#include <config.h>
#include <stdlib.h>
#include <gsl_errno.h>
#include <gsl_histogram.h>
#include <gsl_histogram2d.h>

int
gsl_histogram2d_pdf_sample (const gsl_histogram2d_pdf * p,
			    double r1, double r2,
			    double *x, double *y)
{
  size_t k;
  int status;

/* Wrap the exclusive top of the bin down to the inclusive bottom of
   the bin. Since this is a single point it should not affect the
   distribution. */

  if (r2 == 1.0)
    {
      r2 = 0.0;
    }
  if (r1 == 1.0)
    {
      r1 = 0.0;
    }

  status = gsl_histogram_find_impl (p->nx * p->ny, p->sum, r1, &k);

  if (status)
    {
      GSL_ERROR ("cannot find r1 in cumulative pdf", GSL_EDOM);
    }
  else
    {
      size_t i = k / p->ny;
      size_t j = k - (i * p->ny);
      double delta = (r1 - p->sum[k]) / (p->sum[k + 1] - p->sum[k]);
      *x = p->xrange[i] + delta * (p->xrange[i + 1] - p->xrange[i]);
      *y = p->yrange[j] + r2 * (p->yrange[j + 1] - p->yrange[j]);
      return 0;
    }
}

gsl_histogram2d_pdf *
gsl_histogram2d_pdf_alloc (const gsl_histogram2d * h)
{
  size_t i;
  const size_t nx = h->nx;
  const size_t ny = h->ny;
  const size_t n = nx * ny;

  gsl_histogram2d_pdf *p;

  if (n == 0)
    {
      GSL_ERROR_RETURN ("histogram2d length n must be positive integer",
			GSL_EDOM, 0);
    }

  for (i = 0; i < n; i++)
    {
      if (h->bin[i] < 0)
	{
	  GSL_ERROR_RETURN ("histogram bins must be non-negative to compute"
			    "a probability distribution",
			    GSL_EDOM, 0);
	}
    }

  p = (gsl_histogram2d_pdf *) malloc (sizeof (gsl_histogram2d_pdf));

  if (p == 0)
    {
      GSL_ERROR_RETURN ("failed to allocate space for histogram2d pdf struct",
			GSL_ENOMEM, 0);
    }

  p->xrange = (double *) malloc ((nx + 1) * sizeof (double));

  if (p->xrange == 0)
    {
      free (p);		/* exception in constructor, avoid memory leak */

      GSL_ERROR_RETURN ("failed to allocate space for histogram2d pdf xranges",
			GSL_ENOMEM, 0);
    }

  p->yrange = (double *) malloc ((ny + 1) * sizeof (double));

  if (p->yrange == 0)
    {
      free (p->xrange);
      free (p);		/* exception in constructor, avoid memory leak */

      GSL_ERROR_RETURN ("failed to allocate space for histogram2d pdf yranges",
			GSL_ENOMEM, 0);
    }

  p->sum = (double *) malloc ((n + 1) * sizeof (double));

  if (p->sum == 0)
    {
      free (p->yrange);
      free (p->xrange);
      free (p);		/* exception in constructor, avoid memory leak */

      GSL_ERROR_RETURN ("failed to allocate space for histogram2d pdf sums",
			GSL_ENOMEM, 0);
    }

  for (i = 0; i < nx + 1; i++)
    {
      p->xrange[i] = h->xrange[i];
    }

  for (i = 0; i < ny + 1; i++)
    {
      p->yrange[i] = h->yrange[i];
    }

  {
    double mean = 0, sum = 0;

    for (i = 0; i < n; i++)
      {
	mean += (h->bin[i] - mean) / ((double) (i + 1));
      }

    p->sum[0] = 0;

    for (i = 0; i < n; i++)
      {
	sum += (h->bin[i] / mean) / n;
	p->sum[i + 1] = sum;
      }
  }

  p->nx = nx;
  p->ny = ny;

  return p;
}

void
gsl_histogram2d_pdf_free (gsl_histogram2d_pdf * p)
{
  free (p->xrange);
  free (p->yrange);
  free (p->sum);
  free (p);
}