#include <c_LinkQueue.h>

// 原地初始化：无哨兵模式，初始化 head 和 tail 全部指向 0
c_err_t c_LinkQueue_Init(c_LinkQueue_t* self, c_size_t item_size, c_Allocator_t* allocator) {
    if (!self || item_size == 0) return C_ERR_PARAM;

    self->allocator = (allocator != NULL) ? *allocator : c_DefaultAllocator;
    self->item_size = item_size;
    self->size = 0;
    self->head = NULL;
    self->tail = NULL;

    return C_ERR_OK;
}

// 入队操作 (基于二级指针的完美 O(1) 极致分支优化)
c_err_t c_LinkQueue_Enqueue(c_LinkQueue_t* self, const void* item) {
    if (!self || !item) return C_ERR_PARAM;

    // 1. 分配变长节点空间 (控制壳 + 业务数据一体化)
    c_size_t total_bytes = sizeof(c_LinkQueueNode_t) + self->item_size;
    c_LinkQueueNode_t* new_node = (c_LinkQueueNode_t*)c_Allocator_Alloc(&self->allocator, total_bytes);
    if (!new_node) return C_ERR_NOMEM;

    new_node->next = NULL;
    memcpy(QUEUE_NODE_DATA(new_node), item, self->item_size); // 泛型值深度复制

    // 2. 【二级指针艺术】：消灭空队列插入的分支
    // 如果队列为空，新节点应该挂在 head 上；如果不为空，新节点应该挂在 tail->next 上
    c_LinkQueueNode_t** pp = (self->head == NULL) ? &(self->head) : &(self->tail->next);

    // 一行代码，完美完成旧拓扑到新节点的挂接
    *pp = new_node;

    // 3. 将尾指针直接移到最新插入的节点上，自愈性推进
    self->tail = new_node;
    self->size++;

    return C_ERR_OK;
}

// 出队操作 (O(1) 性能，完美防御下溢)
c_err_t c_LinkQueue_Dequeue(c_LinkQueue_t* self, void* out_item) {
    if (!self || self->size == 0 || !self->head) return C_ERR_OUTOFBOUND;

    // 锁定队头即将被剔除解体的物理节点
    c_LinkQueueNode_t* node_to_free = self->head;

    // 如果用户需要拷出快照副本，执行深度拷贝
    if (out_item) {
        memcpy(out_item, QUEUE_NODE_DATA(node_to_free), self->item_size);
    }

    // 队头指针向后大步滑进一格
    self->head = node_to_free->next;

    // 边界特殊维护：如果出队后队列彻底被掏空了，尾指针 tail 必须安全地缩回 NULL
    if (self->head == NULL) {
        self->tail = NULL;
    }

    // 闭环退还包装内存壳
    c_Allocator_Free(&self->allocator, node_to_free);
    self->size--;

    return C_ERR_OK;
}

// 查看队头元素 (只读原位窥探，零拷贝损耗)
void* c_LinkQueue_Peek(const c_LinkQueue_t* self) {
    if (!self || self->size == 0 || !self->head) return NULL;
    return QUEUE_NODE_DATA(self->head);
}

// 高效清空队列
void c_LinkQueue_Clear(c_LinkQueue_t* self) {
    if (!self) return;

    c_LinkQueueNode_t* curr = self->head;
    while (curr) {
        c_LinkQueueNode_t* next_to_free = curr->next;
        c_Allocator_Free(&self->allocator, curr);
        curr = next_to_free;
    }

    self->head = NULL;
    self->tail = NULL;
    self->size = 0;
}

// 彻底销毁
void c_LinkQueue_Destroy(c_LinkQueue_t* self) {
    if (!self) return;
    c_LinkQueue_Clear(self);
}