From b242f4e0058ed12a52eef7dfc7463da65d7ad382 Mon Sep 17 00:00:00 2001
From: Michael Orlitzky <michael@orlitzky.com>
Date: Sat, 14 Oct 2023 10:31:14 -0400
Subject: [PATCH] src/svgtiny_css.c: implement node_count_siblings() select
 handler

---
 src/svgtiny_css.c | 131 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 131 insertions(+)

diff --git a/src/svgtiny_css.c b/src/svgtiny_css.c
index 80d4de1..ffc9c3e 100644
--- a/src/svgtiny_css.c
+++ b/src/svgtiny_css.c
@@ -43,6 +43,8 @@ static css_error node_has_attribute_substring(void *pw, void *node,
 		const css_qname *qname, lwc_string *substring,
 		bool *match);
 static css_error node_is_root(void *pw, void *node, bool *match);
+static css_error node_count_siblings(void *pw, void *node,
+		bool same_name, bool after, int32_t *count);
 
 
 /**
@@ -1232,3 +1234,132 @@ css_error node_is_root(void *pw, void *node, bool *match)
 	*match = true;
 	return CSS_OK;
 }
+
+
+/**
+ * Used internally in node_count_siblings() to "count" the given
+ * sibling node. It factors out the node type and name checks.
+ */
+static int node_count_siblings_check(dom_node *dnode,
+		bool check_name,
+		dom_string *name)
+{
+	int ret;
+	dom_node_type type;
+	dom_exception exc;
+	dom_string *dnode_name;
+
+	/* We flip this to 1 if/when we count this node */
+	ret = 0;
+
+	if (dnode == NULL) {
+		return ret;
+	}
+
+	exc = dom_node_get_node_type(dnode, &type);
+	if ((exc != DOM_NO_ERR) || (type != DOM_ELEMENT_NODE)) {
+		/* We only count element siblings */
+		return ret;
+	}
+
+	/* ... with the right name */
+	if (check_name) {
+		dnode_name = NULL;
+		exc = dom_node_get_node_name(dnode, &dnode_name);
+
+		if ((exc == DOM_NO_ERR) && (dnode_name != NULL)) {
+			if (dom_string_isequal(name,
+					dnode_name)) {
+					ret = 1;
+			}
+			dom_string_unref(dnode_name);
+		}
+	}
+	else {
+		ret = 1;
+	}
+
+	return ret;
+}
+
+/**
+ * Count the given node's sibling elements
+ *
+ * This counts the given node's sibling elements in one direction,
+ * either forwards or backwards, in the DOM. Keep in mind that the
+ * libdom tree is upside-down compared to the CSS one; so "next" and
+ * "previous" are actually reversed; the default is to count preceding
+ * libdom siblings which correspond to subsequent CSS siblings.
+ *
+ * This operation is central to the CSS :first-child, :nth-child, and
+ * :last-child (et cetera) pseudo-selectors.
+ *
+ * If same_name is true, then only nodes having the same
+ * (case-sensitive) name as the given node are counted.
+ *
+ * \param pw          Pointer to the current SVG parser state
+ * \param node        Libdom SVG node whose siblings we're counting
+ * \param same_name   Whether or not to count only siblings having
+ *                    the same name as the given node
+ * \param after       Count subsequent siblings rather than precedent
+ *                    ones (the default)
+ * \param count       Pointer to the return value, the number of sibling
+ *                    elements
+ *
+ * \return CSS_OK on success, or CSS_NOMEM if anything goes wrong
+ */
+css_error node_count_siblings(void *pw, void *node,
+		bool same_name, bool after, int32_t *count)
+{
+	UNUSED(pw);
+	dom_exception exc;
+	dom_node *dnode; /* node, but with the right type */
+	dom_string *dnode_name;
+	dom_node *next; /* "next" sibling (depends on direction) */
+
+	/* Pointer to the "next sibling" function */
+	dom_exception (*next_func)(dom_node *, dom_node **);
+
+	*count = 0;
+
+	dnode_name = NULL;
+	dnode = (dom_node *)node;
+	if (same_name) {
+		exc = dom_node_get_node_name(dnode, &dnode_name);
+		if ((exc != DOM_NO_ERR) || (dnode_name == NULL)) {
+			return CSS_NOMEM;
+		}
+	}
+
+	/* Increment the reference counter for dnode for as long as
+	 * we retain a reference to it. */
+	dnode = dom_node_ref(dnode);
+
+	next_func = dom_node_get_previous_sibling;
+	if (after) {
+		next_func = dom_node_get_next_sibling;
+	}
+
+	do {
+		exc = next_func(dnode, &next);
+		if (exc != DOM_NO_ERR) {
+			break;
+		}
+
+		/* If next_func worked, we're about to swap "next"
+		 * with "dnode" meaning that we will no longer retain
+		 * a reference to the current dnode. */
+		dom_node_unref(dnode);
+		dnode = next;
+
+		*count += node_count_siblings_check(dnode,
+					same_name,
+					dnode_name);
+	} while (dnode != NULL);
+
+	if (dnode_name != NULL) {
+		dom_string_unref(dnode_name);
+	}
+
+	return CSS_OK;
+}
-- 
2.43.2