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

double
gsl_histogram_pdf_sample (const gsl_histogram_pdf * p, double r)
{
  size_t i;
  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 (r == 1.0)
    {
      r = 0.0;
    }

  status = gsl_histogram_find_impl (p->n, p->sum, r, &i);

  if (status)
    {
      GSL_ERROR_RETURN ("cannot find r in cumulative pdf", GSL_EDOM, 0);
    }
  else
    {
      double delta = (r - p->sum[i]) / (p->sum[i + 1] - p->sum[i]);
      double x = p->range[i] + delta * (p->range[i + 1] - p->range[i]);
      return x;
    }
}

gsl_histogram_pdf *
gsl_histogram_pdf_alloc (const gsl_histogram * h)
{
  size_t i;
  size_t n = h->n;
  gsl_histogram_pdf *p;

  if (n == 0)
    {
      GSL_ERROR_RETURN ("histogram 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_histogram_pdf *) malloc (sizeof (gsl_histogram_pdf));

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

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

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

      GSL_ERROR_RETURN ("failed to allocate space for histogram pdf ranges",
			GSL_ENOMEM, 0);
    }

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

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

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

  for (i = 0; i < n + 1; i++)
    {
      p->range[i] = h->range[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->n = n;

  return p;
}

void
gsl_histogram_pdf_free (gsl_histogram_pdf * p)
{
  free (p->range);
  free (p->sum);
  free (p);
}