#include <mruby.h>
#include <mruby/class.h>
#include <mruby/string.h>
#include <mruby/array.h>
#include <mruby/proc.h>
#include <mruby/variable.h>
#include <mruby/internal.h>
#include <mruby/presym.h>

/*
 * Get the name of a module/class.
 *
 * Returns the fully qualified name of the module/class as a frozen string.
 * If the module/class is anonymous, returns nil.
 *
 * Args:
 *   mrb:  The mruby state
 *   self: The module/class object
 *
 * Returns:
 *   String: The name of the module/class (frozen)
 *   nil:    If the module/class is anonymous
 */
static mrb_value
mod_name(mrb_state *mrb, mrb_value self)
{
  mrb_value name =  mrb_class_path(mrb, mrb_class_ptr(self));
  if (mrb_string_p(name)) {
    mrb_basic_ptr(name)->frozen = 1;
  }
  return name;
}

/*
 * Check if a module/class is a singleton class.
 *
 * Args:
 *   mrb:  The mruby state
 *   self: The module/class object to check
 *
 * Returns:
 *   true:  if the object is a singleton class
 *   false: if the object is not a singleton class
 */
static mrb_value
mod_singleton_class_p(mrb_state *mrb, mrb_value self)
{
  return mrb_bool_value(mrb_sclass_p(self));
}

/*
 *  call-seq:
 *     module_exec(arg...) {|var...| block } -> obj
 *     class_exec(arg...) {|var...| block } -> obj
 *
 * Evaluates the given block in the context of the
 * class/module. The method defined in the block will belong
 * to the receiver. Any arguments passed to the method will be
 * passed to the block. This can be used if the block needs to
 * access instance variables.
 *
 *     class Thing
 *     end
 *     Thing.class_exec{
 *       def hello() "Hello there!" end
 *     }
 *     puts Thing.new.hello()
 */

static mrb_value
mod_module_exec(mrb_state *mrb, mrb_value self)
{
  return mrb_object_exec(mrb, self, mrb_class_ptr(self));
}

/* Helper structure for subclass enumeration */
struct subclass_args {
  struct RClass *c;   /* The parent class to find subclasses of */
  mrb_value ary;      /* Array to collect subclasses into */
};

/*
 * Callback function for mrb_objspace_each_objects to find direct subclasses.
 *
 * This function is called for each object in the object space. It checks if
 * the object is a class whose direct superclass matches the target class.
 *
 * Args:
 *   mrb:  The mruby state
 *   obj:  The current object being examined
 *   data: Pointer to subclass_args structure
 *
 * Returns:
 *   MRB_EACH_OBJ_OK: Continue iteration
 */
static int
add_subclasses(mrb_state *mrb, struct RBasic *obj, void *data)
{
  struct subclass_args *args = (struct subclass_args*)data;
  if (obj->tt == MRB_TT_CLASS) {
    struct RClass *c = (struct RClass*)obj;
    if (mrb_class_real(c->super) == args->c) {
      mrb_ary_push(mrb, args->ary, mrb_obj_value(obj));
    }
  }
  return MRB_EACH_OBJ_OK;
}

/*
 *  call-seq:
 *     subclasses -> array
 *
 *  Returns an array of classes where the receiver is the
 *  direct superclass of the class, excluding singleton classes.
 *  The order of the returned array is not defined.
 *
 *     class A; end
 *     class B < A; end
 *     class C < B; end
 *     class D < A; end
 *
 *     A.subclasses        #=> [D, B]
 *     B.subclasses        #=> [C]
 *     C.subclasses        #=> []
 */
static mrb_value
class_subclasses(mrb_state *mrb, mrb_value self)
{
  struct RClass *c = mrb_class_ptr(self);
  mrb_value ary = mrb_ary_new(mrb);

  if (c->flags & MRB_FL_CLASS_IS_INHERITED) {
    struct subclass_args arg = {c, ary};
    mrb_objspace_each_objects(mrb, add_subclasses, &arg);
  }
  return ary;
}

