From 5ebab24637b744f51ff95fbc4c25908d1db00ffd Mon Sep 17 00:00:00 2001
From: Matthias Kruk <m@m10k.eu>
Date: Tue, 4 May 2021 06:18:24 +0900
Subject: [PATCH] loop: Add cyclic list type

Since we will often cycle through monitors, workspaces, and clients, it
would be beneficial to have a data structure that assists with that.
This commit adds the loop type, which implements a cyclic doubly-linked
list.
---
 loop.c | 150 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 loop.h |  12 +++++
 2 files changed, 162 insertions(+)
 create mode 100644 loop.c
 create mode 100644 loop.h

diff --git a/loop.c b/loop.c
new file mode 100644
index 0000000..19379cd
--- /dev/null
+++ b/loop.c
@@ -0,0 +1,150 @@
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include "loop.h"
+
+struct loop {
+        struct loop *prev;
+        struct loop *next;
+        void *data;
+};
+
+int loop_append(struct loop **loop, void *data)
+{
+	struct loop *new;
+
+	if(!loop) {
+		return(-EINVAL);
+	}
+
+	new = malloc(sizeof(*new));
+
+	if(!new) {
+		return(-ENOMEM);
+	}
+
+	new->data = data;
+	new->prev = new;
+	new->next = new;
+
+        if(*loop) {
+		new->prev = (*loop)->prev;
+		(*loop)->prev = new;
+		new->prev->next = new;
+		new->next = *loop;
+	} else {
+		*loop = new;
+	}
+
+	return(0);
+}
+
+int loop_prepend(struct loop **loop, void *data)
+{
+	struct loop *new;
+
+	if(!loop) {
+		return(-EINVAL);
+	}
+
+	new = malloc(sizeof(*new));
+
+	if(!new) {
+		return(-ENOMEM);
+	}
+
+	new->data = data;
+	new->prev = new;
+	new->next = new;
+
+	if(*loop) {
+		new->prev = (*loop)->prev;
+		(*loop)->prev = new;
+		new->prev->next = new;
+		new->next = *loop;
+	}
+
+	*loop = new;
+
+	return(0);
+}
+
+int loop_remove(struct loop **loop, void *data)
+{
+	struct loop *elem;
+
+	if(!loop) {
+		return(-EINVAL);
+	}
+
+	if(loop_find(loop, NULL, data, (void**)&elem) < 0) {
+		return(-ENOENT);
+	}
+
+	elem->next->prev = elem->prev;
+	elem->prev->next = elem->next;
+
+	if(*loop == elem) {
+	        if(elem == elem->prev) {
+			*loop = NULL;
+		} else {
+			*loop = elem->prev;
+		}
+	}
+
+	free(elem);
+
+	return(0);
+}
+
+int _cmp_ptr(void *left, void *right)
+{
+	return(left == right);
+}
+
+int loop_find(struct loop **loop, int (*cmp)(void*, void*), void *data, void **dst)
+{
+	struct loop *cur;
+
+	if(!loop) {
+		return(-EINVAL);
+	}
+
+	if(!*loop) {
+		return(-ENOENT);
+	}
+
+	if(!cmp) {
+		cmp = _cmp_ptr;
+	}
+	cur = *loop;
+
+        do {
+                if(cmp(cur->data, data) == 0) {
+			*dst = data;
+			return(0);
+                }
+
+                cur = cur->next;
+        } while(cur != *loop);
+
+	return(-ENOENT);
+}
+
+int loop_free(struct loop **loop)
+{
+	if(!loop) {
+		return(-EINVAL);
+	}
+
+	while(*loop) {
+		struct loop *next;
+
+		next = (*loop)->next;
+		free(*loop);
+
+		*loop = (*loop == next) ? NULL : next;
+	}
+
+	return(0);
+}
diff --git a/loop.h b/loop.h
new file mode 100644
index 0000000..fa9de76
--- /dev/null
+++ b/loop.h
@@ -0,0 +1,12 @@
+#ifndef MWM_LOOP_H
+#define MWM_LOOP_H 1
+
+struct loop;
+
+int loop_append(struct loop **loop, void *data);
+int loop_prepend(struct loop **loop, void *data);
+int loop_remove(struct loop **loop, void *data);
+int loop_find(struct loop **loop, int(*cmp)(void*, void*), void *data, void **dst);
+int loop_free(struct loop **loop);
+
+#endif /* MWM_LOOP_H */
-- 
2.47.3