/* :nodoc: */
static VALUE
enumerator_init_copy(VALUE obj, SEL sel, VALUE orig)
{
    struct enumerator *ptr0, *ptr1;

    ptr0 = enumerator_ptr(orig);
    if (ptr0->fib) {
	/* Fibers cannot be copied */
	rb_raise(rb_eTypeError, "can't copy execution context");
    }

    Data_Get_Struct(obj, struct enumerator, ptr1);

    if (!ptr1) {
	rb_raise(rb_eArgError, "unallocated enumerator");
    }

    GC_WB(&ptr1->obj, ptr0->obj);
    ptr1->sel = ptr0->sel;
    if (ptr0->args != 0) {
	GC_WB(&ptr1->args, ptr0->args);
    }
    ptr1->fib  = 0;

    return obj;
}

/* :nodoc: */
static VALUE
enumerator_init_copy(VALUE obj, VALUE orig)
{
    struct enumerator *ptr0, *ptr1;

    if (!OBJ_INIT_COPY(obj, orig)) return obj;
    ptr0 = enumerator_ptr(orig);
    if (ptr0->fib) {
	/* Fibers cannot be copied */
	rb_raise(rb_eTypeError, "can't copy execution context");
    }

    TypedData_Get_Struct(obj, struct enumerator, &enumerator_data_type, ptr1);

    if (!ptr1) {
	rb_raise(rb_eArgError, "unallocated enumerator");
    }

    ptr1->obj  = ptr0->obj;
    ptr1->meth = ptr0->meth;
    ptr1->args = ptr0->args;
    ptr1->fib  = 0;
    ptr1->lookahead  = Qundef;
    ptr1->feedvalue  = Qundef;
    ptr1->size  = ptr0->size;
    ptr1->size_fn  = ptr0->size_fn;

    return obj;
}

static VALUE
enumerator_rewind(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);

    e->fib = 0;
    e->dst = Qnil;
    e->no_next = Qfalse;
    return obj;
}

static VALUE
enumerator_peek_values(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);

    if (e->lookahead == Qundef) {
        e->lookahead = get_next_values(obj, e);
    }
    return e->lookahead;
}

/* :nodoc: */
static VALUE
enumerator_init_copy(VALUE obj, VALUE orig)
{
    struct enumerator *ptr0, *ptr1;

    ptr0 = enumerator_ptr(orig);
    if (ptr0->fib) {
	/* Fibers cannot be copied */
	rb_raise(rb_eTypeError, "can't copy execution context");
    }
    ptr1 = enumerator_ptr(obj);

    ptr1->obj  = ptr0->obj;
    ptr1->meth = ptr0->meth;
    ptr1->args = ptr0->args;
    ptr1->fib  = 0;

    return obj;
}

static VALUE
next_i(VALUE curr, VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);
    VALUE nil = Qnil;
    VALUE result;

    result = rb_block_call(obj, id_each, 0, 0, next_ii, obj);
    e->stop_exc = rb_exc_new2(rb_eStopIteration, "iteration reached an end");
    rb_ivar_set(e->stop_exc, id_result, result);
    return rb_fiber_yield(1, &nil);
}

static VALUE
enumerator_feed(VALUE obj, VALUE v)
{
    struct enumerator *e = enumerator_ptr(obj);

    if (e->feedvalue != Qundef) {
	rb_raise(rb_eTypeError, "feed value already set");
    }
    e->feedvalue = v;

    return Qnil;
}

static VALUE
next_ii(VALUE i, VALUE obj, int argc, VALUE *argv)
{
    struct enumerator *e = enumerator_ptr(obj);
    VALUE feedvalue = Qnil;
    VALUE args = rb_ary_new4(argc, argv);
    rb_fiber_yield(1, &args);
    if (e->feedvalue != Qundef) {
        feedvalue = e->feedvalue;
        e->feedvalue = Qundef;
    }
    return feedvalue;
}