/*
 *  call-seq:
 *     attached_object -> object
 *
 *  Returns the object for which the receiver is the singleton class.
 *  Raises an TypeError if the class is not a singleton class.
 *
 *     class Foo; end
 *
 *     Foo.singleton_class.attached_object        #=> Foo
 *     Foo.attached_object                        #=> TypeError: not a singleton class
 *     Foo.new.singleton_class.attached_object    #=> #<Foo:0x000000010491a370>
 *     TrueClass.attached_object                  #=> TypeError: not a singleton class
 *     NilClass.attached_object                   #=> TypeError: not a singleton class
 */
static mrb_value
class_attached_object(mrb_state *mrb, mrb_value self)
{
  struct RClass *c = mrb_class_ptr(self);
  if (c->tt != MRB_TT_SCLASS) {
    mrb_raise(mrb, E_TYPE_ERROR, "not a singleton class");
  }
  return mrb_obj_iv_get(mrb, (struct RObject*)c, MRB_SYM(__attached__));
}

/*
 * Check if a class/module is an ancestor of another.
 *
 * This function traverses the inheritance chain of `klass` upwards to determine
 * if `super` appears anywhere in the hierarchy. It handles both regular classes/modules
 * and included classes (ICLASS) which represent modules included in the inheritance chain.
 *
 * Args:
 *   klass: The class/module to check (potential descendant)
 *   super: The class/module to search for (potential ancestor)
 *
 * Returns:
 *   true:  if `super` is found in `klass`'s inheritance chain
 *   false: if `super` is not an ancestor of `klass`
 */
static mrb_bool
is_ancestor(struct RClass *klass, struct RClass *super)
{
  struct RClass *c = klass;
  while (c) {
    if (c->tt == MRB_TT_ICLASS) {
      if (c->c == super) return TRUE;
    }
    else {
      if (c == super) return TRUE;
    }
    c = c->super;
  }
  return FALSE;
}

/*
 * Compare hierarchy relationship between two modules/classes.
 *
 * This function determines the ancestor relationship between `self` and `other`.
 * It checks if one is an ancestor of the other by traversing the inheritance chain.
 *
 * Args:
 *   mrb:   The mruby state
 *   self:  The first module/class to compare
 *   other: The second module/class to compare
 *
 * Returns:
 *   true:  if `self` is an ancestor of `other` (self > other)
 *   false: if `other` is an ancestor of `self` (self < other)
 *   nil:   if there's no inheritance relationship between them
 *
 * Raises:
 *   TypeError: if `other` is not a class, module, or included class
 */
static mrb_value
mod_compare_hierarchy(mrb_state *mrb, mrb_value self, mrb_value other)
{
  if (!mrb_class_p(other) && !mrb_module_p(other) && !mrb_iclass_p(other)) {
    mrb_raise(mrb, E_TYPE_ERROR, "compared with non class/module");
  }

  struct RClass *self_c = mrb_class_ptr(self);
  struct RClass *other_c = mrb_class_ptr(other);

  if (is_ancestor(self_c, other_c)) {
    return mrb_true_value();
  }
  if (is_ancestor(other_c, self_c)) {
    return mrb_false_value();
  }
  return mrb_nil_value();
}

/*
 *  call-seq:
 *     mod <= other   -> true, false, or nil
 *
 *  Returns true if mod is a subclass of other or is the same as other.
 *  Returns nil if there's no relationship between the two.
 */
static mrb_value
mrb_mod_le(mrb_state *mrb, mrb_value self)
{
  mrb_value other;
  mrb_get_args(mrb, "o", &other);
  return mod_compare_hierarchy(mrb, self, other);
}

/*
 *  call-seq:
 *     mod < other   -> true, false, or nil
 *
 *  Returns true if mod is a subclass of other. Returns false if mod
 *  is the same as other. Returns nil if there's no relationship between the two.
 */
static mrb_value
mrb_mod_lt(mrb_state *mrb, mrb_value self)
{
  mrb_value other;
  mrb_get_args(mrb, "o", &other);
  if (mrb_obj_equal(mrb, self, other)) {
    return mrb_false_value();
  }
  return mod_compare_hierarchy(mrb, self, other);
}

