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using System;

namespace IStation.Numerics.LinearAlgebra.Solvers
{
    /// <summary>
    /// Stop criterion that delegates the status determination to a delegate.
    /// </summary>
    public class DelegateStopCriterion<T> : IIterationStopCriterion<T>
        where T : struct, IEquatable<T>, IFormattable
    {
        readonly Func<int, Vector<T>, Vector<T>, Vector<T>, IterationStatus> _determine;
        IterationStatus _status = IterationStatus.Continue;

        /// <summary>
        /// Create a new instance of this criterion with a custom implementation.
        /// </summary>
        /// <param name="determine">Custom implementation with the same signature and semantics as the DetermineStatus method.</param>
        public DelegateStopCriterion(Func<int, Vector<T>, Vector<T>, Vector<T>, IterationStatus> determine)
        {
            _determine = determine;
        }

        /// <summary>
        /// Determines the status of the iterative calculation by delegating it to the provided delegate.
        /// Result is set into <c>Status</c> field.
        /// </summary>
        /// <param name="iterationNumber">The number of iterations that have passed so far.</param>
        /// <param name="solutionVector">The vector containing the current solution values.</param>
        /// <param name="sourceVector">The right hand side vector.</param>
        /// <param name="residualVector">The vector containing the current residual vectors.</param>
        /// <remarks>
        /// The individual stop criteria may internally track the progress of the calculation based
        /// on the invocation of this method. Therefore this method should only be called if the
        /// calculation has moved forwards at least one step.
        /// </remarks>
        public IterationStatus DetermineStatus(int iterationNumber, Vector<T> solutionVector, Vector<T> sourceVector, Vector<T> residualVector)
        {
            return _status = _determine(iterationNumber, solutionVector, sourceVector, residualVector);
        }

        /// <summary>
        /// Gets the current calculation status.
        /// </summary>
        public IterationStatus Status => _status;

        /// <summary>
        /// Resets the IIterationStopCriterion to the pre-calculation state.
        /// </summary>
        public void Reset()
        {
            _status = IterationStatus.Continue;
        }

        /// <summary>
        /// Clones this criterion and its settings.
        /// </summary>
        public IIterationStopCriterion<T> Clone()
        {
            return new DelegateStopCriterion<T>(_determine);
        }
    }
}