4 files changed, 99 insertions, 0 deletions

diff --git a/include/serd/serd.h b/include/serd/serd.h
index 4067fa3f..5d0f7290 100644
--- a/include/serd/serd.h
+++ b/include/serd/serd.h
@@ -878,6 +878,21 @@ serd_node_equals(const SerdNode* SERD_NULLABLE a,
                  const SerdNode* SERD_NULLABLE b);
 
 /**
+   Compare two nodes.
+
+   Returns less than, equal to, or greater than zero if `a` is less than, equal
+   to, or greater than `b`, respectively.  NULL is treated as less than any
+   other node.
+
+   Nodes are ordered first by type, then by string value, then by language or
+   datatype, if present.
+*/
+SERD_PURE_API
+int
+serd_node_compare(const SerdNode* SERD_NONNULL a,
+                  const SerdNode* SERD_NONNULL b);
+
+/**
    @}
    @defgroup serd_nodes Nodes
    @{
diff --git a/src/node.c b/src/node.c
index 608f8bfb..fc9869a8 100644
--- a/src/node.c
+++ b/src/node.c
@@ -428,6 +428,33 @@ serd_node_equals(const SerdNode* const a, const SerdNode* const b)
   return true;
 }
 
+int
+serd_node_compare(const SerdNode* const a, const SerdNode* const b)
+{
+  assert(a);
+  assert(b);
+
+  int cmp = 0;
+
+  if ((cmp = ((int)a->type - (int)b->type)) ||
+      (cmp = strcmp(serd_node_string_i(a), serd_node_string_i(b))) ||
+      (cmp = ((int)a->flags - (int)b->flags)) ||
+      !(a->flags & (SERD_HAS_LANGUAGE | SERD_HAS_DATATYPE))) {
+    return cmp;
+  }
+
+  assert(a->flags == b->flags);
+  assert(a->flags & (SERD_HAS_LANGUAGE | SERD_HAS_DATATYPE));
+  assert(b->flags & (SERD_HAS_LANGUAGE | SERD_HAS_DATATYPE));
+  const SerdNode* const ma = serd_node_meta_c(a);
+  const SerdNode* const mb = serd_node_meta_c(b);
+
+  assert(ma->type == mb->type);
+  assert(ma->flags == mb->flags);
+
+  return strcmp(serd_node_string_i(ma), serd_node_string_i(mb));
+}
+
 SerdNode*
 serd_new_uri(const SerdStringView str)
 {
diff --git a/src/node.h b/src/node.h
index eed7cb04..29164dc2 100644
--- a/src/node.h
+++ b/src/node.h
@@ -43,6 +43,12 @@ serd_node_buffer_c(const SerdNode* SERD_NONNULL node)
   return (const char*)(node + 1);
 }
 
+static inline const char* SERD_NONNULL
+serd_node_string_i(const SerdNode* const SERD_NONNULL node)
+{
+  return (const char*)(node + 1);
+}
+
 SerdNode* SERD_ALLOCATED
 serd_node_malloc(size_t length, SerdNodeFlags flags, SerdNodeType type);
 
diff --git a/test/test_node.c b/test/test_node.c
index 466655ef..72bd44e1 100644
--- a/test/test_node.c
+++ b/test/test_node.c
@@ -532,6 +532,56 @@ test_blank(void)
   serd_node_free(blank);
 }
 
+static void
+test_compare(void)
+{
+  SerdNode* xsd_short =
+    serd_new_uri(SERD_STRING("http://www.w3.org/2001/XMLSchema#short"));
+
+  SerdNode* angst =
+    serd_new_plain_literal(SERD_STRING("angst"), SERD_EMPTY_STRING());
+
+  SerdNode* angst_de =
+    serd_new_plain_literal(SERD_STRING("angst"), SERD_STRING("de"));
+
+  SerdNode* angst_en =
+    serd_new_plain_literal(SERD_STRING("angst"), SERD_STRING("en"));
+
+  SerdNode* hallo =
+    serd_new_plain_literal(SERD_STRING("Hallo"), SERD_STRING("de"));
+
+  SerdNode* hello         = serd_new_string(SERD_STRING("Hello"));
+  SerdNode* universe      = serd_new_string(SERD_STRING("Universe"));
+  SerdNode* integer       = serd_new_integer(4, NULL);
+  SerdNode* short_integer = serd_new_integer(4, xsd_short);
+  SerdNode* blank         = serd_new_blank(SERD_STRING("b1"));
+  SerdNode* uri           = serd_new_uri(SERD_STRING("http://example.org/"));
+
+  // Types are ordered according to their SerdNodeType (more or less arbitrary)
+  assert(serd_node_compare(hello, uri) < 0);
+  assert(serd_node_compare(uri, blank) < 0);
+
+  // If the types are the same, then strings are compared
+  assert(serd_node_compare(hello, universe) < 0);
+
+  // If literal strings are the same, languages or datatypes are compared
+  assert(serd_node_compare(angst, angst_de) < 0);
+  assert(serd_node_compare(angst_de, angst_en) < 0);
+  assert(serd_node_compare(integer, short_integer) < 0);
+
+  serd_node_free(uri);
+  serd_node_free(blank);
+  serd_node_free(short_integer);
+  serd_node_free(integer);
+  serd_node_free(universe);
+  serd_node_free(hello);
+  serd_node_free(hallo);
+  serd_node_free(angst_en);
+  serd_node_free(angst_de);
+  serd_node_free(angst);
+  serd_node_free(xsd_short);
+}
+
 int
 main(void)
 {
@@ -552,6 +602,7 @@ main(void)
   test_simple_node();
   test_literal();
   test_blank();
+  test_compare();
 
   printf("Success\n");
   return 0;