#include "list.h"
#include "interrupt.h"

/* 初始化双向链表list */
void list_init (struct list* list) {
   list->head.prev = NULL;
   list->head.next = &list->tail;
   list->tail.prev = &list->head;
   list->tail.next = NULL;
}

/* 把链表元素elem插入在元素before之前 */
void list_insert_before(struct list_elem* before, struct list_elem* elem) { 
   enum intr_status old_status = intr_disable();

/* 将before前驱元素的后继元素更新为elem, 暂时使before脱离链表*/ 
   before->prev->next = elem; 

/* 更新elem自己的前驱结点为before的前驱,
 * 更新elem自己的后继结点为before, 于是before又回到链表 */
   elem->prev = before->prev;
   elem->next = before;

/* 更新before的前驱结点为elem */
   before->prev = elem;

   intr_set_status(old_status);
}

/* 添加元素到列表队首,类似栈push操作 */
void list_push(struct list* plist, struct list_elem* elem) {
   list_insert_before(plist->head.next, elem); // 在队头插入elem
}

/* 追加元素到链表队尾,类似队列的先进先出操作 */
void list_append(struct list* plist, struct list_elem* elem) {
   list_insert_before(&plist->tail, elem);     // 在队尾的前面插入
}

/* 使元素pelem脱离链表 */
void list_remove(struct list_elem* pelem) {
   enum intr_status old_status = intr_disable();
   
   pelem->prev->next = pelem->next;
   pelem->next->prev = pelem->prev;

   intr_set_status(old_status);
}

/* 将链表第一个元素弹出并返回,类似栈的pop操作 */
struct list_elem* list_pop(struct list* plist) {
   struct list_elem* elem = plist->head.next;
   list_remove(elem);
   return elem;
} 

/* 从链表中查找元素obj_elem,成功时返回true,失败时返回false */
bool elem_find(struct list* plist, struct list_elem* obj_elem) {
   struct list_elem* elem = plist->head.next;
   while (elem != &plist->tail) {
      if (elem == obj_elem) {
	 return true;
      }
      elem = elem->next;
   }
   return false;
}

/* 把列表plist中的每个元素elem和arg传给回调函数func,
 * arg给func用来判断elem是否符合条件.
 * 本函数的功能是遍历列表内所有元素,逐个判断是否有符合条件的元素。
 * 找到符合条件的元素返回元素指针,否则返回NULL. */
struct list_elem* list_traversal(struct list* plist, function func, int arg) {
   struct list_elem* elem = plist->head.next;
/* 如果队列为空,就必然没有符合条件的结点,故直接返回NULL */
   if (list_empty(plist)) { 
      return NULL;
   }

   while (elem != &plist->tail) {
      if (func(elem, arg)) {		  // func返回ture则认为该元素在回调函数中符合条件,命中,故停止继续遍历
	 return elem;
      }					  // 若回调函数func返回true,则继续遍历
      elem = elem->next;	       
   }
   return NULL;
}

/* 返回链表长度 */
uint32_t list_len(struct list* plist) {
   struct list_elem* elem = plist->head.next;
   uint32_t length = 0;
   while (elem != &plist->tail) {
      length++; 
      elem = elem->next;
   }
   return length;
}

/* 判断链表是否为空,空时返回true,否则返回false */
bool list_empty(struct list* plist) {		// 判断队列是否为空
   return (plist->head.next == &plist->tail ? true : false);
}