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

namespace HeuristicLab.Analysis.FitnessLandscape {

  public class ColorGradient {

    private SortedList<double, Color> colors;

    public ColorGradient() {
      Clear();
    }

    public void Clear() {
      colors = new SortedList<double, Color>();
    }

    public Color this[double index] {
      get {
        if (colors.Count == 0)
          throw new KeyNotFoundException();
        KeyValuePair<double, Color> lower = colors.First();
        if (index < lower.Key)
          return lower.Value;
        foreach (var upper in colors) {
          if (upper.Key == index)
            return upper.Value;
          if (upper.Key > index) {
            double alpha = (index - lower.Key) / (upper.Key - lower.Key);
            return Color.FromArgb(
              (int)Math.Round(upper.Value.A * alpha + lower.Value.A * (1 - alpha)),
              (int)Math.Round(upper.Value.R * alpha + lower.Value.R * (1 - alpha)),
              (int)Math.Round(upper.Value.G * alpha + lower.Value.G * (1 - alpha)),
              (int)Math.Round(upper.Value.B * alpha + lower.Value.B * (1 - alpha)));
          }
          lower = upper;
        }
        return colors.Last().Value;
      }
      set {
        colors[index] = value;
      }
    }
  }
}