package de.intevation.gnv.raster;

/**
 * A 2D double  valued representation of a raster array.
 * @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a>
 */
public class Raster
{
    /**
     * A kernel can be applied to a raster to fold its values.
     */
    public static class Kernel {

        /**
         * The coefficients of the folding matrix.
         */
        public static final class Coeff {
            /**
             * i delta index of this coefficient.
             */
            public int    di;
            /**
             * i delta index of this coefficient.
             */
            public int    dj;
            /**
             * The weight of this coefficient.
             */
            public double c;

            /**
             * Default constructor
             */
            public Coeff() {
            }

            /**
             * Constructor to set the delta position and the weight of
             * the coefficient.
             * @param di The i delta index.
             * @param dj The j delta index.
             * @param c The weight of the index.
             */
            public Coeff(int di, int dj, double c) {
                this.di = di;
                this.dj = dj;
                this.c  = c;
            }

            /**
             * Returns a string representation of this coefficient.
             * @return The string representation.
             */
            @Override
            public String toString() {
                return String.valueOf(c);
            }

        } // class Coeff

        /**
         * The coefficients of the folding matrix.
         */
        protected Coeff [] coeffs;
        /**
         * The width of the kernel.
         */
        protected int      width;

        /**
         * Default constrcutor.
         */
        public Kernel() {
        }

        /**
         * Constructor for a kernel with a given coefficient matrix
         * with a given width.
         * @param coeffs The coefficients.
         * @param width The width of the kernel.
         */
        public Kernel(Coeff [] coeffs, int width) {
            this.coeffs = coeffs;
            this.width  = width;
        }

        /**
         * Evaluates the 2D Gauss normal distribution a given x, y
         * and a given sigma.
         * @param x The x location.
         * @param y The y location.
         * @param sigma The sigma of the distribution.
         * @return The value at point x, y.
         */
        public static double gauss(double x, double y, double sigma) {
            double s2 = sigma*sigma;
            return 1.0d/(2.0d*Math.PI*s2)*Math.exp(-(x*x + y*y)/(2.0d*s2));
        }

        /**
         * Creates a Gauss kernel with sigma = 1 and width 5.
         * @return The new kernel.
         */
        public static Kernel createGauss() {
            return createGauss(1.0d, 5);
        }

        /**
         * Creates a Gauss kernel with a given sigma and width.
         * @param sigma The sigma value
         * @param width  The width of the kernel.
         * @return The new kernel.
         */
        public static Kernel createGauss(double sigma, int width) {
            Coeff [] coeffs = new Coeff[width*width];
            double sum = 0d;
            for (int j = 0; j < width; ++j) {
                int y = -width/2 + j;
                for (int i = 0; i < width; ++i) {
                    int x = -width/2 + i;
                    double c = gauss(x, y, sigma);
                    coeffs[j*width + i] = new Coeff(x, y, c);
                    sum += c;
                }
            }
            sum = 1.0/sum;
            for (int i = 0; i < coeffs.length; ++i) {
                coeffs[i].c *= sum;
            }
            return new Kernel(coeffs, width);
        }

        /**
         * Evaluates this Kernel at the raster at raster index i, j.
         * @param access The accessor to the raster.
         * @param i The i raster index.
         * @param j The j raster index.
         * @return The folded value at index i, j.
         */
        public double fold(Access access, int i, int j) {

            double s = 0.0d;

            double unused = 0d;

            for (int k = 0; k < coeffs.length; ++k) {
                Coeff coeff = coeffs[k];
                double v = access.get(i + coeff.di, j + coeff.dj);
                if (Double.isNaN(v)) {
                    unused += coeff.c;
                }
                else {
                    s += v * coeff.c;
                }
            }

            return s*(1.0d - unused);
        }

        /**
         * Returns a string representation of this kernel.
         * @return The string representation.
         */
        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder();

            int height = coeffs.length/width;

            for (int j = 0; j < height; ++j) {
                if (j > 0) {
                    sb.append(System.getProperty("line.separator"));
                }
                for (int i = 0; i < width; ++i) {
                    if (i > 0) {
                        sb.append("\t");
                    }
                    sb.append(coeffs[j*width + i]);
                }
            }

            return sb.toString();
        }
    } // class Kernel

    /**
     * Interface of allow special access patterns to the raster,
     * especially at the border.
     */
    public interface Access {

        /**
         * Returns the raster value at a given index point.
         * @param i The i index
         * @param j The j index
         * @return The value of the raster.
         */
        double get(int i, int j);

