// Register a brand-new Obj-C class from sx and prove a sx-defined method
// actually runs when dispatched through `objc_msgSend`.
//
// The flow:
//   1. `objc_allocateClassPair(NSObject, "SxThing", 0)` returns an unregistered Class.
//   2. `class_addMethod(cls, sel_hello, IMP, "v@:")` attaches our sx function as
//      the `hello` method (type encoding "v@:" = void method(id self, SEL _cmd)).
//   3. `objc_registerClassPair(cls)` finalizes it.
//   4. `class_createInstance(cls, 0)` returns an `id` for a fresh instance.
//   5. typed-cast `objc_msgSend` for `void (id, SEL)` and dispatch `hello`.
// If the IMP ran, the global `g_marker` is non-zero and we return it as exit.

#import "modules/std.sx";
#import "modules/ffi/objc.sx";

g_marker : i32 = 0;

// IMP for `hello`. Must use C calling convention so `self` and `_cmd` land in
// x0 and x1 the way the Obj-C runtime expects.
hello_imp :: (self: *void, _cmd: *void) callconv(.c) {
    g_marker = 42;
}

main :: () -> i32 {
    NSObject := objc_getClass("NSObject".ptr);
    SxThing  := objc_allocateClassPair(NSObject, "SxThing".ptr, 0);
    sel_hello := sel_registerName("hello".ptr);

    ok := class_addMethod(SxThing, sel_hello, xx hello_imp, "v@:".ptr);
    if !ok { return 1; }
    objc_registerClassPair(SxThing);

    obj := class_createInstance(SxThing, 0);
    if obj == xx 0 { return 2; }

    // [obj hello]
    msg : (*void, *void) -> void callconv(.c) = xx objc_msgSend;
    msg(obj, sel_hello);

    return g_marker; // 42 if hello_imp ran
}