command_queue: implement command queue functions

Author: SidoShiro

src/utils/command_queue.c

@@ -0,0 +1,47 @@
+#include "command_queue.h"
+
+// Delete first command queue, return head
+struct command_queue *pop_command(struct command_queue *head) {
+    struct command_queue *new_head = NULL;
+    if (!head)
+        return NULL;
+    else if (!head->next) {
+        if (head->data)
+            free(head->data);
+        free(head);
+        return NULL;
+    } else {
+        new_head = head->next;
+        if (head->data)
+            free(head->data);
+        free(head);
+        return new_head;
+    }
+}
+
+// Push command in queue, return head, can have head=NULL for init queue
+struct command_queue *push_command(struct command_queue *head, struct command_queue *new_elt) {
+    if (!head) {
+        return new_elt;
+    }
+    struct command_queue *iter = head;
+    while (iter->next) {
+        iter = iter->next;
+    }
+    iter->next = new_elt;
+    return head;
+}
+
+// Get command queue data, you should known how to cast it
+void *peek_command(struct command_queue *head) {
+    if (head)
+        return head->data;
+    return NULL;
+}
+
+// Get user command enum of the first of the queue
+enum user_command peek_user_command(struct command_queue *head) {
+    if (head)
+        return head->command;
+    return NONE;
+}