#include <stdbool.h> // bool
#include <string.h> // memset()
#include <stdio.h> // fopen()
#include "util.h"
#include "km.h"

#define MAX_BUF_ITEMS (1 << 20)

typedef struct {
  FILE *fh;
  size_t ofs;
  uint64_t buf[MAX_BUF_ITEMS];
} ctx_t;

static inline bool
refill(
  ctx_t * const ctx
) {
  ctx->ofs = 0;
  // D("reading %zu bytes", sizeof(ctx->buf));
  return !!fread(ctx->buf, sizeof(ctx->buf), 1, ctx->fh);
}

static bool
next(
  ctx_t * const ctx,
  uint64_t * const r
) {
  if ((ctx->ofs >= MAX_BUF_ITEMS - 1) && !refill(ctx)) {
    // return failure
    return false;
  }

  // get next value, increment offset
  *r = ctx->buf[ctx->ofs];
  ctx->ofs++;

  // return success
  return true;
}

// get N get_floats
static bool
on_get_floats(
  km_rand_t * const rs,
  const size_t num_vals,
  float * const vals
) {
  ctx_t * const ctx = rs->data;

  // generate results
  for (size_t i = 0; i < num_vals; i++) {
    uint64_t v;

    if (!next(ctx, &v)) {
      // return failure
      return false;
    }

    // add value
    vals[i] = 1.0 * v / RAND_MAX;
  }

  // return success
  return true;
}

// fill sizes callback for system random source
static bool
on_get_sizes(
  km_rand_t * const rs,
  const size_t num_vals,
  size_t * const vals
) {
  ctx_t * const ctx = rs->data;

  // generate results
  for (size_t i = 0; i < num_vals; i++) {
    uint64_t v;

    if (!next(ctx, &v)) {
      // return failure
      return false;
    }

    // add value
    vals[i] = v;
  }

  // return success
  return true;
}

static void
on_fini(
  km_rand_t * const rs
) {
  ctx_t * const ctx = rs->data;

  // close file
  fclose(ctx->fh);

  // free context
  free(ctx);

  rs->data = NULL;
}

// path random source callbacks
static const km_rand_cbs_t
PATH_RAND_CBS = {
  .get_floats = on_get_floats,
  .get_sizes  = on_get_sizes,
  .fini       = on_fini,
};

// init random source from a file (e.g. "/dev/urandom")
// (NOTE: this method is horribly slow, don't use it)
bool
km_rand_init_path(
  km_rand_t * const rs,
  const char * const path
) {
  // open file
  FILE *fh = fopen(path, "rb");
  if (!fh) {
    // return failure
    return false;
  }

  // alloc context
  ctx_t * const ctx = malloc(sizeof(ctx_t));
  if (!ctx) {
    // return failure
    return false;
  }

  // populate context
  ctx->fh = fh;

  // fill buffer
  if (!refill(ctx)) {
    // return failure
    return false;
  }

  // populate random source
  rs->cbs = &PATH_RAND_CBS;
  rs->data = ctx;

  // return success
  return true;
}