using System.Collections.Generic;
using System.Linq;

namespace DTS.Common.Calculations
{
    public static class Resultant
    {
        /// <summary>
        /// generates a resultant channel given input vectors
        /// Will throw an assertion if lengths of data don't match, or if 
        /// units don't match
        /// </summary>
        /// <param name="channels">List of channels to combine via 
        /// sum of squares
        /// </param>
        /// <returns>
        /// resultant vector from sum of squares of inputs
        /// </returns>
        public static ChannelData GenerateResultantChannel(List<ChannelData> channels)
        {
            int length = (from ch in channels select ch.FilteredEU.Length).Max();
            foreach (var ch in channels) { System.Diagnostics.Trace.Assert(ch.FilteredEU.Length == length); }
            //make sure the channels are all the same units and lengths, 
            //we assert here since the higher level should be expected to provide clean inputs
            var units = (from ch in channels select ch.Units).Distinct();
            System.Diagnostics.Trace.Assert(units.Count() == 1);

            var values = new List<double>();

            //in a future version we can parallize this for efficiency
            //values.Add will need to be replaced by an indexer when we do
            for (int i = 0; i < length; i++)
            {
                double d = 0D;
                foreach (var ch in channels)
                {
                    d += ch.FilteredEU[i] * ch.FilteredEU[i];
                }
                values.Add(System.Math.Sqrt(d));
            }

            var cd = new ChannelData(units.First());
            cd.FilteredEU = values.ToArray();
            return cd;
        }
    }
}