    } // interface Access

    /**
     * Interface to decouple the lookup which is needed
     * to map double values to integers.
     */
    public interface ValueToIndex {

        /**
         * Returns the corresponding integer to a given value.
         * @param value The value to be queried.
         * @return The integer value or -1 if no such value was found.
         */
        int toIndex(double value);

    } // interface ValueToIndex;

    /**
     * Brings raster to an integer representation with equal sized bins
     * of integer vaules.
     */
    public static class IsoClasses
    implements          ValueToIndex
    {
        /**
         * Linear scaling factor.
         */
        protected double m;
        /**
         * Linear offset.
         */
        protected double b;
        /**
         * Number of classes.
         */
        protected int    numClasses;

        /**
         * Constructor to build a lookup to transform
         * an raster into an equals sized bin integer array.
         * @param raster The original raster
         * @param numClasses The number of classes.
         */
        public IsoClasses(Raster raster, int numClasses) {

            this.numClasses = numClasses;

            double min =  Double.MAX_VALUE;
            double max = -Double.MAX_VALUE;

            double [] src = raster.raster;

            for (int i = 0; i < src.length; ++i) {
                double x = src[i];
                if (!Double.isNaN(x)) {
                    if (x < min) min = x;
                    if (x > max) max = x;
                }
            }

            /* f(min) = 0, f(max) = numClasses - 1

               I:  0              = m*min + b
               II: numClasses - 1 = m*max + b

               II - I:
               numClasses - 1 = m*(max - min)

               m = (numClasses - 1)/(max - min)
               b = m*min
            */

            if (max == min) {
                m = 0;
                b = 0;
            }
            else {
                m = (numClasses - 1)/(max - min);
                b = m*min;
            }
        }

        /**
         * Implements the double to integer lookup.
         * @param value The value to map.
         * @return The mapped value.
         */
        public int toIndex(double value) {
            return Double.isNaN(value)
                ? -1
                : Math.min(Math.max(0, (int)Math.round(m*value + b)), numClasses-1);
        }
    } // class IsoClasses

    /**
     * Internal representation of the raster.
     */
    protected double [] raster;
    /**
     * The width of the raster.
     */
    protected int       width;

    /**
     * Default constructor. Creates an 0x0 raster.
     */
    public Raster() {
        this(new double[0], 0);
    }

    /**
     * Creates a raster with given values and width.
     * @param raster
     * @param width
     */
    public Raster(double [] raster, int width) {
        this.raster = raster;
        this.width  = width;
    }

    /**
     * The width of the raster.
     * @return The width.
     */
    public int getWidth() {
        return width;
    }

    /**
     * The height of the raster.
     * @return The height.
     */
    public int getHeight() {
        return raster.length / width;
    }

    /**
     * The values of the raster.
     * @return The values.
     */
    public double [] getValues() {
        return raster;
    }

    /**
     * Creates an integer representation of this raster using a
     * given value to index transformer.
     * @param valueToIndex The transformer to map double to integer values.
     * @return The new created integer representation.
     */
    public int [] toIndexed(ValueToIndex valueToIndex) {
        int [] dst = new int[raster.length];
        for (int i = 0; i < raster.length; ++i) {
            dst[i] = valueToIndex.toIndex(raster[i]);
        }
        return dst;
    }

    /**
     * Creates a new raster by applying a kernel to this raster.
     * Access to the raster is continuous at the border.
     * The original raster is not modified.
     * @param kernel The kernel to be applied.
     * @return The new raster.
     */
    public Raster create(Kernel kernel) {
        double [] dst = new double[raster.length];
        Raster r = new Raster(dst, width);
        r.apply(kernel, continueBorder());
        return r;
    }

    /**
     * Creates a new raster by applying a kernel to this raster.
     * Access to the raster is given.
     * @param kernel The kernel to be applied.
     * @param access The access method to the raster.
     */
    public void apply(Kernel kernel, Access access) {
        int height = getHeight();
        for (int j = 0; j < height; ++j) {
            int row = j*width;
            for (int i = 0; i < width; ++i) {
                raster[row + i] = kernel.fold(access, i, j);
            }
        }
    }

    /**
     * Returns a continuous access to the raster. Values
     * at the border are repeated til infinity if indices
     * are accessed outside the defined area.
     * @return The accessor.
     */
    public Access continueBorder() {
        return new Access() {
            int height = getHeight()-1;
            public double get(int i, int j) {
                     if (i < 0)      i = 0;
                else if (i >= width) i = width-1;
                     if (j < 0)      j = 0;
                else if (j > height) j = height;
                return raster[j*width + i];
            }
        };
    }
}
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