/*
 *  call-seq:
 *     mod >= other   -> true, false, or nil
 *
 *  Returns true if mod is an ancestor of other, or the two modules are the same.
 *  Returns nil if there's no relationship between the two.
 */
static mrb_value
mrb_mod_ge(mrb_state *mrb, mrb_value self)
{
  mrb_value other;
  mrb_get_args(mrb, "o", &other);
  return mod_compare_hierarchy(mrb, other, self);
}

/*
 *  call-seq:
 *     mod > other   -> true, false, or nil
 *
 *  Returns true if mod is an ancestor of other. Returns false if mod
 *  is the same as other. Returns nil if there's no relationship between the two.
 */
static mrb_value
mrb_mod_gt(mrb_state *mrb, mrb_value self)
{
  mrb_value other;
  mrb_get_args(mrb, "o", &other);
  if (mrb_obj_equal(mrb, self, other)) {
    return mrb_false_value();
  }
  return mod_compare_hierarchy(mrb, other, self);
}

/*
 *  call-seq:
 *     module <=> other_module   -> -1, 0, +1, or nil
 *
 *  Comparison - Returns -1, 0, +1 or nil depending on whether module
 *  includes other_module, they are the same, or if module is included by
 *  other_module.
 *
 *  Returns nil if module has no relationship with other_module, if
 *  other_module is not a module, or if the two values are incomparable.
 */
static mrb_value
mrb_mod_cmp(mrb_state *mrb, mrb_value self)
{
  mrb_value other;
  mrb_get_args(mrb, "o", &other);

  if (mrb_obj_equal(mrb, self, other)) {
    return mrb_fixnum_value(0);
  }
  if (!mrb_class_p(other) && !mrb_module_p(other) && !mrb_iclass_p(other)) {
    return mrb_nil_value();
  }

  mrb_value cmp = mod_compare_hierarchy(mrb, self, other);

  if (mrb_true_p(cmp)) {
    return mrb_fixnum_value(-1);
  }
  else if (mrb_false_p(cmp)) {
    return mrb_fixnum_value(1);
  }
  else {
    return mrb_nil_value();
  }
}

/*
 * Initialize the mruby-class-ext gem.
 *
 * This function registers all the extension methods to the Module and Class classes.
 * It's called automatically when the gem is loaded.
 *
 * Args:
 *   mrb: The mruby state
 */
void
mrb_mruby_class_ext_gem_init(mrb_state *mrb)
{
  struct RClass *mod = mrb->module_class;

  /* Module methods */
  mrb_define_method_id(mrb, mod, MRB_SYM(name), mod_name, MRB_ARGS_NONE());
  mrb_define_method_id(mrb, mod, MRB_SYM_Q(singleton_class), mod_singleton_class_p, MRB_ARGS_NONE());
  mrb_define_method_id(mrb, mod, MRB_SYM(module_exec), mod_module_exec, MRB_ARGS_ANY()|MRB_ARGS_BLOCK());
  mrb_define_method_id(mrb, mod, MRB_SYM(class_exec), mod_module_exec, MRB_ARGS_ANY()|MRB_ARGS_BLOCK());

  /* Module comparison operators */
  mrb_define_method_id(mrb, mod, MRB_OPSYM(lt), mrb_mod_lt, MRB_ARGS_REQ(1));
  mrb_define_method_id(mrb, mod, MRB_OPSYM(le), mrb_mod_le, MRB_ARGS_REQ(1));
  mrb_define_method_id(mrb, mod, MRB_OPSYM(gt), mrb_mod_gt, MRB_ARGS_REQ(1));
  mrb_define_method_id(mrb, mod, MRB_OPSYM(ge), mrb_mod_ge, MRB_ARGS_REQ(1));
  mrb_define_method_id(mrb, mod, MRB_OPSYM(cmp), mrb_mod_cmp, MRB_ARGS_REQ(1));

  /* Class-specific methods */
  struct RClass *cls = mrb->class_class;
  mrb_define_method_id(mrb, cls, MRB_SYM(subclasses), class_subclasses, MRB_ARGS_NONE());
  mrb_define_method_id(mrb, cls, MRB_SYM(attached_object), class_attached_object, MRB_ARGS_NONE());
}

void
mrb_mruby_class_ext_gem_final(mrb_state *mrb)
{
}