using System;

namespace DTS.Common.Calculations
{
    public class HeadInjuryCriterion
    {
        /// <summary>
        /// Calculates the head injury criterion given a resultant channel, and a desired clip length
        /// </summary>
        /// <param name="resultant">Acceleration vector (x,y,z resultant)</param>
        /// <param name="SPS">Actual sample rate</param>
        /// <param name="clipLengthMS">Length in ms </param>
        /// <returns>MAX Head Injury Criterion over the data input for the clip requested</returns>
        public static HICResult GetHeadInjuryCriterion(ChannelData resultant, double SPS, int clipLengthMS)
        {
            System.Diagnostics.Trace.Assert(SPS > 0, "Actual sample rate must be positive");
            System.Diagnostics.Trace.Assert(clipLengthMS > 0, "Clip length must be positive");

            int maxHICPoint = int.MinValue;
            double maxHIC = int.MinValue;
            int maxHICEndPoint = int.MinValue;

            int maxclip = Convert.ToInt32(Math.Ceiling(clipLengthMS * SPS / 1000D));

            for (int clip = 1; clip <= maxclip; clip++)
            {
                System.Diagnostics.Trace.Assert(clip < resultant.FilteredEU.Length, string.Format("data must be atleast {0} ms", clipLengthMS));
                double clipInSeconds = clip / SPS;
                for (int i = 0; i < resultant.FilteredEU.Length - clip; i++)
                {
                    //note we are exhaustively recalculating sums, we can do this much better without a doubt, but lets get the
                    //first method done (brute force)
                    //also note, definite integral doesn't include last point, so we have to add one point back in
                    double integral = Integral.DefiniteIntegral(resultant.FilteredEU, i, i + clip, SPS);
                    double hic = clipInSeconds * Math.Pow(integral / clipInSeconds, 2.5D);
                    if (hic > maxHIC) { maxHIC = hic; maxHICPoint = i; maxHICEndPoint = i + clip; }
                }
            }
            return new HICResult(maxHIC, clipLengthMS, maxHICPoint, maxHICEndPoint);
        }



        /// <summary>
        /// helper class for storing/handling hic results
        /// </summary>
        public class HICResult
        {
            public int StartSample { get; }
            public int EndSample { get; }
            public int HicLengthMS { get; }
            public double HIC { get; }
            /// <summary>
            /// constructs a new HIC result
            /// </summary>
            /// <param name="hic">HIC value</param>
            /// <param name="hicLength">length of HIC in ms</param>
            /// <param name="endSample">start sample of HIC</param>
            /// <param name="startSample">end sample of HIC</param>
            public HICResult(double hic, int hicLength, int startSample, int endSample)
            {
                StartSample = startSample;
                EndSample = endSample;
                HicLengthMS = hicLength;
                HIC = hic;
            }
        }
    }
}