static VALUE
enumerator_next_values(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);
    VALUE vs;

    if (e->lookahead != Qundef) {
        vs = e->lookahead;
        e->lookahead = Qundef;
        return vs;
    }

    return get_next_values(obj, e);
}

static VALUE
enumerator_block_call(VALUE obj, rb_block_call_func *func, VALUE arg)
{
    int argc = 0;
    VALUE *argv = 0;
    const struct enumerator *e = enumerator_ptr(obj);
    ID meth = e->meth;

    if (e->args) {
	argc = RARRAY_LENINT(e->args);
	argv = RARRAY_PTR(e->args);
    }
    return rb_block_call(e->obj, meth, argc, argv, func, arg);
}

static VALUE
enumerator_rewind(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);

    rb_check_funcall(e->obj, id_rewind, 0, 0);

    e->fib = 0;
    e->dst = Qnil;
    e->lookahead = Qundef;
    e->feedvalue = Qundef;
    e->stop_exc = Qfalse;
    return obj;
}

static VALUE
enumerator_init(VALUE enum_obj, VALUE obj, VALUE meth, int argc, VALUE *argv)
{
    struct enumerator *ptr = enumerator_ptr(enum_obj);

    ptr->obj  = obj;
    ptr->meth = rb_to_id(meth);
    if (argc) GC_WB(&ptr->args, rb_ary_new4(argc, argv));
    ptr->fib = 0;
    ptr->dst = Qnil;
    ptr->no_next = Qfalse;

    return enum_obj;
}

/*
 * call-seq:
 *   obj.to_enum(method = :each, *args)                 -> enum
 *   obj.enum_for(method = :each, *args)                -> enum
 *   obj.to_enum(method = :each, *args) {|*args| block} -> enum
 *   obj.enum_for(method = :each, *args){|*args| block} -> enum
 *
 * Creates a new Enumerator which will enumerate by calling +method+ on
 * +obj+, passing +args+ if any.
 *
 * If a block is given, it will be used to calculate the size of
 * the enumerator without the need to iterate it (see Enumerator#size).
 *
 * === Examples
 *
 *   str = "xyz"
 *
 *   enum = str.enum_for(:each_byte)
 *   enum.each { |b| puts b }
 *   # => 120
 *   # => 121
 *   # => 122
 *
 *   # protect an array from being modified by some_method
 *   a = [1, 2, 3]
 *   some_method(a.to_enum)
 *
 * It is typical to call to_enum when defining methods for
 * a generic Enumerable, in case no block is passed.
 *
 * Here is such an example, with parameter passing and a sizing block:
 *
 *   module Enumerable
 *     # a generic method to repeat the values of any enumerable
 *     def repeat(n)
 *       raise ArgumentError, "#{n} is negative!" if n < 0
 *       unless block_given?
 *         return to_enum(__method__, n) do # __method__ is :repeat here
 *           sz = size     # Call size and multiply by n...
 *           sz * n if sz  # but return nil if size itself is nil
 *         end
 *       end
 *       each do |*val|
 *         n.times { yield *val }
 *       end
 *     end
 *   end
 *
 *   %i[hello world].repeat(2) { |w| puts w }
 *     # => Prints 'hello', 'hello', 'world', 'world'
 *   enum = (1..14).repeat(3)
 *     # => returns an Enumerator when called without a block
 *   enum.first(4) # => [1, 1, 1, 2]
 *   enum.size # => 42
 */
static VALUE
obj_to_enum(int argc, VALUE *argv, VALUE obj)
{
    VALUE enumerator, meth = sym_each;

    if (argc > 0) {
	--argc;
	meth = *argv++;
    }
    enumerator = rb_enumeratorize_with_size(obj, meth, argc, argv, 0);
    if (rb_block_given_p()) {
	enumerator_ptr(enumerator)->size = rb_block_proc();
    }
    return enumerator;
}

static VALUE
enumerator_block_call(VALUE obj, VALUE (*func)(ANYARGS), VALUE arg)
{
    struct enumerator *e;
    int argc = 0;
    const VALUE *argv = 0;

    e = enumerator_ptr(obj);
    if (e->args != 0) {
	argc = RARRAY_LEN(e->args);
	argv = RARRAY_PTR(e->args);
    }
    return rb_objc_block_call(e->obj, e->sel, argc, (VALUE *)argv,
	    func, arg);
}

