#include "ruby.h"
#include <krb5.h>
#include <stdio.h>
#include <strings.h>

static VALUE mKerberos;
static VALUE cTicket;
static VALUE cException;

struct ruby_krb5 {
  krb5_context ctx;
  krb5_creds creds;
  krb5_principal princ;
};

#define OOM_EXCEPT() rb_raise(cException, "%s", "Error mallocing memory");
#define NOSTRUCT_EXCEPT() rb_raise(cException, "%s", "Class not initialized properly (try 'new')");

void Krb5_register_error(int error) {
  rb_raise(cException, "%s", error_message(error));
}

static void kerb_free(void *p) {
  struct ruby_krb5 *kerb;

  if (!p) return;

  kerb = (struct ruby_krb5 *)p;

  // kerb->creds is not a pointer, so we can't check for NULL; however, the
  // implementation of krb5_free_cred_contents does do NULL checking, so it
  // is safe (at least in the MIT version) to call it unconditionally
  krb5_free_cred_contents(kerb->ctx, &kerb->creds);
  if (kerb->princ)
    krb5_free_principal(kerb->ctx, kerb->princ);
  if (kerb->ctx)
    krb5_free_context(kerb->ctx);
  memset(kerb, 0, sizeof(struct ruby_krb5));
  free(kerb);
}

static VALUE Ticket_alloc(VALUE klass) {
  struct ruby_krb5 *kerb;
  krb5_error_code krbret;

  kerb = (struct ruby_krb5 *)malloc(sizeof(struct ruby_krb5));
  if (kerb == NULL) {
    OOM_EXCEPT();
    return Qnil;
  }

  memset(kerb, 0, sizeof(struct ruby_krb5));

  krbret = krb5_init_context(&kerb->ctx);
  if (krbret) {
    Krb5_register_error(krbret);
    return Qnil;
  }

  return Data_Wrap_Struct(klass, NULL, kerb_free, kerb);
}

static VALUE Ticket_initialize(VALUE self, VALUE _user, VALUE _realm) {
  VALUE user = StringValue(_user);
  VALUE realm = StringValue(_realm);

  rb_iv_set(self, "@user", user);
  rb_iv_set(self, "@realm", realm);

  return Qnil;
}

static VALUE Ticket_kerberos_name(VALUE self) {
  VALUE user = rb_iv_get(self, "@user");
  VALUE realm = rb_iv_get(self, "@realm");

  return rb_str_concat(
      rb_str_concat(
        user, rb_str_new2("@")),
      realm);
}

static VALUE Ticket_authenticate(VALUE self, VALUE _pass) {
  char *user = StringValueCStr(Ticket_kerberos_name(self));
  char *pass = StringValueCStr(_pass);

  struct ruby_krb5 *kerb;
  krb5_error_code krbret;

  Data_Get_Struct(self, struct ruby_krb5, kerb);
  if (!kerb) {
    NOSTRUCT_EXCEPT();
    return Qfalse;
  }

  krbret = krb5_parse_name(kerb->ctx, user, &kerb->princ);
  if (krbret) {
    goto failed_pass;
  }

  krbret = krb5_get_init_creds_password(kerb->ctx, &kerb->creds, kerb->princ,
      pass, 0, NULL, 0, NULL, NULL);

  if (krbret) {
    goto failed_pass;
  }

  return Qtrue;

failed_pass:
  Krb5_register_error(krbret);
  return Qfalse;
}

void Init_krb5() {
  mKerberos = rb_define_module("Kerberos");
  cTicket = rb_define_class_under(mKerberos, "Ticket", rb_cObject);
  cException = rb_define_class_under(mKerberos, "Exception", rb_eStandardError);

  rb_define_alloc_func(cTicket, Ticket_alloc);
  rb_define_method(cTicket, "kerberos_name", Ticket_kerberos_name, 0);
  rb_define_method(cTicket, "authenticate", Ticket_authenticate, 2);
}