#include <assert.h>
#include <mmu.h>
#include <errno.h>
#include <x86.h>

#include <kern/syscall.h>
#include <kern/wait.h>
#include <kern/process.h>
#include <kern/pmap.h>
#include <kern/sche.h>
#include <kern/kmalloc.h>

/*
The wait() system call suspends execution of the calling thread
    until one of its children terminates. 
RETURN VALUE
on success, returns the process ID of the terminated child; 
on failure, -1 is returned.
! however the testwait.bin expects a valued return other than simply -1
*/
ssize_t
kern_wait(int *wstatus)
{
again:
	while (xchg(&p_proc_ready->pcb.lock, 1) == 1)
		schedule();
	PROCESS_0 *p_fa = &p_proc_ready->pcb;
	int child_pid = -1;
	struct son_node* p_son = p_fa->fork_tree.sons;
	if (p_son == NULL) {
		xchg(&p_fa->lock, 0);
		return -ECHILD;
	}
	assert(p_son->pre == NULL); // make sure it is the head of the list
/*
struct s_proc {
user_regs; // let it be
kern_regs; // let it be
lock;  // get and release before kfree
statu; // set to IDLE
pid; // keep it util return 
cr3; // let it be
page_list; // recycle it
exit_code; // set to wstatus
priority; // let it be
ticks; // let it be
fork_tree; // already cleared
};
*/
	while (p_son != NULL) {
		if (p_son->p_son->statu == ZOMBIE) {
			while (xchg(&p_son->p_son->lock, 1) == 1)
				schedule();
			// just use this value, which is '(status & 0xFF) << 8' in exit.c::do_exit
			if (wstatus != NULL)
				*wstatus = p_son->p_son->exit_code;
			// recycle_pages in pmap.c
			recycle_pages(p_son->p_son->page_list);
			// remove p_son from p_fa's son list
			if (p_son->pre != NULL) {
				p_son->pre->nxt = p_son->nxt;
			}
			else {
				p_fa->fork_tree.sons = p_son->nxt;
			}
			if (p_son->nxt != NULL) {
				p_son->nxt->pre = p_son->pre;
			}
			// keep p_son's pid for retval, 'cause the pointer will get freed before return
			child_pid = p_son->p_son->pid;
			kfree(p_son);
			// free it in proc table, 'cause in fork I judge free by statu
			xchg(&proc_table[child_pid].pcb.lock, 0);
			proc_table[child_pid].pcb.statu = IDLE; // ! set status be the last state, or die
			goto done;
		}
		p_son = p_son->nxt;
	}
	xchg(&p_fa->lock, 0);
	p_fa->statu = SLEEP; //! sleep after release lock, or it will deadlock
	schedule();
	goto again;
	// 接下来就是你自己的实现了，我们在设计的时候这段代码不会有太大问题
	// 在实现完后你任然要对自己来个灵魂拷问
	// 1. 上锁上了吗？所有临界情况都考虑到了吗？（永远要相信有各种奇奇怪怪的并发问题）
	// 2. 所有错误情况都判断到了吗？错误情况怎么处理？（RTFM->`man 2 wait`）
	// 3. 是否所有的资源都正确回收了？
	// 4. 你写的代码真的符合wait语义吗？
done:
	xchg(&p_fa->lock, 0);
	// panic("Unimplement! soul torture");
	return child_pid;
}

ssize_t
do_wait(int *wstatus)
{
	assert((uintptr_t)wstatus < KERNBASE);
	assert((uintptr_t)wstatus + sizeof(wstatus) < KERNBASE);
	return kern_wait(wstatus);
}