/*
 *  call-seq:
 *    enum.each {...}
 *
 *  Iterates the given block using the object and the method specified
 *  in the first place.
 *
 */
static VALUE
enumerator_each(VALUE obj)
{
    struct enumerator *e;
    int argc = 0;
    VALUE *argv = 0;

    if (!rb_block_given_p()) return obj;
    e = enumerator_ptr(obj);
    if (e->args) {
	argc = RARRAY_LEN(e->args);
	argv = RARRAY_PTR(e->args);
    }
    return rb_block_call(e->method, SYM2ID(sym_call), argc, argv, e->iter, (VALUE)e);
}

static VALUE
lazy_to_enum(int argc, VALUE *argv, VALUE self)
{
    VALUE lazy, meth = sym_each;

    if (argc > 0) {
	--argc;
	meth = *argv++;
    }
    lazy = lazy_to_enum_i(self, meth, argc, argv, 0);
    if (rb_block_given_p()) {
	enumerator_ptr(lazy)->size = rb_block_proc();
    }
    return lazy;
}

/*
 *  call-seq:
 *    e.with_index {|(*args), idx| ... }
 *
 *  Iterates the given block for each elements with an index, which
 *  start from 0.
 *
 */
static VALUE
enumerator_with_index(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);
    VALUE memo = 0;
    int argc = 0;
    VALUE *argv = 0;

    RETURN_ENUMERATOR(obj, 0, 0);
    if (e->args) {
	argc = RARRAY_LEN(e->args);
	argv = RARRAY_PTR(e->args);
    }
    return rb_block_call(e->method, SYM2ID(sym_call), argc, argv,
			 enumerator_with_index_i, (VALUE)&memo);
}

static VALUE
enumerator_size(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);

    if (e->size_fn) {
	return (*e->size_fn)(e->obj, e->args, obj);
    }
    if (rb_obj_is_proc(e->size)) {
        if (e->args)
	    return rb_proc_call(e->size, e->args);
        else
            return rb_proc_call_with_block(e->size, 0, 0, Qnil);
    }
    return e->size;
}

static VALUE
lazy_set_method(VALUE lazy, VALUE args, rb_enumerator_size_func *size_fn)
{
    ID id = rb_frame_this_func();
    struct enumerator *e = enumerator_ptr(lazy);
    rb_ivar_set(lazy, id_method, ID2SYM(id));
    if (NIL_P(args)) {
	/* Qfalse indicates that the arguments are empty */
	rb_ivar_set(lazy, id_arguments, Qfalse);
    }
    else {
	rb_ivar_set(lazy, id_arguments, args);
    }
    e->size_fn = size_fn;
    return lazy;
}

/*
 * call-seq:
 *   enum.each {...}
 *
 * Iterates over the block according to how this Enumerable was constructed.
 * If no block is given, returns self.
 *
 */
static VALUE
enumerator_each(int argc, VALUE *argv, VALUE obj)
{
    if (argc > 0) {
	struct enumerator *e = enumerator_ptr(obj = rb_obj_dup(obj));
	VALUE args = e->args;
	if (args) {
	    args = rb_ary_dup(args);
	    rb_ary_cat(args, argv, argc);
	}
	else {
	    args = rb_ary_new4(argc, argv);
	}
	e->args = args;
    }
    if (!rb_block_given_p()) return obj;
    return enumerator_block_call(obj, 0, obj);
}