#include <assert.h>
#include <getopt.h>
#include <pwd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

#include "io/read_file.h"
#include "util/debug.h"
#include "util/error.h"
#include "util/loop_files.h"
#include "util/versie.h"

static int gn, gc;

static void usage(FILE *f) {
  fprintf(f,
      "Gebruik: staart [-nchV] [BESTAND]...\n"
      "\n"
      "Toon de laatste 10 regels van elk BESTAND naar standaard uitvoer\n"
      "\n"
      "  -n AANTAL   Aantal regels om weer te geven\n"
      "  -c AANTAL   Aantal karakters om weer te geven\n"
      "  -h          Toon deze hulptekst\n"
      "  -V          Toon versienummer\n");
}

// Returns pointer to argument array containing the file names
static char** parse_options(int argc, char **argv, int *n, int *c) {
  int opt;
  while ((opt = getopt(argc, argv, "n:c:hV")) != -1) {
    switch (opt) {
      case 'c':
        *c = atoi(optarg);
        *n = -1;
        break;

      case 'n':
        *c = -1;
        *n = atoi(optarg);
        break;

      case 'h':
        usage(stdout);
        exit(0);

      case 'V':
        drukkedoos_print_versie(stdout);
        exit(0);

      case '?':
        usage(stderr);
        exit(1);
    }
  }

  return argv + optind;
}

static int process(struct filebuf *fb, char*, bool) {
  // handle byte limits
  if (gc != -1) {
    assert(gc >= 0);
    fwrite(fb->buf+fb->sz-gc, 1, gc, stdout);
    goto done;
  }

  assert(gn >= 0);
  size_t n = gn;
  if (fb->buf[fb->sz - 1] == '\n') {
    // if the file has a trailing newline, we should ignore it. So we should
    // except one newline more
    n += 1;
  }

  ssize_t i;
  for (i = fb->sz - 1; i >= 0; i--) {
    if (fb->buf[i] == '\n') n--;
    if (n == 0) break;
  }

  if (i < 0) {
    // we haven't encountered the maximum of newlines, write everything
    fwrite(fb->buf, 1, fb->sz, stdout);
    goto done;
  }

  fwrite(fb->buf + i + 1, 1, fb->sz - i, stdout);

done:
  free_filebuf(fb);
  return 0;
}

int entry_staart(int argc, char **argv) {
  gn = 10;
  gc = -1;
  char **args = parse_options(argc, argv, &gn, &gc);
  return loop_files(args, process);
}