#include "threads"
#include "assert"

#include <stddef.h>

#include <fstream>
 
static coroutine main_coroutine;
static coroutine* current_coroutine = &main_coroutine;

void ctxSwitchDirect(void* src, void* dst) {
	current_coroutine = dst;
}

coroutine* this_coroutine() {
	return current_coroutine;
}

void ?{}(coroutine* this)
{
	this->last = NULL;
      this->name = "A Coroutine";
      this->notHalted = true;
}

void suspend() {
      coroutine* src = this_coroutine();		// optimization

	assertf( src->last == (coroutine*)0, 
		"Attempt to suspend coroutine %.256s (%p) that has never been resumed.\n"
		"Possible cause is a suspend executed in a member called by a coroutine user rather than by the coroutine main.",
		src->name, src );
	assertf( src->last->notHalted, 
		"Attempt by coroutine %.256s (%p) to suspend back to terminated coroutine %.256s (%p).\n"
		"Possible cause is terminated coroutine's main routine has already returned.",
		src->name, src, src->last->name, src->last );

	ctxSwitchDirect( src, src->last );
}

forall(dtype T | coroutine_t(T))
void resume(T* cor) {
	coroutine* src = this_coroutine();		// optimization
	coroutine* dst = this_coroutine(cor);

	if ( src != dst ) {				// not resuming self ?
		assertf( dst->notHalted , 
			"Attempt by coroutine %.256s (%p) to resume terminated coroutine %.256s (%p).\n"
			"Possible cause is terminated coroutine's main routine has already returned.",
			src->name, src, dst->name, dst );
		dst->last = src;					// set last resumer
	} // if
	ctxSwitchDirect( src, dst );				// always done for performance testing
}