of a field by name.
    /// Override to support renamed fields.
    /// </summary>
    public virtual int GetOrdinal(string name, IDataReader source) => source.GetOrdinal(name);

    /// <summary>
    /// Checks if a field value is DBNull.
    /// Override to handle null transformations.
    /// </summary>
    public virtual bool IsDBNull(int ordinal, IDataReader source) => source.IsDBNull(ordinal);

    /// <summary>
    /// Maps a transformed ordinal to the source ordinal.
    /// Override to support column reordering or computed columns.
    /// </summary>
    /// <param name="transformedOrdinal">The ordinal in the transformed output.</param>
    /// <param name="source">The source data reader.</param>
    /// <returns>The corresponding source ordinal, or -1 for computed columns.</returns>
    public virtual int MapOrdinal(int transformedOrdinal, IDataReader source) => transformedOrdinal;
}