/* 
lemon, an example C application using embedded Guile. 
Copyright (C) 2025  Nikolaos Chatzikonstantinou

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libguile.h>

struct pin {
  char digits[6];
  size_t len;
};

void help(void) {
  printf("\n");
  printf("Welcome to the lemon PIN app.\n");
  printf("You may enter your 6-digit PIN number.\n");
  printf("You can also enter the following commands:\n");
  printf("\t- b, go back one digit.\n");
  printf("\t- c, clear all of the input.\n");
  printf("\t- :, enter a unary Guile expression to process the PIN further.\n");
  printf("\t- q, quit the app.\n");
  printf("\t- ?, this help screen.\n");
  printf("\n");
}

void print_pin(const struct pin *pin) {
  size_t i = 0;
  printf("----------PIN----------\n");
  while(i < pin->len) {
    printf("[%hhd]%c", pin->digits[i], i + 1 < 6 ? ' ' : '\n');
    ++i;
  }
  while(i < 6) {
    printf("[ ]%c", i + 1 < 6 ? ' ' : '\n');
    ++i;
  }
  printf("-----------------------\n\n");
}

void *entry(void *data) {
  static int ret;
  struct pin *pin = data;
  char buf[BUFSIZ];
  SCM pin_lisp, proc;
  size_t i;
  pin->len = 0;
  int c = 0;
  while(c != EOF && c != 'q') {
    print_pin(pin);
    printf("Enter PIN (? for help): ");
    fflush(stdout);
    do {
      c = getchar();
      if(c == EOF || c == 'q') {
        break;
      } else if(isdigit(c) && pin->len < sizeof pin->digits) {
        pin->digits[pin->len] = c - '0';
        pin->len += 1;
      } else if(c == '?') {
        help();
      } else if(c == 'b' && pin->len > 0) {
        pin->len -= 1;
      } else if(c == 'c') {
        pin->len = 0;
      } else if(c == ':') {
        if(fgets(buf, sizeof buf, stdin)) {
          i = strlen(buf);
          if(i > 0 && buf[i-1] == '\n') {
            buf[i-1] = 0;
            ungetc('\n', stdin);
          }
          proc = scm_c_eval_string(buf);
          pin_lisp = scm_make_u8vector(scm_from_size_t(pin->len), SCM_UNDEFINED);
          for(i = 0; i < pin->len; ++i) {
            scm_u8vector_set_x(pin_lisp, scm_from_size_t(i), scm_from_char(pin->digits[i]));
          }
          pin_lisp = scm_u8vector_to_list(pin_lisp);
          pin_lisp = scm_call_1(proc, pin_lisp);
          pin->len = scm_to_size_t(scm_length(pin_lisp));
          if(pin->len > 6) {
            pin->len = 6;
          }
          for(i = 0; i < pin->len; ++i) {
            pin->digits[i] = scm_to_char(scm_list_ref(pin_lisp, scm_from_size_t(i)));
          }
        } else {
          c = EOF;
          break;
        }
      }
    } while(c != '\n');
  }
  ret = ferror(stdin) ? EXIT_FAILURE : EXIT_SUCCESS;
  return &ret;
}

int main(void) {
  struct pin pin;
  int *ret = scm_with_guile(entry, &pin);
  return *ret;
}